projects for physics students 2019/20 1. 2d sam supervisor ...€¦ · projects for physics...
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Projects for Physics Students 2019/20
1. 2D SAM – Saturable Absorber Mirrors based on 2D Nanomaterials
Supervisor: Werner Blau
Location: TCD
Laser sources producing sub-picosecond optical pulses are essential for most photonic
technologies. For many medical, industrial and scientific uses, solid-state lasers
constitute the short-pulse source of choice. The primary advantage is that materials can
be processed with precision down to the nanometre scale without heating or damaging
adjacent material due to the fact that extremely high peak powers are incident on the
sample for only about 100 femtoseconds.
Regardless of wavelength, the majority of ultrashort laser systems employ a mode-
locking technique, whereby a non-linear optical element – called saturable absorber -
turns the laser continuous wave output into a train of ultrashort optical pulses. Some
selected 2D nanomaterials are a novel and promising approach to realize saturable
absorber devices with a performance that the existing semiconductor based devices
cannot provide. The objective of this project is to demonstrate a new saturable absorber
device for ultrafast lasers in the lab, that is easily processed, cheaper, more reliable and
versatile, based on available nanostructures.
2. Green Photonics: Ultrafast and Nonlinear Optical Properties and Photonic
Applications of Microbiologically Synthesised Nanocomposites
Supervisor: Werner Blau
Location: TCD
Photonics technology plays an important part in many areas of our daily life. Most active
photonic devices rely on inorganic semiconductors. In addition to raw material cost and
supply concerns, environmental, toxicity and recycling issues, the increasing use of
nanostructures has created a concomitant increase in complexity and cost of fabrication
equipment. In this project, a novel approach to deal with all the above problems by
microbiological fabrication of photonic nanostructures is taken, with the additional benefit
of addressing lifecycle issues and thus contributing to the preservation of our
environment through reuse of heavy metal waste. Originating from a special respiratory
reduction mechanism in some bacteria, microbiologically synthesised inorganic
nanomaterials present uniquely well-defined physical structures with outstanding optical
properties. As such nanostructures can easily be incorporated into similarly
microbiologically fabricated transparent polymer host matrices, practical engineering
materials can be made relatively simply. Specific project goals are their demonstration
in a selected nonlinear optical device, most likely an optical limiter, based on a
microbiologically synthesised nanomaterial.
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3. Plasmon-enhanced upconverting nanoparticles
Supervisor: Professor Louise Bradley
Location: TCD
Upconverting nanocrystals (UCNPs) can be excited using near-infrared excitation and
emit light at wavelengths ranging from 350 nm to 800 nm depending on the nanocrystal
composition. They have been a topic of considerable interest for optical imaging,
microscopy and sensing of biological samples as they provide approximately a factor of
10 improvement in sensitivity compared with traditional UV pumped fluorescent labels.
They are also a promising means for extending the absorption range of solar cells into
the NIR. However, a significant issue with these materials is their low quantum yield. The
objective of this proposal is to enhance the emission/absorption properties and
conversion efficiency UCNPs through interaction with the increased local
electromagnetic field in the vicinity of multi-resonance plasmonic nanostructures. The
project will involve the synthesis and optical characterization of the plasmon-enhanced
upconverting nanoparticles. It may also involve simulation of the structures using a finite
difference time domain method, to design the optimum structure geometries and to
elucidate on the experimental observations. Based on the interests of the student the
project can be more biased toward experimental or computational research.
4.
Electrically tuned plasmonic metasurfaces
Supervisor: Professor Louise Bradley
Location: TCD
Post-fabrication tuning of plasmonic structures and metamaterials across the visible and
near-infrared spectral ranges continues to pose significant challenges. This project will
explore dynamic tuning based on vanadium dioxide (VO2), a phase change material that
can be switched from an insulating to metallic phase both thermally and electrically. The
project will involve the growth of VO2 by plasma laser deposition, the fabrication of
plasmonic structures by e-beam lithography, and characterisation of the phase change
properties of the VO2 and tuning of the plasmonic metasurface properties via the
electrically actuated phase change of the VO2 material. Complementary simulations to
design structures and interpret experimental observations will be performed using finite
difference time domain software. Based on the interests of the student the project can
be more biased toward experimental or computational research.
5.
Predicting molecular self-assembly in two-dimensions
Supervisor: Dr Nuala Caffrey
Location: TCD
Surface-confined self-assembly of functional molecules is a promising method to
fabricate two-dimensional supramolecular structures with predefined morphologies and
functionalities. The 2D morphology, and hence the surface functionality, depends on the
individual molecular shape, the nature and position of its interacting sites, the molecular
electronic properties and the overall topology of the material. Coarse-grained simulation
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models can determine the factors which determine the surface morphology. Here the
molecule is represented by a model building block with a particular shape and
predefined interaction centers.
This project will use lattice Monte Carlo to mimic the self-organisation of molecules into
naturally emerging 2D patterns. Stable structural phases will be found and the conditions
required to induce particular phases determined. The results of the lattice Monte Carlo
simulations will then be validated using density functional theory calculations and the
electronic properties of the resulting networks ascertained. The student will write their
own canonical ensemble Monte Carlo code to achieve this, as well as learn how to use a
density functional theory code to calculate the electronic structure of the molecular
networks.
The aim will be to reproduce correctly the formation of various adsorbed phases which
have been observed experimentally in ultra-high vacuum or at the liquid/solid interface
including exotic fractal metal–organic aggregates (see Figure from Chem. Commun., 51,
14164 (2015)), and to go beyond this to predict molecules which will produce other novel
surface morphologies and functionalities.
6.
Equilibration and the thermodynamics of non-Markovian Environments
Supervisor: Dr Steve Campbell
Location: TCD
Put a smaller system in contact with a larger environment and, thanks to
thermodynamics, the two will equilibrate. If we introduce a second bath at a different
temperature, we enter the rich world of non-equilibrium systems. When all of the players
in this game are classical systems, the various energy exchanges are fairly well
understood. However, for quantum systems and quantum baths things are trickier. In
this project we will explore how properties of the baths affect the equilibration of a
quantum system to its non-equilibrium steady state. In particular, by exploiting a so
called collision-model framework to model the quantum environments, we will examine
how Markovian (memoryless) vs. non-Markovian baths affect the rate of equilibration
and the ensuing non-equilibrium steady state properties. This is a theoretical project that
will involve both analytical and numerical calculations performed with the aid of
Mathematica.
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7.
Quantum Darwinism
Supervisor: Dr Steve Campbell
Location: TCD
The world around us, to the best of our knowledge, is described by quantum mechanics.
Somewhat perversely the defining features of the theory, quantum superpositions, are
not seen on a macroscopic scale. Therefore a fundamental issue facing physics today is
to understand how the familiar classical world around us emerges despite its underlying
description being quantum mechanical. The theory of decoherence goes someway to
elucidating this dichotomy, however it only partially addresses the issue. Quantum
Darwinism has been proposed as a means to explain how, using only the basic tenants
of quantum mechanics, a "classically objective" state can emerge from a fully quantum
description. This is achieved by invoking the notion of "only the fittest information will
survive". In this project we will test the validity of this description starting from a simple
spin-star model that readily exhibits quantum Darwinism and examine under what
conditions classical objectivity is lost. This is a theoretical project that will involve both
analytical and numerical calculations performed with the aid of Mathematica.
