phantoms newsletter issues 7/8 (2002)

PHANTOMS NEWSLETTERJuly/September 2002 - Issues 7/8

Scientific Review articlesNANOMASS project: smart NEMS system for high sensitivity mass detectionF. Perez-Murano et al. (NANOMASS Consortium)

Photoreflectance Spectroscopy of Semiconductor Device Structures J. Misiewicz, G. Sek and R. Kudrawiec

Atomic Nitrogen and Phosphorus Trapped in BuckminsterfullereneJ. A. Larsson and J. C. Greer

Numerical investigation of shot noise suppression in chaotic cavitiesP. Marconcini, M. Macucci, G. Iannaccone and B. Pellegrini

Nucleic Acids Chemistry Group Institute of Molecular Biology of Barcelona - CSIC, Spain

IBM Zurich Research Laboratory & the Microcontact Processing ProjectSwitzerland

Mesoscopic Physics and Nanoelectronics Group CERMIN - UCL, Belgium

Plasma Etching Group Materials Institute - Nantes University, France

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2 PHANTOMS NEWSLETTER. July/September 2002 - Issue 7/8

INTRODUCTIONAn important objective set up by PHANTOMS is to makeindustry aware of the strategic importance of nanoelec-tronics research for the future of Information Technology(IT) in general and of microelectronics in particular. Forthis purpose, the network is promoting industrial partici-pation within the network's activities through interactionswith industry in general as well as other applications-ori-ented groups such as NEXUS.

In this context, PHANTOMS and NEXUS have jointlyset-up a concerted action entitled NanoIndex(Nanotechnology Industry Exchanges - funded by theEuropean Union) aimed at bridging micro and nanotech-nologies.

Under this new activity, PHANTOMS willidentify a group of experts in nanotech-nology who will become active membersof the NEXUS User-Supplier-Clubs(USC). The intention is to establish linksbetween both communities and enable abetter understanding of the future poten-tial of nanotechnology in the context ofmicrosystems-driven applications.

These links will be realised for examplethrough active participation from bothcommunities at USC meetings and joint-ly organised workshops or the exchangeof presentations and relevant informa-tion.

The editorial board would like toacknowledge F. Perez-Murano, J.Misiewicz, J. A. Larsson and M. Macuccias well as their collaborators for theircontributions in this issue and to thePlasma Etching group at the Institute ofMaterials University of Nantes (IMN) forproviding the cover picture.

This bi-monthly publication is supportedby the EU-IST program within the PHAN-TOMS Network activities.

Antonio Correia (Editor)

CONTENTSScientific Review articles 4NANOMASS project: smart NEMS system for highsensitivity mass detectionF. Perez-Murano, N. Barniol, G. Abadal, X. Borrise, J.Verd, M. Villarroya, Z. Davis, A. Boisen, F. Campabadal,E. Figueras, J. Esteve, J. Montserrat, S.G. Nilsson, I.Maximov, E-L. Sarwe and L. Montelius (NANOMASSConsortium)________________________________________9Photoreflectance Spectroscopy ofSemiconductor Device StructuresJ. Misiewicz, G. Sek and R. Kudrawiec

________________________________________14Atomic Nitrogen and Phosphorus Trapped inBuckminsterfullereneJ. A. Larsson and J. C. Greer

________________________________________17Numerical investigation of shot noise sup-pression in chaotic cavitiesP. Marconcini, M. Macucci, G. Iannaccone andB. Pellegrini

PHANTOMS Membership 20List of new PHANTOMS membership submissions

Members Highlights 22- Nucleic Acids Chemistry Group - Institute of Molecular Biology ofBarcelona (IBMB)-C.S.I.C., Spain- IBM Zurich Research Laboratory and the MicrocontactProcessing Project, Switzerland- Mesoscopic Physics and Nanoelectronics Group"Research Center in Micro and Nanoscopic Materials andElectronic Devices" - CERMIN - UCL, Belgium- Plasma Etching Group - Materials Institute, Nantes University,France

Latest publications by PHANTOMS members 26

The PHANTOMS Nanotechnology HUB 30

NanoINDEX Initiative 31

10th & 11th MEL-ARI/NID Workshop 32

Nanoelectronics conferences in Europe 33

Nanoelectronics courses in Europe 33

Nanonews 34

News 35

Nano-vacancies at PHANTOMS 36

Editorial Information & Subscription form 36PHAN

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contact person: Dr. Ramon Compañ[email protected]

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PHANTOMS NEWSLETTER. July/September 2002 - Issue 7/8 3

1. IntroductionThe overall objective of the NANOMASS project is to combinenanofabrication processes with standard microelectronic circuitfabrication to develop of nanomechanical devices with integratedelectronics. It is the aim of the project to explore the new frontiersin research on nanotechnologies to develop functional and usefulsensor devices. The sensor system is composed of a nanome-chanical structure (an array of resonating cantilevers) and aCMOS circuit to confer intelligence to the system. It is the finalobjective to achieve a smart nanoelectromechanical system(NEMS) with superior performance due to the introduction of nan-otechnology into "classical" microsystems technology. Figure 1shows the global concept of the project.

The fabrication of nano-micro systems includes different aspectsthat have to be undertaken simultaneously. In this article, we willshow the different activities and research that are being carried outin the frame of the NANOMASS project. These different aspectsdefine a multidisciplinary research, which is being performed bythe partners of the Consortium. Fields, which are part of theNANOMASS project include: nanofabrication, nanomechanics,microelectronics technology, integrated circuit design, electronics,

physics, and chemistry/biochemistry

2.- The sensing element: A Nanoresonating cantilever.A cantilever can be used as a universal platform for sensing appli-cations by using the deflection of the cantilever or the change inresonant frequency as a signal for measuring different magnitudes[1-3] (see figure 2). Using static deflection heat changes or surfacestress changes due to molecular adsorption can for example bedetected. Using resonating cantilevers mass changes are detect-ed. For mass detection, decreasing the dimensions of the can-tilever to the nanometer scale increases the sensitivity, up to thepoint that it is possible to perform single molecule detection.Practical applications of this kind of sensor based in nanometerscale cantilevers require an appropriate way of detecting thechange in resonant frequency of the cantilever. The nanomass sensor design is based on a laterally resonatingcantilever placed close to a fixed electrode as seen in figure 3 [4-5]. The electrode is used for electrostatic excitation and thecapacitance of the system is used to monitor the cantilever's oscil-lation. Both an AC and a DC voltage component are applied to thedriver electrode. The AC component is for the electrostatic excita-tion and the DC component is for the capacitive readout. The cur-rent through the system is:

where C0 is the static capacitance of the system. The first term is

NANOMASS project: smart NEMS system for high sensitivity mass detection

F. Perez-Murano1,3, N. Barniol1, G. Abadal1, X. Borrise1, J. Verd1, M. Villarroya1, Z. Davis2, A. Boisen2, F.Campabadal3, E. Figueras3, J. Esteve3, J. Montserrat3, S.G. Nilsson4, I. Maximov4, E-L. Sarwe4, L. Montelius4

(NANOMASS Consortium)

1-Dept. Enginyeria Electrònica. Univ. Autònoma de Barcelona. E-08193 Bellaterra. Spain2-Mikroelektronik Centret. Lyngby. Denmark

3-Institut de Microelectrònica de Barcelona (CNM-CSIC) Campus UAB. 08193 Bellaterra. Spain4-Solid State Physics & The Nanometer Consortium, University of Lund, Sweden

e-mail: [email protected]

Figure 1. a) General concept of the project. A smart microsystem isfabricated by combination of nanotechnology for fabricating the nano-resonator and CMOS technology for circuit integration. b) Artistic viewof the concept: Monolithic integration of a nanocantilever and CMOSintegrated circuit.

Figure 2. Use of a cantilever as a sensor of different physical and che-mical magnitudes. The magnitude to be sensed (mass, stress or tem-perature, for example) produces a change of the deflection (a) or reso-nant frequency (b) of the cantilever.


a

b

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the current due to the AC voltage through the cantilever capaci-tance plus any parasitic capacitances in the system. The secondterm is the current from the displacement of the cantilever due tothe lateral vibration and is called the displacement current. Whenthe cantilever is in resonance the vibrational amplitude of the can-tilever will increase thus increasing the displacement current of thesystem. For a proper capacitive readout, the parasitic capaci-tances in the system must be minimized to decrease the first termof equation (1) and make it not too large compared to the secondterm. A high spatial resolution is achieved by making the thinnest dimen-sion of the cantilever (w) perpendicular to oncoming particles, thusa lateral vibration scheme was chosen. This system could be usedin atom lithography [6], measuring particle fluxes in high vacuum,or as a high sensitive gas sensor. The theoretical mass sensitivityof a cantilever with a width, height and length of 1µm, 2 µm and 50µm respectively, is approximately 10-18g for a 1Hz frequency reso-lution. Furthermore, decreasing the dimensions even more themass sensor could theoretically detect single molecules and largeproteins.

3.- Nanofabrication issuesThe fabrication of the nano-cantilever is currently based on twonano-lithography approaches: combination of laser and AFMnanolithography of Al [7-10], and e-beam nanolithography.

Laser lithography on Al combined with dry and wet etching can beused to fabricate suspended silicon structures with sub-micron lat-eral dimensions, such as bridges [7] and cantilever resonators [9].A 7 nm thick Al film is e-beam deposited on top of a sandwich layerconsisting of a 1 µm thick poly Si layer on top of a several mm thickSiO2 layer on a Si wafer. The definition of the mask is performedby direct laser writing in air on the thin Al film [7] For this purpose,a continuous wave argon ion laser beam is focused into a 500 nmdiameter spot, and scanned across the Al surface by means of acomputer-controlled lateral translation system [11]. Exposing the Alfilm at a laser power below a critical value, at which Al evaporates,produces an Al/Si alloy which resistivity is one order of magnitudelower than the resistivity of pure Al [8]. Linewidths as small as 500nm have been achieved. The non-exposed Al is removed by an

85% phosphoric acid etch at room temperature. The remaininglaser defined zones are used as an etch mask to transfer the Al/Sipattern to the underlying layered structure. First, the poly Si layeris etched by anisotropic reactive ion etching (RIE). Next, anisotropic hydrofluoric acid (HF) etch of the thicker SiO2 layerreleases the moving structures and simultaneously removes thetop Al/Si alloy. An example of a cantilever resonator device fabri-cated by this technique is shown in figure 3.b. The cantilever isapproximately 40 µm long, 0.6 µm thick and 500 nm wide and thegap between the driver electrode and the cantilever is 2 µm. Thecantilever is vibrated laterally by applying an AC voltage betweenthe driver and the cantilever. The resonator has been character-ized by optical inspection and a resonant frequency of approxi-mately 290 kHz and a quality factor of approximately 50 have beenobserved. Assuming a frequency resolution of 1 Hz, the mass sen-sitivity is estimated to approximately 1 pg [9]. Laser lithography onAl is a resistless patterning method, which offers a very convenienttool for direct and rapid prototyping of mechanical structures.However, the minimum obtainable linewidth is approximately 500nm.

Similar to laser lithography on Al, it has previously been demon-strated that AFM can be used to locally modify thin Al films by volt-age induced anodization. Positive or negative masks can be pro-duced by respectively etching the resulting nanometer scale Al2O3patterns or by removing the not oxidized Al. The obtained masksare finally transferred to the substrate by RIE [7]. Linewidths below100 nm can be obtained by AFM lithography on Al, which repre-sents an important improvement of the spatial resolution obtainedby laser lithography. However, AFM is not a proper tool for writinglarge areas because of its inherent low writing speed and tip wear.A combined laser and AFM technique has been tested [8] in orderto take advantage of the laser writing speed and the high spatialresolution of AFM. Such a combined technique is based on pre-defining an etch mask by laser lithography, which is localized andsubsequently modified by AFM. Figure 4 shows the procedures forfabricating etch masks for cantilever-driver structures. The com-bined laser/AFM writing yields cantilever structures with smallerlinewidths and thus better mass sensitivity than the purely laserwritten structures.

Recently, an electron beam lithography (EBL) based processinvolving a lift-off defined Al/Cr layer as a mask for SF6-basedreactive ion etching has also been implemented to fabricate thenanocantilevers. Cantilevers with a width of 100 nm and withlengths between 10 µm to 40 µm have been defined by EBL using35 kV exposure on PMMA 950 resist on top of ZEP 520 resist [12].

Defining small cantilever structures with EBL or laser/AFM lithog-raphy in a specified nanoarea on a chip (see section 3) is not triv-ial. One problem is to get the proper alignment between the struc-ture and the nanoarea. Shifts of the cantilever structures withrespect to an integrated electrical circuit of about 3 µm are allowed.Another problem is the difficulty in defining a nanostructure whenthe topographic profile is not flat since the beam has to be focusedat all heights. The height difference on our sensor chips is almost2µm.

4.- Combination of nanofabrication and microfabricationDue to large parasitic capacitances in the cantilever system, it isnot possible to use external capacitive readout to monitor theoscillation amplitude of the cantilever. Therefore the integration of

Figure 3. a) Schematics of the principle of operation of the nanomassdevice: a nanometer wide cantilever is placed very closed to an electro-de. Applying a voltage to the electrode induces the movement of the can-tilever, which is detected by an integrated circuit. b) SEM image of a nano-cantilever fabricated using laser lithography for the patterning.

PHANTOMS NEWSLETTER. July/September 2002- Issue 7/8 5

a

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a CMOS circuit with the cantilever is necessary to avoid the para-sitic capacitances related to large bonding pads and externalwires. The proposed technology for a monolithic integration of thenanosensor and circuitry is based on a standard twin-well, 2-poly-silicon, 2-metal CMOS technology. The two polysilicon layers are:Poly0 that corresponds to the bottom plate of the analog capaci-tors and Poly1 that is used as the top plate of the capacitors andas the gate of the transistors (figure 5).

The selected approach uses already existing CMOS layers for thenanocantilever and has the nanotechnology steps as a post-CMOS process module. The surface of the polysilicon to be usedfor the nanocantilever definition should be as smooth as possibleand it should be possible to grow a thin thermal oxide on top. Thethin oxide is a buffer layer, which is used to ensure a reproduciblelaser lithography. In addition, the thicker the polysilicon the largerthe sensor output. These requirements make Poly0 the onlyCMOS layer that can be used for the cantilever fabrication, sinceit can be modified without changing the transistor characteristics.Furthermore, the inter-poly oxide of the capacitors will be used asthe buffer oxide, so that no additional layer or processing step isnecessary. Finally, the CMOS field oxide is used as the sacrificialoxide layer.

The defined technology starts with the standard CMOS process inwhich the Poly0 module differs from the standard in the LPCVDdeposition temperature that is lowered (580ºC) in order to obtainan as-deposited amorphous silicon layer. With respect to Poly0thickness, a value of 600 nm has been chosen as a compromisebetween sensor performance and technology availability. At theend of the CMOS processing (fig. 5(a)), the passivation layer isalso opened in the cantilever site, where Poly1 is left to protect thethin oxide layer from the different oxide etching steps along theCMOS processing.

After CMOS, the post-processing module starts with a dry etchingof the protective Poly1 layer. After this a thin metal layer is deposit-ed on the oxide and the cantilever pattern is defined by laser/AFM

Figure 4. Procedure for fabricating the nanocantilevers using laser/AFM lithography. Laser lithog-raphy is used to pattern the larger areas and AFM lithography is used to define the smallestareas. The as-modified Al is used as a mask for anisotropic reactive ion etching. The two insertsshow an AFM image of the as-defined mask and an SEM image of a final structure.

Figure 5. Cross-sectional view of the nanocantilever site (a) afterCMOS processing and (b) after complete processing.

Figure 6. Cantilever site and CMOS amplifier (top)and close-up of cantilever with a length of 40µm(bottom).


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or EBL nanolithography. The metal mask is used to transfer thecantilever structure to the oxide and the poly0 by dry etching.Finally, the cantilever is released removing the bottom oxide bywet etching (Fig.5(b)). Figure 6 shows an optical image of the com-plete NEMS system comprising the CMOS circuit and the post-processed nanocantilever. In this case the driver electrode is con-nected to a bonding pad, which will be the connection for the exter-nal applied DC and AC voltages as seen in figure 3. The cantileveris connected to a buffer amplifier circuit, which is explained in thefollowing section.

A set of wafers have been processed following the proposed tech-nology. For monitoring any effect of the post-processing in theCMOS part, the transistor threshold voltages have been measuredin a set of test structures. Results have shown that no significantdifference is obtained before and after post-processing demon-strating the compatibility of the fabrication processes for micro-electronics and nanomechanics.

5.- Microelectronics circuit design issuesThe purpose of the CMOS circuitry is to detect and amplify the cur-rent generated by the cantilever-driver system. This current is ameasure of the amplitude of the cantilever oscillation movement,and in consequence, it provides the frequency response of thecantilever.

One of the main objectives when designing this circuitry has beenthe reduction of the parasitic capacitance, Cpa, due to the metallines that connect the cantilever with the circuit and the inputcapacitance of the amplifier. A small value of this parasitic capaci-tance is required to detect a small current level (20 nA) at the res-onant frequency (about 1 MHz).

The minimum distance between the cantilever and the circuit isfixed by the CMOS-design rules. As it has been already explainedin the previous section, the circuitry has been integrated with a 2.5µm CMOS 2-polysilicon 2-metal technology from CNM. Therequirements of the nanofabrication process also increase thenumber of layers necessary on the area (protection steps), so spe-cial care has to be taken in the layout to avoid additional parasiticcapacitance. The implemented layout yields a stray capacitanceon the order of 20 fF (including cantilever capacitance and metalpads to the circuitry).

Two different designs of the read-out circuitry have been imple-mented: (a) Current Amplifier circuits, called CA, and (b) BufferingAmplifiers, called BA. The two basic requirements for the CMOScircuitry are: (1) it has to be able to detect a low current around 20nA and (2) the bandwidth has to be larger than 1 MHz.

The Current Amplifiers (CA) or trans-impedance amplifiers arebased on an operational amplifier with a resistive feedback, com-monly called feedback ampmeters. The principal advantage of thiskind of circuits is the fact that the effect of the parasitic capacitance(Cpa) is negligible by virtually grounding it through the operationalamplifier. Figure 7a shows one of the designs for the CA circuits. Itis based on a T-configuration feedback with a shunt capacitance,C to guarantee an acceptable stability. With this configuration anacceptable gain of almost 2x106 V/A is obtained without having tointegrate high values of resistance.

