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Symposium on Surface and Nano Science
2013
Special Symposium of The Thin Film and Surface Physics Division
The Applied Physics Society of Japan
SSNSrsquo13
Symposium on Surface and Nano Science 2013 Zao January 15ndash18 2013
Symposium Program (The slot for each talk includes 3-5 min discussion after the talk)
January 15 (Tuesday) (1700ndash1820) Registration (1830ndash2030) Opening amp Welcome Dinner Opening Remarks Shuji Hasegawa Session A (2030ndash2210) Chair Matthias Scheffler A-1 (2030ndash2053)
Peter Varga (Vienna Univ of Tech amp Brno Univ of Tech) (Invited) ldquoNanostructures at Metal Oxide Surfacesrdquo
A-2 (2053ndash2111) Tadaaki Nagao (National Institute for Materials Science) (Invited) ldquoElectromagnetic standing waves in low-dimensional nano objects complementary approach by electron energy loss and optical spectroscopyrdquo
A-3 (2111ndash2129) Toyo Kazu Yamada (Chiba University) (Invited) ldquoGiant magnetoresistance through a single moleculerdquo
A-4 (2129ndash2147) Masakazu Ichikawa (University of Tokyo) (Invited) ldquoQuantum theory of localized plasmons in metal nanostructuresrdquo
A-5 (2147ndash2210) Geoff Thornton (University College London) (Invited) ldquoUltrathin CeO2(111) films to investigate water gas shift catalysisrdquo
January 16 (Wednesday) Session B (800ndash912) Chair Hiroshi Daimon B-1 (800ndash818)
Kenta Arima (Osaka University) (Invited) ldquoEffect of Water Growth on Quality of GeO2Ge Revealed by in-situ XPSrdquo
B-2 (818-836) Tadaaki Kaneko (Kwansei Gakuin University) (Invited) ldquoInstability control of Si-sublimated SiC surfaces under various Si pressures for SiC etching and epitaxial graphene growthrdquo
B-3 (836-854) Kazushi Miki (National Institute for Materials Science) (Invited) ldquoSelf-Assembled Monolayer-Capped Gold Nanoparticle 2D-arrays as Enhanced Catalysisrdquo
B-4 (854-912) Katsuyuki Fukutani (University of Tokyo) (Invited)
ldquoSubsurface hydrogen reactivity and molecular caprdquo (912ndash1500) Free Discussion and Lunch Session C (1500ndash1630) Chair Wolf-Dieter Schneider C-1 (1500-1518)
Fumihiko Matsui (Nara Institute of Science and Technology) (Invited) ldquoPhotoelectron diffraction of graphite and graphenerdquo
C-2 (1518-1536) Fumio Komori (University of Tokyo) (Invited)
ldquoGrowth and electronic structure of graphene on one-dimensionally- modulated SiC substraterdquo
C-3 (1536-1554) Chuhei Oshima (Waseda University) (Invited) ldquoRadiation Damage of Graphene sheets with a few-keV Electronsrdquo
C-4 (1554-1612) Yoshikazu Homma (Tokyo University of Science) (Invited) ldquoSecondary Electron Image Contrast of Graphene and Its Application to in-
situ Observation of Graphene Segregation on Nirdquo C-5 (1612-1635)
Thomas Greber (Universitaumlt Zuumlrich) (Invited) ldquoIce assembly in the h-BNRh(111) nanomeshrdquo
(1630ndash1640) Coffee Break
Session D (1640ndash1828) Chair Geoff Thornton D-1 (1640-1658)
Hiroshi Imada (RIKEN) (Invited) ldquoSpatially resolved scanning tunneling luminescence spectroscopy of p-type GaAs(110)rdquo
D-2 (1658-1716) Hiroo Omi (NTT) (Invited) ldquoControl of self‐assembly of erbium silicates and erbium oxides on Si wafers for silicon photonicsrdquo
D-3 (1716-1734) Yuji Kuwahara (Osaka University) (Invited) ldquoNanoscale Evaluation of Optical Activity of Chiral Perylene Derivative Studied by Scanning-Tunneling-Microscopy-Induced Light Emission Techniquerdquo
D-4 (1734-1752) Jiro Matsuo (Kyoto University) (Invited) ldquoSputtering with large cluster ion beamsrdquo
D-5 (1752-1810) Megumi Akai-Kasaya (Osaka University) (Invited) ldquoNon-equilibrium structural fluctuation of one-dimensional polydiacetylene nanowirerdquo
D-6 (1810-1828) Yousoo Kim (Riken) (Invited) ldquoSingle-molecule chemistry on an ultrathin MgO filmrdquo
(1830ndash2030) Dinner Session E (2030ndash2204) Chair Takanori Koshikawa E-1 (2030-2053)
Karl-Heinz Ernst (Universitaumlt Zuumlrich) (Invited) ldquoInelastic electron tunneling induced unidirectional motion of single moleculesrdquo
E-2 (2053-2116) Wolf Widdra (MartinLuther Univ amp Max Planck Inst) (Invited) ldquoGrowth adsorption and electronic properties of sexithiophene on noble metal surfaces From monolayers to thin filmsrdquo
E-3 (2116-2134) Shohei Chiashi (University of Tokyo) (Invited) ldquoWater on lsquoHydrophobicrsquo Carbon Nanotube Surfacerdquo
E-4 (2134-2204) Matthias Scheffler (Max-Planck-Gesellschaft) (Invited) ldquoThe Materials Genome Initiative ndash the basic-science componentrdquo
January 17 (Thursday) Session F (800-917) Chair Shuji Hasegawa F-1 (800-823)
Wolf-Dieter Schneider (Ecole Polytech Feacutedeacuterale de Lausanne) (Invited) ldquoTransport properties and electronic structure of individual metallic nanocontacts on dielectric supports A local viewrdquo
F-2 (823-841) Chien-Cheng Kuo (National Sun Yat-sen University) (Invited) ldquoStabilized the AuSi(111) phase by ordered surface decoration of indiumrdquo
F-3 (841-859) Takashi Uchihashi (NIMS) (Invited) ldquoSurface Superconductor Si(111)-radic7timesradic3)-In Fluctuation Effects and Molecular Controlrdquo
F-4 (859-917) Toru Hirahara (University of Tokyo) (Invited) ldquoIn situ Magnetotransport measurements of ultrathin Bi films on Si(111)rdquo
(917ndash1520) Free Discussion and Lunch Session G (1520-1655) Chair Wolf Widdra G-1 (1520-1538)
Wataru Yashiro (Tohoku University) (Invited) ldquoA multiple-wave X-ray diffraction phenomenon and its application to surface crystallographyrdquo
G-2 (1538-1556) Kouichi Hayashi (Tohoku University) (Invited) ldquoX-ray fluorescence holography and its applicationsrdquo
G-3 (1556-1614) Tadashi Abukawa (Tohoku University) (Invited) ldquoSurface structure analysis using 3D reciprocal-maprdquo
G-4 (1614-1637) Michael Altman (Hong Kong Univ of Science and Technology) (Invited) ldquoGrowth Magnetism and Ferromagnetic ldquoGaprdquo in Fe Films on the W(111) Surfacerdquo
G-5 (1637-1655) Takanori Koshikawa (Osaka Electro-Communication University) (Invited) ldquoNovel development of very high brightness and highly spin-polarized electron gun with compact 3D spin manipulatorrdquo
(1655ndash1705)Coffee Break
Session H (1705-1829) Chair Peter Varga H-1 (1705-1723)
Taku Suzuki (National Institute for Materials Science) (Invited) ldquoSpin dependent 4He+ ion-surface interactionrdquo
H-2 (1723-1741) Teruo Ono (Kyoto University) (Invited) ldquoCurrent-induced domain wall motion Intrinsic pinning and two barrier stabilityrdquo
H-3 (1741-1759) Sakura N Takeda (Nara Institute of Science and Technology) (Invited) ldquoInitial Stage of Metal Adsorption on Si(111) Real Time Monitoring by RHEEDrdquo
H-4 (1759-1811) Keiji Doi (University of Tokyo Yukio Hasegawa Lab) ldquoSpin-polarized scanning tunneling microscopy of Co thin films on Ag(111)rdquo
H-5 (1811-1829) Hirokazu Fukidome (Tohoku University) (Invited) ldquoEpitaxy of Graphene on Si(100) and Si(111) Faces Simultaneously Formed on Si(100) Substraterdquo
(1830ndash2030) Dinner Session I (2030-2215) Chair Thomas Greber I-1 (2030-2048)
Akira Ishii (Tottori University) (Invited) ldquoTheory and Experiment of Palladium Catalysis for Ligand-free Coupling Reaction on Sulfur-modified Aurdquo
I-2 (2048-2106) Shiro Yamazaki (Osaka University) (Invited) ldquoCurrent- and Force-Induced Atom Switchingrdquo
I-3 (2106-2129) Henning Neddermeyer (Martin-Luther-Universitaumlt Halle-Wittenberg) (Invited) ldquoThe art of growing ordered thin films of BaTiO3rdquo
I-4 (2129-2147) Iwao Matsuda (University of Tokyo) (Invited) ldquoOscillatory Relaxation of Photovoltage on a Si Surfacerdquo
I-5 (2147-2205) Tadahiro Komeda (Tohoku University) (Invited) ldquoObservation of Cross-over of Vibration and Kondo Resonance Excitation by High Resolution STSrdquo
Closing Remarks Takanori Koshikawa
January 18 (Friday) (1000) Checkout amp Departure
Nanostructures at Metal Oxide Surfaces
PVarga
Institute of Applied Physics Vienna University of Technology CEITEC (Central European Institute of Technology) at Brno University of Technology
Oxides are the ideal templates for growing metallic cluster Because of their low surface energy most of the metals are growing as islands nucleating at surface defects To achieve not only self organized- but also self-assembled growth the defects where the metal atoms nucleate preferentially should show long range order In this talk two different templates will be discussed First the four layer thick alumina film which can be grown self limited by oxidation of AlNi3(111) and second the surface of Fe3O4(001) These results are based on STM images with high resolution combined with ab-initio calculations The alumina film on AlNi3(111) form a nano-mesh with holes down to the substrate and with a distance of 4nm forming a hexagonal super-structure[1] By filling those holes with few atoms of Pd afterwards almost every metal grow as clusters showing the same hexagonal symmetry The size of the clusters can be varied between a few atoms up to around 1500 atoms before the cluster they coagulate and form a thin polycrystalline film [2] We have grown Fe and Co clusters and determined their magnetic properties The second template which will be discussed is the surface of Fe3O4(0001) which reconstruct in such a way that well ordered single metal atoms can be stabilized on it with remarkable thermal stability[3] So far Au and Pd atoms were grown self-assembled and the mechanism of CO activated sintering of Pd atoms will be shown [1] M Schmid G Kresse A Buchsbaum E Napetschnig S Gritschneder M Reichling P Varga Phys Rev Lett 99 (2007) 196104 [2]A Buchsbaum M De Santis HCN Tolentino M Schmid P Varga Phys Rev B 81 (2010) 115420 [3]Z Novotny G Argentero Z Wang M Schmid U Diebold G S Parkinson Phys Rev Lett 108 (2012) 216103
001
Electromagnetic standing waves in low-dimensional nano objects complementary approach by electron energy loss and optical spectroscopy
CV Hoang G Han and T Nagao
International Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Tsukuba 305-0044 Japan
E-mail NAGAOTadaakinimsgojp In the past decade concept of the surface plasmon as well as those of the low-dimensional variants have become increasingly important in nanotechnology since their optical properties are strongly dependent on the size and the shape of the small objects This closely relates to the goal of nanotechnology which is to provide the appropriate nano-architecture to embody the building blocks with desired functions for novel photonics devices In this presentation we present our recent study on the plasmon confinement effects in subnanometer-scale low-dimensional objects such as nano-discs and atomically-thin nanorods For the propagating modes of atomic-scale plasmons the energy dispersion curves of plasmons locate far from the light line and thus the probing methods with large momentum scanning range become powerful Thus we can adopt low-energy electron energy loss spectroscopy (EELS) to elucidate the fundamental aspects of plasmonic excitation up to the large momentum for Landau damping With this scheme we were able to clarify the plasmonic bands for different Low-D metallic structures such as atomic sheets and atomic wires With these measurements we were able to elucidate the quantum aspects of the ultimately small systems Along with the study of propagating modes of plasmons we studied the formation of standing-wave plasmon in nano discs and atom chains which are optically detectable through the dipolar resonance These modes were compared in detail with EELS results in combination with high-resolution electron diffraction and scanning electron micrographs to correlate the electromagnetic properties of the objects to their nanometer-scale structure These standing wave plasmons are confined in finite-sized nano-objects and strongly couple to the light for example the infrared absorption for indium atomic chains is so strong as they can be regarded as optical atom-scale antennae In this contribution we plan to introduce our recent studies on the optical absorption by excitations of standing-wave plasmons in Ag nanodiscs and in an array of atomic chains of metallic indium on silicon substrates in comparison with our electron energy loss spectroscopy By tuning the growth conditions we tuned the size of these nano-objects and the resonance frequency of the optical absorption was also systematically shifted as a function of their size The observed behavior was found to be different from that of the plasmonic resonators expected from surface plasmon polariton scenario
002
Giant magnetoresistance through a single molecule
T K Yamada12
S Schmaus23 A Bagrets
34 Y Yamagishi
1 F Evers
34 W Wulfhekel
23
1 Graduate School of Advanced Integration Science Chiba University Japan
2 Physikalisches Institut Karlsruhe Institute of Technology Germany
3DFG-Centre for Functional Nanostructures Karlsruhe Institute of Technology Germany
4 Institut fuumlr Nanaotechnologie Karlsruhe Institute of Technology Germany
Exploring spin-polarized transport characteristics of single molecules is a promising
direction of research with an outlook for potential application in future nano-scale electronic
devices the functionality of which will employ not only charge but also the electrons spin