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Onsager Entanglement for High Efficiency Mobile Power
Supervisor Dave Carroll
Location: Wake Forest University
This project seeks to further develop power scavenging technologies for ambient sources. Power scavenging at relatively low temperatures is inefficient according to Carnot. However, by coupling multiple scavenging modalities together, these inefficiencies can be circumvented, at least in part. Recent work by our group has shown that by coupling piezo-electric materials and thermoelectric materials into a meta-structure (with specific symmetries), the combined
power scavenging can exceed the expected linear combination of the modalities individuality. The phenomena is well described by Onsager’s nonequilibrium approaches and has led to the development of wearable power sources capable of charging phones, ipads, sensors and more. The team is now trying to apply these materials in larger arrays for space suites in a project sponsored by NASA and aimed at Mars exploration
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9.
AC driven Per-LED
Supervisor Dave Carroll
Location: Wake Forest University
The WFU group has pioneered the use
of AC-drive for the creation of high
brightness, very high efficiency lighting
systems. Such systems, from home
interior illumination to laptop displays,
represent more than 25% of all the
electricity generated in the U.S. and
very nearly this amount in Europe.
Unfortunately, lighting developed so far,
while bright and efficient (exceeding 300 LPW at 30,000 Cd/m2) has had a single
important drawback, and that is lifetime. A modern commercial LED can last 100,000
hours without failure, and so any replacement technology must do the same. At the
moment, no other lighting system has come close. That is all about to change. We have
recently developed a new inorganic perovskite material that has shown high brightness
and efficiency, but also tremendous robustness. Indeed, we have shown that devices
made from it can even function under water for thousands of hours! These amazing
devices, can be made in any color, and are completely flexible. Moreover, they are quite
simple to process. The next steps in this remarkable development is to increase its
overall efficiency, pushing the boundaries of light generation through the control of spin
statistics in the structure using nano-scale antennae imbedded in the emitter
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Topological Quantum Memory Elements
Supervisor Dave Carroll
Location: Wake Forest University
The development of universal quantum computing systems requires the development of stable quantum memory elements. Over the past few years this has taken a number of divergent pathways, most involving cryogenic arrays of spin systems. In this program we are examining an orthogonal approach through the use of topologically complex, symmetry protect states associated with 2D dichalcogenide systems. Such systems are known for their CP – protected edge states,
and modification of these edge states so that the accumulation of geometric Berry’s phases can be constructed may provide a unique mechanism for the fabrication of quantum memory. We have already developed the curious topological systems (as shown) and are now beginning detailed investigation into electronic properties
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Spin optoelectronics in magnetic materials
Supervisor: Jean Besbas, K. Rode, J. M. D. Coey
Location: TCD
The Spin Hall Effect (SHE) is the spin-dependent deflection of a current in conductive materials with high spin-orbit coupling. This effect, which allows generating a spin current, i.e. a flow of angular momentum in a thin film, is currently under scrutiny for its potential applications in magnetic recording. Recent developments have shown that the photon spin, or helicity, of an externally applied laser light can sometimes be a source of SHE.1 More recently the change of conductance induced by light helicity has been proved sensitive to the SHE in low band gap semiconductor BiSbTeSe and unexpectedly in metallic platinum (Fig. 1).2 The interest of these discoveries is twofold. First, they establish a new way to universally measure and characterize the SHE with optical excitation and an electrical detection. Second, it could possibly lead to optoelectronic devices making use of the spin of the electron. For long, it was believed that metals could not be affected by the helicity of the light in the way that semiconductors are.3 However, this paradigm has been revisited with the discovery of helicity-dependent magnetic switching in ferrimagnets.4,5 Therefore, we plan to take a new step ahead and characterize the interplay between SHE and the helicity-dependent photoconductance of ferrimagnetic metals. In this project, the student will be involved in the development of an experiment allowing the measurement of the SHE by using the dependence of the conductivity on the helicity of a laser beam. The work will be centered in the state-of-the-art CRANN photonics laboratory. The setup will consist of a far-field microscope and will utilize continuous and femtosecond pulse of laser light to affect the photoconductance. The student will take an important part in mounting and aligning the microscope, electrically interfacing and measuring the samples. We are planning to investigate various thin film magnetic materials such as SrRuO3, LaMnO3 and the newly developed Mn2RuxGa (MRG) from the Magnetism and Spin Electronics Group. Further experiments could be performed on heavy metals with a high SHE such as Pt and Ta.
Figure 1: Helicity dependent photovoltage as a function of position on a Pt stripe for I= 6 mA. The SHE yields a signal at the edges of the Pt microstructure.2 1 K. F. Mak, K. L. McGill, J. Park, and P. L. McEuen, Science 344, 1489 (2014). 2 Y. Liu, J. Besbas, Y. Wang, P. He, M. Chen, D. Zhu, Y. Wu, J. M. Lee, L. Wang, J. Moon, N.
Koirala, S. Oh and H. Yang, Nat. Commun. 9, 2492 (2018). 3 F. Dalla Longa, J. T. Kohlhepp, W. J. M. De Jonge, and B. Koopmans, Phys. Rev. B 75,
224431 (2007). 4 C. D. Stanciu, F. Hansteen, A. V. Kimel, A. Kirilyuk, A. Tsukamoto, A. Itoh, and Th. Rasing,
Phys. Rev. Lett. 99, 047601 (2007). 5 S Mangin, M. Gottwald, C-H. Lambert, D. Steil, V. Uhlíř, L. Pang, M. Hehn, S.
Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, M. Aeschlimann, and E. E.
Fullerton, Nat. Mater. 13, 286 (2014).
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Spin Liquids Supervisor: M. Venkatesan Z. Gercsi, and J. M. D. Coey
Location: TCD
The spin liquid is an unusual quantum state of matter which is thought to exhibit a quantum phase transition at T = 0 to an unusual disordered collective magnetic state. By
far the simplest example from a chemical point of view is Mn [1,2]. This is the stable phase above 725 C, but it can be stabilized by arc melting. The structure is cubic, with two different sites 8c and 12d as illustrated in the figure below. It is believed that the Mn on 8c sites in nonmagnetic, whereas that on 12d sites carries a moment but the topology of these sites, which form linked triangles, is such that the antiferromagnetic nearest-neighbour interactions are completely frustrated. Recently, we made a surprising discovery; When we prepared a Mn3Al2 alloy, expecting the Al to occupy 8c positions, we found that the alloy was strongly ferromagnetic, with a moment of 1.3 µB per formula, and a Curie temperature of about 600 K. We want to understand how adding Al, which is nonmagnetic, can have such a big effect on the Mn spin liquid. Also, we need to know if the Mn3Al2 alloy is really ferromagnetic, or ferrimagnetic. In this project, the student will prepare a series of Mn5-xAlx alloys, and trace out the magnetic phase diagram as a function of x. In this way be can begin to understand how breaking the frustration breaks up the spin liquid. The work will involve preparing the alloys by are melting, and characterizing them by X-ray diffraction and magnetometry. A neutron diffraction experiment in the Netherlands to determine the magnetic order is possible.
The cubic crystal structure of Mn. A triangle of 12d Mn atoms is highlighted.