The principle of operation of the buffer amplifiers (BA) is based onthe amplification of the ac voltage generated at the cantilever, Vg,due to the capacitive voltage divider constituted by the parasiticcapacitance, Cpa, and the driver-cantilever capacitance, Cp. Thesecircuits are based on a buffer amplifier and a voltage follower (seefigure 7b). The buffer amplifier is a CMOS amplifier biased as

Figure 7 a) Schematic diagram of a current amplifier (CA) circuit along withthe electrical model. b) Schematic of a Buffer Amplifier (BA) circuit alongwith the electrical model c) Hspice simulation of the frequency response ofVout for the cantilever-BA circuit system. The dependence of resonancepeak magnitude with respect to the parasitic capacitance (Cpa) can beobserved. d) Hspice simulation of the frequency response of Vout for thecantilever-CA circuit system.


a

d

c

b

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source-follower (common drain configuration). The voltage at theVg node controls the M1 current, this current is mirrored and ampli-fied through (M3, M4) and finally the voltage drop on M2 as a loadis measured. This type of circuit is normally used for level shiftingand buffering purposes. The voltage follower has been added inorder to be capable of driving the output pad capacitance alongwith the stray capacitance of all the electrical test equipment (Cl isaround 30 pF or more).

Figures 7.c and 7.d are the results of the HSPICE simulation [13]of the frequency response of the NEMS system for each of theconditioning circuits. In these simulations a 40 µm length, 1 µmwidth and 0.6 µm thick Polysilicon cantilever has been used. Theexpected resonant frequency is in this case at 887 kHz. Recently,[14], we have obtained the frequency response of the cantileversignal from electrical measurements using BA circuits. Theseexperimental results fit very well with the simulations.

6.- Conclusions and outlookThe Nanomass project is exploring the opportunities and chal-lenges in the fabrication and development of NEMS. The combi-nation of nanomechanics (a resonating nanocantilever) andCMOS circuits allows the fabrication of smart nanosystems withimproved performance compared to pure microsystems becauseof the enhanced sensitivity for mass detection provided by thesmaller dimensions of the cantilever.

We have demonstrated the viability of the approach and we haverecently achieved the first results of the electrical characterizationof the cantilever oscillation. Currently, several aspects of the real-ization of the device are being addressed in order to optimize itsperformance. Among others, these aspects include:

-Optimization of nanopatterning processes, i.e., EBL andlaser/AFM lithography-Use of SOI wafers in order to fabricate the nanocantilever in crys-talline silicon instead of on polysilicon-Improvement of the CMOS circuits to increase the maximum fre-quency operation and to add intelligence to the system-Fabrication of arrays of cantilever to introduce differential readingand redundancy

The Nanomass project is, at present, more focused on design andfabrication technologiesthan on applications of the realizeddevices. However, we expect that once the technological aspectsare more developed, the applications of the cantilever system(vapor, biomolecules, etc) will open up to a wide range of excitingexperiments in the applied as well as in the fundamental area.

AcknowledgementsNanomass project has been financed by the FET program undercontract numbers IST-1999-14053 and IST-2001-33068. We alsoacknowledge additional financial support form the Spanish CICYTproject Nanobiotec (DPI2000-0703-C03)

References[1] T. Thundat, E.A. Wachter, S.L. Sharp and R.J. Warmack,. Appl. Phys.Lett. 66, 1695-1697 (1995)[2] R. Berger, Ch. Gerber, H.P. Lang, J.K. Gimzewski. Microelectronic Eng.35 (1997) 373.[3] J. Fritz, M.K. Baller, H.P. Lang, H. Rothuizen, P. Vettiger, E. Meyer, H.-J. Güntherodt, C. Gerber and J.K. Gimzewski, Science 288, 316-318(2000).[4] G. Abadal, Z.J. Davis, B. Helbo, X. Borrisé, R. Ruiz, A. Boisen, F.Campabadal, J. Esteve, E. Figueras, F. Pérez-Murano, N. Barniol.Nanotechnology 12 100 (2001).[5] Z. J. Davis, G. Abadal, B. Helbo, O. Hansen, F. Campabadal, F. Pérez-Murano, J. Esteve, E. Figueras, R. Ruiz, N. Barniol and A. Boisen,Transducers '01 Conference, Technical Digest, pp. 72-75 (2001).[6] U. Drodofsky,, M. Drewsen, T. Pfau, S. Nowack and J. Mlynek,Microelectronic Engineering 30, 383-386, 1996.[7] A. Boisen, K. Birkelund, O. Hansen and F. Grey, J. Vac. Sci. Technol. B16, 2977-2981, 1998.[8] G. Abadal, A. Boisen, Z.J. Davis, O. Hansen and F. Grey, Appl. Phys.Lett. 74, 3206-3208, 1999.[9] Z.J. Davis, G. Abadal, O. Kuhn, O. Hansen, F. Grey and A. Boisen, J.Vac. Sci. Technol. B 18, 612-616, 2000.[10] G. Abadal, Z.J. Davis, A. Boisen, F. Pérez-Murano, N. Barniol, X.Borrisé. Probe Microscopy, 2, 121-128 (2001)[11]M. Müllenborn, H. Dirac, J.W. Petersen . Applied Physics Letters 66,3001-3003 (1995)[12] N.Barniol, G.Abadal, X.Borrise, F. Pérez-Murano, J.Verd, M.Villarroya,Z.Davis, A.Boisen, O. Hansen, B. Helbo, F.Campabadal, E.Figueras,J.Esteve, J.Montserrat, S.G.Nilsson, I.Maximov, E-L.Sarwe, L.Montelius.Proceedings of nano-7 / ecosss-21 conference. [13] HSPICE User's manual (version H92), Meta software Inc. Campbell,California (1992)[14] J. Verd et al. Unpublished.


IntroductionMost of the present electronic and optoelectronic semiconductordevices utilize low-dimensional systems like quantum wells, wiresand dots, and their different combinations. In the long way fromsubstrate wafer to full operating device there is a need to carry outa lot of characterisation experiments, including optical methods,which seem to be ideal for studying the fundamental electronicproperties.

Modulation spectroscopy has proven to be a powerful experi-mental technique for characterisation of semiconductors andreduced dimensionality semiconductor structures, including mod-ern device structures [1-3]. The basic idea of modulation spec-troscopy is a very general principle of experimental physics.Instead of directly measuring an optical spectrum, the derivativewith respect to a certain parameter is evaluated. This kind ofspectroscopy has been shown to be sensitive to critical point tran-sitions in the Brillouin zone with resulting spectrum having sharpderivative-like features and little, if any, featureless background.Moreover, weak features, which otherwise might be difficult toobserve in absolute absorption or reflection spectrum, can beenhanced. The derivative nature of this experimental methodenables observation of a large number of sharp spectral features,even at room or elevated temperatures, including those related toexcited state transitions in low-dimensional structures, in contrastto common emission-like experiments such as photolumines-cence, which usually probe only the ground states.

Modulation techniques, which can be used in the contactless,non-destructive modes are still not very popular in the devicestructure characterisation. The aim of the present paper is toshow a few examples of application of one particular modulationmethod called photoreflectance (PR) to the investigation of opti-cal properties of semiconductor device structures and to proposeit as an essential support for technology and design of novel andfuture electronics based on nanoscale low-dimensional semicon-ductor objects.

Experimental techniqueModulation techniques like photoreflectance take an advantage ofthe application of a small periodic perturbation to a physical prop-erty of the investigated structure. The change in the optical func-tion is only a small fraction of its unperturbed value, typically 1part in 104 or less. The perturbation can easily be accomplishedby varying some parameters associated with the sample or exper-imental system in periodic fashion and measuring the normalisedchange in the optical function. It is possible to modulate a varietyof parameters, e.g. wavelength of light, sample temperature,applied stress or electric field. In photoreflectance spectroscopyof semiconductor structures the varying parameter is the internalelectric field (built-in field at the surface or interface). The modu-lation is caused by photoexcited electron-hole pairs created bythe pump source (usually laser). Photon energy of the pumpbeam is generally larger than the band gap of the semiconductorbeing under study (weak below band gap photomodulation isexcluded here). Photoexcited electron-hole pairs are separatedby the built in electric field and therefore some of the charged sur-

face or interface trap states are neutralised and the built-in field isreduced. In photoreflectance, normalised change of the reflectivi-ty coefficient (∆R/R) is measured. It reflects the changes in thedielectric function (ε = ε1 + iε2), that can be described as follows

where α and β are the Seraphin coefficients, ∆ε1 and ∆ε2 are thephotoinduced changes in the real and imaginary part of the unper-turbed dielectric function, respectively.

In Figure 1, a schematic diagram of a photoreflectance apparatusis shown. High-resolution monochromator is a core of the setupand in a connection with a halogen or xenon lamp serves as aprobe light source. The probe beam is focused on the sample.The same spot is also illuminated by the pump beam (modulationsource) chopped with a given frequency. The intensity of the lightreflected from sample is detected by a suitable photodetector(photodiode or photomultiplier). The signal includes two compo-nents: a DC one proportional to R, and a AC one proportional to∆R, where the reflectivity changes are extracted through the useof a lock-in amplifier tuned to the modulation frequency. As aresult a spectrum of ∆R/R is recorded by a personal computer.For the sake of simplicity optical elements like mirrors or lensesare not shown in Fig. 1. In order to prevent the detection of thestray laser light an appropriate longpass glass filter is used in frontof photodetector. In our original PR setup a double detector sys-tem is used, for photoluminescence background and residualstray light compensation.

Quantum dot laser structureA lot of effort has been made so far to use specific properties ofquantum dots in optoelectronic semiconductor devices like quan-tum dot-based lasers. The QD semiconductor laser constructionsinclude low as well as high power applications, especially fortelecommunication systems, like for example EDFA amplifierspump sources operating at 980 nm and they can compete withstandard quantum well lasers [4-7]. There will be presented here

Fig. 1. Scheme of apparatus for photoreflectance measurements

PHOTOREFLECTANCE SPECTROSCOPY OF SEMICONDUCTOR DEVICE STRUCTURES

J. Misiewicz, G. Sek and R. Kudrawiec

Institute of Physics, Wroclaw University of TechnologyWybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland


PR measurement results obtained on such a QD edge emittinglaser structure grown by MBE at Microstructure Laboratory,Technical Physics, Würzburg University. The sample was grownon Si-doped GaAs substrate. The device structure was preced-ed by 300 nm of n-type GaAs buffer layer. The active part of thedevice consisted of In0.6Ga0.4As self-assembled quantum dots onthin wetting layer embedded between 3 nm thick GaAs layers.The active region is surrounded by Al0.4Ga0.6As cladding layers(p and n type, respectively) which are preceded byAl0.33Ga0.67As/GaAs short period superlattice playing a role ofBragg reflectors for electrons. Therefore, such structure is calledimproved carrier confinement laser. The sample is covered by100 nm p-type GaAs cap.

In Figure 2, a PR spectrum for this sample is presented, meas-ured at liquid nitrogen temperature. There are a lot of transitionsabove the band gap energy of GaAs, connected withAl0.33Ga0.67As/GaAs superlattice. However, for us the most inter-esting is the quantum dot layer, for which the transitions areobserved below 1.5 eV, i.e. GaAs band gap energy. We observefour transitions. Two related to quantum dots (fundamental andexcited one) and two related to wetting layer quantum well. Ourenvelope function calculations show that in such wetting layerquantum well (approx. 4 ML thick) we have only one electron,one heavy hole and one light hole confined state. Hence, onlytwo optical transitions are possible, one heavy hole and one lighthole related ones (WL1 and WL2, respectively). The electronicstructure of such In0.6Ga0.4As quantum dots has been investigat-ed in detail, especially by high excitation PL and single dot spec-troscopy [8,9]. These data show that we can deal with two differ-ent kind of dots for this indium content. For one of them only twoquantum dot optical transitions are expected. Our PR resultagrees with that very well, also in the values of transition ener-gies (QD1, QD2). The conclusion is that photoreflectance spec-troscopy performed on million of dots embedded in a full laserstructure is able to detect all transitions related to the deviceactive region: quantum dots and to wetting layer as well.

Vertically coupled double quantum dotsThe interdot coupling is of special interest because it is a way ofcreating artificial molecules [10], which offer the possibility toimplement new computational concepts [11]. To construct aquantum computer one must create feasible basic quantumgates. Wu et al. [12] have reported a novel method for imple-menting quantum gates using coupled quantum dot molecules,where the artificial molecules consist of two asymmetric, verti-cally stacked, quantum dots.

The samples, investigation of which is presented here, weregrown by MBE on unintentionally doped GaAs substrates atMicrostructure Laboratory, Technical Physics, WürzburgUniversity. A 300 nm thick GaAs buffer layer was followed by twoIn0.6Ga0.4As quantum dot layers separated by GaAs layer ofthickness 3, 5 or 10 nm. The whole structure was capped by 45nm of GaAs.

In Figure 3, we show the PR spectra for coupled In0.6Ga0.4Asdouble quantum dot structures differing only in the thickness ofGaAs separating layer. The PR spectra for all three samples canbe divided into two parts. The strong feature at 1.52 eV is relat-ed to the GaAs band gap transition. The low energy part of thespectra exhibit several transitions related to QDs and to the wet-ting layer (WL). In order to identify the observed features wehave calculated the energy levels in our double quantum dot andwetting layer double quantum well (WLDQW) (created from thetwo wetting layers) system. For DQWs we have used standardenvelope function calculations including strains. For the DQDswe have used the effective mass approximation for lens-shapedquantum dots, that was previously developed by Wójs et al. [13].Our dot is modelled by a part of the sphere formed on a thin wet-ting layer of thickness of 4 ML with a dot height and dot diame-ter of 2.5 and 18 nm respectively, conserving the typical geome-try for that indium content. The comparison of these theoreticalresults with the experimental ones obtained from the PR spectrais presented in Fig. 4. Good agreement has been obtained afterincluding the exciton binding energy. For InGaAs quantum well

Fig. 2. PR spectrum of In0.6Ga0.4As/GaAs quantum dot laser structure.

Fig. 3. Photoreflectance spectra of three DQD structures with various separatingGaAs layers [14]


transitions it should be about 8 meV, whereas for excitons inInGaAs DQDs the binding energy reaches about 20 meV anddepends on the indium concentration and dot shape.

For the three various barrier thicknesses of GaAs layer, thestrength of the electronic coupling between the dots and the wet-ting layer wells varies. For both, WLDQW and DQD systems thetransitions split, and the splitting decreases with increasing bar-rier width, demonstrating a strong dependence on the barrierwidth. In the case of 10 nm GaAs layer, no splitting has beenobserved, showing that almost uncoupled case has beenachieved. More details concerning these investigations can befound in Ref. [14].

RCE detectorThe development of the 1.3 and 1.55 µm fiber telecommunica-tion creates need to construct not only emitters, but also suitabledetectors in this spectral range. One of the possible solutions isan InGaAs/InP resonant cavity enhanced (RCE) detector. Wepresent here the results concerning a device structure designedfor 1.3 µm emission and grown by MOVPE at Faculty ofMicrosystems Electronics and Photonics, Wroclaw University ofTechnology. The structure was deposited on semi-insulating InPsubstrate which was covered by 1 µm of epitaxial, undoped InPbuffer layer. Then, there was grown a Bragg reflector consistingof 15 repetitions of In0.53Ga0.47As (101.4 nm) and InP (90.5 nm)pairs of layers. It is followed by three layers creating a cavity: InP(405 nm), In0.53Ga0.47As (200 nm) and InP (405 nm). Where thesurface plays a role of the top reflector and the In0.53Ga0.47Aslayer is the active part of the detector.

In Figure 5 a comparison of reflectance spectra is shown for sim-ple In0.53Ga0.47As/InP Bragg reflector and for full structure of theRCE detector. In the Bragg reflector spectrum we see a broadmaximum at 1.3 µm where the reflectivity exceeds 90 %, where-as a strong minimum is observed for RCE detector structure,almost exactly at the same wavelength. Such properties of thereflectivity spectra confirm that the device is correctly preparedfor particular wavelength.

The results from modulation spectroscopy, e.g. photoreflectance,can give us additional information on the structure. First of all,PR is sensitive to optical transitions in the structure. Really, bandgap transitions, related to both used materials, are seen in themodulation spectra shown in Fig. 6. There is also presented acomparison of the spectra for Bragg reflector and RCE detector.In both of them we observe oscillation-like features connectedwith the band gap transition in In0.53Ga0.47As and InP layers.

However, in the detector spectrum an additional feature at 1.3µm is seen. It does not match to any possible optical transition inthis structure. This is a cavity mode related feature. It is worth tonote here, that it is seen in PR spectrum but the modulationmechanism is different in this case and we do not deal with elec-tromodulation for optical cavity. This is rather optical path modu-lation, because when the sample is illuminated by a pump beam,the dielectric function of the cavity layers is influenced. Hence,the refractive index is also changed and the optical path of lightthrough the cavity is different. Therefore, it is possible to see thephotoinduced changes in reflectivity, and to detect a non-zeroPR signal. Such an optical path modulation gives a first deriva-tive-like feature, which is confirmed in Fig. 6, in the RCE detec-tor PR spectrum. Thus, photoreflectance is also suitable for opti-cal cavity devices characterisation.

Quantum well laser structureCurrently, InP-based structures belong to the most popular in thelong distance telecommunication light emitters applications. Wewould like to present investigation of InGaAsP/InP laser struc-tures designed for 1.55 µm. The goal was to study the influenceof post-growth modification, like annealing and capping with adielectric film, on optical properties and band lineup of the quan-tum well (QW) active region.

Samples used in this study were grown by gas source molecularbeam epitaxy on n-doped (100) InP substrates at the Centre forElectrophotonic Materials and Devices, Department ofEngineering Physics, McMaster University in Hamilton, Canada.The active region consisted of three compressively strained 5 nm

Fig. 4. Transition energy vs GaAs separating layer thicknessFig. 5. Comparison of reflectivity spectra for In0.53Ga0.47As/InP Bragg reflector and

full RCE detector.

Fig. 6. Comparison of room temperature reflectivity spectra for In0.53Ga0.47As/InPBragg reflector and full RCE detector.


thick quantum wells of In0.76Ga0.24As0.85P0.15 separated by 10 nmthick In0.76Ga0.24As0.52P0.48 barriers lattice-matched to InP. Thecompositions have been chosen so that the In/Ga ratio remainsconstant throughout the wells and barriers. This 'partial' laserstructure is completed with 80 nm upper and lower claddingregions of a 1.15 quaternary layer (In0.76Ga0.24As0.39P0.61) dopedwith 5x1017 cm-3 Be and Si, respectively, and capped withundoped InP, In0.53Ga0.47As and InP layers. The InP shield wasremoved before the deposition of the dielectric film. 1000 Å thicksilicon oxide, silicon nitride or silicon oxynitride films were deposit-ed by electron cyclotron resonance plasma enhanced chemicalvapour deposition (ECR-PECVD). Afterwards, samples were alsoprocessed by Rapid Thermal Annealing (RTA) at 780 °C through60 seconds. The technological details have been published else-where [15,16].