As the first step towards this goal we present giant magneto-resistance (GMR)
measurements of single hydrogen phthalocyanine (H2Pc) molecules contacted by two
ferromagnetic electrodes Using a spin-polarized scanning tunnelling microscopy (SP-STM)
at 4K single molecules were addressed and their conductance in dependence of the
magnetization of the electrodes was measured Magnetic Co nano-islands on Cu(111) and Co
coated W tips were used as ferromagnetic electrodes to make a CoH2PcCo single molecular
junction The different magnetization directions were naturally achieved as the Co nano-
islands can either be magnetized into or out of the Cu substrate plane A GMR of +60 was
observed which is significantly larger than the tunnelling magneto resistance of +5 obtained
from direct tunnelling measurements between the tip and the nano-islands without the
involvement of H2Pc molecules [1]
Elaborated density functional theory electronic structure and transport calculations have
been employed to get insight into the bonding and conduction mechanisms of H2Pc molecules
attached to Co electrodes A partial charge transfer from the Co surface to H2Pc is predicted
implying that (i) molecules are chemisorbed on Co(111) surface and (ii) the quasi-degenerate
LUMO states of H2Pc being positioned close to the Fermi level provides the main transport
channel through the molecule Calculated magneto-resistance values agree reasonably well
with the experimental observations
From the experiments of the CoH2PcCo single molecular junction the hybridization of
LUMO states of H2Pc with Co 3d minority spin states was found to be the key to generate
large positive GMR which indicates different GMR for H2Pc and antiferromagnet Mn as
majority spin states dominate around the Fermi energy of Mn With the spin-polarized STM
at 4K we measured magneto-resistance through the FeH2PcMn single molecular junction
H2Pc single molecules were deposited on Mn(001) ultrathin films grown on an Fe(001)-
whisker The bct Mn(001) ultrathin films are known to have layer-wise antiferromagnetic
coupling between atomic layers which was directly observed by SP-STM magnetic images
[2] An Fe-coated W tip was gently approached to the molecule and the conductance in
contact was measured Since the coercive field of MnFe(001) is much smaller than that of the
FeW tip it is possible to switch only the magnetization of the MnFe(001) which was
directly confirmed by a reverse of magnetic contrast in STM images In this way we
succeeded to measure GMR through the same single molecule and obtained surprisingly a
negative magneto resistance of -54 [3] ie anti-parallel coupling between Fe and the top
most Mn layer has lower resistance which is comparable to the case of the CoH2PcCo
003
junction Possible reason of the polarity switch of GMR is that the spin transport through the
H2Pc single molecule is dominated by minority and majority spins for CoH2PcCo and
FeH2PcMn junctions respectively
Our experimental results show that the single phthalocyanine molecules can be used for
near-future spintronics devices Hybridization of molecular orbital with spin states of 3d nano
metals is the key to obtain large magneto resistance
[1]S Schmaus A Bagrets Y Nahas TK Yamada A Bork F Evers
and W Wulfhekel
Nature Nanotechnology 6 185 (2011)
[2]TK Yamada MMJ Bischoff GMM Heijnen T Mizoguchi and H van Kempen
Physical Review Letters 90 056803 (2003)
[3]A Bagrets S Schmaus A Jaafar D Kramczynski TK Yamada M Alouani W
Wulfhekel and F Evers Nano Letters 12 5131 (2012)
004
Quantum theory of localized plasmons in metal nanostructures Masakazu Ichikawa
Department of Applied Physics the University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656
ichikawaaptu-tokyoacjp
The application of surface plasmons has recently opened a new field of plasmonics Many theoretical studies of surface plasmons and surface-plasmon polaritons using the hydrodynamic method semi-classical method random-phase approximation (RPA) and time-dependent local density approximation have been reported [1] These studies have mainly focused on the surface plasmon excitations However the coupling phenomena between the bulk and surface plasmons play important roles in the plasmon excitations whose contributions to the plasmon excitations have not yet been studied Analytical expressions of the dielectric functions for the plasmon excitations also have not been obtained
In this study quantum theoretical studies on localized surface and bulk plasmons in metal nanostructures are performed using the RPA in the high frequency condition [2] since the RPA can well explain the bulk plasmon excitation phenomena in a uniform electron gas This study is a generalization of the previous one on metal thin films [3]
An effective Coulomb potential for metal nanostructures is calculated for the high frequency condition using the RPA where the many-body Coulomb interaction between conduction electrons is considered The non-local dielectric function is derived for the effective potential ndash the poles of the potential give the localized surface and bulk plasmon excitation energies The excitation energies can be analytically calculated for a metal nano-sphere and a nano-shell when the electron density is assumed to have a step function shape at surfaces The energies agree with those calculated using semi-classical methods [1] The terms for coupling between the localized surface and bulk plasmons appear in the effective potential which reduce the inelastic scattering cross section of an incident electron by the bulk plasmon excitation The local dielectric function is however derived for the electric field which has the Drude dielectric function formula with the
local electron density dependence 2 21 ( )p
ω ωminus r
Position dependent inelastic scattering probability of the incident electron by the plasmon excitations are also derived using the Wignerrsquos distribution function formula [4] This formula is useful for explaining the recent study that the surface and bulk plasmon excitation energies increase with the decrease of the size of Ag nanoparticles which was performed by STEM-EELS [5] [1] J M Pitarke et al Rep Prog Phys 70 1 (2007) [2] M Ichikawa J Phys Soc Jpn 80 044606 (2011) [3] M Ichikawa Phys Rev B 10 2416 (1974) [4] M Ichikawa and Y H Ohtsuki Phys Rev B 10 1129 (1974) [5] A Scholl et al Nature 483 421 (2012)
005
Ultrathin CeO2(111) films to investigate water gas shift catalysis
Geoff Thornton
London Centre for Nanotechnology UCL
As model systems for the study of supported metal-oxide catalysts ceria ultrathin films have
attracted significant interest The growth of such insulating oxide films of a few nanometre
thickness allows the application of many electron-based techniques which cannot be easily used on
native oxide single crystal surfaces We have prepared CeO2(111) films on Pt(111) and Re(0001) of
varying thickness from 06 - 3 nm consisting of discrete oxide islands to near complete oxide
coverage and investigated them using a variety of imaging and spectroscopic techniques including
STM LEED LEEM and XPEEM The films are prepared via evaporation of cerium metal onto the
substrates followed by oxidation by annealing in a partial pressure of O2 to form isolated islands of
CeO2(111) with widths up to 200 nm
Filled states atomic resolution STM has been used to characterise a host of defect structures
observed on the surface of the ceria films Surface and subsurface oxygen vacancies are observed
and display similar signatures to those on the native single crystal suggesting that these ceria
ultrathin films are good topographic models for the single crystal surface Water molecules
originating from the background vacuum can also be observed on these films using room
temperature STM
Low energy electron microscopy (LEEM) and synchrotron x-ray photoemission electron
microscopy (XPEEM) have also been used to characterise the structure and local oxidation states of
the ceria films Bright- and dark-field LEEM show similar film topographies to those found using
STM and also indicated the presence of rotational domains of ceria which can also occasionally be
observed in STM Resonant XPEEM of the Ce 4f region provides high sensitivity towards the
oxidation state of the cerium and has high spatial resolution to permit interrogation of individual
oxide islands
Gold supported on ceria forms an important catalyst for the low-temperature water-gas-shift
reaction and STM has also been employed to investigate the behaviour of single gold atoms on the
surface of CeO2(111) films on Pt(111) We observe that single gold atoms are stable on ceria
surfaces even at room temperature and appear to have a number of preferred adsorption sites
006
Effect of Water Growth on Quality of GeO2Ge Revealed by in-situ XPS
Kenta Arima 1 Atsushi Mura 1 Iori Hideshima 2 Takuji Hosoi 2 Heiji Watanabe 2 Zhi Liu 3 1 Dept Precision Sci and Tech Osaka Univ 2 Dept of Material amp Life Science Osaka Univ
3 Advanced Light Source Lawrence Berkeley National Lab
E-mail arimaprecengosaka-uacjp
Germanium (Ge) is regarded as an advanced substrate and channel material because it has higher mobilities for both holes and electrons than those of Si Germanium oxide (GeO2) is one of the key materials in
Ge-based transistors However GeO2 is permeable and soluble in water unlike the more familiar silicon oxide (SiO2) This implies that GeO2 films will react with water vapor in air In this paper water growth on GeO2 films on a Ge(100) substrate and their effect on the electronic properties of GeO2 films are investigated using in-situ
X-ray photoelectron spectroscopy[1 2] at relative humidity (RH) values from 0 to approximately 45[3 4] Water adsorbs at low RHs and continues to grow gradually up to ~1 RH probably forming hydroxyls (Fig 1(a)) Water grows rapidly above 1 RH indicative of the formation of a molecular water film We show that
the energy separation between Ge4+ and Ge0+ signals in Ge3d spectra increases with RH until it reaches 1 (Fig 1(b)) In addition we confirmed the collapse of an initial abrupt GeO2Ge interface in this range indicating that water molecules in the gas phase infiltrate into the permeable GeO2 film and water-related
species accumulate at the GeO2Ge interface We propose that water-related species emit electrons to the Ge bulk and positive charges are created in GeO2 close to the GeO2Ge interface which is the origin of the specific features of Ge3d spectra in Figs 1(b) and 1(c) These positive charges are likely to be the cause of
the reported negative shift of the flatband voltage in Ge-based MOS capacitors with air-exposed GeO2 Acknowledgement The work was supported by a Grant-in-Aid for Young Scientists (A) (Grant No 24686020) from Japan Society for the
Promotion of Science The Advanced Light Source is supported by the Director Office of Science Office of Basic Energy
Sciences of the US Department of Energy under Contract No DE-AC02-05CH11231
References [1] M Salmeron et al Surf Sci Rep 63 pp 169-199 2008
[2] DF Ogletree et al Nucl Instrum Methods Phys Res Sect A 601 151-160 2009
[3] K Arima et al J Phys Chem C 114 pp 14900-14906 2010
[4] K Arima et al J Surf Sci Soc of Japan 32 pp 368-373 2011
10-8 10-6 10-4 10-2 100
00
03
06
09
12
Wat
er
thic
kness
(nm
)
RH ()
Hydroxylation
Molecular H2O film
10-8 10-6 10-4 10-2 100
30
32
34
36
ΔE (
Ge
4+-G
e0+)
(eV
)
RH ()
10-8 10-6 10-4 10-2 100
06
07
08
09
10
10-8 10-6 10-4 10-2 100
08
09
10
11
12
fw
hm (
eV)
RH ()
fwhm
(eV
)
RH ()
Ge0+
Ge4+
(a) (b) (c)
Fig 1 (a) (b) and (c) are water growth of the annealed GeO2Ge sample energy separations between Ge4+ and Ge0+ peaks (∆E ) full widths at half-maximum (fwhm) of Ge4+ and Ge0+ peaks as a function of RH respectively Open symbols represent values taken after the evacuation of water vapor from the chamber
007
Instability control of Si-sublimated SiC surfaces under various Si pressures for SiC etching and epitaxial graphene growth
Tadaaki Kaneko
Faculty of Science and Technology Kwansei Gakuin University Japan Email kanekokwanseiacjp
An extremely high temperature nanoscale process technology beyond 2000oC for single crystal SiC surfaces has attracted attention for the growth of higher quality epitaxial graphene as well as the fabrication of higher performance SiC power devices Thermal decomposition of SiC becomes prominent when the temperature exceeds 1600oC At the surface in this temperature range Si sublimation dominates in high vacuum so that the remaining excess C atoms bring about considerable stoichiometric imbalance A simple way to remove the residual C atoms from the surface is to supply a moderate quantity of Si flux where the impinged Si reacts with the C by forming volatile species This surface reaction provides an etching function of thermally decomposed SiC surfaces By considering the etching rate and the surface stoichiometry to be controlled simultaneously by simply changing Si partial pressures various kinds of morphological instabilities arise associated with site-dependent local stoichiometric imbalance in step-terrace structures of the SiC surfaces One extreme case as a result of the controlled instability and stoichiometry is the growth of epitaxial graphene of the defined layer-number in conjunction with SiC etching So far however none of studies has dealt with the instability beyond 2000oC behind the SiC etching and the graphene growth It is mainly because 2000oC SiC processing has been extremely difficult due to the physical limitation of thermostablility of the components used