References: [1] J. A. M. Paddison et al Phys. Rev. Letters 110 267207 (2013) [2] H. Nakamura et al, J Phys. Cond. Mat., 9 4601 (1997)
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3D printing of permanent magnets Supervisor: Z. Gercsi, M. Venkatesan and J. M. D. Coey
Location: TCD
3D printing of magnetic materials offers novel and creative ways to design magnets with new shapes and functionalities that are not possible with current manufacturing technologies. In this project, we explore the properties of 3D-printed magnetic circuits based on high performance Sm-Fe-N permanent magnets, which were discovered in TCD [1], and are now produced commercially in Japan [2]. The Sm2Fe17N3 powder, prepared by a low-temperature gas-phase interstitial modification [3], will be used for the printing. The powder has superior corrosion resistance and thermal stability compared to Nd2Fe14B powder. It exhibits a room-temperature coercivity of 690 kAm-1, with an isotropic remanence of 700 kAm-1. The maximum energy product for the powder, assuming full density, is 162 kJm-3. A magnetic circuit comprises a magnet and an airgap, and optionally soft iron to guide
the flux. The design of magnetic circuits is an art, facilitated by computer simulation. The
permanent magnet behaves like a battery that is the source of the magnetomotive force
(mmf) (the magnetic analogue of emf), as it is the segment of the circuit where the
magnetic potential rises. Rare earth permanent magnets are particularly suited for use in
ironless circuits, where flux is confined to the magnets themselves and to the airgap.
Flux concentration is achievable in special designs where the flux density in the airgap
exceeds the remanent induction of the magnet, Bg/Br > 1.
The project involves designing and printing magnets of different shapes from using melt-
spun Sm-Fe-N powders, manufactured in Japan. The 3D printer is based in the new
Additive Manufacturing Laboratory in CRANN/AMBER. They will be characterized in
detail by high resolution microscopy and SQUID magnetometry. We are particularly
interested in printing magnet shapes that cannot be manufactured by traditional methods
of injection moulding, and an initial goal after measuring the density and magnetization
achievable with simple shapes and Fe/Sm-Fe-N composites, will be to realize a design
that cannot be produced in any other way together with a magnetizing method. The
developed magnets circuits may then be used for various experiments in our magnetism
research group, such as the new Kerr microscope.
References: [1] J. M. D. Coey and Sun Hong, J Magn Magn Mater 87 L251-254 (1990) [2] T. Iriyama et al, IEEE Trans. Magn., 28 2326 (1992) [3] R. Skomski, Ch 4 in Rare-Earth Iron Permanent Magnets (J. M. D. Coey, editor) Clarendon
Press, Oxford 1996, p178
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Understanding the factors limiting charging time and power delivery in
supercapacitors.
Supervisor: Professor Jonathan Coleman
Location: TCD
Note: This is not a lab-based project but involves finding, extracting and analysing
published data.
Supercapacitors are energy storage devices midway between capacitors and batteries
which store energy via the storage of electrons and ions at a conductor/electrolyte
interface. Supercapacitors don’t store huge amounts of energy, however, they can be
charged very quickly and deliver their energy rapidly which makes them suitable for high
power applications. However, there is currently no quantitative understanding of the
factors limiting their power delivery/charging time. Recently Prof Coleman’s group have
developed a simple model for understanding the equivalent problem in batteries. It is
straightforward to convert this model to represent supercapacitors. This project will
involve searching the literature for supercapacitor capacity versus charging rate data
(thousands of papers are available). The data will then be fit to the model to output the
charging time constant. Another equation will be used to fit the time constant data to
various physical parameters such as electrode thickness, conductivity, porosity etc. This
will allow us to understand the relationship between charging time (and hence power)
limitations and physical materials properties.
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Do lithium ion batteries based on 2D materials have overly-long charging times?
Supervisor: Professor Jonathan Coleman
Location: TCD
With the growing popularity of mobile electronics, bigger, better batteries are urgently
required. One approach is to identify new electrode materials which can store more
lithium than is currently possible. Recently, 2-dimensional materials such as graphene,
MoS2 and phosphorene have been shown to store large quantities of lithium. However,
there are indications that such electrodes are very slow to charge. This may be a
consequence of the fact that the nanosheets making up the electrode tend to lie parallel
to the electrode surface, forcing ions to travel round them and so increasing the length of
the path ions need to take during charging (or discharging). This project will perform
careful measurements of the charging time of electrodes made from various 2D
materials of various sizes. The aim is to determine if charging times are slower than
other materials and investigate the causes
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Reinforcing nanosheet networks with insulating nanotubes
Supervisor: Jonathan Coleman
Location: TCD
Networks of 2D materials such as graphene can be easily formed into networks which
are useful in a range of applications such as printed electronic devices and battery
electrodes. However, such networks are very brittle. This has been resolved for battery
electrodes by adding carbon nanotubes. The nanotubes reinforce the networks and
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have the added advantage of increasing the conductivity. However, if the network is to
be used in an electronic device (such as channel material in a transistor), conductivity
enhancements must be avoided. One solution would be to use Boron Nitride nanotubes
(BNNTs) which are strong yet insulating. This project will fabricate networks of 2D
nanosheets such as MoS2 reinforced with BNNTs. It will involve measuring both
mechanical properties and conductivity as a function of BNNT content to ascertain the
level of reinforcement and ensure the conductivity is unaffected.
17.
Adhesion thermomechanics of roll-to-roll nanoimprint lamination for tissue
scaffolds
Supervisor: Professor Graham Cross
Location: TCD
While nano/microfabrication is the cornerstone of advances in information and
communications technology, other industries that could greatly benefit from
miniaturization cannot easily incorporate the highly specialized methods and materials of
semiconductor manufacturing. Roll-to-roll nanoimprint lamination (R2RNIL) allows
efficient, deterministic nanostructuring throughout a 3D volume, a problem remaining
largely unsolved to date. A prime motivation is realizing scaffolds suitable for use as
internal bandages in regenerative medicine: These require multiscale structuring that
goes beyond existing additive manufacturing capabilities like 3D-printing which is limited
to micrometre resolution, or stochastic techniques like electrospinning which produce
large volumes of nanoporous materials but generally at one length scale. With R2RNIL,
in-plane (xy) control of all micrometre to nanometre dimensioning is realized, while more
limited z direction modulation is possible by evolving lamination period. In this project the
role of temperature and speed will be studied for successful lamination of
nanostructured surfaces with dimensions critical to controlling stem cell replication and
devolution into specific phenotypes (muscle, bone, tendon, etc.)
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18.
Optimized heat conduction by channelling in a microscopic inelastic contact
Supervisor: Professor Graham Cross
Location: TCD
The problem of heat conduction across contacting solids is important in both
fundamental statistical mechanics and applied physics. It has also become a obstacle to
progress in the performance of solid-state electronics, and is a major factor contributing
to the breakdown of Moore’s Law we are now experiencing. The Solid State Thermal
Interface Materials (SSTIM) is a novel solution to the solid-solid interface thermal
bottleneck. It consists of a compliant array of rigid, high thermal conductivity micro-
bridges that use local plasticity to overcome contact resistance. The SSTIM concept
attempts to address the 5 order-of-magnitude gap between ideal thermal contact
resistances achieved in highly specialized laboratory experiments and what is realized in
practice for the consumer electronic devices we use every day. In this applied physics
computer simulation project, we will model the thermal transport at a microscopic solid
state contact under the conditions of plastic deformation. Using multi-physics finite
element simulation techniques, we will investigate the role of diamond indenter shape
and low thermal conductivity surface layers on SSTIM heat bridge performance, and
attempt to find ideal geometries that maximize heat conduction for minimum mechanical
force.