Figure 7 shows room temperature PR and PL spectra for as-grown, as-grown annealed, and SiO2 capped annealed samples.In photoluminescence spectra only one peak related to funda-mental confined state transition in quantum well is seen, whereasthree transitions are observed in the PR spectra. Besides theheavy hole ground state transition (1HH-1C), two additional tran-sitions related to QW region are clearly seen at shorter wave-lengths (higher energies). The transition energies have beenobtained from the fitting procedure according to the first derivativeGaussian line shape, which is the most appropriate PR line fit inthe case of confined state transitions at room temperature [1-3].The two higher energy features have been identified as 2HH-1Cand 1LH-1C basing on the envelope function calculations per-formed for the non-modified structure. The former transition is for-bidden one, but in this case the electric field of the p-i-n laserstructure breaks the selection rules making possible its observa-tion.

Significant blue shift of all those features has been observed afterthe post-growth processing of the samples. The blue shift is

already observed for the annealed sample but strongly enhancedfor capped and then annealed structure. Generally, the blue shiftof the ground state transition is stronger than that for the 1LH-1Cand 2HH-1C ones for all post-growth modified samples anddepends on the stoichiometry of the dielectric layer [17]. It evenreaches 55 meV that is equivalent to more than 100 nm reflectingthe changes of the quantum well profile due to the interdiffusioneffects and so called intermixing of the quantum well. Theseeffects have been previously investigated for similar structures byphotoluminescence and a blue shift has been already observed forthe ground state transition [16]. However, photoreflectance givesan opportunity for more detailed investigations of the QW shapechanges due to the observation of higher order transitions. Theobserved shifts of the PR features are a result of two effects: bandgap changes of the QW layer due to the atom migration inducedlayer composition and strain distribution as well as changes of thewell profile. It is obvious that the change of QW profile from asquare-like to a rounded-like have to shift different energy levels indifferent way. In investigated structures the blue shift is associat-ed with the discussed above shift of energy levels inside thepotential well and a change of the band gap energy of the wellmaterial. The value of the band gap depends on the compositionof the well material, which changes during the post-growth modifi-cation. For our case diffusion of group V atoms takes placebecause group III atoms concentration is kept constant in theactive region. In consequence the band gap increases for the wellmaterial and decreases for the barrier material near the QW inter-face. It causes, that the band gap changes gradually in the growthdirection, in contrast to sharp step like potential of the perfectsquare quantum well. Generally, the observed blue shift of the QWtransitions is a sum of an increase of a band gap energy and anincrease or decrease of the level energy in the well potential. Inour case this sum is positive and in consequence the blue shift ofall three QW transitions has been observed.

Fig. 7. Room temperature PL and PR spectra. Symbols - experiment; solid redlines - PR curve fits.

Fig. 8. Energy difference between the second and the first heavy hole levels ver-sus the blue shift of the ground state transition.

Fig. 9. Dependence of the blue shift on the microwave power of the ECR-PECVDprocess.


From the energy difference between the second and the first heavyhole transitions the energy difference between the second and thefirst heavy hole levels (E2HH-E1HH) can be obtained. This E2HH-E1HHenergy difference versus the blue shift of the ground state transi-tion is presented in Fig. 8 for as-grown, as-grown annealed andfour capped samples with various composition of SiON layer. It isseen, that the stronger blue shift of the ground state transition, thesmaller energy difference between heavy hole levels in the well.Such result is expected and means that strongly modified QW arewider and shallower.

The influence of the microwave power during the dielectric layerdeposition in the ECR-PECVD process has been also investigat-ed. Figure 9 shows a dependence of the PR and PL features blueshift versus the microwave power.

It can be read from Fig. 9, that first of all the blue shift detected inemission (PL) and absorption-like (PR) experiments versus themicrowave power is the same, within an experimental error.Additionally, the PR spectra make possible the observation of high-er order transitions, which are evidently less shifted, reflecting thechanges of the well profile due to the intermixing effect which canbe tuned by the microwave power of the ECR-PECVD process.

ConclusionsPhotoreflectance spectroscopy has been presented as a powerfultechnique for the non-destructive characterisation of low dimen-sional semiconductor structures, especially those which can beapplied as an active medium in novel semiconductor devices. Thismodulation technique usually allows obtaining more informationabout the sample at room temperature than common optical meth-ods at low temperatures. The possibility of probing the excitedstate transitions, including those with weak oscillator strength,belongs to the main advantages. It makes detailed investigation ofdifferent kind of structures in broad group of devices from semi-conductor lasers or detectors to quantum computer logical ele-ments possible.

AcknowledgmentsThe photoreflectance results presented here have been obtainedon samples manufactured at different laboratories. Therefore theauthors are grateful for the structures to: A. Forchel from TechnicalPhysics, Würzburg University, J. Wójcik and D. A. Thompson fromCentre for Electrophotonic Materials and Devices, McMasterUniversity, Hamilton, and M. Tlaczala from Faculty ofMicrosystems Electronics and Photonics, Wroclaw University ofTechnology. One of the authors (G.S.) acknowledges also thefinancial support from the Foundation for Polish Science.

References[1] F. H. Pollak, Modulation spectroscopy of semiconductors andsemiconductor microstructures, in Handbook on Semiconductors,Vol. 2, pp. 527-635, edited by M. Balkanski, Elsevier Science,Amsterdam, 1994.[2] J. Misiewicz, P. Sitarek, G. Sek, Introduction to the photore-flectance spectroscopy of semiconductor structures, WroclawUniversity of Technology Press, Wroclaw, 1999.[3] J. Misiewicz, P. Sitarek, G. Sek, Opto-electronics Review 8, 1(2000).[4] F. Schäfer, J. P. Reithmaier, A. Forchel, Appl. Phys. Lett. 74,2915 (1999).[5] M. Kamp, M. Schmitt, J. Hofmann, F. Schäfer, J. P. Reithmaier,A. Forchel, Electronic Lett. 35, 2036 (1999).[6] F. Klopf, J. P. Reithmaier, A. Forchel Appl. Phys. Lett. 77, 1419(2000).[7] F. Klopf, J. P. Reithmaier, A. Forchel, P. Collot, M. Krakowski, M.Calligaro, Electronics Lett. 37, 353 (2001).[8] M. Bayer, A. Forchel, P. Hawrylak, S. Fafard, G. Narvaez, Phys.Stat. Sol. B 224, 331 (2001).

[9] P. Hawrylak, G. A. Narvaez, M. Bayer, A. Forchel, Phys. Rev.Lett. 85, 389 (2000).[10] R. Akis, D. K. Ferry, Phys. Rev. B 59, 7509 (1999).[11] S. Benjamin, N. F. Johnson, Appl. Phys. Lett. 70, 2321 (1997).[12] N. J. Wu, M. Kamada, A. Natori, H. Yasunaga, Jpn. J. Appl.Phys. 39, 4642 (2000).[13] A. Wójs, P. Hawrylak, S. Fafard, L. Jacak, Phys. Rev. B 54,5604 (1996).[14] G. Sek, K. Ryczko, J. Misiewicz, M. Bayer, F. Klopf, J. P.Reithmaier, A. Forchel, Solid State Commun. 117, 401 (2001).[15] M. Boudreau, M. Boumerzoug, P. Mascher, P.E. Jessop, Appl.Phys. Lett. 63, 3014 (1993).[16] J. F. Hazell, D. A. Thompson, N. Bertsch, J. G. Simmons, B. J.Robinson, G. I. Sproule, Semicond. Sci. Technol. 16, 986 (2001).[17] R. Kudrawiec, G. Sek, W. Rudno-Rudzinski, J. Misiewicz, J.Wójcik, B. J. Robinson, D. A. Thompson, P. Mascher, Mater. Sci.Engeen. B (2002), in press.


IntroductionTrapping of atoms inside of fullerene shells is known as endohe-dral doping and the resulting complex is denoted as A@C60, withA the atomic species trapped within buckminsterfullerene. Thepossibility of endohedrally doping C60 was suggested shortly afterthe discovery of the molecule [1], and the encapsulation of a widevariety of metal atoms has been achieved using arc dischargetechniques. In recent years the range of atoms encapsulated byC60 have been extended using ion implantation techniques[2,3,4,5]. Early studies revealed that rare gas atoms trappedinside buckminsterfullerene sit at the center of the carbon cage,but most atoms are found to strongly interact with the cage andsit in off-center sites. It was found that C60 endohedrally dopedwith nitrogen and phosphorus showed an electron spin reso-nance (ESR) signal that could be identified with the ground stateof the two atomic species nitrogen and phosphorus [3,4,5]. Thisgave rise to speculation about the nature of the endohedral bond-ing of group V atoms. Within this short review, we will discuss theproperties of endohedral nitrogen and phosphorus from a quan-tum chemistry perspective [6,7,8,9] and show that a clear pictureof the electronic and structural properties of N@C60 and P@C60emerges when theoretical findings are compared with existingexperimental results.

Electronic structure and geometryImmediately upon production of N@C60, it was found that thecomplex was soluble, the hyperfine interaction is isotropic, andthe electronic spins state is S=3/2 [1], as in atomic nitrogen. All ofthese facts indicate that the nitrogen is trapped within the carboncage, and is highly suggestive that the nitrogen dopant atomretains, to a remarkable degree, the characteristics of a freeatom. Both electron spin resonance (ESR) and electron nucleardouble resonance measurements (ENDOR) indicate that the spinstates correspond to nitrogen's atomic ground state, and thatthere is little, or no chemical bonding between the dopant andfullerene [3,4,5].

Against this backdrop of experimental findings, we investigatedthe properties of N@C60 and P@C60 using electronic structuretheory methods, in particular, density functional theory (DFT) andHartree-Fock (H-F) [6,7,8,9]. The aim of our studies was tounderstand how open shell systems could be encapsulated bybuckminsterfullerene, yet not chemically react with the carboncage. We chose both correlated (DFT) and uncorrelated (H-F)electronic structure methods to verify our findings because, as

we will discuss, the bonding (or rather lack of bonding) in thesesystems is unusual.

The fact that the nitrogen atom has not reacted with the carboncage, is suggestive that the endohedral group V atoms sits at thecenter of buckminsterfullerene preserving the icosohedral (Ih)symmetry of the molecule. Indeed, we can state that an energyminimum for the atom is at the cage center [6,7,8], and we havecalculated the vibrational spectra for nitrogen and phosphorus atthe cage center. Comparison to experimental vibrational frequen-cies extracted from the temperature dependence of the hyperfineinteraction reveals the computed values to be in good agreement[7].

However, the calculations can only state with certainty that thecentral position is a local energy minimum. There has been somecontroversy for the case of phosphorus, with semi-empiricalmethods indicating that the P atom can sit in off-center sites. Toexplore this, we have performed ab initio calculations at theseproposed sites, but we are unable to identify any local minimumwith the carbon cage other than the central site. Furthermore, ourcalculations reveal that other sites with the fullerene cage aresubstantially higher in energy than the central Ih symmetric site[8]. Given experimental evidence that there is no substantialbonding to the fullerene cage, the agreement between experi-mental and theoretical vibrational frequencies, and that ab initiocalculations suggest all off center sites are substantially higher inenergy, provides us confidence that both group V atoms, nitrogenand phosphorus, are situated at the center of the buckminster-fullerene molecule.

AbstractImmediately after the discovery of buckminsterfullerene, it was proposed to encapsulate atoms within the molecule's hollow car-bon shell. Shortly thereafter, metallic atoms were trapped inside fullerenes as the complexes formed during arc discharges. In

recent years, approaches such as ion implantation have allowed for a variety of atoms to be encapsulated, including the group Vatoms nitrogen and phosphorus. Amazingly, it is found that the highly reactive atoms N and P do not bond when encapsulated byC60. The ability to trap open shell atoms within fullerenes offers unique possibilities for nanotechnology and quantum computing.

Atomic Nitrogen and Phosphorus Trapped in Buckminsterfullerene

J. A. Larsson and J. C. Greer

NMRC, University College, Lee Maltings, Prospect Row, Cork, Ireland

Figure 1 - Electrostatic potential of a point charge within buckminsterfullerene. Thecurve shows that within a radius of ca. 1.5 Å the potential inside the cage is roughlyconstant.


We next consider the electronic structure of the endohedral com-plexes. From spectroscopy studies, it is clear that the groundelectronic state is a spin quartet (S=3/2); i.e. three unpaired elec-trons. We have applied spin unrestricted calculations where elec-tron orbitals for spin pairs are allowed to differ. For our purposes,what this implies is that for the Ih central site, we can perform aspin unrestricted calculation and check to see if the spin squaredeigenvalue S2= 3/2(3/2+1) is approximately preserved, implyingno spin contamination. We indeed find that there is essentially nospin contamination, revealing the quartet spin state is stable atthe Ih symmetric geometry, without spin mixing.

Initially, for our calculations we chose the electron occupancies tocorrespond to the ground states of C60 and nitrogen (or phos-phorus) as determined in Ih symmetry. We found that the orbitalenergies corresponding to the C60 cage are essentially undis-turbed for endohedral nitrogen and essentially only one orbital isshifted in energy for the case of endohedral phosphorus [6]. Theatomic energy levels are shifted down in energy for N and Pdopants, and these energy shifts can be largely ascribed to theelectrostatic potential of the fullerene cage; see fig. 1. To verifythat the orbital occupancies were not biased by the occupancieschosen in Ih symmetry, we removed all spatial symmetry con-straints and find the energies and degeneracies confirm theorbital occupancies found in Ih symmetry. This is an importantpoint, as the open shell orbitals of the endohedral dopants arelower in energy than filled C60 orbitals. Naively, one could expectthat the filled fullerene orbitals could transfer to the open shells ofthe dopant atoms and thus lower the energy of the complex.However, this does not occur and can be understood from a vari-ety of perspectives. One simple explanation is that difference inthe ionization potential for C60 (7.6 eV), and the electron affinityfor nitrogen (~0 eV) makes charge transfer energetically unfavor-able in the absence of chemical bonding. A further considerationis that the radius of buckminsterfullerene molecule is 3.54Ångström, hence the group V dopant atoms are relatively faraway from the carbon atoms, and as a crude approximation, thecomplex is chemically "dissociated".

In fig. 2, we have plotted the charge difference density for nitro-gen in C60. The plot reveals very little charge is transferred to thefullerene cage (outer ring), and the buildup of charge in the cen-ter of the plot reveals that the charge on the endohedral atom hascontracted upon encapsulation, indicating clearly the repulsivenature of the interaction between dopant atom and cage. Asthese calculations were reported, Dinse et al [10] reported chargecontraction at the nitrogen nucleus within fullerene, as detectedby ENDOR spectroscopy.

Nature of the bondingIt turns out that the N@C60 and P@C60 are metastable complex-es: the energy after formation is lower than the energy of a singlebuckminsterfullerene and separated atom. Hence the dissocia-tion process is exothermic, again a result observed experimen-tally and found by calculation. This last fact combined with ourprevious findings, leads to a very simple picture for the trappingof the group V atoms in C60. After the piercing the cage by ionimplantation, the dopant atoms are pinned at the center of thecage by a repulsive interaction with the π orbital network normalto the fullerene surface [7].

In fig. 3, we plot the exothermic formation energy against theatomic radii for helium, nitrogen, neon, and phosphorus. The plotreveals that upon encapsulation, these dramatically differentatomic species interact with the fullerene cages in a similar man-ner, with repulsion pinning the atoms in the center of the cage.The atoms are repelled by the interior surface of the fullerene,and by moving to the center of the cage are able to maximize thedopant atom-carbon distance; the repulsive interaction to thecage is minimized. The idea that the group V dopant atoms wishto maximize the average distance between themselves and thecarbon cage is further born out by another example. A qualitativepicture of bonding to silicon surfaces is captured in fig. 4, wherea carbon double bond is shared with two silicon atoms, repre-senting a dimer on a Si (100) p2x2 reconstruction. The bondingto silicon surface results in a slight distortion to the fullerene cage.We find that the group V atoms move off-center in this case dueto the increased volume in the fullerene cage, thereby again max-imizing the mean distance to the carbon atoms.

Figure 2 - Charge difference density ρ(N@C60) - ρ(C60) - ρ(N) in a cut planethrough buckminsterfullerene with the nitrogen atom located at the center of thecage. The plot reveals there is little charge transfer to fullerene cage and that theatomic charge cloud on nitrogen contracts upon encapsulation (note: the chargedensity scale is logarithmic).

Figure 3 - Exothermic binding energies for He, N, Ne, P as a function of atomicradii <r>. In terms of geometry and binding energies, the group V and rare gasatoms behave similarly as endohedral dopants.


Finally, we examine why bonding to the fullerene cage is inhibited[9]. To investigate this point, a study was undertaken on P bond-ing to hemifullerenes and other graphitic-like molecules, includingC60. The results of the study are very consistent: group V atomscan bond to graphitic-like surfaces if the curvature of the carbonsurface is away from the phosphorus atom. For planar graphiticsurfaces, the bonding to phosphorus induces a curvature in thesystem, again with the curvature away from the phosphorus atom,and interestingly, the optimal curvature for bonding is close invalue to the natural curvature of the exterior of the C60 cage.Hence the group V atoms bond readily with the π-orbitals normalto the buckmisterfullerene on the outside of the cage, but withinthe cage the orientation of the π-orbitals induces a non-bondinginteraction with the dopant atom.

SummaryExperimental and computational studies clearly indicate that nitro-gen and phosphorus retain, to a remarkable degree, their atomicproperties when encapsulated by buckminsterfullerene. Theatoms do not bond to the carbon cage and remain in a quartet spinstate. Essentially, the endohedral complex contains an open-shellatom that is shielded from its external environment by the C60 mol-ecule.

It is well known that fullerene molecules can be positioned usingscanning probe microscopies on a variety of surfaces. Hence, forthe fullerenes doped with endohedral group V atoms, the possibil-ity exists to manipulate open shell atoms on surfaces, withoutchemically reacting to the external environment. This coupled withthe fact that the electronic spin states for the complexes have thelongest lifetimes reported for any molecules (and are comparableto coherence times of defects in solids), offers exciting possibilities

for solid state spintronics and quantum computing [11,12].

AcknowledgmentsWe thank our collaborators J. Dobado, W. Harneit, S. Melchor, D.Suter, J. Twamley, and A. Weidinger, and the European Union forfunding through the IST FET project QIPD-DF and the RTN net-work ATOMCAD.