We have developed a novel component material of carburized TaC in order for independent control of Si and C partial pressures by constructing a semi-closed container with all the material system confined inside Thanks to its catalytic effect for the C to attach and the Si to detach from 1600oC to 2200oC the Si partial pressure can be precisely controlled nearby the thermal equilibrium vapor pressure curve even in the single isothermal environment In this study morphological changes of 4H-SiC 0001 with the decrease of the Si pressure are discussed where the total process mode changes from SiC etching to epitaxial graphene growth As the surface approaches to C-rich various kinds of morphological instabilities appears in the mechanism of SiC step edge retraction such as step bunching meandering pinning then gradually converts to graphene by reflecting the morphological characteristics of the underlying SiC interface layer Those instabilities are considered to be attributed to the site-dependent formation of excess C along the SiC step edges where the rate of the step retraction is preferentially reduced Control of Si pressure is a key to suppress the instabilities and therefore to grow high quality graphene as well
008
Self-Assembled Monolayer-Capped Gold Nanoparticle 2D-arrays as Enhanced Catalysis
K Miki12 K Isozaki13 T Taguchi12 1 National Institute for Materials Science 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan
2 University of Tsukuba 1-1-1 Tennodai Tsukuba Ibaraki 305-8577 Japan 3 International Research Center for Elements Science Institute for Chemical Research Kyoto University
Gokasho Uji Kyoto 611-0011 Japan mikikazushinimsgojp
Gold nanoparticles (AuNPs) have been extensively studied as one of useful heterogeneous catalyst because of their high stability and catalysis based on redox properties For the purpose of designing highly active catalysts showing molecular recognition-based high reaction rates andor selectivities AuNPs were conventionally supported inside mesoporous or polymer materials Although the surface modification of AuNPs enables us to develop drug delivery or sensor applications based on the molecular recognition taken place inside the spherical interface around AuNPs it has not been focused in catalytic approaches because surface-capping was potentially thought to cancel the catalysis of AuNPs The compatibility of surface modification and catalysis of AuNPs demonstrates a new concept for highly active catalysts like natural metalloenzymes Recently we found that 2D-arrays of alkanethiol-capped AuNPs showed an unprecedented high catalysis on silane alcoholysis reactions originated from the molecular recognition inside hydrophobic spherical interface around AuNPs[1] This work reports the first catalytic enhancement effect of alkanethiol-self-assembled monolayer (SAM) on AuNP catalyst supported on gold substrates
2D-array of dodecanethiol-capped 10 nm-sized AuNP (10Dod-array) was fabricated on thiol-terminated gold thin film (10 times 10 cm) with high coverage (gt95) by our original method (Figure 1a)[2] The close-packed hexagonal ordering of AuNPs was confirmed by SEM observations and SAXS analyses (BL40B2 in Spring-8) The fabricated 10Dod-array catalyst (030 nmol of Au) was immersed into the mixture solution of silanes (015 mmol) and alcohols (328 mmol) with a gentle stirring The reaction yields were determined by GC analyses together with the assignment of products by 1H 13C NMR and HR-MS (ESI)
Various gold materials-catalyzed n-butanolysis reactions of dimethylphenylsilane revealed the over 12 times higher catalysis of 10Dod-array than other gold materials (Figure 1b) From the results of catalytic reactions with a range of silanes alcohols and alkanethiols capping AuNPs the hydrophobic interface of 2D-arrayed AuNPs was found to act as a molecular recognition field where substrate molecules are encapsulated inside alkanethiol-SAM and thus easily access to the catalyst surface Finally we discovered the molecular recognition-based metalloenzyme-like catalytic mechanism of AuNP 2D-arrays through detail experiments on temperature dependence of the catalysis combined with the aggregation property of AuNP colloids
In conclusion we found a catalytic enhancement effect of interfacial alkanethiol-SAM on catalytic silane alcoholysis reactions by AuNPs with the molecular recognition-based catalytic mechanism This finding demonstrates a potent applicability of SAM functionalizations for metallic nanoparticle catalysts as a new concept to design higher catalysis and selectivity References [1] T Taguchi K Isozaki K Miki in press in Advanced Materials 24 (2012)DOI 101002adma201202979 [2] K Isozaki T Ochiai T Taguchi K Nittoh K Miki Appl Phys Lett 97 221101 (2010)
Figure 1 (a) Schematic illustration of 10Dod-array (b) Various gold materials-catalyzed n-butanolysis of dimethylphenhylsilane
009
Subsurface hydrogen reactivity and molecular cap
K Fukutani Institute of Industrial Science University of Tokyo
E-mail fukutaniiisu-tokyoacjp
Molecular hydrogen is dissociatively adsorbed on transition metal surfaces like Pd whereas hydrogen dissociation is strongly activated on noble metal surface like Au Adsorbed hydrogen on a metal is occasionally absorbed into bulk exothermically eventually forming a hydride which is of technological importance for hydrogen storage and purification Such absorbed hydrogen is furthermore claimed to play a significant role for hydrogenation reactions of hydrocarbon molecules [1] In aimed at gaining further insight into hydrogen absorption and hydrogenation reaction we have investigated hydrogen interaction with clean Pd and AuPd alloy surfaces with thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA) that allows for high-resolution depth profiling of hydrogen [2] When a Pd(110) surface was exposed to H2 at a low temperature TDS revealed desorption peaks at ~150 K and ~300 K The low temperature feature was further decomposed into two components labeled as 1 and 3 In combination with NRA the high temperature peak was attributed to hydrogen adsorbed on the surface while 3 and 1 were assigned to hydride phases [3] Reactivity of these species towards hydrogenation of C4H8 was investigated by TDS It was found that hydrogeneation occurs in presence of 1 or 3 species while surface-adsorbed hydrogen is not responsible for hydrogenation When H2 was dosed to an Au07Pd03 alloy surface on the other hand a single desorption peak was recognized at ~250 K with a tailing feature which is different from both the pure Pd(110) and Au(110) surfaces Examination of the Au07Pd03(110) surface with low-energy electron diffraction and Auger electron spectroscopy revealed that Au segregates at the surface of the alloy After close examination of the surface composition and hydrogen depth profile it was found that hydrogen dissociates at minor Pd sites on the surface and absorbed into bulk We furthermore demonstrate a molecular cap effect capping the Pd site with CO molecules disturbs the H2 dissociation ie hydrogen absorption and also suppresses desorption of absorbed hydrogen from the bulk [4] References [1] M Wilde et al Ang Chem Int Ed 47 (2008) 9289 [2] K Fukutani Curr Opin Solid St M 6 (2002) 153 [3] S Ohno et al submitted [4] S Ogura et al submitted
010
Photoelectron diffraction of graphite and graphene Fumihiko Matsui1 Tomohiro Matsushita2 Hirosuke Matsui1 Naoyuki Maejima1
Ryo Ishii1 Shinji Koh1 Hiroshi Daimon1 Silvan Roth3 Adrian Hemmi3 Thomas Greber3 Juumlrg Osterwalder3
1Nara Institute of Science and Technology 2SPring-8JASRI 3Universitaumlt Zuumlrich 8916-5 Takayama Ikoma Nara Japan 630-0192
Two-dimensional photoelectron angular distributions from a graphite single crystal
and graphene monolayers were measured by using circularly polarized soft x-ray and Mg Kα radiations In the diffraction patterns the forward focusing peaks and radii of diffraction rings around them appear which indicate the direction and distance to the neighboring atoms A holographic reconstruction algorithm (SPEA-MEM) based on the fitting of elemental diffraction patterns for various C-C bond distances was applied to the full set of measured data Clear nanometer-scale real-space images of several graphite layers were reconstructed It is noteworthy that the diffraction rings due to in-plane scattering become much dominant over the forward focusing peaks owing to interlayer scattering in the case of graphite that has a large interlayer separation Photoelectron diffraction patterns from graphene layer grown on SiC Cu and Rh surfaces were compared A single layer atomic image was reconstructed for the graphene monolayer These are the first examples of the holographic reconstruction by photoelectron diffraction for layered and monolayer materials Fig1 (a) The real part of the photoelectron
wave function and (b) the photoelectron diffraction intensity distribution in the real space 120594(r) from the central carbon atom in a C13 cluster (c) The enlargement of (a) (d) Simulated photoelectron diffraction pattern 120594(120579120601)
from a C253 cluster References [1] F Matsui T Matsushita H Daimon J Phys Soc Jpn 81 (2012) 114604
[2] F Matsui H Matsui T Matsushita K Goto N Maejima N Nishikayama K Tanaka H Daimon SSNSrsquo11
011
Growth and electronic structure of graphene on one-dimensionally-modulated SiC substrate
Fumio Komori Institute for Solid State Physics the University of Tokyo 5-1-5 Kashiwanoha Kashiwa-shi Chiba 277-8581 Japan
komoriisspu-tokyoacjp Engineering of the gapless graphene Dirac bands has been studied for understanding and
useful applications of distinctive electronic properties due to their chiral nature I will discuss two topics on the electronic states of graphene grown on one-dimensionally-modulated SiC substrates One is anisotropy of the group velocity [1] and the other is an energy gap at the Dirac energy ED for graphene nanoribbons In the experiments we used vicinal SiC(0001) substrates with a step-and-terrace structure for the graphene growth and the electronic states were measured by angle-resolved photoemission spectroscopy ARPES Fabrication of high-quality and nanostructured graphene on macroscopic area of a semiconductor substrate itself is also one of the challenging issues in graphene research
Anisotropy of the group velocity has been studied using the samples prepared by thermal decomposition of the SiC(0001) substrate Graphene covers both the (0001) terraces and the steps of the substrate and macroscopically-continuous graphene was prepared The group velocity of this graphene is lower in the direction perpendicular to the substrate step edges while that in the direction parallel to the substrate step edges is the same as that for graphene on a flat surface The results are consistent with the recent theoretical calculations[2] Graphene nanoribbons were prepared by carbon molecular beam epitaxy of the 6radic3 x 6radic3
structure and a hydrogen treatment [3] on the vicinal substrate We optimized the substrate temperature and the carbon deposition rate to ensure a homogeneous growth of the 6radic3 x 6radic3 structure on the terraces without thermal decomposition of the substrate The width of graphene nanoribbon on the substrate terrace is 15 nm The top of the π band of the graphene nanoribbon was 0015 eV below the Fermi energy No signal from the π band was detected by ARPES above the top of the π band indicating the gap formation at ED References 1 K Nakatsuji et al Phys Rev B85 (2012) 195416 2 S Okada and T Kawai Jpn J Appl Phys 51 02BN05 (2012) 3 C Riedl et al J Phys D Appl Phys 43 374009 (2010)
012
Radiation Damage of Graphene sheets with a few-keV Electrons Yukiko Miyakoshi1 Genki Odahara2 Tatsuya Nagata1 and Chuhei Oshima1
1 Department of Applied Physics Waseda University 3-4-1 Okubo Shinjuku-ku Tokyo 169-0072 Japan 2Energy Technology Research Institute NIAIST 16-1 Onogawa Tsukuba 305-8569 Japan
In the last SSNS12 we reported in-situ growth of single- bi- and triple-layer graphene sheets on Ni(111) and polycrystalline surfaces through carbon segregation and fabricated the self-standing graphene sheet In this work we observed changes in SEM images and electron diffraction patterns by means of low-energy scanning electron microscope with transmission electron diffraction optics (SPA-LEED optics) and compared with the Raman spectra Here we summarized them as follows
(1) The observed SEM images indicated large defect growth which seemed to be related strongly with surface contamination of SiO2 particles
(2) The ratio of spot intensities to the background intensity in transmission electron diffraction patterns decreased gradually with increasing electron dose
(3) The corresponding changes in Raman spectra were extremely large both the intensity and the shape of the peak changed because of the high sensitive properties of enhancement based on electronic resonance
013
Secondary Electron Image Contrast of Graphene and its Application to In Situ
Observation of Graphene Segregation on Ni Yoshikazu Homma Yuta Momiuchi Kazuki Yamada and Hiroki Kato