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Atomic force microscopy studies of graphene self-assembly
Supervisor: Professor Graham Cross
Location: TCD
The Cross Group recently discovered1 that 2D materials like graphene can
spontaneously slide, peel and tear via intrinsic thermodynamic forces. This self-
assembly behaviour is reminiscent of capillary dewetting of a liquid droplet from a
hydrophobic surface, and operates in air at scales ranging from nanometres to the
nearly visible. Pleat structures formed by the process consist of a folded-back ribbon
adhered by van der Waals forces to its host sheet below. Nucleation of an embryonic
pleat spontaneously sets in motion growth (moving to the lower right in the figure) by
peeling from the substrate and tearing the sheet. Two conditions enable this self-
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assembly: First is large area superlubricious incommensurate contact of the ribbon
crystal lattice to its host sheet that allows it to slide almost free of friction over long
distance, and second is the presence of an interfacial force arising from interface
thermodynamics that spontaneously propels the ribbon forward. These structures may
eventually form the basis for THz scale nanoelectromechanical systems. In this project,
we will employ atomic force microscopy (AFM) with diamond probes to characterize
pleat nucleation and growth.
Graphene self-assembly imaged by atomic force microscopy.
[1] Annett J., Cross, G. L. W., Self-assembly of graphene ribbons by spontaneous self-tearing
and peeling from a substrate, Nature 535, 271-275, (2016).
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Au films for applications in plasmonic applications
Supervisor: Prof. John Donegan
Location: TCD
Gold (Au) is the key material for plasmonic applications owning to its strong optical
response and its resistance to chemical processes. Studies have shown that Au think
films. Our studies have shown that monolayer adhesion of metals such as Ti, Ta and W
are all very effective at reducing the tendency for de-wetting of the films.
In this project, we will look at a set of samples with large Au grains, and compare with
normal films having small grains, to determine how movement of the adhesion metals
along the grain boundaries affects the de-wetting behavior. We will determine the
activation energy for the de-wetting behavior and using TEM and other surface analysis
techniques, we will look for methods that further enhance the long-term stability of Au-
films in high-power plasmonic applications.
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21.
Printing and characterization of Fresnel Zone Plate lenses in optical waveguides
Supervisor: Prof. John Donegan
Location: TCD
The Nanoscribe 3D printing tool can produce optical waveguides with thickness less than
1 micron. This allows for a very fast fabrication of waveguide devices. The Fresnel zone
plate is a structure that focusses light within a waveguide, increasing the optical intensity
by upto a factor of 20. This in turn allows us to observe strong nonlinear optical effects.
In this project, the student will become familiar with making waveguide structures and then
fabricating the zone plate structures. This will be followed by optical and structural
characterization of the waveguide structures including the generation of nonlinear effects.
The project is mostly experimental but will deal with aspects of modelling optical
waveguides.
22.
Athermal operation of semiconductor lasers at 1.3 m with high order gratings
Supervisor: Prof. John Donegan
Location: TCD
The Photonics group in TCD has developed a new method to develop single mode lasers.
This involves using a grating with high order which then allows for a simple fabrication
process. To date, these lasers have been demonstrated at 1.5 m but recently the group
has now developed lasers which will operate at 1.3 m.
In this project, we will study the performance of these lasers and how they vary with the
parameters of the high order grating, including depth and width of the slots that form the
grating. Studies will be carried out of both single mode lasers and laser arrays to see how
their performance changes will the design of the grating and the slots that form the laser
device. The work is mostly experimental but will also involve modelling of semiconductor
laser devices.
23.
Understanding the Production of Biofuel by Thermal Degradation of Biomass
using TGA-MS
Prof. Stephen Dooley
Location: TCD
Biofuel produced from biomass is a promising and sustainable solution to the multiple
energetic challenges the planet is facing such as; global warming, fossil fuel depletion and
increase in energy consumption per capita. [1] Thermal decomposition or pyrolysis of
biomass to produce liquid fuel has attracted a lot of interest due to the potential to use
existing infrastructure.[2] Even though the technology is well established, the scientific
understanding of the physical phenomena is lacking.
This project aims to improve our understanding of the physical-chemistry phenomena
behind biofuel formation during the thermal decomposition of biomass in order to predict
and tailor their properties. The idea behind this project is to determine the role of the
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polymerisation of the various constituents of the biomass typically, cellulose,
hemicellulose and lignin.
This project is experimentally based and will involve TGA-MS measurements, detailed
kinetic modelling and various characterization techniques (TEM and SEM) can be
included.
[1] M.I. Jahirul, M.G. Rasul, A.A. Chowdhury and Nanjappa Ashwath, Energies, 2012, 5.
[2] S. Chakraborty, V. Aggarwal, D. Mukherjee and K. Andras, Asia-Pac. J. Chem. Eng. 2012, 7.
24.
Moleular Physics and Machine Learning Modelling of Isomer Populations of
Lignocellulosic Derived Carbohydrates in Alcohol Solutions
Prof. Stephen Dooley
Location: TCD
The depletion of oil reserves and global environmental concerns necessitates the
development of alternative processes for producing fuels from renewable sources. Of key
interest is the production of ‘green’ biofuels components from the reaction of
lignocellulosic biomass in alcohols. For example, potential biofuel components 5-
ethoxymethylfurfural and ethyl levulinate can be readily produced through the reaction of
biomass derived carbohydrates, D-glucose and D-fructose, with ethanol and a Brønsted
acid. However, comprehension of even basic reaction kinetic and mechanistic details of
such systems is currently lacking, and thus represents one of the barriers to designing a
viable process for fuel synthesis. It is well known in aqueous solutions that carbohydrates
such as D-glucose and D-fructose can exist as 5 different isomers. The distribution of
these isomers can have a significant effect on the reaction mechanism and kinetics for
form biofuel components. Such key information has yet to be determined for D-fructose or
D-glucose in alcohol solutions.
During this project, the student will further advance molecular thermodynamic, machine
learning and data science techniques to model the molecular physics details of how these
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carbohydrates dynamically reaction alcohol solutions. The student will work with a team
of three post doctors and two graduate students in the Sustainable Energy Laboratory of
Prof Stephen Dooley at Trinity College Dublin. The key aim of this project will be to
determine the effect of temperature and hydrogen cation concentration on the isomeric
distribution of lignocellulosic derived D-fructose and D-glucose in alcohol solutions.
Experience with sophisticated spectroscopic techniques such as liquid phase 1H and
13C Nuclear Magnetic Resonance (NMR) spectroscopy and/or mass spectrometry will
also be gained. Interest in the numerical modelling of basic molecular physics processes
will be needed.
25.
Raman characterisation of group-10 transition metal dichalcogenides
Supervisor: Professor Georg Düsberg
Location: Universität der Bundeswehr, München, Germany
Recent research in two-dimensional (2D) atomically thin materials focusses on suitable
materials for application in FETs and sensor devices. Next to the first produced 2D-
Material Graphene, the semiconductors of the Group-6 transition metal dichalcogenides
(TMDs) such as MoS2 and WSe2 were intensely studied. These materials have direct
bandgaps in the visible light regime (1 eV)1 when present as monolayers.