References[1] J.R. Heath, S.C. O'Brien, Q. Zhang, Y. Liu, R.F. Curl, H.W.Kroto, F.K. Tittel and R.E. Smalley, Journal of the AmericanChemical Society 107 7779 (1985)[2] R. Tellgmann, N. Krawez, S.-H. Lin, I. V. Hertel and E. E. B.Campbell, Nature 382 407 (1996)[3] T. Almeida Murphy, Th. Pawlik, A. Weidinger, M. Höhne, R.Alcala, and J.-M. Spaeth, Physical Review Letters 77 1075 (1996)[4] B. Pietzak, M. Waiblinger, T. Almeida Murphy, A. Weidinger, M.Höhne, E. Dietel and A. Hirsch, Chemical Physics Letters 279 259(1997) [5] B. Pietzak, M. Waiblinger, T. Almeida Murphy, A. Weidinger, M.Höhne, E. Dietel and A. Hirsch, Carbon 36 613 (1998)[6] J. C. Greer, Chemical Physics Letters, 326 567 (2000)[7] J. A. Larsson, J.C. Greer, W. Harneit and A. Weidinger, Journalof Chemical Physics, 116 7849 (2002)[8] J. A. Larsson and J.C. Greer, Molecular Physics, in press(2002)[9] S. Melchor, J. A. Dobado, J. A. Larsson and J. C. Greer, sub-mitted (2002)[10] N. Weiden, B. Goedde, H. Kass, K.P. Dinse, M. Rohrer 851544 Physical Review Letters (2000)[11] W. Harneit, 65 32322 Physical Review A (2002)[12] D. Suter and K. Lim, 65 52309 Physical Review A (2002)

Figure 4 - A model of C60 bonded to a silicon surface. The resulting bond lengthsand cage distortion (in Å) are close to those buckminsterfullerene bonded to largersurface models. The cage distortion results in the endohedral nitrogen being dis-placed downward toward the surface, by 0.126 Å.



IntroductionIn the last decade, the field of shot noise in mesoscopic deviceshas received significant attention, due to a series of extremelyinteresting theoretical and experimental results. Jalabert et al. [1]showed, using random matrix theory, that shot noise in a chaoticcavity defined by two constrictions is suppressed, with respect tothe value predicted by Schottky's theorem [2], by a factor (Fanofactor) depending on the ratio of the number of modes propagatingin the input constriction to that in the output constriction: if the twoconstrictions are identical, the suppression factor is 1/4. Blanterand Sukhorukov [3] have later presented a semi-classical demons-tration of the same result, using a Boltzmann-Langevin approach.These results have received experimental confirmation with anexperiment by Oberholzer et al. [4], in which shot noise suppres-sion by a factor 1/4 has been measured for a symmetric cavitydefined by means of electrostatic depletion in a GaAs/AlGaAsmodulation doping heterostructure. More recently, Sukhorukov etal. [5] have investigated the Fano factor for cascaded cavities inthe assumption of phase incoherence between different cavities. Inthis contribution, instead, we present a discussion of the behaviorof shot noise for a fully phase coherent structure containing onechaotic cavity or two cascaded cavities. We consider also the caseof a cavity in which transport is diffusive as a consequence of alarge number of randomly distributed scatterers. In another article,Oberholzer et al. [6] have presented some interesting experimen-tal results on the shot noise suppression in a chaotic cavity subjectto a perpendicular magnetic field, as well as a simple theoreticalmodel to account for such results. We apply a scattering matrixapproach to the calculation of noise in a similar structure and dis-cuss the results with relationship to Ref. [6], focusing specificallyon the analysis of the behavior of the conductance and of theFano factor of the cavity as a function of magnetic field.

ModelWe consider cavities defined, for simplicity, by hard walls, althoughour method can treat in principle an arbitrary potential landscape.Each cavity is coupled to the outside by means of identical cons-trictions, as shown in the inset of fig. 1: in a classical picture, oncean electron has entered the cavity from the input constriction, it willundergo a large number of reflections on the cavity walls, until itwill leave from one of the two constrictions. From a quantummechanical point of view, we can instead think of diffraction in thecavity, which leads to partial waves leaving from the input and out-put constrictions. Both in the semiclassical and in the quantummechanical picture, shot noise suppression is due to Pauli exclu-sion in the cavity, where the available states have a partial andfluctuating occupancy.

We have used two different numerical models for simulations withand without magnetic field. In the absence of magnetic field we usean approach based on the calculation of the Green's functions ofthe complete structure by means of the recursive composition [7,8]

of elementary sections, for each of which the Green's functionscan be evaluated analytically. Once the Green's function matrix forpropagation from a location on the input lead to a location on theoutput lead is available, it is straightforward [7] to compute thetransmission and reflection matrices, which contain the informationneeded to evaluate the Fano factor, as discussed later in this sec-tion. The recursive Green's function method is particularly conven-ient for the simulation of structures combining hard walls and acomplex geometry, since it does not involve matching wave func-tions and their normal derivatives, which requires particular care athard-wall boundaries [9].

For the simulations in the presence of a magnetic field, we haveinstead adopted the scattering matrix technique. In particular, toanalyze a 2-dimensional device on the x,y plane (assuming x asthe direction of current propagation) and subject to a uniformorthogonal magnetic field B=[0,0,B]T, we have chosen the specificgauge for the vector potential suggested by Governale and Böse[10]: A=[0,Bx,0]T. We have defined a uniform discretization alongthe x direction, with a resolution ∆x such that the vector potentialand the scalar potential have negligible variations along x within adiscretization mesh. Therefore, within each transverse section ofwidth ∆x, the vector potential is constant, and the scalar potentialdepends only on y. With our choice of gauge, by solving theSchrödinger equation in each transverse section located around xi,we find that the n-th eigenmode has an energy

equal to

(the eigenenergy in the absence of a magnetic field) and a trans-verse eigenfunction

which differs only for a phase factor from the eigenfunction

for B=0; in particular

where e is the elementary electron charge,reduced constant and

is the value of the vector potential in the i-th transverse section. Forthe application of the scattering matrix method, we have dividedthe structure into slices, each of which extends from xi to xi+1, the-reby straddling two consecutive transverse sections. Thereforeeach slice contains only one discontinuity, located exactly in the

Numerical investigation of shot noise suppression in chaotic cavities

P. Marconcini, M. Macucci, G. Iannaccone and B. Pellegrini

Dipartimento di Ingegneria dell'Informazione, Università di Pisa, Via Diotisalvi, 2, I-56122 PISA, Italy

AbstractWe perform a numerical investigation of the suppression of shot noise, with respect to the full shot value predicted by Schottky's

theorem, in chaotic cavities with ballistic or diffusive transport, as well as in the presence of a magnetic field. Results are dis-cussed with reference to the recent theoretical and experimental literature.

is Planck's

middle. Using the mode-matching technique [9], we have obtainedthe reflection and transmission matrices for the electrons impin-ging onto the left side of the slice (r and t) and for those impingingonto the right side Therefore we can construct the scattering matrix S of the slice

In order to limit discretization errors, we need to choose ∆x in sucha way that the magnetic field flux threading a slice is much lessthan h/2πe, so that discretization errors are made negligible. Thenwe have recursively combined the scattering matrices of all the sli-ces, obtaining the scattering matrix of the overall structure. Fromits sub-matrix t, we have derived the matrix t' of the transmissioncoefficients normalized with respect to the probability current flux,the generic element of which is

(with νn being the group velocity of the n-th mode). Finally, wehave computed the value of the conductance

and of the power spectral density of the shot noise

(with wn being the eigenvalues of the matrix t't'† and V the exter-nally applied voltage), following Büttiker's approach [11].Knowing that the full shot noise power spectral density is given by2e|I|=2e|V|G, the Fano factor γ can be computed as

ResultsWe have initially tested our approach retrieving the known result[1] for shot noise suppression in a single chaotic cavity with awidth of 5 µm and a length of 7.5 µm; the input and output cons-trictions are identical and 1 µm wide, 0.25 µm long. The Fano fac-tor is reported in fig. 1 as a function of the Fermi energy of theimpinging electrons, while the inset contains a sketch of the cavitygeometry.As the Fermi energy is increased, the number of propagatingmodes increases, so that a chaotic behavior ensues and the Fanofactor fluctuates around the value 1/4. In our calculations we con-sider a maximum of about 60 propagating modes, plus a few tensof evanescent modes. The fluctuations are due to the complexinterference patterns that are established in the chaotic cavity:they would be damped in a model including dephasing effects. Then we have investigated the shot noise suppression in two cas-

caded cavities, whose geometry is sketched in the inset of fig. 2:the dimensions of the cavities and of the constrictions are thesame as those for the single cavity. Results are reported in fig. 2:we notice that the same suppression factor 1/4 is obtained as forthe single cavity. This result differs from that in Ref. [5], which isobtained in the hypothesis of phase incoherence between thecavities. Further work is needed to determine what happens if onlypartial phase coherence exists and what the actual situation in anexperimental device is.

We have then investigated the shot noise suppression in a cavitywith diffusive transport, caused by the presence of 400 randomlylocated scatterers, each of which consists of a square hard-wallobstacle with a side of 50 nm. The resulting potential landscape issketched in fig. 3.

The cavity is 5 µm wide, 7.75 µm long, and the constrictions are 1µm wide and 0.75 µm long. The Fano factor is reported as a func-tion of the Fermi energy of the impinging electrons in fig. 4: wenotice that the suppression factor is almost 1/3, as in a purely dif-fusive wire [12]. Thus, diffusive scattering prevails and the chaoticbehavior of the cavity is quenched. For the investigation of the noise behavior of a cavity in the pre-sence of a magnetic field, we have applied the scattering matrixtechnique outlined in the previous section to a cavity with thesame geometrical dimensions as the one studied for the diffusivecase, but without the randomly located scatterers, and with theinclusion of a uniform magnetic field perpendicular to the planecontaining the device.

We report, in fig. 5, the behavior of the conductance through thecavity as a function of the Fermi energy, for different values of themagnetic field: B=0, 7, 14, 21 mT. We observe that for the casewith B=0 the conductance shows fast oscillations that are due tointerference effects, and that the conductance steps are completelywashed out. In this calculation we have considered up to about 35propagating modes and a few tens of evanescent modes.

Figure 1 - Fano factor in a single chaotic cavity as a function of the Fermi energy;the inset contains a sketch of the cavity. The dashed line indicates the theoreticalvalue 1/4.

Figure 2 - Fano factor for two coherent cascaded cavities as a function of the Fermienergy; the inset contains a sketch of the device. The dashed line indicates the the-oretical value 1/4.

Figure 3 - Potential landscape in a diffusive cavity.


If we compare the average conductance for a given value of theFermi energy with that computed, in the same condition, for a sin-gle constriction, we find that it corresponds to one half of such avalue: in other words the resulting resistance equals the series ofthe resistances due to the constrictions, as expected [1]. As themagnetic field is increased, we notice that conductance quantiza-tion is progressively recovered and that conductance steps havean amplitude corresponding to one single conductance quantum.This can be interpreted in terms of a semiclassical model similar tothat of Ref. [6]: in the presence of a magnetic field, electrons tendto travel in cyclotron orbits, whose radius R is given by R=vm/eB,where v is the electron velocity and m is the effective mass. As thecyclotron radius becomes comparable with the size of the cavity,skipping orbits start forming along its walls and the chaotic beha-vior of the cavity begins to disappear. For values of the magneticfield that yield orbits small compared to the size of the cavity, trans-port is mediated by edge states crawling along the perimeter andthe overall conductance corresponds to that of a single constric-tion. Conductance quantization is first recovered for lower valuesof the energy, since they correspond to a smaller cyclotron radius,

if we consider the electron velocity for the calculation of the cyclo-tron radius equal to the Fermi velocity. For the cavity size beingtaken into account and the considered range of energies, we findthat edge states are formed for values of the magnetic field of theorder of tens of millitesla. This value differs from that reported inRef. [6]: the reasons for this discrepancy should be investigatedmore in detail, since they are in part to be attributed to the limitedvalue of the Fermi energy that we have considered in order to con-tain the size of the numerical problem, and also to details of theexperiment, such as the effective geometry of the cavity on whichmeasurements have been performed. We also notice, for the lar-gest magnetic field reported in fig. 5, that the energy intervalsspanned by each conductance step tend to be of equal amplitude,instead of exhibiting the quadratic increase expected from hard-wall confinement. This is the consequence of the effective parabo-lic confinement due to the action of the magnetic field [13], whichleads to a uniform spacing of the eigenvalues. In fig. 6 we show theFano factor as a function of the Fermi energy for the same seriesof values of the magnetic field.

The suppression factor, oscillating around 1/4 for B=0, declines asB is increased, until shot noise is completely quenched for theenergy intervals in which full conductance quantization is recove-red. The reason for noise disappearance is the same as that for thereappearance of the conductance steps, i.e. the formation of edgestates that crawl along the cavity walls without giving rise to chao-tic behavior.

Conclusions We have presented a numerical investigation of shot noise sup-pression in chaotic mesoscopic cavities, including the effect of dif-fusive regions and of a perpendicular magnetic field. The recursi-ve Green's function method has been used for the investigation ofthe structures without magnetic field, while in the presence of amagnetic field calculations have been performed with the scatte-ring matrix approach and the gauge choice of Ref. [10]. We findthat, in the hypothesis of complete phase coherence, two casca-ded cavities exhibit the same shot noise suppression factor of 1/4as a single cavity and that, if randomly placed scatterers are addedin a cavity to make transport diffusive, the Fano factor is very closeto that for a diffusive wire, without any constriction. We then focuson the analysis of the conductance and noise behavior in the pre-sence of a magnetic field, observing that, as the magnetic fieldincreases and edge states start forming, conductance quantizationis gradually recovered and noise is quenched, due to the disappe-arance of the chaotic behavior. Further work is planned to compa-re with experimental results obtained on specific devices, and tointroduce partial decoherence effects.

References[1] R. A. Jalabert, J.-L. Pichard & C. W. J. Beenakker, Europhys. Lett. 27,255, (1994)[2] W. Schottky, Ann. Phys. (Leipzig) 57, 541, (1918)[3] Ya. M. Blanter & E. V. Sukhorukov, Phys. Rev. Lett. 84, 1280, (2000)[4] S. Oberholzer, E. V. Sukhorukov, C. Strunk, C. Schönenberger, T.Heinzel & M. Holland, Phys. Rev. Lett. 86, 2114, (2001)[5] S. Oberholzer, C. Schönenberger, E. V. Sukhorukov & C. Strunk, cond-mat/0105403, (2001)[6] S. Oberholzer, E. V. Sukhorukov & C. Schönenberger, Nature 415, 765,(2002)[7] F. Sols, M. Macucci, U. Ravaioli & Karl Hess, J. Appl. Phys. 66, 3892,(1989)[8] M. Macucci, A. Galick, and U. Ravaioli, Phys. Rev. B 52, 5210, (1995)[9] M. Macucci and Karl Hess, Phys. Rev. B 46, 15357, (1992)[10] M. Governale and D. Böse, Appl. Phys. Lett 77, 3215, (2000)[11] M. Büttiker, Phys. Rev. Lett. 65, 2901, (1990)[12] C. W. J. Beenakker, M. Büttiker, Phys. Rev. B 46, 1889, (1992)[13] Y. Takagaki and K. Ploog, Phys. Rev. B 51, 7017, (1995)

Figure 4 - Fano factor in a diffusive cavity. The dashed line indicates the theoreticalresult 1/3 for a diffusive conductor.

Figure 5 - Conductance through a chaotic cavity for different values of the perpendi-cular magnetic field. The various curves are vertically shifted by 2 conductance units,for representation purposes.

Figure 6 - Fano factor for a chaotic cavity for different values of the magnetic field.The various curves are vertically shifted by 1 unit for representation purposes. Thedashed lines indicate the reference value 1/4.


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Nucleic Acids Chemistry Group

Ramon Eritja leads the Nucleic Acids Chemistry group at the Institute of MolecularBiology of Barcelona (IBMB)-C.S.I.C. The research group also consists of 2 postdocs, 1PhD students and 1 visiting researcher.

The group's research interests cover the synthesis of modified oligonucleotides and theconjugation of oligonucleotide derivatives to molecules or materials of interest in molecu-lar electronics. Nucleic acids (ADN and ARN) formed by long chains of nucleotides play an important roleon the genetic inheritance. It is possible to prepare in the laboratory small versions ofnucleic acids known as oligonucleotides. The aim of our group is the study of the method-ology used for the preparation of oligonucleotides and related compounds as well as the study of their properties. In particularone of the main research efforts of the group deals with the synthesis of modified oligonucleotides for the assembly of nanopar-ticle based electronic devices. The aim of this project is the development of methods for the fabrication of nanoelectronicdevices using the self-assembly properties of DNA. In this project oligonucleotides are used to direct nanoparticles to adopt apredetermined distribution using the base-pairing properties of nucleic acids. To this aim, nanoparticles are linked to oligonu-cleotides of defined sequence. Also, the incorporation of oligonucleotides to metal electrodes and the selective coating of DNAwith metals to obtain nanowires is being studied in collaboration with other groups.

The group has a laboratory suitable for organic synthesis as well as the equipment for oligonucleotide synthesis, purificationand analysis. The group has strong links with several industrial and academic research groups. The group participates in aE.E.C.C. project: BIOAND.For additional information, please contact Ramon Eritja at email: [email protected]

MEMBERS HIGHLIGHTS 1Nucleic Acids Chemistry Group - Institute of

Molecular Biology of Barcelona (IBMB)-CSIC, Spain

Professor Ramon Eritja

Ramon Eritja is the leader of the Nucleic Acids Chemistry Group at the Institute ofMolecular Biology of Barcelona (IBMB)-C.S.I.C. in Spain. He obtained his PhD fromUniversity of Barcelona in 1983 and joined the Department of Molecular Genetics at theIBMB in 1989 after spending 3 years working at the Beckman Research Institute of Cityof Hope, Duarte, CA, USA and 1 year at University of Colorado at Boulder, CO, USA.During 1994 and 1999 he was group leader at EMBL, Heidelberg, Germany. Hisresearch interests include the methodology of solid phase synthesis applied to thepreparation of oligonucleotide and peptide derivatives and the study of the propertiesand applications of these compounds. He has published/presented near 200 papers inthese areas.

Selected Publications1. "Synthesis of oliognucleotides carrying anchoring groups and their use in the preparation of oligonucleotide-gold conjugates", B.G. de la Torre, J.C.Morales, A. Aviñó, D. Iacopino, A. Ongaro, D. Fitzmaurice, D. Murphy, H. Doyle, G. Redmond, and R. Eritja Helv. Chim. Acta, in press (2002).2. "DNA and protein templated self-assembly of nanoparticle architectures in solution", D. Iacopino, A. Ongaro, L. Nagle, R. Eritja, and D. Fitzmaurice,Angew. Chem. Ed. Int Engl., in press (2002).3. "Toward DNA.-mediated self assembly of carbon naotube-based molecular devices", K.A. Williams, P. Veenhuizen, B.G. de la Torre, R. Eritja andC. Dekker Proc. 11th Kirchberg conference, in press (2002).