Department of Physics Tokyo University of Science
Shinjuku Tokyo 162-8601 Japan
Secondary electron emission from the mono-layered material of graphene is of great interest Graphene exhibits different secondary electron contrasts depending on the number of layers and where it is located on insulator on conductor or suspended in space Here we discuss scanning electron microscopy (SEM) imaging of graphene on Ni substrates comparing image contrasts for a clean surface at high temperatures and an air-exposed surface Graphene specimens were prepared by surface segregation from Ni substrates When a Ni substrate doped with carbon was heated to 800-900˚C in the SEM chamber graphene segregated on the surface [1] The segregation temperature depended on the carbon concentration On a polycrystalline Ni surface the grain contrast depending on the crystallographic orientation of the local Ni surface was much greater than the contrast formed by graphene and it was not easy to distinguish graphene from Ni grains in a static SEM image On the other hand the edges of graphene appeared much clearer at the front of graphene segregation even in a low magnification image The graphene edge images showed either bright or dark contrast depending on the direction of the edge in the SEM chamber Thus the edge contrast is created by a topographic effect just like atomic step images [2] However the contrast is much higher than that of atomic steps and it is observable even on non-atomically flat surfaces When a partially graphene-overed Ni surface was exposed to air and was observed by SEM the image contrast changed drastically The bare part of the surface was oxidized and appeared brighter than the graphene covered part This can be used for distinguishing graphen from the bare Ni surface In-situ SEM is a simple way and suitable for observing a large area graphene formation Our in-situ observation elucidated a crystalline orientation effect on the segregation of graphene [3] The nucleation sites of graphene on a polycrystalline Ni surface were analyzed based on the in-situ observation
[1] J C Shelton J MBlakely Surf Sci 43 493 (1974) [2] Y Homma M Tomita and T Hayashi Ultramicrosco 52 187 (1993) [3] K Takahashi Ki Yamada H Kato H Hibino and Y Homma Surf Sci 606 728 (2012)
014
Ice assembly in the h-BNRh(111) nanomesh
Haifeng Ma1 Marcella Iannuzzi2 Yun Ding 2 Huanyao Cun 1 Juumlrg Hutter 2 Juumlrg Osterwalder1 and Thomas Greber 1
1 Physik-Institut der Universitaumlt Zuumlrich Switzerland
2Physikalisch Chemisches Institut der Universitaumlt Zuumlrich Switzerland
(corresponding author T Greber e-mail greberphysikuzhch)
The hexagonal boron nitride nanomesh [1] features a modern nanotemplate [2] where molecules may be trapped by help of lateral electrostatic fields [3] It can be used as a laboratory with nanometer sized test-tubes where hundreds of processes and its diversifications can be studied under the same conditions [4] We will report on variable temperature scanning tunneling microscopy (STM) and barrier height spectroscopy investigations on ice formation below the desorption temperature of water at about 150 K and concomitant density functional theory (DFT) calculations that include Tersoff-Hamann simulations and tunneling barrier height calculations [56]
The nanomesh pores may harbor about 40 water molecules that assemble into two-dimensional crystallites The ice rules are satisfied and hydrogen bonds to the substrate are found [7] The measurement of the tunneling barrier by means of dIdz spectroscopy reveals the arrangement of the individual dipoles of the water molecules in the ice flakes and allows the study of proton disorder At lower water coverage the seed formation of the ice flakes may be studied Figure 1 shows an STM image of a very low water coverage where 11 water induced protrusions are observed The triple clusters may however not be stabilized by 3 water molecules only The distance between the protrusions rather corresponds to the in-plane lattice constant of hexagonal Ice Ih In accordance with theory the experiment indicates homodromic complexes A homodromic structure is cyclic and each water molecule offers one proton and one oxygen lone pair in the ring This leads a sense of rotation of the structure (see Figure 2)
Fig 1 STM image of the h-BNRh(111) nanomesh with small clusters at 34 K (10times10 nm2) The clusters assemble inside the 2 nm pores The predominant species are single- and triple-protrusion clusters The image was acquired at Vs = minus002 V and It = 50 pA From [8]
015
Comparison with theory emphasizes these triple protrusions to represent ice oligomers (n=65) ie preferentially hexamers but also pentamers [8] For pentamers the calculated bond energy per water molecule is in average 25 meV lower than in the hexamer where the bond energy is 430 meV per H2O Pentamers as shown in Figure 2 are also relatively stable since the transformation into a hexamer requires an additional water molecule and thermal activation that includes the breaking of a hydrogen bond in the homodrome of the pentamer
Fig2 DFT structure for an ice pentamer on h-BNRh(111) (a) Optimized structure Note in this example the homodromic arrangement of the water molecules is clockwise The odd molecules 135 have a hydrogen bond to the substrate (b) Simulated STM topography (c) Simulated electrostatic potential image From [8]
A careful analysis of the experimentally determined triangle foot-prints of the ice seeds indicates that they are distorted away from the shape of an equilateral triangle For a given distortion they are more chiral than expected from a random distribution and from theory The implications of the chirality may eg be reflected in the formation of amorphous ice It will be interesting to investigate whether this expression is bound to confined water on a hydrophilic surface or not The distortions in the hydrogen bond network must impose significant anharmonicities in the interaction potentials Furthermore several competitive interactions contribute to the structure of the ice oligomers in the pores of h-BN nanomesh the H-O bonds the H-N bonds between the oligomer and the surface as well as the electrostatic field induced α bonding [9] due to the local work function gradient near the rims of the pores
[1] M Corso et al Science 303 (2004) 217 [2] A Goriachko and H Over Z Phys Chem 223 (2009) 157 [3] H Dil et al Science 319 (2008) 1826 [4] HF Ma et al Front Phys China 5 (2010) 387 [5] Y Ding et al JPCC 115 (2011) 13685 [6] Y Ding et al J Phys Condens Matter 24 (2012) 445002 [7] HF Ma et al ChemPhysChem 11 ( 2010) 399 [8] HF Ma et al Langmuir 28 (2012) 15246 [9] T Greber e-J Surf Sci Nanotechnol 8 (2010) 62
1
2
3
45
a
d b c
016
Spatially resolved scanning tunneling luminescence
spectroscopy of p-type GaAs(110)
Hiroshi Imada1 Tomoko K Shimizu
1 Naoki Yamamoto
2 and Yousoo Kim
1
1RIKEN Advanced Science Institute Japan
2Department of Condensed Matter Physics Tokyo Institute of Technology Japan
In order to better understand the physics that dominate the energy conversion
transfer and redistribution in nanometer-scale surface systems we constructed an
experimental setup for photon detection which is based on a cryogenic scanning
tunneling microscope (STM) As has been previously reported the spatial resolution of
this technique scanning tunneling luminescence (STL) can reach the atomic level
The luminescence of p-type GaAs(110) upon electron injection from an STM tip
corresponds to the electronic transition from the conduction band minimum to the
acceptor band inside the bulk This indicates that photon emission occurs in large
volume because the electron diffusion length is about 100 nm in GaAs In contrast
however STL photon maps show atomically fine distributions Weak luminescence was
obtained when the electrons were selectively injected into a Ga site in the first layer
Here we discuss the role of the local density of state for electron injection from which
we propose a plausible mechanism for photon emission in p-type GaAs
017
Control of self‐assembly of erbium silicates and erbium oxides on Si wafers for silicon
photonics
Hiroo Omia) and Takehiko Tawara
NTT Basic Research Laboratories NTT Corporation 3‐1 Wakamiya Morinosato Atsugi
Kanagawa 243‐0198 Japan
Erbium‐doped nano‐scale materials have received much attention due to their great potentials as light
emitting materials and for optical light amplifiers on silicon wafers at the telecommunications wavelength
In their application to silicon photonics it is desirable to locate these materials only on specific areas of
silicon wafers However previous studies have investigated the fabrication of light‐emitting diodes or
optical waveguides on a macro scale by using a top‐down technology In order to align the nanostructures
only on the desired area however it is better to combine self‐formation techniques and the top‐down
technique to attain low‐cost throughput On the other hand recent progress in the research of
rare‐earth‐doped materials has shown that erbium silicates and erbium oxides and erbium‐doped yttrium
silicates are good candidates for application as light amplifiers on silicon wafers [1] In this presentation
we will demonstrate that the self‐assembly formation of erbium silicates and erbium oxides can be
controlled by lithographical patterning of silicon substrates Erbium oxides were deposited on
intentionally patterned Si substrates by rf‐sputtering at room temperature and then annealed in Ar gas
ambience at the temperatures below 1200 Synchrotron X‐ray diffraction atomic force microscopy
cross‐sectional transmission electron microscopy and micro photoluminescence revealed that crystalline
erbium oxides several hundred nanometers in size are preferentially aligned on the area of the line and
space mesa and trench patterns and that islands of erbium silicates with nanoscale size are self‐assembled
on the region of non‐patterned Si(111) wafers The presence of erbium silicates on the non‐patterned Si
indicates that the thermal annealing produces erbium silicates as a result of the reaction Er2O3 + Si + O2 =
Er2SiO5 We also observed 15‐m photoluminescence of Er3+-ions with clear Stark splits from the
self‐assembled erbium oxides and erbium silicates indicating that the crystalline quality is good enough
for the applications As for optical properties time‐resolved PL measurements indicate that the lifetimes of
the PL from the transition between 4I152‐4I132 in the erbium oxide and erbium silicate are on the order of 10
s From the fitting of the decay curves of the erbium oxides with the Yokota‐Tanimoto equation we
derived the energy migration interaction parameter CDD and energy transfer interaction parameter CDA to
be 10times10‐36 and 19times10‐42 cm6s which indicates energy migration plays a very important role in the
self‐assembled crystals
[1] H Omi et al AIP Advances 2 012141 (2012)
018
Nanoscale Evaluation of Optical Activity of Chiral Perylene Derivative
Studied by STM-LE Technique
Y Kuwahara A Fujiki A Saito M Akai-Kasaya
Department of Precision ScienceampTechnology Graduate School of Engineering Osaka
University Suita Osaka 565-0871 Japan
E-mail kuwaharaprecengosaka-uacjp
Chirality which is one of the most essential properties of biological
molecules[1] has been evaluated through optical response to circularly polarized light
ie optical activity Optical activity is hence used as an identical term representing
chirality Thus far optical diffraction limit of proving light have prevented nanoscale
evaluation of optical activity[2] so that a causality between an emergence of optical
dissymmetry and molecular structuralelectronic configurations is still controversial
Here we present single-molecule-level evaluation of optical activity on the basis of
scanning tunneling electron induced light emission detection technique[34] We detect
left and right circularly polarized light (CPL) emissions from chiral Perylene derivative
molecules adsorbed on the substrate and find a novel chirality with an inverted sign
and an approximately 100-fold enhancement for the optical dissymmetry in contrast to
those in the isolated condition which is induced by an intermolecular interaction in the
molecular assembly Our research provides essential information to elucidate the
emergence of optical activities of chiral systems by a combination of the analysis of
single-molecule-level optical properties and structuralelectronic configurations and
theoretical investigations or predictions
References
[1] Karagunes G Coumoulos G Nature 1938 142 162
[2] Riehl J P Richardson F S Chemical Reviews 1986 86 1
[3] Uemura T Furumoto M Nakano T Akai-Kasaya M Saito A Aono M
Kuwahara Y Chemical Physics Letters 2007 448 232
[4] Fujiki A Miyake Y Oshikane Y Akai-Kasaya M Saito A Kuwahara Y
Nanoscale Research Letters 2011 6 347
019
Sputtering with large cluster ion beams
Jiro Matsuoab
a Quantum Science and Engineering Center Kyoto University Gokasho Uji Kyoto 611-0011 Japan b CREST Japan Science and Technology Agency (JST) Chiyoda Tokyo 102-0075 Japan
Email matsuojiro7skyoto-uacjp