However, these TMDs have shown to be prone to degrade at environmental conditions.
Recent research puts emphasis also on group-10 TMDs such as PtSe2 which have
proven to be stable in air for over a year2. These group-10 TMDs provide strong
tunability of the electrical and optical properties2 making them suitable for FETs and
sensor devices3.
The incorporation of PtSe2 based FETs in state of the art device fabrication present in
the semiconductor industry required scalable processes with reliable reproducibility. This
can only be achieved by controlling a well understood wafer-scale growth process of
these materials. Getting insight in the critical fabrication parameters and analysing the
resulting material characteristics is thereby the main task.
This project covers the task of performing Raman measurements providing a fast and
nondestructive method suitable to gain knowledge about material distribution, quality
and film thickness. Reliable thickness data will be obtained by AFM measurements to
characterize a layer number depended behaviour of the specific Raman modes.
REFERENCES
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1. Yim, Chanyoung; Lee, Kangho; McEvoy, Niall; O’Brien, Maria; Riazimehr, Sarah; Berner,
Nina C. et al. (2016): High-Performance Hybrid Electronic Devices from Layered PtSe 2 Films
Grown at Low Temperature. In ACS Nano 10 (10), pp. 9550–9558. DOI:
10.1021/acsnano.6b04898.
2. Yu, Zhihao; Pan, Yiming; Shen, Yuting; Wang, Zilu; Ong, Zhun-Yong; Xu, Tao et al. (2014):
Towards Intrinsic Charge Transport in Monolayer Molybdenum Disulfide by Defect and
Interface Engineering. In Nat Commun 5 (1), p. 3042. DOI: 10.1038/ncomms6290.
3. Zhao, Yuda; Qiao, Jingsi; Yu, Zhihao; Yu, Peng; Xu, Kang; Lau, Shu Ping et al. (2017): High-Electron-Mobility and Air-Stable 2D Layered PtSe2 FETs. In Advanced materials (Deerfield Beach, Fla.) 29 (5). DOI: 10.1002/adma.201604230.
26.
Transition Metal Dichalcogenide Doping
Supervisor: Professor Georg Düsberg
Location: Universität der Bundeswehr, München, Germany
Transition metal dichalcogenides (TMDs), such as e.g. MoS2, WSe2 represent a large
family of layered 2D materials, which cover a broad variety of electronic, optical and
mechanical properties and therefore can serve as the functional part in various
microelectronic devices. Due to the materials monolayer nature the properties of 2D
materials strongly depend on the environment, which makes control and modification of
the surface chemistry a powerful tool to obtain changes in the materials behaviour.
Functionalization of the monolayer surface can lead to doping via charge transfer,
resulting in improved electrical properties, which is then exploited in chemiresistor or
ChemFETs for chemical sensing. The suggested project focuses on the diverse
possibilities of doping TMDs by decorating the surface with organic molecules or
inorganic nanoparticles. Results on the hybrid inorganic-organic structures will be
monitored by techniques, like Raman spectroscopy, XPS, and scanning probe
techniques.
REFERENCES
Berner, N. C. et al. Understanding and optimising the packing density of perylene bisimide layers
on CVD-grown graphene. Nanoscale 7, 16337–42 (2015).
Kim, H. et al. Optimized single-layer MoS2 field-effect transistors by non-covalent
functionalisation. Nanoscale 10, 17557–17566 (2018).
27.
Modelling polaritons in dielectric nanostructures (theoretical/computational)
Supervisor: Professor Paul Eastham
Location: TCD
Polaritons are quasiparticles that occur in semiconductors, and are part photon and part
exciton. Because of this they may be useful as part of the energy conversion process
between light and electricity in photovoltaics. However, this requires trapping of the
polariton in a region of space, an effect usually achieved using an optical cavity. In this
project you will explore whether polaritons can, in fact, be trapped without the use of
optical cavities, in structures such as two-dimensional semiconductor sheets or
nanoscale crystallites. This project is theoretical and computational, and will involve
using existing computational packages to develop and analyse simulations of light
propagation in nanostructured dielectrics.
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28.
Optimal networks for robust synchronization (theoretical/computational)
Supervisor: Professor Paul Eastham
Location: TCD
It was noted by Huygens that two clocks, placed on opposite sides of a wall, begin to tick
together. This phenomenon of synchronization is a general one, which occurs for many
other oscillating systems, and as such it plays an important role in physics, engineering,
and biosciences. An important example is the synchronization required for electrical
power grids to operate. In this project you will explore a simplified model of a system of
many oscillators connected together (the Kuramoto model). You will develop a
computational method that can determine how these oscillators can be connected up in
such a way that they will all synchronize.
29.
Geometry of disordered networks: from 2D to 3D
Supervisor: Mauro Ferreira
Location: TCD
This project attempts to study the geometry of networks created by 2D sheets randomly
deposited on an insulating substrate forming a 3D pile. If the sheets are conducting and
the network is sufficiently dense, we may transform an otherwise insulating material into
a conducting one. The conductivity of such a material is crucially dependent on the type
of contacts that exists between neighbouring sheets and the statistics of such contacts is
essential to understand the physical properties of these materials. The project consists
of carrying out a thorough study of the statistics and the geometry of such networks. The
project involves a good balance of analytical and numerical work and is a good
opportunity to put in practice a number of concepts learned throughout your degree.
30.
Physical properties of nanowire networks
Supervisor: Mauro Ferreira
Location: TCD
Abstract: Thin films composed of networks made of an array of nanowires have been
attracting a lot of attention due to their promising physical properties. The goal of the
present project is to develop simple theoretical models capable of describing the
physical properties of such networks. Transport, optical, thermal and magnetic are some
of the possible physical properties to be investigated. In order to achieve this, we must
separate the project in two complementary parts: one involving the development of a
macroscopic model and another which consists of the microscopic details of the
network. The student will be in charge of developing such models and will involve good
analytical and numerical skills.
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31.
Stretching/compressing 2D materials to mimic human eye adaptation:
Supervisor: Prof Andres Castellanos-Gomez
Location: Consejo Superior de Investigaciones Científicas (CSIC), Instituto de
Ciencia de Materiales de Madrid (ICMM)
Two-dimensional (2D) materials have triggered the interest of the scientific community
focusing on optoelectronics because of their very high performance in photodetection
applications. Apart from the high performance in photodetectors, 2D materials present a
special feature that distinguishes them from 3D semiconducting materials: mechanical
deformations have a strong impact on their optical properties. This feature can be
exploited to mimic the remarkable adaptation ability of the human eye to very different
illumination conditions. In this project we will fabricate optical modulators and
photodetectors whose spectral response could be adjusted by means of an external
deformation to achieve devices that can effectively operate under high illumination as
well as under dark conditions.
32.
Testing Information scrambling on a quantum computer Supervisor: John Goold
Location: TCD
Eggs do not unscramble. Local information gets spread over global degrees of freedom
and complexity emerges which renders recovery of local information from local
operations on your physical system impossible. The same is true in quantum mechanics.