Left: structure of the chemicals used for the preparation of oligonucleotides carrying thiolgroups. Above: Hybridization and melting process of oligonucleotide-gold nanoparticleconjugates followed by UV-visible spectroscopy (Figure courtesy of the group of Dr.Gareth Redmond, National Microelectronics Research Center (NMRC), Cork, Ireland)

InstitutionConsejo Superior de Investigaciones Cientificas CSIC http://www.csic.es

GroupNucleic Acid Chemistry Group http://ibmb.csic.es

Group AddressJordi Girona 18-26 Barcelona 08034, Spain

Contact PersonRamon Eritja Tel +34-93-4006145 Fax +34-93-2045904 [email protected]

Group informationnº of Permanent position: 1nº of Post-docs: 2nº of PhD students: 1nº of visiting researchers: 1

Participating ProjectsBiomolecule driven assembly of nanoparticle basedelectronic devices [BIOAND] IST

Instruments & Equiment availableDNA synthesizer UV spectrophotometer HPLC equipment

Areas of ExpertiseDNA synthesis; RNA synthesis; Peptide synthesis;Hybridization Properties of Oligonucleotides; Nonradioactive labelling


IBM Zurich Research Laboratory and the Microcontact Processing Project

The IBM Zurich Research Laboratory is the European branch of IBM Research. Its threeresearch areas are Communication Systems, Computer Science, and Science & Technology.The latter area encompasses projects in computational materials science, display technolo-gies, micro-contact processing, micro- and nanomechanics, nanoscale science, optical net-working, photonics as well as transport and magnetism in layered structures. The micro-con-tact processing project is currently investigating soft lithography, a printing and molding tech-nique based on transferring a pattern from an elastomeric stamp to a solid substrate by con-formal contact. This technique has been developed to reliably replicate nano-features in alow-cost, large-area, high-resolution patterning process. Thin patterned elastomeric layerssupported on laterally stiff, but bendable back planes allow accurate replication of metal fea-tures, biomolecules, fluids, and UV-sensitive polymers over large areas with high yield. Thismethod is especially suitable for the replication of diffractive optical components and to han-dle organic and biological materials not compatible with the solvents needed in classical lith-ographies.

The group consists of five permanent members and three postdoc/Ph.D. students with inter-disciplinary know-how in (bio/polymer) chemistry, physics, materials science, surface science,and nanotechnology. Using sophisticated equipment, they endeavor to solve complex prob-lems associated with nanopatterning and molecular engineering of surfaces. Recent resultsinclude the printing of biomolecules as small as single antibodies (10 nm), etching of thickmetal features that have been selectively protected by printed monolayers (negative printing)or by an inverted method (positive micro-contact printing). Printing dimensions have beenreduced to such an extent that grain boundaries between metal clusters start to dominateelectrical conduction. Thiol printing as well as the printing of catalysts followed by electrolessplating of such metals as nickel or copper have been developed into large-area processes.Finally, the group is also active in molding polymers for diffractive optical elements, pattern-ing of resists by light stamps, and direct processing and biopatterning by means of microflu-idic capillary systems. The group has a solid research background and extensive experiencefrom collaboration with industrial partners/business units in driving scientific results to techno-logical maturity. For additional information, please contact Dr. Bruno Michel by email: [email protected]

MEMBERS HIGHLIGHTS 2

IBM Zurich Research Laboratory and the Microcontact Processing Project,Switzerland

Dr. Bruno Michel

Bruno Michel is the manager of theMicrocontact Processing Project at theIBM Zurich Research Laboratory. Heobtained a Ph.D. in biochemistry fromthe University of Zurich and joined theIBM Zurich Research Laboratory in1986 to work on imaging and manipula-tion of biomolecules and self-assem-bled monolayers by scanning probemicroscopes. After several years ofconducting basic research on self-assembled monolayers, molecularinterfacing, and molecular engineeringof surfaces, he started to work on softlithography. Since 1996 he has headedthe micro-contact processing project,which focuses on the development oflarge-area, high-resolution printing andthe processing of solid substrates usingapproaches such as micro-contactprinting of thiols followed by selectiveetching of metals, printing of biologicalmolecules, microfluidic processing,light stamps, printing of catalysts fol-lowed by plating of metal, and moldingagainst elastomeric masters.

Nanopatterning by softlithography for (a) bioprint-ing, (b) polymer molding, (c)light stamp patterning ofresist, (d) printing of catalystand plating of metal, (e)printing of monolayers fol-lowed by a selective etch-ing, and (f) fluidic patterning.Printing is done using a thinpatterned elastomer layeron a solid backplane (cen-ter). This provides the easeof use and the mechanicalstability to print over zoneslarger than 10 cm (top) withhigh accuracy (distortionmap, bottom).

InstitutionIBM Zurich Research Laboratory ZRLhttp://www.zurich.ibm.com/

GroupMicrocontact Processing Group Conprint http://www.zurich.ibm.com/st/microcontact/index.html

Group AddressScience & Tecnology Department Saeumerstrasse 4, Rueschlikon CH-8803, Switzerland

Contact PersonBruno Michel Tel +411 724 86 48 Fax +41 724 89 58 [email protected] http://www.zurich.ibm.com/~bmi

Group informationnº of Permanent position: 5nº of PhD / postdocs: 3

Participating ProjectsConductive characteristics and mass fabricationof nanoscale integrated circuit nanowires[NANOWIRES] ESPRIT 4 Partner Patterning of biomolecules on sensor surfaces[BIOPATT] BIOTECH Partner Processing on a Nanometre Scale [PRONANO]ESPRIT 3 Partner

Instruments & Equiment availableLithography; SEM; XPS; STM; AFM;Ellipsometry; FTIR; Profilometry

Areas of ExpertiseSurface Science; Soft Lithography; SelfAssembly; Biopatterning

Selected Publications1."Printing Meets Lithography: Soft Approaches to High Resolution Patterning", B. Michel et al., IBM J.Res. Develop. 45 (5), 697-719, 2001. 2."Defect-Tolerant and Directional Wet-Etch Systems for Using Monolayers as Resists", M. Geissler, H.Schmid, A. Bietsch, B. Michel, and E. Delamarche, Langmuir, 18 (6), 2374-2377 (2002).3."Size and Grain-Boundary Effects of a Gold Nanowire Measured by Conducting Atomic ForceMicroscopy", A. Bietschand B. Michel, Appl.Phys. Lett. 80 (18),3346-3348 (2002).4."Positive MicrocontactPrinting", E.Delamarche, M.Geissler, H. Wolf, and B.Michel, J. Am. Chem.Soc. 124 (15), 3834-3835 (2002).


Professor Vincent F. Bayot

Vincent Bayot was born in Belgium, in 1963. He received is Engineering degree in Appliedphysics in 1986 from the Université catholique de Louvain (UCL) and his PhD degree from UCLin 1991. After staying at Princeton University for a postdoc until 1992, he joined the FNRS(Fonds National de la Recherche Scientifique, Belgium) until 1998 and then became professorat UCL. Since his PhD he has been involved in low-dimensional electronic systems and meso-scopic physics, mostly in III-V compounds (quantum Hall effect, ballistic and coherent transport),but also in carbon nanotubes, semi-metals, nano-magnetic materials, nanofabrication tech-niques, SOI quantum devices and nanoelectronics. He has more than 170 publications in inter-national journals and conferences. He is currently president of the multi-disciplinary "ResearchCenter in Micro and Nanoscopic Materials and Electronic Devices" - CERMIN (www.nano.be) -at UCL which groups about 120 people mainly from nano-physics, nano-materials, nano-elec-tronics, nano-biotechnology, microelectronics and microsystems.

Mesoscopic physics and Nanoelectronics Group

Vincent, in connexion with many members of CERMIN, leads the UCL Micro andNanofabrication Clean Room Facilities (MNCRF) which hosts about 20 research projects byabout 35 to 40 people. MNCRF is a multi-disciplinary platform for projects ranging from micro-electronics to self-assembly and nano-biosensors. His own group consists of 2 postdocs, 6 PhDstudents, and 8 engineers and technicians shared with users of the MNCRF.

The group's research interests cover ballistic and coherent transport, mainly in III-V materials;ballistic devices; ultimate CMOS; single-electron devices in SOI (SET and SEM); nano-fabrica-tion techniques (e-beam and nano-imprint lithography); and more recently nano-biosensors.The research in coherent transport investigates UCFs and weak localization phenomena innano-cavities of various shapes and materials. This is in order to study the effect of confinementand spin-orbit coupling on electron coherence. This is of particular importance for quantum com-puting that requires long dephasing times.Ballistic transport is also studied in these materials up to room temperature and at microwavefrequencies. This work is focused on the physics underlying ballistic transport and on the use of ballistic effects in advanceddevices.Silicon-on-insulator is used to develop new single-electron devices (SET and SEM), as well as advanced MOS architectures fordeep submicron devices. High-resolution e-beam lithography is also developed for all the above mentioned studies, as well as nano-imprint in collaborationwith CERMIN researchers. The group is starting to work on nano-biosensors.The group uses 2 clean rooms and a very low temperature/high field/microwave laboratory for transport and thermodynamic meas-urements. The group has many collaborations with various labs in Europe (IEMN-Lille, NHMFL-Grenoble, DIMES-Delft, Salamanca,…) and the US (Princeton, Ohio, Yale, Delphi,…) and is part of ajoint laboratory with IEMN-Lille. The group also actively participates in the national pole in nano-physics(PAI/UIAP) and in various EC projects such as QUEST, SODAMOS, SASEM and NANO-TERA.For additional information, please contact Vincent Bayot at email: [email protected]

See also www.nano.be

MEMBERS HIGHLIGHTS 3 Mesoscopic physics and Nanoelectronics Group

Research Center in Micro and Nanoscopic Materials andElectronic Devices - CERMIN - UCL, Belgium

Institution: Université catholique de Louvain UCLhttp://www.ucl.ac.beResearch center in micro and nanoscopicmaterials and electronic devices CERMIN http://www.cermin.ucl.ac.be

Group:Mesoscopic Physics and Nanoelectronics

Group address:DICE Place du Levant, 3 Louvain-la-Neuve 1348 Belgium

Contact person: Vincent François Bayot Tel 32 10 47 25 57 Fax 32 10 47 25 98 [email protected]

Participating projects: Ballistic nanodevices for terahertz dataprocessing [NANO-TERA] Nanoelectronic and microwave devices Physics of nanostructures Self-Aligned Single Electron Memoriesand Circuits [SASEM] SOurce Drain Architecture for AdvancedMOS technology [SODAMOS]

Instruments & Equiment:Very low-T and High fields Full SOI-CMOS fab line e-beam Nano-lithography nano-imprint Microscopies (e-beam, local probe,...) Electrical and microwave characterization

Areas of expertise:Exp. solid state physics; Mesoscopicphysics; Nanoelectronics ; III-V nanostruc-tures; SOI nanostructures; Nanofabrication

Fig 1 : GaAs/AlGaAs heterostructure on top of which gates define a ballistic cavity inwhich transport is coherent at low temperature.Fig 2 : SEM image of the cross section of a SOI single-electron memory device. One cansee the Si quantum dot (˜10x20 nm) embedded in the gate oxide (black) on top of theMOS channel.Fig 3 : High-resolution Philips SEM-FEG e-beam lithography system with Raith laserstage. Resolution as high as 5 nm have been obtained.Figs 4&5 : Very low temperature laboratory for transport and thermo-dynamic measure-ments. An He3 refrigerator and a dilution fridge with base temperature lower than 20mK(as measured on the RuO thermometer) are combined with a 17T magnet and an in siturotating platform.

Selected Publications1. "Quantum Transport in a multiwalled carbon nanotube" L. Langer, et al.Phys. Rev. Lett. 76, (1996) 479.2. "Giant Low Temperature Heat Capacity of GaAs Quantum Wells nearLandau Level Filling =1", V. Bayot et al., Phys. Rev. Lett. 76, (1996) 4584.3. " Self-aligned SOI nano flash memory device ", X. Tang, et al., Solid StateElectronics, 44 (2000) 2259.4. " Evidence for Spin-Orbit Effects in an Open Ballistic Quantum Dot ", B.Hackens et al., Physica E 12 (2002) 833.


MEMBERS HIGHLIGHTS 4

Plasma Etching group at the Institute of Materials University of Nantes (IMN),France

Dr. Christophe Cardinaud

Christophe Cardinaud is a CNRSresearch fellow. Since 1998 he runs thePlasma Etching group at the Institute ofMaterials University of Nantes (IMN). In1985 he obtained his PhD fromUniversity Pierre et Marie Curie Parisand joined the Plasmas and Thin FilmsLaboratory at IMN to work on the dryetching of materials with application inmicroelectronics, using low pressurereactive plasmas. At present hisresearch interests include deep etchingin SiO2 for integrated optics andMOEMS, etching of organosilicon low-kmaterials for advanced microelectronics,plasma processes for nanometer scalepatterning in the fields of nanoimprintlithography and of Si-containing resistfor DUV lithography. He has pub-lished/presented over 100 papers/com-munications on the topics of plasma pro-cessing and surface analysis.

Plasma Etching group

The research group consists of 4 permanent people and 4 PhD students.The group's research interests cover materials for application in micro/opto-electronics andmicro/nano-technology. The group's research activity is directed to the description and theunderstanding of the mechanism of plasma etching or of plasma treatment that are imple-mented or needed in such technologies. Research topics cover fundamental aspects andrecurrent issues in plasma etching as well as process development. The strategy devel-oped includes extensive studies in the domain of plasma diagnostics, surface analysis andprocess modelling, with the aim to identify the key parameters of etching processes andmechanisms as well as plasma-surface interaction.The research into deep etching of SiO2 focuses on the need to achieve a high etch rateand a large etch selectivity with respect to mask. Other requirements include good profilecontrol and low sidewall roughness. The group has recently investigated Si and SiO2 etch-ing in fluorocarbon plasma by varying substrate bias, excitation power, total pressure, gasmixture and residence time. In particular it has carried out a complete characterisation ofCHF3 and C2F6 plasmas in mixture with H2 or CH4 that includes composition and flux of rad-ical and ionic species. Other important work is in modelling of deep cryogenic etching of Siin SF6-O2.The group participates to the IST NANOTECH and CHANIL projects on nanoimprint lithog-raphy. Research work on plasma processes concerns the fabrication of stamps in Si andSiO2, the transfer into these materials of imprinted patterns using the imprinted polymer asa mask. The key points are the control of pattern dimension (stamp fabrication), the behav-iour to plasma environment of the polymers developed for printing.The topic on DUV lithography takes place within the IST project CRISPIES. Si-containingresists offer a sufficiently low absorbance at 157 nm, but their too low etch resistance inhalogen-based plasmas make the use of a bilayer scheme inevitable. The work concernsthe modification of the material in O2, SF6, CF4 plasmas and their mixtures. Recently wehave described the kinetics of conversion of PDMS into SiOx in oxygen plasma.Investigation of the behaviour of other Si-containing material, as well as the effect of theaddition of a small amount of fluorinated species is under progress. Another important chal-lenge is the understanding and reduction of line edge roughness that is a common stum-bling block for dry-developed resists.

The group's equipment consists of an ICP etchingdevice equipped with numerous diagnostics:Langmuir probe, mass spectrometry, optical emis-sion spectrometry, in-situ real-time multi-wave-length ellipsometry, quasi in-situ photoelectronspectrometry. Numerical methods for process mod-elling include particule in cell and Monte-Carlo.

For additional information, please contactChristophe Cardinaud at email:[email protected] or connect toIMN web site at: http://www.cnrs-imn.fr.

Selected Publications1. "Langmuir probe measurements inan inductively coupled plasma: elec-tron energy distribution functions inpolymerizing fluorocarbon gases usedfor selective etching of SiO2", F.Gaboriau, M-C. Peignon, G. Cartry, L.Rolland, D. Eon, Ch. Cardinaud, G.Turban J. Vac. Sci. & Technol. A20,919-927 (2002).2. "High density fluorocarbon plasmaetching of new resists suitable fornanoimprint lithography", F. Gaboriau,M-C. Peignon, A. Barreau, G. Turban,Ch. Cardinaud, K. Pfeiffer, G.Bleidissel, G. Grützner, MicroelectronicEngineering 53 501-505 (2000).3. "Proposal for an etching mechanismof InP in CH4 - H2 mixtures based onplasma diagnostics and surface analy-sis", Y. Feurprier, Ch. Cardinaud, B.Grolleau, G. Turban, J. Vac. Sci. &Technol. A16, 1552-1559 (1998).

InstitutionCentre National de la Recherche Scientifique,Centre d'Elaboration des Materiaux et d'EtudeStructurale CNRS/CEMES http://www.cnrs.fr/

GroupInstitut des Materiaux Jean Rouxel Laboratoire desPlasmas et des Couches Minces IMN-LPCM http://www.cnrs-imn.fr/

Group AddressIMN-LPCM 2, Rue de la Houssinière BP 32229 Nantes F-44322 France

Contact PersonChristophe Cardinaud Tel +33 2 40 37 39 61 Fax +33 2 40 37 39 59

Christophe.Cardinaud@cnrs-imn.

Group informationnº of Permanent position: 4nº of PhD students: 4

Participating ProjectsChances for a NanoImprint Lithography based fabri-cation technology [CHANIL] IST-1999-13415Partner Critical Resist and Processing Issues at 157nmLithography addressing the 70nm node [157CRISPIES] IST-2000-30143 Partner

Instruments & Equiment availablePlasma reactors; XPS

Areas of ExpertisePlasma processes (etching, deposition & surfacetreatment) Plasma diagnostics (optical emission spectroscopy,mass spectrometry, Langmuir probe) Surface analysis (XPS, ellipsometry, FTIR, SEM,TEM, AFM/STM)

Modeling of plasma processes



Latest publications by PHANTOMS members (1) Applied Physics Letters

High-resolution patterning of semiconductors using electron-beam-assisted wet etching G. Richter, G. Schmidt, and L. W. Molenkamp(Physikalisches Inst. (EP3), Univ. Würzburg, Germany), M. Bibus (Physikalisches Inst. der RWTH Aachen, Germany), J. de Boeck (IMEC, B-3001 Leuven, Belgium).