Ar cluster ion beams have great potential for novel applications such as nano-processing sputtering of organic materials and SIMS measurements Recently SIMS analysis and molecular depth profiling of soft materials have been demonstrated using large Ar cluster ion beams The multiple collisions and high-density energy deposition of these ions on solid surfaces enhance the sputtering and secondary ion yields and also reduce residual surface damage compared with other techniques We have demonstrated the cluster size effect on secondary ion emission and damage formation [1] but there have been very few studies on the effect of cluster size on the sputtering yield
We have examined the size dependence of the sputtering yield of silicon using the double deflection technique This technique allows the use of size-selected cluster ion beams with a beam current of a few nA Focused Ar cluster beams with an approximate diameter of 1 mm were irradiated to sputter silicon samples The total sputtered volume was measured with a 3D optical surface profiler (Zygo Maxim NT) The ion dose used in these experiments was approximately 1times1016 ionscm2 which was sufficiently high to measure to the sputtered depth (~100 nm) The incident energy and cluster size varied from 10 to 60 keV and from 500 to 5000 respectively The sputtering yield of Ar500 with energy of 60 keV which corresponds to a velocity of 120 eVatom is approximately 500 atomsion The sputtering yield of silicon with monomer Ar ion with energy of 120 eV is approximately 01 atomsion The enhancement observed in the sputtering yield was approximately one order of magnitude and this is much lower than what we expected from the model proposed for small clusters (n lt 10)
A possible sputtering model for large cluster ions together with the enhancement effect on the yield and lowering of the threshold energy for sputtering will be presented in conjunction with surface analysis techniques [1] J Matsuo S Ninomiya Y Nakata Y Honda K Ichiki T Seki and T Aoki ldquoWhat size of cluster is most
appropriate for SIMSrdquo Applied Surface Science 255 (2008) 1235ndash1238
020
Non-equilibrium structural fluctuation of one-dimensional
polydiacetylene nanowire
Megumi Akai-Kasaya1 Yuji Kuwahara1 and Masakazu Aono2
1Graduate School of Engineering Osaka University Suita Osaka 565-0871 Japan
2 Nano System
Functionality Center National Institute for Materials Science (NIMS) 3-13 Sakura Tsukuba Ibaraki
305-0003 Japan contact e-mail kasayaprecengosaka-uacjp
An individual straight polydiacetylene (PDA) wire with few micrometer lengths can be
fabricated on a solid surface by using a scanning tunneling microscopy (STM) probe tip at
designated positions as shown in Fig1 The fully extended conjugated backbone of the PDA is
expected to function as an electrically conducting nanowire The PDA is one of conjugated
conducting polymers which have semiconducting or insulating nature intrinsically and metallic
state upon dense chemical doping We have revealed that an anomaly fluctuating current
increase was observed as shown in Fig 2(a) when a high electric field ie more than 6 Vnm
was applied between a STM tip and substrate Before and after the large current flow we could
confirm a stable PDA wire on the surface The transition from base state to the excite state
abruptly occured and vice versa
We propose that the injected charge excites a non-equilibrium structural fluctuation of the
PDA wire A DFT (Density Functional Theory) calculation for a singly ionized (one electron
removed) PDA polymer wire exhibited a quite high unsteadiness compared with stable results
for other conducting polymer materials In the calculation which was never converged an
remarkable structural fluctuation has been observed The high electric field would be needed to
make ionized states of the polymer wire When the field goes back to lower magnitude induced
charge in the polymer can escape to the substrate surface and the polymer will settle down
The polaronic state of induced charge can propagate along the polymer wire An extreme
condition ie strictly straight long polymer wire adjacent charge source and extremely high
field enhances the ionization efficiency In other words ionized valence in the polymer is not
necessarily to be one Polymer might be able to include high density charges which can convert
the semiconducting nature of the PDA into metallic An optional control of the carrier density
would enhance the capabilities of the use of organic molecules as molecular switches and wire
connections in the future molecular nano-technologies
8 molecules (26nm)
6molecules (19nm)
11 molecules (35nm)
Figure 1 STM images of the fabricated PDA wires with various spacing and a molecular structure of the PDA backbone
7molecules (22nm)
4 molecules (13nm)
-100 0 100 200 300 400 500-20
-10
0
10
20
30
40
-3
-1
1
3
5
7
(b)
(a)
(c)
Cu
rren
t (n
A)
Time (μs)
0
-1
-2
-3
Bia
s
Vo
ltag
e (V
)
Figure 2 (a) Tunneling current after metallic transition (b) Normal tunneling current (c) Applied voltage
021
Single-Molecule Chemistry on an Ultrathin MgO Film
Jaehoon Jung1 Hyung-Joon Shin2 Maki Kawai3 and Yousoo Kim1 1 Advanced Science Institute RIKEN Japan
2 School of Mechanical and Advanced Materials Engineering UNIST Korea 3 Department of Advanced Materials Science The University of Tokyo Japan
Ultrathin oxide film grown on metal substrate has been a subject of great interest
not only as a supporting material for chemically active nanoparticles but also as a catalyst in the field of heterogeneous catalysis We have demonstrated that the chemical reactivity for water dissociation on an ultrathin MgO film supported by the Ag(100) substrate depends greatly on film thickness and be enhanced compared to that achieved with their bulk counterpart using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations [1] The change of chemical reactivity of ultrathin MgO film depending on the film thickness can be explained by the strengthening of the interaction between the oxide and metal interface layers [2] This result implies that the artificial manipulation of the local structure at the oxide-metal interface is expected to play a pivotal role in controlling the catalytic activity of oxide film We have also examined and compared the water dissociation on three model systems with defects at the oxide-metal interface of the 2-ML MgOAg(100) ndash an O vacancy (Fig 1a) an Mg impurity or an O impurity ndash with the case of on the MgO film without defects using periodic DFT calculations [2] Our results clearly show that such structural imperfections at the interface can improve the chemical reactivity of the MgO film supported by an Ag substrate This is closely correlated with the accompanied change of charge distribution of the oxide surface due to the accumulation of transferred charge density at the interface (Fig 1b) In addition the chemical reactions on the ultrathin oxide film surface can be tuned by interface defects regardless of the charging of adsorbates
In this talk a recent result of coupling between molecular vibration and surface phonon in the CO hopping process on MgOAg(100) with tunneling electrons will also be introduced [3]
[1] H-J Shin J Jung K Motobayashi S Yanagisawa Y Morikawa Y Kim and M
Kawai Nat Mater 9 442 (2010) [2] J Jung H-J Shin Y Kim and M Kawai Phys Rev B 82 085413 (2010) J Am
Chem Soc 133 6142 (2011) J Am Chem Soc 134 10554 (2012) [3] H-J Shin J Jung M Kawai and Y Kim submitted
Figure 1 (a) Water dissociation on MgOAg(100) with interface O vacancy and (b) charge density difference map
(a) (b)
022
Inelastic electron tunneling induced unidirectional motion of single molecules Karl-Heinz Ernst Empa Swiss Federal Laboratories for Materials Science and Technology Uumlberlandstrasse 129 CH-8600 Duumlbendorf University Zurich Winterthurerstrasse 190 CH-8057 Zuumlrich karl-heinzernstempach Manipulation of single molecules at surfaces with the scanning tunneling microscope (STM) has been performed for more than a decade After an introduction into chirality and chiral surface science I will present results of manipulation experiments performed with single molecules of the hydrocarbon propene on Cu(211) Inelastic electron tunneling (IET) has been applied to excite molecular vibrations in the molecule Exceeding the threshold energy for certain vibrational excitations we observe different actions like hopping rotation inversion of the handedness and dehydrogenation All actions are mode-selective that is only certain vibrations cause a certain action The product of the single molecule chemical reaction can be also identified by IET-action spectroscopy ie hopping was observed after excitation of a C-H stretching vibration in the =CH2 group of the product Finally I will present the activation of a chiral molecular rotor by electron attachment that leads to unidirectional rotation A clever combination of four unidirectional rotors into one molecule leads then to unidirectional translation of the molecular machine
023
Growth adsorption and electronic properties of sexithiophene on noble metal surfaces From monolayers to thin films
R Hammer1 A Houmlfer1 M Kiel1 K Duncker1 S Ghanem2 A Blaumlttermann1 T Leopold1 S
Wedekind1 and W Widdra12
1 Institute of Physics Martin-Luther-Universitaumlt Halle-Wittenberg Halle Germany 2 Max Planck Institute of Microstructure Physics Halle Germany
Organic π-conjugated molecules like alpha-sexithiophene (6T) are used as active layers in light-emitting diodes solar cells and field effect transistors Their potential for low cost and flexible devices has driven many investigations in the field Nowadays the interface between organic layers and metal contacts is of particular interest as the injection of electrons and holes is crucial for the performance of the devices This has motivated also our study on adsorption growth and electronic properties of highly-ordered thin films on noble metal substrates
Growth and properties of 6T on different noble metal surfaces as Au(111) Au(110) Au(001) and Ag(001) have been studied by variable-temperature scanning tunneling microscopy (STM) scanning tunneling spectroscopy (STS) and low energy electron diffraction (LEED) On all substrates highly-ordered chiral structures within the monolayer are found Whereas the aspect of chirality is absent in the bulk crystal structure and in gas phase we find different chiral structures mostly in all-trans configuration in all systems studied within the first two monolayers On herring-bone reconstructed Au(111) a rather weak adlayer-substrate interaction leads to dominating molecule-molecule interactions and an incommensurate 6T structure in the monolayer [1] In contrast the stronger molecule-substrate interaction on the unreconstructed Ag(001) leads to commensurate and homochiral structures with molecules aligned in the [110] high-symmetry direction [2] Whereas most structures are formed by linear all-trans molecules also highly ordered domains of molecules which have undergone a concerted trans-cis isomerization between the 4th and 5th thiophene ring are found between right- and left-handed domains The significant influence of 6T on the metal surface reconstruction is demonstrated on Au(100) and Au(110) Whereas 6T adsorption leads to a partial quenching of the Au(100) reconstruction [3] it leads to spectacular 1D growth on Au(110) Based on ARPES and STS the band offsets as well as the positions of the different molecular orbitals with respect to the Fermi level have been determined Their differences on different substrates and for different film thickness will be discussed Finally an outlook towards femtosecond spectroscopy and microscopy on these systems will be given
[1] M Kiel K Duncker C Hagendorf and W Widdra Physical Review B 75 195439 (2007) [2] K Duncker M Kiel A Houmlfer and W Widdra Physical Review B 77 155423 (2008) [3] A Houmlfer K Duncker M Kiel S Wedekind and W Widdra Physical Review B 83 075414 (2011)
024
Water on ldquoHydrophobicrdquo Carbon Nanotube Surface
Shohei Chiashi1 Takahiro Yamamoto
2 and Yoshikazu Homma
3
1Department of Mechanical Engineering The University of Tokyo Bunkyo Tokyo
113-8656 Japan 2Department of Liberal Arts Faculty of Engineering and Department of Electrical
Engineering Tokyo University of Science Chiyoda Tokyo 102-0073 Japan 3Department of Physics Tokyo University of Science Shinjuku Tokyo 162-8601
Japan
The behavior of water molecules on a solid surface is of great interest but is difficult
to be explored experimentally We used single-walled carbon nanotubes (SWNTs) to
probe the behavior of water molecules on the surface at room temperature in water
vapor Because of the one-dimensional singular density of states of electrons resonant
optical measurements can be performed for an SWNT otherwise the sensitivity to a
small amount of water molecules is too low Furthermore the optical transitions in an
SWNT are strongly influenced by the surrounding environment of the monolayer
material of the SWNT
Based on photoluminescence and Raman scattering measurements of individual
SWNTs suspended between micropillars in water vapor together with molecular
dynamics simulations we found that water molecules form a stable adsorption layer of
1-2 monolayer thick on the nanotube surface and they show a rapid adsorption and
desorption phenomena at a critical pressure This adsorption layer is created by lateral