Information scrambling is now currently a hot topic in quantum systems and basic ideas
can be studied in what is known as random unitary circuits. The task of this project is to
first write code to generate dynamics on a random unitary circuit where 2-qubit gates are
sampled from the Clifford group. The behaviour of the total correlations of the quantum
state as a function of time and to try to measure it on a simulated version of the IBM
quantum computer. To undertake the project the student should be good at
programming and have excellent mathematical skills and a good understanding of
quantum mechanics.
33.
Energy fluctuations in quantum refrigerators Supervisor: John Goold Location: TCD
Quantum thermal machines are quantum dynamical systems that convert random heat
into a useful output. Refrigerators are a very important class of such machines, since
cooling is an essential prerequisite for many nascent quantum technologies such as
quantum computation. In this theoretical project we will investigate a simple model of a
quantum refrigerator, in order to understand how different kinds of energy resources
affect cooling performance. In particular, we will explore how driving the refrigerator with
a coherent field (e.g. laser light) differs from thermal driving (e.g. light from an
incandescent bulb), specifically in regard to fluctuations of energy. The student will have
the opportunity to learn about open quantum systems and how to predict their dynamics.
Since this is a project in theoretical physics. The student should have excellent
mathematical skills.
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34.
Steady state heat transport in Fibonacci quasi crystals. Supervisor: John Goold Location: TCD The aim of this project is to study the heat transport in the simplest realisation of a quasi-
crystal which is the Fibonacci chain where the diagonal energies are modulated
according to the Fibonacci series. The set up will employ tools from scattering theory
and open systems in order to evaluate the current as a function of both the strength of
the potential energy and system size. This will enable us to extract current scaling from
finite size scaling and explore the conjecture of the existence anomalous diffusion with a
continuously varying exponent. Potential applications are in the direction of heat current
engineering in nanostructure which do not have Bloch theorem. This is a project in
theoretical physics. The student is required to have excellent mathematical and
numerical skills.
35.
Nanomechanics of click-chemistry anchored single dsDNA molecules interacting with small organic molecules Supervisor: Professor Martin Hegner Location: TCD
The nanomechanics of individual natural polymers such as the dsDNA can be
investigated by scanning probe microscopy and optical tweezers force spectroscopy.
Normally the individual nucleic-acid based molecules are anchored to micron scaled
spheres that are acting as molecular handles to be trapped in highly focused laser
beams. The anchoring to the interface is usually provided using biomolecular
recognition, we will explore the possibility to enhance the binding using click chemistry
modified tailor made ends and compare to existing protocols. The molecules will be
visualised using scanning probe microscopy and the mechanics investigated by pulling
the individual molecules with optical tweezers. The individual dsDNA mechanics shows
a characteristic signature in its natural environment. While interacting with biological
molecules or small organic molecules the mechanics can be significantly altered and
indicate adverse or biological relevant effects. In particular the students will:
1. Learn how to prepare and purify tailor made dsDNA molecules that enable click
chemistry anchoring to modified polystyrene microspheres.
2. Design a coupling protocol for click chemistry modified molecules and compare to
3. current protocols applying biomolecular recognition
4. Operate a scanning force microscope to visualise the generated molecules
5. Measure nanomechanics of the generated dsDNA while they interact with buffers
6. and small organic molecules using optical tweezers technology
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36.
Experimental studies of foam-fibre interactions
Supervisor: Professor Stefan Hutzler
Location: TCD
This experimental project concerns structure and properties of foam-fibre dispersions
and the resulting solidified samples. The so-called foam forming process can be used for
paper making but also for the production of novel fibrous materials made from natural
fibres, such as found in peat.
The work will be carried out in close collaboration with a PhD student.
References:
Haffner B, Dunne FF, Burke SR, Hutzler S (2017), Ageing of fibre-laden aqueous foams,
Cellulose 24 231-239.
Burke SR, Möbius ME, Hjelt T, Hutzler S (2019), Properties of lightweight fibrous structures
made by a novel foam forming technique, Cellulose 26, 2529-2539.
37.
Experimental studies of foam-film interactions
Supervisor: Professor Stefan Hutzler
Location: TCD
Soap films can be used as model systems for the study of failure statistics. The project
will involve data gathering and analysis for a range of different experimental set-ups,
such as films formed in rings or bubble arrays in cylinders.
The work will be carried out in close collaboration with a PhD student.
38.
Development of an Electron Counting Circuit with Nanosecond-scale Sensitivity
Supervisor: Professor Lewys Jones
Location: TCD
The internship will be based in the Advanced Microscopy Laboratory
(www.tcd.ie/crann/aml).
A sole-use desk and PC will be provided to the student. Lab-bench space will be
provided in TTEC Unit 7.
In many fields of imaging and microscopy analogue sensors and detection are being
replaced with all digital approaches. Electron microscopy is now beginning this exciting
modernisation, bringing all digital imaging to atomic-resolution microscopy.
In 2018, a previous student working in the group achieved the first successful hardware
implementation of a new digital pulse read-out system. Live waveforms were captured
using a PC streaming oscilloscope, and the signal gradient was subsequently used to
identify individual electron impact events (see figure). This impressive achievement lead
21
to a UK&IRL patent filing, three international conference
presentations, and a research paper being written.
The current implementation is still limited though;
because of the limited clockspeed of the streaming
oscilloscope (32MHz) electron impacts are recorded with
a relatively poor timing precision which can lead to event
pile-up. Further, the PC-streaming data handling
approach is bandwidth limited by the USB connection,
and buffering limited by the available RAM (16Gb).
Instead a new alternative strategy is proposed, to take
advantage of flexible logic design to perform genuine
edge detection pulse counting in hardware. New
education focussed development boards (see figure) now
allow students
to access the capabilities of field programmable gate
arrays (FPGAs) at a sub €400 price point. Such hardware
should allow counting speed to be increased by ~15x (to
450MHz), while also reducing the subsequent data
transmission bandwidth needed by ~2,000x. This would
enable higher signal-noise images to be recorded as well
as enabling movie acquisition for the first time (rather
than just single frames) without the need to purchase
additional RAM.
The role of the student will be to replicate the previous
software-streaming + numerical-analysis approach but in genuine hardware logic. The
will gain experience in the use of benchtop waveform generators, digital oscilloscopes,
as well as visual block-level programming. The student will benefit from the assistance
of the on-site professional support staff in the AML, as well as being fully embedded in
the research group.
Ideal Candidate: The ideal candidate will have an interest in electronics and/or
programming. Previous experience is not necessary as all training will be provided.
Expected Outcomes: The configured FPGA
will be used to record data to contribute to a new
research manuscript in the group. The student
will also be expected to produce poster and/or
deliver a seminar as part of the ‘AML
Nanotechnology Seminar’ series.
Budget / Resource Plan: The project will utilise
a Digilent Artix-7 FPGA Development Board
(€330), exact model TBD. Approx. €100 is
allocated for BNV termination connectors,
cables and other minor electronics incidentals.
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39.
Prediction and Measurement of Electron Lenses Aberrations
Supervisor: Professor Lewys Jones
Location: TCD
The internship will be based in the Advanced Microscopy Laboratory
(www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student.
Abstract:
Transmission electron microscopy (TEM) is an invaluable tool in modern materials
science. The performance of these instruments depends on many factors, including
importantly the quality of the construction and alignment of the electron lenses.