Applied Physics Letters -- August 26, 2002 -- Volume 81, Issue 9, pp. 1693-1695

Characterization of spin valves fabricated on opaque substrates by optical ferromagnetic resonance A. Barman, V. V. Kruglyak, and

R. J. Hicken (School of Physics, Univ. of Exeter, UK), C. H. Marrows, M. Ali, A. T. Hindmarch, and B. J. Hickey (Dep. of Physics and Astronomy, Univ. of Leeds, UK).

Applied Physics Letters -- August 19, 2002 -- Volume 81, Issue 8, pp. 1468-1470

Measurement of high electron temperatures in single atom metal point contacts by light emission A. Downes, Ph. Dumas, and M. E.

Welland (Nanoscale Science Lab., Dep. of Engineering, Univ. of Cambridge, UK). Applied Physics Letters -- August 12, 2002 -- Volume 81, Issue 7, pp. 1252-1254

Neutral gas temperature estimate in CF4/O2/Ar inductively coupled plasmas Brett A. Cruden, M. V. V. S. Rao, Surendra P. Sharma, and M.Meyyappan (Plasma Research Lab., NASA Ames Research Center, California). Applied Physics Letters -- August 5, 2002 -- Volume 81, Issue 6, pp. 990-992

Surface-modified GaAs terahertz plasmon emitter J. Darmo, G. Strasser, T. Müller, R. Bratschitsch, and K. Unterrainer (Inst. für Festkörperelektronik,Technische Univ. Wien, Austria). Applied Physics Letters -- July 29, 2002 -- Volume 81, Issue 5, pp. 871-873

Carbon nanotube scanning probe for profiling of deep-ultraviolet and 193 nm photoresist patterns Cattien V. Nguyen, Ramsey M.

D. Stevens, Jabulani Barber, Jie Han, and M. Meyyappan (NASA Ames Research Center, California), Martha I. Sanchez, Carl Larson, and William D. Hinsberg (IBM

Almaden Research Center, San Jose, California). Applied Physics Letters -- July 29, 2002 -- Volume 81, Issue 5, pp. 901-903.

Electronic properties of multiwalled carbon nanotubes in an embedded vertical array Jun Li, Ramsey Stevens, Lance Delzeit, Hou Tee

Ng, Alan Cassell, Jie Han, and M. Meyyappan (NASA Ames Research Center, California). Applied Physics Letters -- July 29, 2002 -- Volume 81, Issue 5, pp. 910-912

Room-temperature polariton lasers based on GaN microcavities Guillaume Malpuech(1), Aldo Di Carlo(2), Alexey Kavokin(3), Jeremy J.

Baumberg(1), Marian Zamfirescu(3), Paolo Lugli(2). (1)Dep. of Physics and Astronomy, Univ. of Southampton, UK. (2)INFM-Dep. of Electrical Ing., Univ. of Rome "Tor

Vergata," Italy. (3)LASMEA, CNRS-Univ. Blaise Pascal-Clermont-Ferrand II, France. Applied Physics Letters -- July 15, 2002 -- Volume 81, Issue 3, pp. 412-414

Field electron emission from individual carbon nanotubes of a vertically aligned array V. Semet, Vu Thien Binh, P. Vincent, and D. Guillot

(Lab. d'Emission Electronique, DPM-CNRS, Univ. Lyon 1, France), K. B. K. Teo, M. Chhowalla, G. A. J. Amaratunga, and W. I. Milne (Engineering Dep., Univ. of

Cambridge, UK), P. Legagneux and D. Pribat (Thalès R&T France, Domaine de Corbeville, Orsay, France). Applied Physics Letters -- July 8, 2002 -- Volume 81, Issue

2, pp. 343-345

Correlation between the gain profile and the temperature-induced shift in wavelength of quantum-dot lasers F. Klopf, S. Deubert,

J. P. Reithmaier, and A. Forchel (Technische Physik, Univ. Würzburg, Germany). Applied Physics Letters -- July 8, 2002 -- Volume 81, Issue 2, pp. 217-219

Anti-domain-free GaP, grown in atomically flat (001) Si sub-µm-sized openings B. J. Ohlsson (Solid State Physics, Lund Univ., Sweden), J.-

O. Malm (Materials Chemistry, Lund Univ., Sweden), A. Gustafsson and L. Samuelson (Solid State Physics, Lund Univ., Sweden). Applied Physics Letters -- June 17,

2002 -- Volume 80, Issue 24, pp. 4546-4548

Enhanced transparency ramp-type Josephson contacts through interlayer deposition Henk-Jan H. Smilde, Hans Hilgenkamp, Guus

Rijnders, Horst Rogalla, and Dave H. A. Blank (Low Temperature Division, Dep. of Applied Physics and MESA + Research Inst., Univ. of Twente, The Netherlands).

Applied Physics Letters -- June 17, 2002 -- Volume 80, Issue 24, pp. 4579-4581

On the role of interface states in low-voltage leakage currents of metal-oxide-semiconductor structures F. Crupi and C. Ciofi (Dip.

di Fisica della Materia e Tecnologie Fisiche Avanzate and INFM, Univ. degli Sudi di Messina, Italy), A. Germanò (Facoltà di Ingegneria, Univ. degli Sudi di Messina, Italy),

G. Iannaccone (Dip. di Ingegneria della Informazione, Univ. degli Sudi di Pisa, Italy), J. H. Stathis (IBM Research Division,New York), S. Lombardo (Ist. Nazionale di

Metodologie e Tecnologie per la Microelettronica (IMETEM), Italy). Applied Physics Letters -- June 17, 2002 -- Volume 80, Issue 24, pp. 4597-4599

Degradation of the dielectric permittivity of a strongly oriented Ba0.25Sr0.75TiO3 layer by replacing a SrRuO3 electrodewith an Ag one Yu. A. Boikov and T. Claeson (Physics and Engineering Physics, Chalmers Univ. of Technology and Univ. of Gothenburg, Sweden). Applied Physics

Letters -- June 17, 2002 -- Volume 80, Issue 24, pp. 4603-4605

Mechanical properties of high-aspect-ratio atomic-force microscope tips G. Jänchen and P. Hoffmann (Inst. of Applied Optics, Swiss Federal

Inst. of Technology Lausanne, Switzerland), A. Kriele and H. Lorenz (Sektion Physik and Center for NanoScience (CeNS), Univ. of Munich, Germany), A. J. Kulik (Inst.

of Nuclear Engineering, Swiss Federal Inst. of Technology Lausanne, Switzerland), G. Dietler (Inst. of Condensed Matter Physics, Univ. of Lausanne, Switzerland). Applied

Physics Letters -- June 17, 2002 -- Volume 80, Issue 24, pp. 4623-4625

Properties of carbon onions produced by an arc discharge in water N. Sano, H. Wang, I. Alexandrou, M. Chhowalla, K. B. K. Teo, and G. A. J.

Amaratunga (Dep. Engineering, Univ. Cambridge, UK) K. Iimura (Dep. Chemical Engineering, Himeji Inst. Technology, Shosha, Japan). J. Applied Physics -- September

1, 2002 -- Volume 92, Issue 5, pp. 2783-2788

The interface screening model as origin of imprint in PbZrxTi1-xO3 thin films. I. Dopant, illumination, and bias dependence M. Grossmann,

O. Lohse, D. Bolten, U. Boettger, and T. Schneller (Inst. für Werkstoffe der Elektrotechnik, RWTH Aachen, Germany), R. Waser (Inst. für Werkstoffe der Elektrotechnik,

RWTH Aachen, Germany; Inst. für Festkörperforschung, Research Center Jülich, Germany). J. Applied Physics -- September 1, 2002 -- Vol. 92, Iss. 5, pp. 2680-2687

The interface screening model as origin of imprint in PbZrxTi1-xO3 thin films. II. Numerical simulation and verification M.

Grossmann, O. Lohse, D. Bolten, and U. Boettger (Inst. für Werkstoffe der Elektrotechnik, RWTH Aachen, Germany), R. Waser (Inst. für Werkstoffe der Elektrotechnik,

RWTH Aachen, Germany; Inst. für Festkörperforschung, Research Center Jülich, Germany). J. Applied Physics -- September 1, 2002 -- Vol. 92, Iss. 5, pp. 2688-2696

Journal of Applied Physics


Latest publications by PHANTOMS members (2)

Nanotechnology

Phys. Rev. A

Adsorption behavior and current-voltage characteristics of CdSe nanocrystals on hydrogen-passivated silicon K. Walzer (1), U.

J. Quaade (1), D. S. Ginger (2), N. C. Greenham (2), K. Stokbro (1). (1)Mikroelektronik Centret (MIC), Technical Univ. of Denmark, Lyngby, Denmark. (2)Cavendish Lab.,

Cambridge, UK. J. Applied Physics -- August 1, 2002 -- Volume 92, Issue 3, pp. 1434-1440

Coercivity enhancement above the Néel temperature of an antiferromagnet/ferromagnet bilayer C. Leighton (Dep. of Chemical

Engineering and Materials Science, Univ. of Minnesota), H. Suhl (Dep. of Physics, Univ. of California, San Diego, California), Michael J. Pechan and R. Compton (Dep. of

Physics, Miami Univ., Oxford, Ohio), J. Nogués (Dep. de Física, Univ. Autonoma de Barcelona, Spain), Ivan K. Schuller (Dep. of Physics, Univ. of California, San Diego,

California). J. Applied Physics -- August 1, 2002 -- Volume 92, Issue 3, pp. 1483-1488.

Effect of Ga implantation on the magnetic properties of permalloy thin films D. Ozkaya L and R. M. Langford (Dep. of Materials, Univ. of

Oxford, UK), W. L. Chan (Chinese University of Hong Kong Science Centre Shatin, Hong Kong), A. K. Petford-Long (Dep. of Materials, Univ. of Oxford, UK). J. Applied

Physics -- June 15, 2002 -- Volume 91, Issue 12, pp. 9937-9942

Domain nucleation in arrays of perpendicularly magnetized dots S. P. Li (Lab. de Photonique et de Nanostructures, CNRS, France / Nanoscale

Science Lab., Dep. of Engineering, Univ. of Cambridge, UK), A. Lebib and Y. Chen (Lab. de Photonique et de Nanostructures, CNRS, France), Y. Fu and M. E. Welland(Nanoscale Science Lab., Dep. of Engineering, Univ. of Cambridge, UK). J. Applied Physics -- June 15, 2002 -- Volume 91, Issue 12, pp. 9964-9968

Field emission properties of carbon nanohorn films J.-M. Bonard, R. Gaál, S. Garaj, L. Thien-Nga, and L. Forró (Faculté des Sciences de Base, École

Polytechnique Fédérale de Lausanne, Switzerland), K. Takahashi and F. Kokai (Inst. Research-Innovation, Japan), M. Yudasaka (ICORP-JST, Nanotubulites Project,

Japan), S. Iijima (Inst. Research - Innovation, Japan / NEC Fundamental Research Lab., Japan / Meijo Univ., Japan). J. Applied Physics -- June 15, 2002 -- Volume 91,

Issue 12, pp. 10107-10109

Quantitative x-ray photoelectron spectroscopy study of Al/AlOx bilayers Xavier Batlle, Bart Jan Hattink, and Amílcar Labarta (Dep. Física

Fonamental, Univ. Barcelona, Spain), Johan J. Åkerman, Roberto Escudero, and Ivan K. Schuller (Dep. of Physics, Univ. of California, San Diego). J. Applied Physics -

- June 15, 2002 -- Volume 91, Issue 12, pp. 10163-10168

Neutral gas temperature estimates in an inductively coupled CF4 plasma by fitting diatomic emission spectra Brett A. Cruden,

M. V. V. S. Rao, Surendra P. Sharma, and M. Meyyappan (NASA Ames Research Center, Moffett Field, California). J. Applied Physics -- June 1, 2002 -- Volume 91, Issue

11, pp. 8955-8964

Suppression of spontaneous emission in incomplete opaline photonic crystal S. G. Romanov, T. Maka, and C. M. Sotomayor Torres (Inst.

of Materials Science and Dep. of Electrical and Information Engineering, Univ. of Wuppertal, Germany), M. Müller and R. Zentel (Inst. for Organic Chemistry, Dep. of

Chemistry and Pharmacy, Univ. of Mainz, Germany). J. Applied Physics-- June 1, 2002 -- Volume 91, Issue 11, pp. 9426-9428

Structural, thermal, and magnetic properties of Ni2MnGa J. Enkovaara, A. Ayuela and R. M. Nieminen (Lab. of Physics, Helsinki Univ. of Technology,

Finland) L. Nordström (Dep. of Physics, Uppsala Univ., Sweden). Journal of Applied Physics -- May 15, 2002 -- Volume 91, Issue 10, pp. 7798-7800.

Lattice strain and lattice expansion of the SrRuO3 layers in SrRuO3/PbZr0.52Ti0.48O3/SrRuO3 multilayer thin films C. L. Jia,

J. Rodríguez Contreras, U. Poppe, H. Kohlstedt, R. Waser, and K. Urban (Inst. für Festkörperforschung, Forschungszentrum Jülich GmbH, Germany). J. Applied Physics

-- July 1, 2002 -- Volume 92, Issue 1, pp. 101-105

Interplay between GaN and AlN sublattices in wurtzite AlxGa1-xN alloys revealed by Raman spectroscopy A. L. Alvarez (Dep. de

Ciencia y Tecnología de los Materiales, Univ. Miguel Hernández, Alicante, Spain), F. Calle, E. Monroy, J. L. Pau, M. A. Sanchez-Garcia, E. Calleja, and E. Muñoz (ISOM

and Dep. de Ingeniería Electrónica, ETSI Telecomunicación (UPM), Madrid, Spain), F. Omnes and P. Gibart (CRHEA-CNRS, Parc Sophia Antipolis, Valbonne, France), P.

R. Hageman (Katholieke Univ. Nijmegen, Fac. der Natuurwetenschappen, The Netherlands). J. Applied Physics -- July 1, 2002 -- Volume 92, Issue 1, pp. 223-226

Hole transport in coupled SiGe quantum dots for quantum computation Paul A. Cain and Haroon Ahmed (Microelectronics Research Centre,

Cavendish Lab., Univ. of Cambridge, UK), David A. Williams (Hitachi Cambridge Lab., Hitachi Europe Ltd., Cavendish Lab., UK). J. Applied Physics -- July 1, 2002 --

Volume 92, Issue 1, pp. 346-350

Ultrahigh resolution of lead zirconate titanate 30/70 domains as imaged by piezoforce microscopy S Dunn, C P Shaw, Z Huang and

R W Whatmore (Building 70 (Nanotechnology), Cranfield Univ., UK). Nanotechnology 13 (August 2002) 456-459

Forecasting the development of nanotechnology with the help of science and technology indicators Ramón Compañó and Angela

Hullmann (European Commission, Brussels, Belgium). IoP Electronic Journals, Nanotechnology, Volume 13, Number 3, (June 2002). Published 26 April 2002

Atomic diffraction from nanostructured optical potentials G. Lévêque, C. Meier, R. Mathevet, C. Robilliard, and J. Weiner (Lab. de Collisions,

Agrégats et Réactivité, UMR 5589 du CNRS et l'Univ. Paul Sabatier, Toulouse, France), C. Girard (Centre d'Elaboration de Matériaux et d'Etudes Structurales,Toulouse,

France), J. C. Weeber (Lab. de Physique de l'Univ. Bourgogne, Dijon, France). Phys. Rev. A 65, 053615 (2002). Print Issue of May 2002


Latest publications by PHANTOMS members (3) Phys. Rev. B

Modelization of resistive heating of carbon nanotubes during field emission P. Vincent, S. T. Purcell, C. Journet, and Vu Thien Binh (Lab.

d'Émission Électronique, Univ. Lyon-1, Villeurbanne , France). Phys. Rev. B 66, 075406 (2002). Print Issue of 15 August 2002

Semiclassical theory of shot noise in ballistic n+-i-n+ semiconductor structures: Relevance of Pauli and long-rangeCoulomb correlations G. Gomila (Research Center for Bioelectronics and NanoBioScience, Dep. d'Electrònica, Univ. Barcelona, Spain), I. R. Cantalapiedra (Dep.

de Física Aplicada, Univ. Politècnica Catalunya, Barcelona, Spain), T. González (Dep. Física Aplicada, Univ. Salamanca, Spain), L. Reggiani (INFM-National

Nanotechnology Lab. and Dip. Ingegneria dell'Innovazione, Univ. Lecce, Italy). Phys. Rev. B 66, 075302 (2002). Print Issue of 15 August 2002.

Conductance oscillations in metallic nanocontacts P. Havu, T. Torsti, M. J. Puska, and R. M. Nieminen (Lab. of Physics, Helsinki Univ. of Technology,

Finland). Phys. Rev. B 66, 075401 (2002). Print Issue of 15 August 2002

Surface enhanced Raman spectroscopy as a probe for local modification of carbon films A. Ilie, C. Durkan, W. I. Milne, and M. E.Welland (Engineering Dep., Cambridge Univ., Cambridge , UK). Phys. Rev. B 66, 045412 (2002). Print Issue of 15 July 2002

Line narrowing in single semiconductor quantum dots: Toward the control of environment effects C. Kammerer(1), C. Voisin(1), G.

Cassabois(1), C. Delalande(1), Ph. Roussignol(1), F. Klopf(2), J. P. Reithmaier(2), A. Forchel(2) and J. M. Gérard. (1)LPMC-Ecole Normale Supérieure,Paris Cedex 05,

France. (2)Technische Physik, Univ. Würzburg, Germany. (3)LPN-CNRS, Bagneux, France. Phys. Rev. B 66, 041306(R) (2002). Print Issue of 15 July 2002

Enhanced light emission of InxGa1-xAs quantum dots in a two-dimensional photonic-crystal defect microcavity T. D. Happ, I.

I. Tartakovskii, V. D. Kulakovskii, J.-P. Reithmaier, M. Kamp, and A. Forchel (Technische Physik, University Würzburg, Germany). Phys. Rev. B 66, 041303(R) (2002).

Print Issue of 15 July 2002

Dissipation and noise in adiabatic quantum pumps M. Moskalets(1,2) and M. Büttiker(1). (1)Dep. de Physique Théorique, Univ. de Genève,

Switzerland. (2)Dep. of Metal and Semiconductor Physics, National Technic Univ. "Kharkov Polytechnic Inst.," Ukraine. Phys. Rev. B 66, 035306 (2002). Print Issue of 15

July 2002

Dominance of charged excitons in single-quantum-dot photoluminescence spectra M. Lomascolo (1,2), A. Vergine (1), T. K. Johal (1), R.