hydrogen bonding of water molecules confined in the weak van der Waals potential of
the surface The adsorption layer is thermodynamically in equilibrium with the external
vapor and liquid phases around room temperature It has a clear interface with the
external phase and uniform condensation energy These features indicate that the water
layer is not a part of bulk water or a simple adsorption layer Therefore it can be
regarded as a separate phase of water which differs from bulk solid liquid and vapor
phases The adsorption layer does not grow thicker and behaves as a hydrophobic
surface paradoxically
025
The Materials Genome Initiative ndash the basic-science component
Matthias Scheffler Fritz-Haber-Institut der Max-Planck-Gesellschaft
Faradayweg 4-6 D-14195 Berlin Germany schefflerfhi-Berlinmpgde
Presidents of the United States sometimes launch science and technology initiatives A well-known example is that on Nanotechnology initially announced by President Clinton in a speech at Caltech in January 2000 In June 2011 President Obama announced the Materials Genome Initiative (MGI) [1] with the aim to accelerate advanced materials discovery and deployment
The word genome when applied in this non-biological context refers to a fundamental building block toward a larger purpose It may also refer to methodology that goes analog to that of the Human Genome Project In fact materials science -- surface and interface science is a (most) important part of it -- is producing a lot of data Clearly the MGI can only be successful when this information is properly disseminated but so far much of the scientific information that may be of interest for other studies is not even published or it is hidden (and not searchable) as supplementary information Note that information gathered in the context of some surface-science or catalysis research may well be relevant for other fields such as coatings or corrosion-resistant materials just to mention one example
Science based on huge data sets will be different It will add a new level enabling us to identify so far hidden relationships trends and insight In order to be successful we need to improve synergies and collaborations We need to create a searchable table of more than 100000 different materials and systems We need veracityreliability marks and we need new analysis tools For sure we also need to look behind this table We must not overlook the dangers of such approach and also support the genius individuals Starting from an US NSF workshop in December 2012 [2] I will try to analyze the challenges the potential and the possible problems of the MGI for fundamental science of materials What do we need to do to make the MGI a success Is the community ready and willing to go in this direction
1) Materials Genome Initiative for Global Competitiveness (Executive Office of the President National Science and Technology Council) httpwwwwhitehousegov sitesdefaultfilesmicrositesostpmaterials_genome_initiative-finalpdf
2) MGI workshop at the US National Science Foundation December 2012 httpsmaterials-genome sitesuchicagoeduabout-mgi
026
Transport properties and electronic structure of individual metallic nanocontacts on dielectric supports A local view
Wolf-Dieter Schneider
Institute of Condensed Matter Physics Ecole Polytechnique Feacutedeacuterale de Lausanne (EPFL)
CH-1015 Lausanne Switzerland and
Fritz-Haber-Institute of the Max-Planck-Society D-14195 Berlin Germany Email wolf-dieterschneiderepflch
Contacts between metallic nanostructures and semiconducting or dielectric supports are expected to constitute the basic building blocks of future nanoscale electronics and nano catalysts We investigate with low-temperature scanning probe techniques the transport properties of individual nanocontacts formed between flat metallic islands and their supporting substrates The observed differential conductance spectra reveal a suppression at small bias voltages characteristic for the presence of dynamical Coulomb blockade phenomena Calculations based on the theory of environmentally assisted tunneling agree well with the measurements allowing us to determine the capacitances and resistances of the contacts which depend systematically on the island-substrate contact area [1] These findings facilitate quantitative investigations of electrical nanocontacts and are important for future studies of the physical and chemical properties of supported nanostructures in relation to superconductivity magnetism and catalysis [2]
[1] C Brun K-H Muumlller I P Hong F Patthey C Flindt and W-D Schneider Phys Rev Lett 108 126802 (2012) [2] X Shao Y Cui W-D Schneider N Nilius H-J Freund J Phys Chem C 116 17980 (2012)
027
Stabilized the AuSi(111) phase by ordered surface decoration of indium
Chien-Cheng Kuo (jcckuogmailcom)Department of physics National Sun Yat-sen University Kaohsiung 80424 Taiwan
Ordered metallic adatoms on the semiconductor surface has been demonstrated to show many fascinating phenomena in the past decades The electronic properties like band disper-sion can be signifcantly changed only by subtle surface decoration [1-2] This provides a pos-sibility of tuning electronic structures of the surface by changing the symmetry or even the Rashba spin-orbit splitting through the ordered surface decoration One of the famous ordered structure for the interesting 2D metallic state radic3timesradic3 phase of Au overlayer on Si(111) ex-hibits complicated domain evolution sensitive both to the coverage and to the temperature [3] Surprisingly this rich diversity becomes stable and homogeneous even the sub-monolayer in-dium adsorbs on the surface The domain structures melt to form a homogenous radic3timesradic3-(Au In) reconstruction with free of domain-walls [4] Meanwhile indium will be saturated at ~ 015 ML and starts to aggregate as clusters at higher coverage Nevertheless the frst-principle cal-culation indicates the existence of the possible radic3timesradic3-(Au In) structure at higher indium cov-erage with the band dispersion changing dramatically [5] Herein the higher indium coverage on radic3timesradic3-Au was shown by using atomic resolution scanning tunneling microscopy By de-positing 1 ML In on reg-radic3timesradic3-Au and subsequent annealing at 600 degC a homogenous 2radic3timesradic3-(Au In) surface structure was observed We found that the indium coverage of the 2radic3timesradic3-(Au In) is 08 ML and is stable both at 300 K and at 78 K This 2radic3timesradic3-(Au In) shows three domains on the surface and a slow domain shifting within one domain Further analysis and comparison with the theoretical study will also be addressed in advance
[1] J N Crain K N Altmann C Bromberger and F J Himpsel Phys Rev B 66 205302 (2002)
[2] R Corteacutes A Tejeda J Lobo C Didiot B Kierren D Malterre E G Michel and A Mascaraque Phys Rev Lett 96 126103 (2006)
[3] T Nagao S Hasegawa K Tsuchie and S Ino C Voges G Klos H Pfnur and M Henzler Phys Rev B 57 10100 (1998)
[4] D V Gruznev I N Filippov D A Olyanich D N Chubenko I A Kuyanov A A Saranin A V Zotov and V G Lifshits Phys Rev B 73 115335 (2006)
[5] C-H Hsu W-H Lin V Ozolins and F-C Chuang Phys Rev B 85 155401 (2012)
028
Surface Superconductor Si(111)-(radic7timesradic3)-In
Fluctuation Effects and Molecular Control
Takashi Uchihashi International Center for Materials Nanoarchitectonics National Institute for
Materials Science1-1 Namiki Tsukuba Ibaraki 305-0044 Japan Email address UCHIHASHITakashinimsgojp
Abstract Recently the Si(111)-(radic7timesradic3)-In surface reconstruction has drawn intense interest because electron transport measurements [1] unambiguously demonstrated a superconducting transition of a metal adatom-induced silicon surface [2] This class of surface system offers opportunities for finding unique superconductors with an ideal two-dimensional character and with a space-inversion symmetry breaking due to the presence of surface [3] Here we report on quantitative analysis on the behavior of the resistive transition of Si(111)-(radic7timesradic3)-In around the transition temperature (Tc) The sheet resistance (R) of the sample was measured by a linear four-point-probe configuration which was realized by Ar ion sputtering through a shadow mask We found that the temperature dependence of R above Tc is well described by parallel conduction due to Cooper pair fluctuation (Aslamazov-Larkin term [4]) Significant deviation of a universal parameter from the theoretical prediction also indicates the contribution of normal electron fluctuation (Maki-Thompson term [4]) A minute residual resistance was identified below Tc which may be ascribed to a vortex-driven electron dissipation We also describe our first attempt to control the superconducting properties of the Si(111)-(radic7timesradic3)-In surface by organic molecular layers Co-phthalocyanine (Pc) molecules were found to be grown epitaxially on the Si(111)-(radic7timesradic3)-In surface The Co-Pc molecules exhibit quasi-triangular lattice with a 8times4 commensurability against the ideal Si(111) 1times1 surface despite the four-fold symmetry of the molecule This indicates a relatively strong interaction between the molecules and the Si(111)-(radic7timesradic3)-In Even after the molecular growth the sample was found to exhibit a clear superconducting transition This promises the use of molecules to control the properties of surface superconductors References [1] T Uchihashi et al Phys Rev Lett 107 207001 (2011) also see Viewpoint in Physics 4 92 (2011) [2] T Zhang et al Nature Phys 6 104 (2010) [3] KYaji et al Nature Communications 1 17 (2010) [4] M Tinkham Introduction to Superconductivity (McGraw-Hill New York 1996) 2nd ed Chapt 8
029
In situ Magnetotransport measurements of ultrathin Bi films on Si(111)
Masaki Aitani Toru Hirahara and Shuji Hasegawa University of Tokyo Department of Physics 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033
hiraharasurfacephyssu-tokyoacjp
Bulk states of Bismuth are semimetallic but the surface states are highly metallic and spin-split due to strong spin-orbit coupling and inversion asymmetry (Rashba effect) This Rashba splitting has been studied mainly by spin- and angle- resolved photoemission spectroscopy [1-2] Furthermore it was recently shown that surface-state conductivity is dominant in an epitaxial ultrathin film of 25 Å thickness [3] Although many magnetotransport measurements of Bi films have been performed historically reporting weak anti-localization effects (WAL) the contribution from the surface states on the magnetotransport properties have not been discussed in detail The mainly reason is that the films studied in the previous reports are amorphous or granular [4]
In this study we performed in-situ four-probe conductivity measurements of ultrathin single-crystalline Bi(111) films formed on Si(111) at low temperature under magnetic field As shown in Fig 1 we observed WAL effects and also the increase of resistance with decreasing temperature below 4K which can be attributed to the electron-electron interaction Based on the Hikam-Larkin-Nagaoka equation we estimated the phase coherence length In the presentation we will show the details of the analyses and discuss the contribution from the surface and the bulk states
[1] T Hirahara et al Phys Rev B 76153305 (2007) [2] T Hirahara et al Phys Rev Lett 97 146803 (2006) [3] T Hirahara et al Appl Phys Lett 91 202106 (2007) [4] F Komori S Kobayashi and W Sasaki Jounal of the Physical Society of Japan 52 368
(1983)
Fig1 Change of conductivity by WAL effect at 08K for ultrathin Bismuth films which have different thickness Dots are experimental data and fitted lines to Hikami-Larkin-Nagaoka equation are shown
030
A multiple-wave X-ray diffraction phenomenon and its application to surface crystallography
Wataru Yashiro1 Yoshitaka Yoda2 Kazushi Miki3 and Toshio Takahashi4 1Institute of Multidisciplinary Research for Advanced Materials (IMRAM) Tohoku University Katahira 2-1-1 Aoba-ku Sendai 980-8577 Japan 2Japan Synchrotron Radiation Research Institute (JASRI) 1-1-1 Kouto Sayo-gun Sayo-cho Hyogo 679-5198 Japan 3Organic Nanomaterials Center National Institute for Material Science (NIMS) 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan 4The Institute for Solid State Physics (ISSP) the University of Tokyo 5-1-5 Kashiwanoha Kashiwa Chiba 277-8581 Japan Email wyashirotagentohokuacjp
The phase problem in surface crystallography has been an extensively researched subject in recent years Using x rays for surface structure analysis is advantageous in that it enables highly precise easy-to-interpret analysis Since the advent of synchrotron radiation sources in the early 1980s the surface x-ray diffraction (SXD) technique has become a powerful tool for determining atomic positions and strains near surfaces In SXD analysis intensity distribution along crystal truncation rods (CTRs) perpendicular to the crystal surface is measured and then compared with those
calculated for several structure models that are physically possible To model independently determine three-dimensional strain distributions atomic coordinates and ultimately the electron density of a crystal surface the phase of the scattering amplitude along the CTRs has to be retrieved Various methods for this have been developed since the mid-1980s and more actively studied for the last decade We have proposed a method to obtain information on the phase of CTR scattering using a multiwave x-ray diffraction phenomenon modulation of the intensity of CTR scattering