This project will attempt to understand
the performance of current generation
TEM lenses using both computer
simulation and practical experimental
measurements. Computer simulations
using COMSOL will be performed to
understand the effects of magnetic field
saturation as well as the focal properties
of electromagnetic lenses [1]. The
student will first build the model
geometry in the simulation environment
and then investigate the influence of various properties including lens-power, polepiece
shape and gap-separation. The influence on focal-length will be identified and if possible
optimised.
In addition to these simulations, and subject to progress, the student will have the
opportunity to undertake their own experimental contrast transfer function (CTF)
measurements using a JEOL-2010 TEM in the Advanced Microscopy Laboratory (AML).
These measurements will involve recording carefully calibrated images of few-
nanometre thick amorphous carbon
films to determine the CTF as a
function of defocus [2]. From these
measurements the coefficient of
spherical aberration (a key measure
of quality) will be calculated for the
lens system.
Ideal Candidate: The ideal candidate will have an interest in electron microscopy and/or
programming. Previous experience is not necessary as all training will be provided.
Good general computer skills will be essential. Experience with MatLab, ImageJ or
Python would be advantageous.
Expected Outcomes: The successful outcome of this project will see the student
develop tools to predict and experimentally verify the spherical aberration of one of the
TEM instruments in the Advanced Microscopy Laboratory (JEOL-2010).
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40.
Evaluation of 3D Printed polymers for Electron Microscope Sample
Holders/Supports
Supervisor Professor Lewys Jones
Location: TCD
The internship will be based in the Advanced Microscopy Laboratory (www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student. Lab-bench space will be
provided in TTEC Unit 7.
Abstract:
X-ray microanalysis is a powerful tool in the transmission electron microscope (TEM) for the identification of chemical species. However, the sample holders and support grids used often comprise of metals (especially copper and steel) and can cause either unwanted signal absorption/shadowing [1] or unwanted system peaks (data artefacts). Typical copper grid geometries are shown below, having a diameter of 3.05 mm:
The aim of this project is to determine the suitability of using new generation high-resolution two-photon polymer printers such as the NanoScribe GT2 in the AMBER Additive Research Lab (ARL) for the printing of TEM grids. Lower resolution higher temperature printers such as the 3Gence F340 will be evaluated for larger sample cartridge component printing, including the use of the polymer PEEK [2]. The student will be required to first reproduce the 3D geometry of existing grids (like those shown above) using 3D design software (Solidworks), before converting the files for 3D printing. Following the 3D printing, the student will assess the mechanical suitability of the printed part including evaluating any expansion or shrinkage of the material. Ideal Candidate: The ideal candidate will have an interest in nanoscience or electron microscopy. Good computer skills will be necessary and experience in 3D graphics/design would be a bonus. Specific previous experience is not necessary as all training will be provided. Expected Outcomes: On successful completion of this project we will have 3D printed a polymer TEM grid and assessed it’s suitability for imaging use. Any shrinkage/expansion resulting from the printing will be evaluated and corrected, and the vacuum compatibility of the polymer will be assessed. Electrical conductivity will be verified both of as-printed grids, and of gold-coated grids. Budget Plan: The project will require printing the prototype grids in the Additive Research Lab (approx. €300), and subsequent characterisation of their performance using a JEOL2100 TEM in the Advanced Microscopy Lab (approx. €200). Smaller costs, such as gold coating etc., will be absorbed by the Ultramicroscopy group.
24
References: [1] J. Kraxner, M. Schäfer, O. Röschel, G. Kothleitner, G. Haberfehlner, M. Paller, and W. Grogger, Ultramicroscopy 172, 30 (2017). [2] S. Koshiya and K. Kimoto, Micron 93, 52 (2017).
41.
Analysing 3D Printed Metal Parts using X-rays and Electrons
Supervisor: Professor Lewys Jones
Location: TCD
The internship will be based in the Advanced Microscopy Laboratory (www.tcd.ie/crann/aml ). A sole-use desk and PC will be provided to the student. Lab-bench space will be provided in TTEC Unit 7.
3D printing, or additive manufacturing, is a rapidly evolving area of industry. However, it as a new technology it poses many challenges in materials characterisation and certification. Many existing metrics of materials properties, structure, and strength now need to be re-evaluated. This project aims to determine some micro-scale properties of 3Dprinted metal parts; including the surface-finish/porosity, crystal structure, or traces of chemical impurity. Small metal test ‘coupons’ will be designed and manufactured in the AMBER Additive Research Lab (ARL) under supervision before being evaluated using scanning electron microscopy (SEM) for both surface finish and composition. Electron backscattered diffraction (EBSD) will be used to determine variation is surface crystal structure where possible. X-ray micro-CT will be used to study the presence (if any) of internal voids or of sputter into nearby unfused powder. The implications for component integrity and also powder recycling will be evaluated. Ideal Candidate: An interest in electron microscopy or 3D drawing (CAD) or 3D printing would be beneficial. Specific previous experience is not necessary as all training will be provided. Expected Outcomes: The student will contribute to an ongoing study of the suitability of 3D printing techniques in high-performance failure-critical industries. Budget Plan: This project will require 3D printing in titanium (approx. €250) followed by characterisation using SEM and micro-CT (approx. €200). Incidental additional SEM consumables costs will be absorbed by the Ultramicroscopy group.
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42.
Development of an electroless deposition process for 3D printed RF components
Supervisor: Professor David McCloskey
Location: TCD
Ideally candidate will have interest/ working knowledge of chemical processing.
This project will develop an electroless deposition process to work with polymer and
ceramic 3D printed RF components. In our group we are using additive manufacturing to
produce custom 3D parts for next generation wireless communications systems (5G
networks). These networks will use a denser cell networks and higher frequencies to
service more users with high bandwidth applications such as Virtual Reality, Augmented
Reality, Mobile video on demand. These new frequencies under investigation require non-
standard components which are either extremely expensive, or impossible to find. The
resolution of modern stereolithographic 3D printers has improved to such a level that
custom parts can be directly printed. One issue is that these parts require a metal interface
in order to perform properly [1]. Electroless deposition is a process where non conducting
materials can be coated with a thin layer of conducting metal [2]. This allows a cheap and
scalable process for development of prototype devices [3].
The student will develop this process, and apply to test waveguide and resonator
structures. The performance of the devices will be characterised, and the process
optimised to produce smooth continuous, conformal coatings. If successful this process
will then be applied to technologically relevant designs produced in collaboration with
Nokia Bell Labs.
References:
[1] Otter, William & Lucyszyn, Stepan. (2016). 3-D printing of microwave components for 21st
century applications. 1-3. 10.1109/IMWS-AMP.2016.7588327.
[2] J. Shen, M. Aiken, C. Ladd, M. D. Dickey and D. S. Ricketts, "A simple electroless plating
solution for 3D printed microwave components," 2016 Asia-Pacific Microwave Conference
(APMC), New Delhi, 2016,pp.1-4. doi: 10.1109/APMC.2016.7931434
[3] Mandke, Yashodhan & Henry, Rabinder. (2017). Review of Additive Manufacturing 3D Printed
Microwave Components for Rapid Prototyping.
[4] Ghazali, Ifwat & Chahal, Premjeet & Park, Kyoung Youl. (2018). 3D Printed Metallized Plastic
Waveguide for Microwave Components. Advancing Microelectronics. 45. 12-16. 10.4071/2380-
7016-45.2.1.