Rinaldi (1), A. Passaseo (1), R. Cingolani (1), S. Patanè (3), M. Labardi (4), M. Allegrini (4), F. Troiani (5) and E. Molinari (5). (1) NNL National Nanotechnology Lab. of

INFM, Univ. di Lecce, Italy. (2) IMM-CNR, Istit. per la Microelettronica e Microsistemi, Campus Universitario, Italy. (3) INFM and Dip. Fisica della Materia e Tecnologie

Fisiche Avanzate, Univ. di Messina, Italy. (4) INFM and Dip. di Fisica "Enrici Fermi," Univ. di Pisa, Italy. (5) INFM National Research Center on nanoStructures and

Biosystems at Surfaces (S3) and Dip. di Fisica, Univ. di Modena e Reggio Emilia, Italy. Phys. Rev. B 66, 041302(R) (2002). Print Issue of 15 July 2002

Switching current of a Cooper pair transistor with tunable Josephson junctions P. Ågren, J. Walter, and D. B. Haviland (Nanostructure

Physics, Stockholm Center for Physics, Astronomy and Biotechnology, Sweden). Phys. Rev. B 66, 014510 (2002). Print Issue of 1 July 2002

Domain pattern formation and kinetics on ferroelectric surfaces under thermal cycling using scanning force microscopy V.

Likodimos, M. Labardi, and M. Allegrini (INFM and Dip. di Fisica, Univ. di Pisa, Italy). Phys. Rev. B 66, 024104 (2002). Print Issue of 1 July 2002

Properties of small carbon clusters inside the C60 fullerene R. Astala, M. Kaukonen, and R. M. Nieminen (Lab. of Physics, Helsinki Univ. of

Technology, Finland), G. Jungnickel and T. Frauenheim (Univ./Gesamthochschule Paderborn, Germany). Phys. Rev. B 65, 245423 (2002). Print Issue of 15 June 2002

First-principles study of the blue bronze K0.3MoO3 J.L. Mozos, P. Ordejón and E. Canadell (Ins. Ciència Materials Barcelona, CSIC, Barcelona, Spain).

Phys. Rev. B 65, 233105 (2002). Print Issue of 15 June 2002

Resonant effect of Zener tunneling current M. Morifuji, T. Imai, and C. Hamaguchi (Dep. Electronic Engineering, Osaka Univ., Japan), A. Di Carlo (INFM-

Dep. Electronic Engineerig, Univ. Rome "Tor Vergata" , Italy), P. Vogl, G. Böhm, G. Tränkle, and G. Weimann (Walter Schottky Inst., Technical Univ. Munich, Germany).

Phys. Rev. B 65, 233308 (2002). Print Issue of 15 June 2002

Accurate density functionals: Approaches using the adiabatic-connection fluctuation-dissipation theorem Martin Fuchs and

Xavier Gonze (Unité PCPM, Univ. Catholique de Louvain, Belgium). Phys. Rev. B 65, 235109 (2002). Print Issue of 15 June 2002

Oscillations in the differential transmission of a semiconductor microcavity with reduced symmetry G. Dasbach(1), A. A.

Dremin(1,2), M. Bayer(1), V. D. Kulakovskii(1,2), N. A. Gippius(1,3) and A. Forchel(1). (1)Technische Physik, Univ. Würzburg, Germany. (2)Inst. of Solid State Physics,

Russia. (3)General Physics Inst., Moscow, Russia. Phys. Rev. B 65, 245316 (2002). Print Issue of 15 June 2002

Tunneling-induced luminescence from adsorbed organic molecules with submolecular lateral resolution Germar Hoffmann,

Laurent Libioulle, and Richard Berndt (Inst. für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Germany). Phys. Rev. B 65, 212107

(2002). Print Issue of 1 June 2002

Conformations of a molecular wire adsorbed on a metal surface J. Kuntze and R. Berndt (Inst. für Experimentelle und Angewandte Physik der

Univ. Kiel, Germany), P. Jiang, H. Tang, A. Gourdon, and C. Joachim (CEMES-CNRS, Toulouse Cedex, France). Phys. Rev. B 65, 233405 (2002). Print Issue of 15 June

2002

Relaxation of excited electrons in an electron gas: A mean-field approach with charge and spin polarizations I. Nagy (1,2), M.

Alducin (3) and P. M. Echenique (4,5). (1) Dep. Theoretical Physics, Inst. Physics, Technical Univ. of Budapest, Hungary. (2) Donostia International Physics Center, San

Sebastián, Spain. (3) Dep. Ingeniería Eléctrica, E.T.S.I.I., Univ. País Vasco, Bilbao, Spain. (4) Dep. Física Materiales, Univ. País Vasco, San Sebastián, Spain. (5) Centro

Mixto CSIC-UPV/EHU, San Sebastián, Spain. Phys. Rev. B 65, 235102 (2002). Print Issue of 15 June 2002

Transition from strong to weak coupling and the onset of lasing in semiconductor microcavities R. Butté(1) G. Delalleau(1) A. I.

Tartakovskii(1) M. S. Skolnick(1) V. N. Astratov(1) J. J. Baumberg(2) G. Malpuech(3),(4) A. Di Carlo(3) A. V. Kavokin(4) and J. S. Roberts(5). (1)Dep. Physics - Astronomy,

Univ. Sheffield, UK (2)Dep. Physics - Astronomy, Univ. Southampton, UK (3)INFM-Dep. Electrical Engineering, Univ. Rome, Italy (4)LASMEA (UMR 6602 CNRS), Univ.

Blaise Pascal Clermont-II, France (5)Dep. of Electronic and Electrical Engineering, Univ. of Sheffield, UK. Phys. Rev. B 65, 205310 (2002). Print Issue of 15 May 2002


Latest publications by PHANTOMS members (4) Phys. Rev. Lett

Review of Scientific Instruments

The Journal of Chemical Physics

Role of Surface Plasmons in the Decay of Image-Potential States on Silver Surfaces A. García-Lekue(1), J. M. Pitarke(1,2), E. V. Chulkov(2,3),

A. Liebsch(4) and P. M. Echenique(2,3). (1)Materia Kondentsatuaren Fisika Saila, Zientzi Fakultatea, Euskal Herriko Unibertsitatea,Bilbo, Spain. (2)Donostia International

Physics Center(DIPC) and Centro Mixto CSIC-UPV/EHU, Donostia, Spain. (3) Materialen Fisika Saila, Kimika Fakultatea, Euskal Herriko Unibertsitatea, Donostia, Spain. (4)

Inst. Festkörperforschung, Forschungszentrum Jülich, Germany. Phys. Rev. Lett. 89, 096401 (2002). Print Issue of 26 August 2002

Exchange Bias in Spin-Engineered Double Superlattices P. Steadman, M. Ali, A. T. Hindmarch, C. H. Marrows, and B. J. Hickey (Dep. Physics -

Astronomy, E. C. Stoner Lab., Univ. Leeds, UK), Sean Langridge, R. M. Dalgliesh, and S. Foster (ISIS, Rutherford Appleton Lab., Chilton, UK). Phys. Rev. Lett. 89, 077201

(2002). Print Issue of 12 August 2002

Anisotropy and Interplane Interactions in the Dielectric Response of Graphite A. G. Marinopoulos(1), L. Reining(1), V. Olevano(1), A. Rubio(2),

T. Pichler(3,4), X. Liu(3), M. Knupfer(3) and J. Fink(3). (1)Lab. Solides Irradiés, CNRS/CEA, École Polytechnique, France. (2)Dep. Física Materiales, Facultad Químicas,

Euskal Herriko Unibertsitatea, Centro Mixto CSIC-UPV/EHU and Donostia International Physics Center (DIPC), San Sebastián/Donostia, Spain. (3)Inst. für Festkörper und

Werkstofforschung, Dresden, Germany. (4)Inst. für Materialphysik, Univ. Wien, Austria. Phys. Rev. Lett. 89, 076402 (2002). Print Issue of 12 August 2002

Current-Voltage Curves of Atomic-Sized Transition Metal Contacts: An Explanation of Why Au is Ohmic and Pt is Not S. K.

Nielsen(1), M. Brandbyge(2), K. Hansen(1), K. Stokbro(2), J. M. van Ruitenbeek(3) and F. Besenbacher(1). (1)Interdisciplinary Nanoscience Center (iNano), CAMP and Dep.

of Physics and Astronomy, Univ. of Aarhus, Denmark. (2)Mikroelektronik Centret (MIC), Technical Univ. of Denmark, Denmark. (3)Kamerlingh Onnes Lab., Univ. Leiden, The

Netherlands. Phys. Rev. Lett. 89, 066804 (2002). Print Issue of 5 August 2002

Ultrafast Coherent Electron Transport in Semiconductor Quantum Cascade Structures F. Eickemeyer, K. Reimann, M. Woerner, and T.

Elsaesser (Max-Born-Inst. für Nichtlineare Optik und Kurzzeitspektroskopie, Berlin, Germany), S. Barbieri and C. Sirtori (Thales-CSF, Lab. Central de Recherches, Orsay,

France), G. Strasser, T. Müller, R. Bratschitsch, and K. Unterrainer (Inst. für Festkörperelektronik und Mikrostrukturzentrum, Technische Univ., Wien, Austria). Phys. Rev.

Lett. 89, 047402 (2002). Print Issue of 22 July 2002

Chaotic Dot-Superconductor Analog of the Hanbury Brown-Twiss Effect P. Samuelsson and M. Büttiker (Dép. de Physique Théorique, Univ. de

Genève, Switzerland). Phys. Rev. Lett. 89, 046601 (2002). Print Issue of 22 July 2002

Temperature Control of Electronic Channels through a Single Atom Gérald Dujardin, Andrew J. Mayne, and Franck Rose (Lab. de Photophysique

Moléculaire, Univ. Paris-Sud, France). Phys. Rev. Lett. 89, 036802. Print Issue of 15 July 2002

Hidden In-Plane Anisotropy of Interfaces in Zn(Mn)Se/BeTe Quantum Wells with a Type-II Band Alignment D. R. Yakovlev (1,2), A. V.

Platonov (1,2), E. L. Ivchenko (2), V. P. Kochereshko (2), C. Sas (1), W. Ossau (1), L. Hansen (1), A. Waag (3), G. Landwehr (1) and L. W. Molenkamp (1). (1) Physikalisches

Inst. der Univ. Würzburg, Germany. (2) A. F. Ioffe Physico-Technical Inst., Russian Academy of Sciences, St. Petersburg, Russia. (3) Abteilung Halbleiterphysik, Univ. Ulm,

Germany. Phys. Rev. Lett. 88, 257401 (2002). Print Issue of 24 June 2002

Quantum Conductance in Semimetallic Bismuth Nanocontacts J. G. Rodrigo, A. García-Martín, J. J. Sáenz, and S. Vieira (I.U. Ciencia Materiales "Nicolás

Cabrera" and Lab. de Bajas Temperaturas, Dep. Física Materia Condensada, Univ. Autónoma de Madrid, Spain). Phys. Rev. Lett. 88, 246801 (2002). Print Iss. 17 June 2002

Two-Electron Quantum Dot Molecule: Composite Particles and the Spin Phase Diagram A. Harju, S. Siljamäki, and R. M. Nieminen (Lab. of

Physics, Helsinki Univ. of Technology, Finland). Phys. Rev. Lett. 88, 226804 (2002). Print Issue of 3 June 2002

Abrasive Wear on the Atomic Scale E. Gnecco, R. Bennewitz, and E. Meyer (Inst. Physics, Univ. Basel, Switzerland). Phys. Rev. Lett. 88, 215501 (2002). Print

Issue of 27 May 2002

Atomic-Scale Structure of Dislocations Revealed by Scanning Tunneling Microscopy and Molecular Dynamics J. Christiansen(1),(2)

K. Morgenstern(3),(4) J. Schiøtz(1) K. W. Jacobsen(1) K.-F. Braun(3) K.-H. Rieder(3) E. Lægsgaard(4) and F. Besenbacher(4). (1)CAMP and Dep. of Physics, Technical Univ.

of Denmark (2)Materials Research Dep., Risø National Lab., Roskilde, Denmark (3)Inst. für Experimentalphysik, FB Physik, Freie Univ. Berlin, Germany (4)CAMP and Dep.

of Physics and Astronomy, Univ. of Aarhus, Denmark. Phys. Rev. Lett. 88, 206106 (2002). Print Issue of 20 May 2002

Development of a versatile SMOKE system with electrochemical applications J.R. Hampton, J.L. Martínez-Albertos and H.D.

Abruña (Dep. Chemistry -Chemical Biology, Baker Lab., Cornell Univ., Ithaca, New York). Review of Sci. Instruments -- August 2002 -- Vol. 73, Issue 8, pp. 3018-3021

Polarization-modulation near-field optical microscope for quantitative local dichroism mapping L. Ramoino, M. Labardi, N. Maghelli,

L. Pardi, and M. Allegrini (INFM and Dip. di Fisica, Univ. di Pisa, Italy) S. Patanè (INFM and Dip. di Fisica della Materia e Tecnologie Fisiche Avanzate, Univ. di Messina,

Italy) Review of Scientific Instruments -- May 2002 -- Volume 73, Issue 5, pp. 2051-2056

Energy dependence of diffractive and rotationally inelastic scattering of D2 from NiAl(110) D. Farías and R. Miranda (Dep. de

Física de la Materia Condensada C-III, Inst. Nicolás Cabrera, Univ. Autónoma de Madrid, Spain), K. H. Rieder (Fachbereich Physik, Freie Univ. Berlin, Germany). The

Journal of Chemical Physics -- August 1, 2002 -- Volume 117, Issue 5, pp. 2255-2263

Interaction of molecular and atomic hydrogen with (5,5) and (6,6) single-wall carbon nanotubes J.S. Arellano (A. Física Atómica Molecular

Aplic., Univ. Autónoma Metropolitana Azcapotzalco, México), L. M. Molina (Inst. Physics-Astronomy, Univ. Aarhus, Denmark), A. Rubio (Dep. Física Materiales, Univ. PaísVasco,San Sebastián, Spain), M. J. López and J. A. Alonso (Dep. Física Teórica, Univ. Valladolid, Spain). J. Chem. Physics -- August 1, 2002 -- Vol. 117, Iss. 5, pp. 2281

A helium atom scattering study of the H/NiAl(110) adsorption system D. Farías (Dep. Física Materia Condensada & Inst. Nicolás Cabrera, Univ.

Autónoma Madrid, Spain), M. Patting & K. H. Rieder (Fachbereich Physik, Freie Univ. Berlin, Germany). J. Chem. Physics - July 22, 2002 - Vol. 117, Iss. 4, pp. 1797-1803

The Phantoms Nanotechnology HUB www.phantomshub.comThis computational hub is a repository of simulationcodes useful for modelling and design of nanoscaleelectron devices. Many groups in universities and rese-arch centers have developed advanced simulationsoftware, which could be of interest for the generalnanotechnology community: the mission of the PHAN-TOMS hub is to become the virtual venue where manyof these codes can be run by registered users, sharinginsights and comparing results. To make this initiative successful, contributions fromresearchers active in the field of modelling of nanosca-le structures and devices are solicited. Authors whowish to contribute their codes need only to provide theexecutables (in the form of Linux binaries) and a LaTeXdocument (with encapsulated PostScript figures) con-taining a tutorial. In order to keep the hub user-friendlyand valuable for its users, we ask that particular carebe spent in the preparation of the tutorial document:sufficient detail should be included to enable an avera-ge user to successfully supply inputs and run the pro-grams. A few template input files are also appreciated.

The Phantoms Nanotechnology HUBThe preprint archiveThis archive is a repository of preprints in the field of modelling and design in nanotechnology. We are developing a search inter-face to make access to the material in the archives as straightforward as possible: please let us know any suggestion you mayhave for improvement, using the e-mail address indicated in the home page. We are soliciting contributions both to the preprintand to the simulation code archive: the former can be submitted through the WEB interfaces linked from the home page with avery simple procedure. As far as codes are concerned, please contact the e-mail addresses listed on the home page.

Available codes Abinit: ABINIT is a package whose main program allows to find the total energy,charge density and electronic structure of systems made of electrons and nuclei(molecules and periodic solids) within Density Functional Theory, using pseudopo-tentials and a planewave basis. CircDot: The program computes, including Coulomb interaction, the chemi-cal potential in a 2-dimensional circular quantum dot. Dew2D: Poisson-Schrödinger simulations of a deep etched wire. GatePot: code for the computation of the bare confinement potential produced bypolygonal gates. MCCI: Monte Carlo Configuration Generation Computer Program for the Calculationof Electronic States of Atoms, Molecules, and Quantum Dots.MCDot: Monte Carlo simulator for single-electron circuits. Nanotcad1D: 1D self consistent Schrödinger-Poisson solver for quantum devices. Nanotcad2D: 2D self consistent Schrödinger-Poisson solver for quantum devices. Octopus: program aimed at the ab initio virtual experimentation on electron/iondynamics in external electromagnetic fields of arbitrary intensity, shape and fre-quency in a hopefully ever increasing range of systems types. QCAsim: code for the simulation of QCA circuits. QCDot: Hartree-Fock ground state calculation for 2D chaotic quantum dots. QCL: QCL is a hight level, architecture independent programming language forquantum computers. QevoFFT: The program compute the time evolution of a quantum particle locatedin a fixed 1D potential plus an external oscillating field via a FFT algorithm. RGF2D: this code computes the transmission and reflection coefficients through a2D mesoscopic structure, using the recursive Green's function formalism.Shortdev: code for the computation of the autocorrelation function of electron velo-cities in a short device. Transiesta: electron transport along molecular structures.


NanoINDEX: Nanotechnology Industry Exchanges NEXUS and PHANTOMS, have jointly set-up since June 2002 a concerted action aimed at bridging micro and nanotechnologies.Under this new activity entitled NanoINDEX (funded within the IST programme), PHANTOMS will identify a group of experts in nano-technology who will become active members of the NEXUS User-Supplier-Clubs. The intention is to enable a better understandingof the future potential of nanotechnology in the context of microsystems-driven applications.

The NEXUS User Supplier Club (USC)

The objective of NEXUS USCs is to provide a forumthat brings users and suppliers together to share tech-nological and commercial information on MST.Currently, there are seven active USCs established onthe basis of the NEXUS market assessment which pre-dicted significant growth in specific applications,namely:

Aerospace and Geophysics Automotive CAD Tools Household Appliances Industrial Process Control Medical Devices MEMS Packaging Peripherals and Multimedia Pharmaceutical & Analytical Telecommunications

An important objective set up by PHANTOMS is to makeindustry aware of the strategic importance of nanoelectro-nic research for the future of information technology (IT) ingeneral and of microelectronics in particular. For this pur-pose, the network hopes to promote industrial participationwithin the network's activities through interactions withindustry in general as well as other applications-orientedgroups such as NEXUS. In this context, nanoINDEX hasbeen set-up to establish strong links between the micro-technologists of NEXUS and the nano-technologists ofPHANTOMS. Clearly, the User-Supplier-Clubs of theNEXUS Association will form the basis for such an inter-action.