caused by an excitation of a Bragg reflection [1-3] We demonstrated that our method can be applied for not only analysis of strain fields near crystal surfaces to which the phase of CTR scattering is sensitive [2] but in-situ observation of synchrotron-radiation-induced time evolution of amplitude reflectivity with only a 001 degree of crystal rotation which allows the area that is irradiated by the x-ray beam to be unchanged during the measurement [3] Our method is a powerful tool that provides structural information in crystals which is difficult to be unveiled by conventional intensity
measurements along CTRs
[1] T Takahashi et al Phys Rev B 62 3630 (2000) [2] W Yashiro et al Surf Sci 550 93 (2004) [3] W Yashiro et al J Appl Phys 110 102210 (2011)
031
X-ray fluorescence holography and its applications
K Hayashi1 N Happo2 and S Hosokawa3
1 Institute for Materials Research Tohoku University Sendai 980-8577 2 Graduate School of Information Science Hiroshima City University Hiroshima
731-3194 3Department of Physics Graduate School of Science and Technology Kumamoto
University Kumamoto 860-8555
X-ray analyses such as X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) are useful for structure analyses with atomistic order However since they require adequate structure models and data-fitting procedures determinations of atomic arrangements are not straightforward On the other hand X-ray fluorescence holography (XFH)[1] can provide 3D atomic images around specific elements by a simple Fourier transformation The recent technical advances provide a data set with extremely high statistical accuracy and can display light atoms such as oxygen Moreover the reconstructible volume has widened up to few nm in a radius This feature makes us possible to analyze middle-range local structure which offers more information than the short range local structure obtained by XAFS Although the sample of XFH needs a regular orientation of atomic arrangement around a specific element it is not limited to systems with a long-range order but can also be applied to cluster surface adsorbates quasicrystal and impurities
Recently we found two important points to obtain quantitative information from XFH data One is multiple-energy holograms with over eight different X-ray energies using the inverse mode The multiple-energy X-ray holography can reconstruct atomic images even of light elements And in our ZnTe experiment the intensities of Zn and Te atoms at each position coincide with those obtained from the calculated ZnTe holograms Another one is the use of reference samples In the case of the mixed crystal of Zn04Mn06Te we measured the holograms of both Zn04Mn06Te and the reference ZnTe under same experimental conditions and successfully estimated the local lattice distortion in the mixed crystal by comparing the atomic images of the both samples[2] Moreover in the case of a shape-memory alloy related material of Ti05Ni044Fe006 we measured its holograms at the parent phase (225 K) and the commensurate phase (100 K) Since the reconstructed image of the parent phase played a role of the standard sample structure we could find a nano-structure at the lower temperature by comparing the both atomic images at the parent and commensurate phases[3]
Now our XFH works are moving to the structural analyses of dopants in thin films such as diluted ferromagnetic semiconductors We have obtained some interesting results approaching to the mechanism of the occurrence of the room temperature ferromagnetism In our presentation we will show the brief theory of the XFH and the recent applications in Japan
[1] K Hayashi et al J Phys Condens Matters 24 093201 (2012) [2] S Hosokawa N Happo and K Hayashi Phys Rev B 80 134123 (2009) [3] W Hu et al Phys Rev B 80 060202(R) (2009)
032
Surface structure analysis using 3D reciprocal-map
Tadashi Abukawa
Tohoku University Institute of Multidisciplinary Research for Advanced Materials
2-1-1 Katahira Aobaku Sendai 980-8577
abukawatagentohokuacjp
When hundreds of 2D diffraction-patterns are collected as a function of the sample azimuthal
rotation by Weissenberg RHEED (W-RHEED) a 3D reciprocal-map can be reconstructed from the
patterns Using a typical RHEED screen we can obtain a large volume of the 3D reciprocal map up
to the temperature limit of crystals Since the whole reciprocal map was obtained by a scan of the
azimuthal angle it typically took ~10 min for the measurement of the 3D reciprocal map The large
3D reciprocal-map and the fast measurement are key advantages of the W-RHEED Thanks to the
large 3D reciprocal-map we can calculate a 3D Patterson map with a high special-resolution
(~003nm) as the Fourier transformation of the reciprocal-map The surface structure can be directly
solved by analysis of the Patterson map
Here we show two examples of the surface structure analysis by the W-RHEED The structure of
Si(111)-5x2-Au surface is one of the long standing problems in the surface science Recently Barke
et al experimentally revised the Au coverage to be 06 ML [1] and a new 06ML model was proposed
by a first-principles theory [2] We have determined the arrangement of the Au atoms and their
positions referred to the substrate by W-RHEED and thus propose a new structure model for the
Si(111)5x2-Au with 06ML Au
Fe(001)-1x1-O surface has attracted attentions as a stable target for the electron spin detector[3]
We have prepared Fe(001)-1x1-O surface on a MgO(001) substrate[3] The structure model by
W-RHEED will be compared with the model determined by XRD [4]
Acknowledgments This work was supported in part by KAKENHI (B) 17360016 and (A) 20244042
References
[1] I Barke et al Phys Rev B 79 155301 (2009)
[2] S Erwin et al Phys Rev B 80 155409(2009)
[3] T Okuda et al Rev Sci Instruments 79 123117 (2008)
[4] S S Parihar et al Phys Rev B 81 1ndash6 (2010)
033
Growth Magnetism and Ferromagnetic ldquoGaprdquo in Fe Films on the W(111) Surface
Q Wu1 R Zdyb2 E Bauer3 MS Altman1
1Department of Physics Hong Kong University of Science and Technology Hong Kong
2Institute of Physics Marie Curie-Skłodowska University Lublin Poland 3Department of Physics Arizona State University Tempe Arizona USA
phaltmanusthk
The growth structure and magnetism of Fe films on the W(111) surface were investigated using low energy electron microscopy (LEEM) diffraction (LEED) spin polarized LEEM (SPLEEM) and work function measurements [1] In contrast to an earlier report that Fe grows with fcc structure following initial pseudomorpic layer growth [2] no evidence is found for the formation of fcc Fe over the entire thickness range studied up to 18 monolayers (ML) Observations are instead consistent with the growth of a well-ordered laterally (tensile) strained bcc Fe layer that gradually relaxes vertically and develops increasing disorder with increasing thickness Ferromagnetic order appears at 6 ML but surprisingly vanishes at 8 ML and reappears just as suddenly at 9 ML during Fe deposition at room temperature (Fig 1(a)) This ferromagnetic ldquogaprdquo closely resembles behavior that was reported previously for FeW(110) films [3] Ferromagnetism between 6-8 ML also vanishes at only six degrees above room temperature (Fig 2(a)) The magnetization direction of a mono-domain structure remains constant before and after the ldquogaprdquo at 8-9 ML until the formation of a multi-domain structure at about 12 ML Variations of exchange asymmetry in spin-polarized elastic electron scattering are also observed with increasing film thickness particularly above 12 ML that indicate changes in the spin-polarized electron band structure above the vacuum level The evolution of magnetism and exchange asymmetry with increasing thickness and the appearance of the ferromagnetic gap are attributed to structural and morphological changes in the strained Fe layer which eventually lead to a relaxed although highly disordered bcc Fe layer
5 6 7 8 9 10
00
10
20
P A
ex (x
10-2
)
Thickness (ML)
0 3 6 9 12 15 18
-30
-20
-10
00
10
20
30
P A
ex (x
10-2)
Thickness (ML)
a
Fig 1 SPLEEM magnetic asymmetry (PAex) as a function of Fe film thickness during deposition (a) at room temperature (2988K) for the indicated incident electron energies (b) at 70 eV at the indicated temperatures A ferromagnetic lsquogaprsquo is observed between 8-9 ML at room temperature (grey shading) The thickness range above 12ML that a multi-domain structure appears is identified in (a) References [1] Funding from the Hong Kong RGC under grant HKUST_60111 is acknowledged [2] J Kołaczkiewicz and E Bauer Surf Sci 420 157 (1999) [3] HJ Elmers J Hauschild H Fritzsche G Liu U Gradmann U Koumlhler Phys Rev Lett 75 2031 (1995)
30 eV b 2988K 3023K
38 eV 3039K
70 eV 3044K 3051K
10 eV
034
Novel development of very high brightness and highly spin-polarized electron gun with compact 3D spin manipulator
T Koshikawa 1) T Yasue1) M Suzuki1) K Tsuno1) S Goto2)
XG Jin3) and Y Takeda4) 1) Osaka Electro-Communication Univ 18-8 Hatsu-cho Neyagawa 572-8530
2) San-yu Electronic Corp 1-22-6 Hyakunin-cho Shinjuku Tokyo 167-0073
3) School of Engineering Nagoya Univ Furo-cho Chigusa Nagoya 468-8602
4) Aichi Synchrotron Radiation Center 250-3 Yamaguchi-cho Seto 489-0965
We have already developed a novel high brightness and high spin-polarized low energy electron
microscope (SPLEEM) [1-3] and applied it to clarify the magnetic property of [CoNix]yW(110) and
AuCoNi2W(110) during growth of ultra thin films Such thin multi layered films are important for
current-driven domain-wall-motion devices [4] Our developed SPLEEM can make us the dynamic
observation of the magnetic domain images possible However the size of the spin-polarized electron
gun is large and we have started to develop a new compact spin-polarized electron gun with a new
idea In principle two devices are necessary to operate 3-dimensional spin direction one is a spin
manipulator which changes the out-of-plain spin direction and another one is a spin rotator which
can change the in-plain spin direction We have proposed a multi-pole Wien filter which enables
3-dimensional spin operation with one device Fig 1 shows results of magnetic images and
magnetic asymmetries of Co(4ML)W(110) vs the polar and azimuthal which are obtained with
angles 8 pole 3D spin manipulation
Fig 1 Magnetic images and asymmetries of Co (4ML) W (110) These images were obtained with the novel developed compact 3D spin manipulator
1) XG Jin et al Appl
Phys Express 1
045002 (2008)
2) N Yamamoto et al
J Appl Phys 103
064905 (2008)
3) MSuzuki et al
Appl Phys Express
3 026601 (2010)
4) TKoyama et al
Appl Phys Express
1 101303 (2008)
035
Spin dependent 4He+ ion-surface interaction Taku Suzuki
National Institute for Materials Science Tsukuba Japan A 4He+ ion has either up or down spin like electrons The spin of a 4He+ ion beam can be polarized by optical pumping The spin-polarized 4He+ ion beam has an unique character that is a sensitivity to surface magnetism We have developed a novel analytical method for surface magnetic structure using low energy polarized 4He+ ion beam (spin-polarized ion scattering spectroscopy (SP-ISS)) SP-ISS is capable of analyzing surface spin of outermost surfaces with element selectivity I will discuss our recent results by SP-ISS [1-3] [1] T Suzuki H Kuwahara Y Yamauchi Surf Sci 605 (2011) 1197 [2] T Suzuki Y Yamauchi Phys Rev A 82 (2010) 042709 [3] T Suzuki Y Yamauchi S Hishita Phys Rev Lett 107 (2011) 176101 E-mail suzukitakunimsgojp
036
Current-induced domain wall motion Intrinsic pinning and two barrier stability
Teruo Ono
Institute for Chemical Research Kyoto University Japan
Electrical displacement of a domain wall (DW) is a prospective method for information
processing in new type of magnetic non-volatile memories and logic devices[1-4] Such novel spintronic devices require a low DW drive current and a high DW de-pinning field for stable information retention We show that CoNi multilayer with perpendicular magnetic anisotropy is a promising material that satisfies these requirements An electric current can drive a DW in one direction regardless of the polarity of a magnetic field in a CoNi nano-wire with perpendicular magnetization ie the current can drive a DW against a magnetic field Furthermore both the DW velocity and the threshold current density for the DW motion show almost no dependence on the external magnetic field These counter-intuitive behaviors can be interpreted as the consequence that the intrinsic pinning mechanism determines the threshold current and the adiabatic spin torque dominates the DW motion in this system [5-11] The established field-insensitivity of the electrical DW motion is promising for future spintronics applications based on the DW motion
This work was partly supported by a Grant-in-Aid for Scientific Research (S) and Funding program for world-leading innovative R amp D on science and technology (FIRST program) from the Japan Society for the Promotion of Science References [1] A Yamaguchi et al Phys Rev Lett 92 (2004) 077205 [2] S S P Parkin et al Science 320 (2008) 190 [3] D A Allwood et al Science 309 (2005) 1688 [4] S Fukami et al 2009 symposium on VLSI technology Digest Tech Pap 230 (2009) [5] T Koyama et al Nature Materials 10 (2011) 194 [6] T Koyama et al Appl Phys Lett 98 (2011) 192509 [7] K Ueda et al Appl Phys Express 4 (2011) 063003 [8] D Chiba et al Appl Phys Express 3 (2010) 073004 [9] H Tanigawa et al Appl Phys Express 2 (2009) 053002 [10] T Koyama et al Appl Phys Express 1 (2008) 101303 [11] T Koyama et al Nature Nanotechnology 7 (2012) 635
037
Initial Stage of Metal Adsorption on Si(111) Real Time Monitoring by RHEED
S N Takeda Y Ohnishi Y Tanaka S Yasui K Matsuta K Shima H Daimon
Nara institute of Science and Technology (NAIST) Nara Japan sakuramsnaistjp
Metal adsorption on Si(111) 7times7 surface has attracted much attention due to
the formation of various beautiful surface structures having less defects and large domain sizes Those surface structures are summarized in phase diagrams for various metal species At the initial stage of metal adsorption on Si(111) however RHEED pattern only shows 7times7 symmetry Thus the phase diagram indicates the structure at this stage remains to be unchanged (7times7) On the other hands according to the several STM works the adsorbed atom tends to nucleate within a half of 7times7 unit cell and form rather regular cluster array
To see the effect of regular cluster array on the RHEED patterns we recorded the 7times7 RHEED pattern during metal adsorption on Si(111) for various metals (Mg K Li Mg Bi Pb and In) at the initial stage Though RHEED pattern shows no symmetry change we found there is a rich variety of 7times7 pattern in terms of spot intensity distribution at this stage With the help of STM images in the literature and by us we concluded that such intensity modulation corresponds to the change of the structure factor brought by the formation of a specific cluster within each 7times7 unit cell Thanks to the long range order of the cluster array RHEED can monitor the process of cluster formation during deposition This technique may be useful for the precise control of metal coverage for preparation of regular cluster array
038
Spin-polarized scanning tunneling microscopy of Co thin films on Ag(111)
Keiji Doi Yasuo Yoshida Yukio Hasegawa
The Institute of Solid State Physics The University of Tokyo 5-1-5 Kashiwa-no-ha Kashiwa Chiba 277-8581Japan
Spin-shy‐polarized13 scanning13 tunneling13 microscope13 (SP-shy‐STM)13 enables13 us13 to13
investigate13 magnetic13 systems13 on13 surfaces13 and13 complicated13 magnetic13 structures13
of13 magnetic13 thin13 films13 in13 atomic-shy‐scale13 spatial13 resolution13 [1]13 In13 this13 study13 we13
have13 investigated13 the13 magnetic13 properties13 of13 Co13 thin13 films13 grown13 on13 Ag(111)13
substrate13 using13 SP-shy‐STM13 The13 technique13 has13 been13 applied13 to13 Co13 thin13 films13 on13
Cu(111)13 Pt(111)13 and13 Ir(111)13 substrates13 [113 2]13 but13 it13 has13 never13 utilized13 for13
CoAg(111)13 probably13 because13 strong13 Moire13 contrasts13 on13 the13 Co13 layers13 may13
hinder13 the13 magnetic13 contrast13 Very13 recently13 it13 was13 reported13 by13 using13
surface-shy‐magneto-shy‐optical13 Kerr13 effect13 technique13 that13 Co13 thin13 films13 on13 Ag(111)13
behave13 as13 ferromagnetic13 nano-shy‐magnets13 [3]13 Using13 an13 out-shy‐of-shy‐plane13 magnetized13
tip13 we13 measured13 dIdV13 images13 at13
various13 magnetic13 fields13 on13 Co13 islands13
and13 obtained13 a13 hysteresis13 behavior13 as13
shown13 in13 Fig13 113 indicating13 their13
ferromagnetic13 nature13 In13 the13
presentation13 I13 would13 discuss13 the13
details13 of13 our13 experimental13 results13
13
e-shy‐mail13 address13 pind-shy‐i2isspu-shy‐tokyoacjp13 13
[1]13 R13 Wiesendanger13 Rev13 Mod13 Phys13 8113
149513 (2009)13
[2]13 J13 Bickel13 et13 al13 Phys13 Rev13 B13 8413 05445413
(2011)13
[3]13 Y13 Saisyu13 et13 al13 J13 Appl13 Phys13 11013 05390213
(2011)13
Fig13 113 dIdV13 hysteresis13 loop13 with13 dIdV13
images13 taken13 on13 a13 Co13 island13 (-shy‐040V)13
Red13 and13 blue13 colors13 correspond13 to13
upward13 and13 downward13 sweeps13 of13 the13
magnetic13 field13 respectively13 Black13 and13
white13 arrows13 indicate13 the13 magnetization13
direction13 of13 the13 tip13 and13 sample13
039
Epitaxy Of Graphene On Si(100) And Si(111) Faces Simultaneously Formed On Si(100) Substrate
Hirokazu Fukidome1 Yusuke Kawai2 Takayuki Ide1 Hidetoshi Miyashita2 Masato Kotsugi3 Takuo Ohkouchi3 Yoshiharu Enta4
Toyohiko Kinoshita3 Koji Horiba5 Naoka Nagamura5 Satoshi Toyoda5 Toshihiro Shinohara5 Masaharu Oshima5 Maki Suemitsu1
1Research Institute of Electrical Communications Tohoku University Sendai 980-8577 Japan 2School of Engineering Tohoku University Sendai 980-8579 Japan
3JASRISPring-8 Hyogo 679-5148 Japan 4Graduate School of Science and Technology Hirosaki University Aomori 036-8561 Japan
5Department of Applied Chemistry The University of Tokyo Tokyo 113-8656 Japan
ABSTRACT
Epitaxial graphene (EG) on SiC substrates [1] formed by Si sublimation from the SiC surface is one of the feasible methods for fabrication of graphene in the industry However the high cost in realizing large-sized SiC wafers forms a serious disadvantage of this method To solve this problem Suemitsu and his coworkers have developed a method to fabricate an epitaxial graphene on silicon (GOS) [2] In the GOS technology EG grows on the surface of a SiC thin film preformed on Si substrates by annealing in vacuum Furthermore it has been clarified by Fukidome et al [3] that the GOS technology can easily control the two types of the electronic structure of graphene semiconducting and metallic by simply tuning the orientation of the Si substrate used in the process The GOS technology thus enables realization of new graphene-based mulitifunctional devices having both logic and photonic functions We here demonstrate by using microfabricated Si(100) substrates that the two types of graphene can in fact realized within a single Si substrate
The first step is the growth of a 3C-SiC thin film on a microfabricated Si(100) substrate The microstructre is patterned by electron-beam lithography on oxidized Si(100) substrates and by a vertical etching with a fast atomic beam of SF6 Next we etched this pattern with TMAH to form Si(100) and (111) faces Then 3C-SiC thin films are grown on this microfabricated Si(100) substrate by gas-source MBE using monomethylsilane The second step is the EG formation on this microfabricated SiCSi(100) substrate by annealing in ultrahigh vacuum Micro-Raman spectra from the 3C-SiC(100) and 3C-SiC(111) portion both indicated G and Grsquo bands the principal vibration modes of graphene [4] Furthermore the Grsquo band in 3C-SiC(100)Si(100) is a single peak while the one in 3C-SiC(111)Si(111) consists of multiple peaks This result indicates that the stacking and the electronic structure of EG differ depending on the orientation of the Si face underneath the graphene We have thus demonstrated that EG can be formed on both Si(100) and Si(111) faces microfabricated on a single Si(100) substrate The stacking and the electronic structure of graphene are controllable by use of this orientation control We still observe defect-related D bands in a significant amount The next challenge is to improve the quality of graphene This work was partly supported by a Grant-in-Aid for Specially Promoted Research (Kakenhi 23000008)
REFERENCES
1 A J van Bommel et al Surf Sci 48 463-472 (1975) 2 M Suemitsu et al e-J Surf Sci Nanotech 7 311-313 (2009) 3 H Fukidome et al J Mater Chem 21 17242 (2011) 4 M A Pimenta et al Phys Chem Chem Phys 9 1276 (2007)
040
Theory and Experiment of Palladium Catalysis for Ligand-free 13 13 13 13 13 13 13
Coupling13 Reaction on Sulfur-modified Au
Mami Yokoyama1 _Akira Ishii1 Kengo Nakada1 Mitsuhiro Arisawa2 Mohammad
Al-Amin2 Tetsuo Honma3 Yusuke Tamenori3 Satoshi Arai4 Naoyuki Hoshiya2 3
Takatoshi Sato2 Masaki Takeguchi5 Miyazaki Tsuyoshi5 and Satoshi Shuto2
1T Department of Applied Mathematics and Physics Tottori University Koyama Tottori 680-8552 Japan 2 Faculty of Pharmaceutical Sciences Hokkaido University Kita-12 Nishi-6 Kita-ku Sapporo 060-0812 Japan 3 Japan Synchrotron Radiation Research Institute 1-1-1 Kouto Sayo-cho Sayo-gun Hyogo 679-5198 Japan 4 Furuya Metal Company Limited Minami-otsuka 2-37-5 Toshima-ku Tokyo 170-0005 Japan 5 National Institute for Materials Science Address 1-2-1 Sengen Tsukuba 305-0047 Japan
Sulfur-modified Au-supported Palladium SAPd[1] is an environmentally sustainable
ideal catalyst although its actual active species has not been clear SAPd can repeatedly
catalyze several palladium couplings without adding any ligand and the leached Pd in
the whole reaction mixure is less than 1 ppm Here we discovered SAPd has about 10
layers of Pd nano particles whose size is about 5 nm on sulfur-modified gold surface
by using X-ray absorption near edge structure (XANES) and transmission electron
microscopy (TEM) analysis[2]
Theoretically we found the stable structure of Pd catalyst on the S-terminated Au(111)
[3] by DFT calculations using the program package VASP [4] In this paper using DFT
calculation we present the structure of PdSO4Au(111) because SO4 adsorption on gold
plate can be considered as a possible structure in the experiment We also investigated
PdSO4Pd(111) as a first step calculation for SAPd catalyst on nano-particle Pd on
Gold as found in our experiment We found that the non-flat structure of Pd surface
with SO4 is important for existence of divalent Pd in the ligand-free coupling reaction
References
[1] Hoshiya N Shimoda M Yoshikawa H Yamashita YShuto S Arisawa M J Am
Chem Soc 2010 Jun 2132(21)7270-2
[2] M Arisawa M Al-Amin1 T Honma Y Tamenori S Arai N Hoshiya T Sato M
Yokoyama A Ishii M Takeguchi M Tsuyoshi Satoshi Shuto
[3] MYokoyama AIshii KNakada MArisawa and SShuto to be published
[4] GKresse and JHafner PhysRevB 47 RC558 (1993)
041
Current- and Force-Induced Atom Switching
S Yamazaki1 R Takatani1 D Sawada1 Y Sugimoto1 M Abe2 and S Morita3
P Pou4 R Perez4 P Mutombo5 P Jelinek5
1 Graduate School of Engineering Osaka University 2 Graduate School of Engineering Nagoya University 3 The Institute of Scientific and Industrial Research Osaka University 4
Dpto de Fis Teor de la Mat Cond Universidad Autonoma de Madrid 5 Institute of Physics Academy of Sciences of the Czech Republic
yamazakiafmeeiengosaka-uacjp
Atom switching phenomena have been found at various systems such as a molecule [1] and Si buckling dimer row on Si(001) surface [2] Here we introduce a new atom switching system Si tetramer (Si4) It is the atom switching where both current (STM)-induced switching and force (AFM)-induced switching occur simultaneously
Si4 is firstly reported at 1994 as a Si nano cluster formed by self-assembling of deposited Si adatom on Si(111)-7x7 at room temperature [3] However because switching phenomena at Si4 was not realized understanding of a structure model (including a number of Si atoms) and imaging mechanism of dramatic bias dependence of Si4 image has not been understood
To find out a structure model of Si4 and origin of dramatic bias-dependence of image we have studied Si4 using a low temperature STM a room temperature AFMSTM simultaneous measurement and first-principle simulation Firstly by building up Si4 using lateral atom manipulation we have proofed that ldquoSi4ldquo is consist of really four Si atoms Low temperature STM images agree to simulated images meaning proposed structure model of Si4 is confirmed We have found out that the origin of dramatic bias-dependence is caused by current-induced atom switching and also force-induced atom switching between two equivalent ldquoasymmetric squaresrdquo Namely as shown Fig 1 (up) when applied bias is higher than certain bias Si4 looks like ldquocrossrdquo shape due to downward atom switching induced by inelastic scattering of tunnelling current While as shown in Fig 2 (lower) when tip-sample distance is short Si4 looks like ldquosquarerdquo shape due to upward atom switching induced by attractive short range force acting between a Si atom of Si4 and an atom at tip apex
We have measured switching noise to investigate a detail mechanism of current-induced switching as shown in Fig 2 Switching quantum yield is proportional to current and as shown in Fig 3 exponentially proportional to applied bias meaning the mechanism of the switching is current-induced inelastic scattering [3] In our measurement limit current-induced switching is observed above 085V this value is higher than both switching barrier height (07 eV) and LUMO (05 eV) of Si4 estimated by first-principle calculation Sub-atomic mapping of switching yield will be discussed as well [Fig 3 inset]
[1] Peter Liljeroth et al Science 317 1203 (2007) [2] Kenji Hata et al Phys Rev Lett 89 286104 (2002) [3] Hideyuki Tanaka et al Jpn J Appl Phys 33 3696 (1994)
Time [s] 0 10
Fig 2 Switching noise Fig 3 Quantum YieldFig 1 Current-induced downward (upper) and Force-induced upward switch (lower)
085 090 095 100
1E-9
1E-8
1E-7
1E-6
Quan
tum
Yie
ld p
er
ele
ctr
on
Bias[V]
500pA UPtoDOWN 500pA DOWNtoUP 20pA UPtoDOWN 20pA DowntoUP
-090V
-094V
-099V
Theory A B Min(AB) STM
= ~
cup
cap
= ~
Theory A B Max(AB) AFM
042