NEXUS was established, by the EU as aEuropean network of excellence inmicrosystems. The network has evolvedand matured and is, currently, the largestforum for the microsystem community

across the world, the majority of which are industrial. NEXUS is uniqueamongst other networks in that its structure is driven by technologyusers (market pull) as opposed to suppliers (technology push).Through its User-Supplier-Clubs (USCs), NEXUS has established anefficient means of disseminating information relating to applications,trends and market opportunities for microsystems.


PRESS RELEASES RELATED TO PHANTOMSPHANTOMS computational hub boosts design of nanoscale electron devices

http://nanotechweb.org/yournews/index.cfm?action=show_in_full&magid=ntw&id=3550European Computational HUB (PHANTOMS Network)

http://nanodot.org/article.pl?sid=02/08/02/0710253&mode=thread&thresholdSmall world, big opportunities http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v418/n6899/full/nj6899-04a_fs.html

The following addresses will help you find out more about the networks of PHANTOMS/NEXUS as well as about nanoINDEX:Laurence Chassouant, NEXUS Office Secretariat - [email protected] www.nexus-mems.comorDr. Antonio Correia, Co-ordinator PHANTOMS - [email protected] www.phantomsnet.com/

11th MEL-ARI/NID Workshop to be held in Toulouse (France), 5-7 February 2003

The 11th MEL-ARI/NID Workshop will take place at the Toulouse Centre deCongrès Pierre Baudis, Toulouse (France), from 5th to 7th of February, 2003. Toulouse is well known for its significant role in aeronautics and space, but Toulouseknow-how is also heavily invested in other major fields like electronics, health-relat-ed industries, food processing, strategic services, information technology, etc. Thecalled "Ville Rose" is also in the forefront of other advanced technologies like micro-biology, biotechnology, etc. The 11th MEL-ARI/NID workshop will gather participants in the projects funded with-in the NID pro-active initiative. Presentations from the EU projects and invited talksfrom experts outside the NID initiative will take place during the workshop and be focused on the application of abroad range of nano-scale technologies to information processing and on the perspectives for replacing mainstreamapproaches, such as CMOS, when they will reach the expected physical limits for miniaturisation.

Questions regarding NID Projects & EUDr. Ramon CompañoEuropean Commission - DG Information Society (Future & Emerging Technologies)Rue de la Loi 200, B-1049 Bruxelles, BelgiumE-mail: [email protected]

PHANTOMS OrganisationDr. Antonio CorreiaCMP CientificaE-mail: [email protected]

Local OrganisationDr. Christian JoachimCEMES/CNRS-FranceE-mail: [email protected]

MEL-ARI/NID Working Groups are open for those colleagues interested. Contact the Working Group coordinator to participate.

- WG Nanofabrication (Yong Chen - [email protected]) - WG Devices (Christian Pacha - [email protected])- WG Theory (Jim Greer - [email protected])- WG Self-Assembly (Jurriaan Huskens - [email protected])

The mission of the working groups is to enhance the research between the NID projects in particular to: - Exchange information of current work - Enhance the collaboration in the projects and promote new ones - Solve particular technological problems - Looking for areas of common ground between different technologies - Give contributions to the roadmap

10th MEL-ARI/NID meeting and Finnish Workshop on Nanoscience were hold inHelsinki during the first week of July.

With more than 130 participants from 14 different nationalities, the meeting served as a discussion forum on the Nanoelectronics rese-arch EU projects, as well as presenting the most recent Finnish trends in research in nanotechnology to the audience. The whole pro-gram included a total of 20 talks and 14 posters.

For the MEL-ARI/NID workshop, not only partners from the 4 reviewed EU projects assisted but also researchers, partners in diffe-rent projects, joined the meeting for discussion of their own working plans.

The Finnish workshop covered fields such as fabrication of nanostructures, transport processes, functional materials based on supra-molecules or chips for bioprocess state analysis. Olli Ikkala, from the Helsinki University of Technology, presented his group’s rese-arch on functional materials. Ikkala explained that when working with comb-shaped supramolecules, self-organisation is achievedoverall the material and not just locally as it is the case with molecules. The supramolecules are connected by physical interactionsand by recognition.

Ramon Compaño, from the European Commission introduced some of the key points of the VI EU Framework Program and heannounced that the IST/NID call including new instruments will be hold by the end of 2003. Compaño mentioned that the 11500 EoI,received last June in Brussels, will be published in September.

The next MEL ARI NID Workshop will take place in Toulousse, France next February 2003. It will be open for everyone interested.

32 PHANTOMS NEWSLETTER. July/September 2002- Issue 7/8

NANOELECTRONICS CONFERENCES IN EUROPE(October-November 2002)

NANOELECTRONICS COURSES IN EUROPE* New Bachelor and Masters education in Nanotechnology University of Copenhagen, Denmark Starting September 2002http://www.nano.ku.dk/

* Summer School on: Nano and Giga Challenges in Microelectronics Research and Opportunities Moscow, RussiaSeptember 10-13, 2002 http://www.atomicscaledesign.net/Moscow/index.shtml

* IX International Summer School "Nicolas Cabrera": "Molecular Electronics And Nanostructures" Residencia LaCristalera, Miraflores de la Sierra, Madrid, Spain September 16-20, 2002 http://www.inc.uam.es/summerschool2002/

* Nanotubes & Nanostructures 2002 Frascati, Italy September 23-26, 2002 http://www.lnf.infn.it/conference/nn2002/

* Scanning Electron Microscopy - Imaging and Microanalysis: SEM 2002 Chalmers University of Technology,Gothenburg, Sweden October 22-24, 2002 http://fy.chalmers.se/microscopy/SEM2002/index.html

* Molecular organization and dynamics at bordering and surfaces November 01, 2002 University Ulm, Germanyhttp://www.phantomsnet.com/phantom/net/files/CourseGermany.pdf

* Master in Physics / Nanophysics University of Antwerp, Belgium Deadline for registration: October 15, 2002http://www.ua.ac.be/main.asp?c=_WETNAT01


∗∗ International Conference On Physics Of Electronic Materials PHYEM'02 October 01-04, 2002 Kaluga, Russiahttp://www.kspu.kaluga.ru/conf/phyem/econf.htm

∗∗ Advanced Study Institute - Scanning Probe Microscopy: Characterization, Nanofabrication and DeviceApplication of Functional MaterialsOctober 01-13, 2002 Albufeira, Algarve - Portugalhttp://www.cv.ua.pt/ASINATO/SPM/

∗∗ Second Circular ICMM 2002 VIIIth International Conference on Molecule-Based Magnets October 5-10, 2002 Congress Palace of Valencia, Spainhttp://www.uv.es/%7Euimm/icmm_2002/

∗∗ International Workshop on Challenges in Predictive Process Simulation October 13-17, 2002 Prague, Czech Republichttp://www.ihp-ffo.de/chipps/02/

∗∗ Congress "Materiaux 2002" October 21 - 25, 2002 Tours, Francehttp://www.materiaux2002.net/

∗∗ HETECH-2002: 12th European Heterostructure Technology Workshop October 27-29, 2002 The Trevithick Buildings, Cardiff School of Engineering,

Cardiff University, Wales, UK http://www.cf.ac.uk/engin/news/confs/hetech/

∗∗ IST 2002: Partnerships for the FutureNovember 04-06, 2002 Bella Center, Copenhagen, Denmark http://europa.eu.int/information_society/programmes/research/ist_event_2002/index_en.htm

∗∗ Nanofair 2002-European Nanotechnology SymposiumNovember 25-26, 2002 Strasbourg (Alsace), Francehttp://www.nanofair.com

NANONEWSSmall world, big opportunities At last nanotechnology is moving from the realm of hype and hope into the real world, with jobsand funding appearing on both sides of the Atlantic. Paul Smaglik considers the options. Nanotechnology is beginning to bridgethe gap between hype and reality. The word may have been in use for years, but it has never really been properly defined. Fewinstitutes actually specialized in the area, and the kind of massive funding increases that can revolutionize a field and create manynew jobs were only promises. Naturejobs 418, 15 August 2002, 4 - 6 (2002); doi:10.1038/nj6899-04a http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v418/n6899/full/nj6899-04a_fs.html

Intel Unveils World's Most Advanced Chip-Making Process Intel Corporation today unveiled several technology break-throughs that the company has integrated into its new 90-nanometer (nm) process, the most advanced semiconductor manufac-turing process in the industry. Intel already has used this process to build record-breaking silicon structures and memory chips.Intel will put this process into volume manufacturing next year using 300 mm wafers - Article 2 (13 August, 2002) http://www.intel.com/pressroom/archive/releases/20020813tech.htm

Nanotubes grown in place Stanford University researchers have grown individual nanotubes directly between pairs of elec-trodes. The researchers built arrays of metal electrodes, then coaxed nanotubes to form, suspended, in the gaps between them,said Hongjie Dai, an assistant professor of chemistry at Stanford (13 August, 2002) http://www.trnmag.com/Stories/2002/080702/Nanotubes_grown_in_place_080702.html

Chip keeps atoms in line An international team of scientists has found a way to coax arrays of evenly-distributed clusters of metalatoms to form automatically on the surface of a silicon wafer (13 August, 2002) http://www.trnmag.com/Stories/2002/080702/Chip_keeps_atoms_in_line_080702.html

Intellectual Property Rights in Nanotechnology Intellectual property rights are essential in today's technology-driven age.Building a strategic IP portfolio is economically important from both an offensive and defensive standpoint. Applicable areas inNanotechnology to which intellectual property rights can apply are presented. Some challenging issues surrounding the acquisi-tion of IP rights in Nanotechnology are also presented. http://www.nanomagazine.com/articles/iprnanotech

Turning On the "Nanolight": Nanometer-Scale LightSource is First to Show Single-MoleculeElectroluminescence Using photon emissions from individ-ual molecules of silver, researchers at the Georgia Institute ofTechnology have created what may be the world's smallestelectroluminescent light source (09 August, 2002)http://gtresearchnews.gatech.edu/newsrelease/NANO-LIGHT.htm

Experts debate at Nano-7 conference Physics Nobel Laureates Heinrich Rohrer and Leo Esaki, and renowned chemist GeorgeM. Whitesides shared their views on nanotechnology with an audience that was all ears at the joint Nano-7/Ecoss-21 Conferencein Malmö, Sweden in mid-summer (09 August, 2002) http://nanotechweb.org/yournews/index.cfm?action=show_in_full&magid=ntw&id=3603

Nanolab lights the way for Swiss optoelectronics firms A new nano and micro technology laboratory in Zurich is helping Swissoptoelectronics companies exploit nanotechnology to quickly bring to market cutting edge lasers for industrial applications.(08 August, 2002)http://www.swissinfo.org/sen/Swissinfo.html?siteSect=105&sid=1263485

IBM, Nion Scientists Create World's Highest Resolution Electron MicroscopeIBM and Nion Co. researchers have developed innovative technology to peer deepinside materials and view atoms interacting in different environments at a resolutionnever before possible. With computer-chip features shrinking to atomic scales, thisbreakthrough addresses scientists' urgent need to see more clearly the details ofmaterials used in manufacturing semiconductors.http://physicsweb.org/article/news/6/8/6http://www.research.ibm.com/resources/news/20020808_sub-angstrom.shtml

Nanotechnology Volume 13, Number 4, August 2002 As a service to authors and to the international physics community, all

Weekly updated at http://www.phantomsnet.com/phantom/net/nanonews.html

Multicolored electroluminescen-ce from single silver moleculesoccurs within the electricallydiscolored region of an activa-ted silver oxide film. The colorvaries with the size of the clus-ter. Copyright: Proceedings of theNational Academy of Sciences

Comparison with previous performance for Ge30Si70Figure from IBM web page


NEWSNano-technology raises high expectations A nano-product is small but effective "Nano technology is one of the hottest researchobjects today. It will change everything. It means a new industrial revolution. It is difficult even to imagine its outcome. Its impact onthe economy and society will be huge". (20 August, 2002) http://www.cordis.lu/finland/en/spot-9.htm

Mapping of Excellence Mapping of excellence is an initiative developed in the context of strengthening excellence in the EuropeanResearch Area, launched in March 2001 and conducted in co-operation with the Member States and the States Associated to the 5thFramework Programme. The first mapping of excellence exercise is a 'pilot exercise' limited to three areas- Economics, Life sciencesand Nanotechnology (13 August, 2002) http://www.cordis.lu/nanotechnology/src/structuring.htm

Nanoscience and Nanotechnology in the EC Research Programmes The European Commission aims at creating a favourableclimate for nanotechnology research and development. This is pursued through supporting a wide range of actions, first of all longterm research projects of significant size that normally comprise both academic and industrial partners, and focus on multi-discipli-nary aspects. Documents in pdf, word and power point formats available for download (13 August, 2002) http://www.cordis.lu/nanotechnology/src/era.htm

Putting nano in the Picture A 26' documentary film on nanotechnology is currently being produced and will be available in October.This page presents information for the press and interested citizens about Community support for research and technological devel-opment in nanosciences and nanotechnologies (13 August, 2002) http://www.cordis.lu/nanotechnology/src/pressroom.htm

Future and Emerging Technologies from the 5th to the 6th Framework Programme In the period 2003-2006, Future and EmergingTechnologies (FET in short) will build on the experience and achievements of the 5th Framework Programme (FP), while optimisingits ways of operation and taking advantage of the new instruments – Integrated Projects and Networks of Excellence (NoEs). (29July, 2002) http://www.cordis.lu/ist/fet5t6.htm

Foresight document sheds light on future of European research A European area of science and technology foresight may oneday become a reality, according to a working document issued by the European Commission's Research DG. The guide outlinesopportunities offered by the Sixth Framework programme for research (FP6) for supporting cooperation in the field of identifyingpromising future trends in science and technology in Europe. It aims to inform researchers and institutes involved in foresight activ-ities, as well as sponsors and users of this work, on funding opportunities offered by the programme. It also outlines the researchpriorities relevant to foresight and the funding instruments that can be used. (22 July, 2002) http://dbs.cordis.lu/fep-cgi/srchidadb?CALLER=NEWS_RTD2002_EN&ACTION=D&QM_EN_RCN_A=18711

Converging Technologies Can Improve Human Performance The convergence of nanoscale research with other sciences andtechnologies has created a vast opportunity to enhance human performance, scientists say in a report released today titled"Converging Technologies for Improving Human Performance." The report, issued by the National Science Foundation (NSF) andDepartment of Commerce, examines the integrated role of nanotechnology, biotechnology, information technology, and cognitive sci-ence in improving mental and physical performance. Article 2. (10 July, 2002) http://www.newswise.com/articles/2002/7/CONVERG.NSF.html

http://www.phantomsnet.com/phantom/net/news.html

NANONEWSX Rays Stack Up A relatively new x-ray imaging technique has made its first forayinto the third dimension. Using a computer algorithm and high energy x rays,researchers were able to visualize two nanometer-scale, etched patterns stackedone on top of the other (06 August, 2002) High Resolution 3D X-Ray DiffractionMicroscopy Phys. Rev. Lett. 89, 088303 (print issue of 19 August 2002)http://focus.aps.org/v10/st6.html

Semiconductors stride ahead An efficient radiation emitter that could speed up cancer detection rates and nano-sized light sourcesthat could lead to smaller optoelectronic devices were among the breakthroughs reported this week at the 26th InternationalConference on the Physics of Semiconductors. Other highlights of the Edinburgh meeting included the development of electrical com-ponents from nanowires, and a step towards semiconductor 'qubits', which could form the basis of a practical quantum computer. (02August, 2002) http://nanotechweb.org/articles/news/1/8/2/1

Nano-Optics Redefine Rules for Optical Processing A new class of devices is smashing the size, manufacturing, cost and relia-bility hang-ups that have hampered optical elements to date. (01 August, 2002) http://www.commsdesign.com/design_corner/OEG20020801S0021

X ray sandwich."Oversampling" the x-ray dif-fraction pattern of a disorderedmaterial can be used to deter-mine its structure. Researchershave now applied the methodto a stacked pair of etched pat-terns including this one. Phys. Rev. Lett. 89, 088303


EDITORIAL INFORMATIONJuly/September 2002, Issues 7/8.PHANTOMS Newsletter is published by CMP Cientifica Editor: Antonio CorreiaAssociated editor: Adriana Gil ([email protected])

Phantoms Newsletter contains information about theEuropean network on nanoelectronics, including scientificreview articles, Phantoms members highlights and vacancies,nanoelectronic conferences and nanonews. Letters to the editor and articles are welcome for publication.For any question please contact the editor at: [email protected] copies of this issue have been printed.

Subscription rates are (Euros/year): -Phantoms members: free-nonmembers (Europe): 75 -nonmembers (non-European countries): 100

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Cover picture:NIL stamp: 100 nm lines etched in SiO2, height 400 nm. Courtesy of the Plasma Etching group at the Institute of Materials University of Nantes (IMN).


NANO-VACANCIES AT PHANTOMSPhD/Postdoc positions at the Spintronics Group, Würzburg University, (Germany). Fields ranging from molecularbeam epitaxy; nanolithography; high resolution transport experiments. Contact: Laurens Molenkamp at [email protected]

Post doc position at RWTH Aachen, Institut für Hableitertechnik, (Germany) in the field of Terahertz technology(characterization by femtosecond laser based optoelectronic techniques of innovative devices for future ultrafast THzelectronic applications and communication systems) Contact: P. Haring Bolivar at [email protected]

PhD studentship at the Magnetic Nanostructures Group, Instituto de Microelectronica de Madrid, CSIC (Spain) inthe field of magnetic nanostructures. Contact: Gaspar Armelles at [email protected]; Alfonso Cebollada [email protected]; José Luis Costa Kramer at [email protected]

Ph.D. position, Postdoc position at the Nanooptics Group, Syddansk Universitet, (Denmark) in the fields of evanes-cent wave spectroscopy and dynamics and/or on nanooptical waveguides. Contact: Horst-Günter Rubahn at [email protected]

PhD Studentship at the Nanotechnology Group of Cranfield University, (UK) in the field of materials science. Contact: Dr Steve Dunn at [email protected]

Postdoc position at the Nanoscale Physics Group, Purdue University, (USA). Fields: Scanning Probe Microscopy,Molecular and Bio-molecular electronics, UHV Techniques. Contact: Ron Reifenberger at [email protected] - request information about Birck Nanoscale post-docs.

phantoms newsletter issues 7/8 (2002)

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