[5] A review of electroless nickel plating, Loto, C.A. Silicon (2016) 8: 177.
https://doi.org/10.1007/s12633-015-9367-7
Fig.1
(a) 3D printed
(b)Example of complexity of a 3D printed part. This
is a monopulse antenna array which usually consists
of multiple components, now printed as a single
compact part.
26
43.
Integrated polymer refractive index sensors based on whispering gallery mode
optical detection.
Supervisor: Professor David McCloskey
Location: TCD
Light can be efficiently trapped in micron scale dimensions using devices known as
whispering gallery mode resonators. These are spherical or cylindrical shaped devices
which act like tiny interferometers, and exhibit sharp dips in transmission when coupled to
via fibres or waveguides. The positon and full width half maximum of these dips are
strongly dependant on the refractive index of the surrounding environment. This allows
the use of these devices as extremely sensitive refractive index sensors [1]. By correctly
functionalising these devices trace amounts of chemicals or biological particles can be
detected. This project will develop the UV lithography process necessary to produce
whispering gallery mode resonators in SU8 using the facilities available in CRANN. The
ultimate goal of the project is to combine this technique with integrated turbulent
microfluidics a chemical or biosensor with sensitivity in the ppb range.
References:
[1] Optical microcavities, Kerry Vahala.
[2] C. Delezoide et al., "Vertically Coupled Polymer Microracetrack Resonators for Label-Free
Biochemical Sensors," in IEEE Photonics Technology Letters, vol. 24, no. 4, pp. 270-272,
Feb.15, 2012. doi: 10.1109/LPT.2011.2177518
44.
Characterisation of thin film thermoelectrics
Supervisor: Professor David McCloskey
Location: TCD
Thermoelectric materials allow the direct conversion of heat flux into electrical current
and vice versa. As such they can be used to generate electrical power using waste heat.
Another important application of thermoelectrics is as solid state coolers. When a current
is passed through a thermoelectric material heat will be extracted from one contact and
deposited at the other. As such we can use this effect as a heat pump. Since it is a solid
state device it have no moving parts and no vibration which has resulted in its adaptation
for niche markets such as CCD array cooling, space applications and temperature
control of laser diodes.
Standard Thermoelectric Modules utilise bulk semiconductor alloys such as Bi2Te3 and
BiSbTe. They consist on an array of alternating n and p type semiconductor legs which
27
are connected electrically in series and thermally in parallel. Typical leg lengths are of
the order of 2-3mm. A new class of thermoelectric cooler is emerging utilising thin films
with thickness in the range of 10μm. These devices can be embedded in the lithographic
design of electronic and optoelectronic devices allowing a much smaller footprint and
higher energy efficiency. Under high heat flux conditions seen in integrated circuits thin
film thermoelectrics clearly out-perform their bulk counterparts. Commercial thin film
TECs are currently available as standalone external modules, but as of yet a fully
integrated TEC with optoelectronic device has remained elusive.
Figure 1 (a) Commercial thin film thermoelectric modules (b) Thin film modules
compared to conventional bulk modules for same cooling power. (c) Cooling
performance chart for comparison of bulk vs thin film. Even measuring the
performance of these devices becomes challenging as small temperature differences
must be accurately measured over distances as short as 10μm. In our research
group we have developed optical and electronic techniques to measure thermal
conductivity, volumetric heat capacity, electrical conductivity, Seebeck and Peltier
Coefficients, electrical and thermal interface conductances. These are all the
parameters required to measure the device performance. This project will apply
these techniques to investigate the thermoelectric performance of thin film polymer
thermoelectric coolers. Particular attention will be paid to minimising the electrical
interface conductance which limits the performance of thin film TECs.
References: [1] http://www.mouser.com/pdfDocs/Laird_ThinFilmThermoelectricHandbook.pdf [2] Coatings 2018, 8(7), 244; https://doi.org/10.3390/coatings8070244
[3] Handbook of thermoelectrics, D.M. Rowe, Chapter 58
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45.
Field Effect Phase Modulation in 2D Nanomaterials
Supervisor: Professor David McCloskey
Location: TCD
Surface normal optical modulators are attractive devices for a wide range of applications
such as free-space photonic links for mobile platforms [1], chip-to-chip optical
interconnects [2], high-speed transceivers [3], optical correlators [4], and optical vector-
matrix multipliers [5]. These devices use a large array of lithographically defined pixels
which can modulate the amplitude of the reflected light to encode and transmit information
in a massively parallelised fashion (See Fig.1).
Figure 2 (a) Schematic of single pixel multiple quantum well structure for 1550nm. (b) Micrograph of typical pixel designs from above, and typical SMA connected package. (c) Image of a 2x128 modulator array. [6]
Surface-normal modulators (SNMs) are conventionally based on multi-quantum well
structures and can achieve modulation frequencies above hundreds of kilohertz, with
demonstrations in InP up to 40 GHz [6]. Achieving this performance requires expensive
fabrication techniques with slow and costly regrowth steps, and back-etching. Due to the
weak interaction of light with individual QWs a large stack must be made up to 5 μm which
limits the bandwidth to MHz range.
Recently it has been demonstrated that the reflectivity of 2D semiconducting materials can
be effectively controlled through electrical gating [7]. The tunability results from the effects
of injected charge carriers which broaden the spectral width of excitonic interband
transitions by the creation of trions [8], resulting in a large change of complex refractive
index.
This project will develop an interferometry setup to measure the phase shift on reflection
from test devices produced through the AMBER centre. We will investigate theoretically
and experimentally the limits in switching frequencies for these devices.
References
[1] “Large aperture multiple quantum well modulating retroreflector for free space optical data
transfer on unmanned aerial vehicles,” Opt. Eng., vol. 40, pp. 1348–1356
29
[2] “High-speed, dual-function vertical cavity multiple quantum well modulators and
photodetectors for optical interconnects,” Opt. Eng., vol. 40, pp. 1186–1191
[3]“High-speed integrated optoelectronic modulation circuit,” IEEE Photon. Technol. Lett., vol. 13,
no. 2, pp. 626–628.
[4] “Design and evaluation of a multiple quantum well SLM based optical correlator,” in Optical
Pattern Recognition XI, Proc. SPIE, vol. 4043, pp. 66–71.
[5] Development of a large high-performance 2-D array of GaAs-AlGaAs multiple quantum-well
modulators,” IEEE Photon. Technol. Lett., vol.15, no. 10, pp. 1531–1533, (2003).
[6] Surface-Normal Ge/SiGe Asymmetric Fabry–Perot Optical Modulators Fabricated on Silicon
Substrates," in Journal of Lightwave Technology, 31, 3995 (2013).
[7] Giant Gate tunability of Optical Refractive index in Transition Metal Dihalcogenide
Monolayers, Nano Lett. ,17, 3613 (2017)
[8]Control of strong light-matter interaction in Monolayer WS2 through electric field gating, Nano
Lett.DOI:10.1021/acs.nanolett.8b02932 (2018)
46.
A study of growth and magnetic properties of Au-capped Fe atomic-width
nanowire arrays self-assembled on a vicinal platinum single crystal surface
Supervisor: Cormac McGuinness
Location: TCD
The magnetic properties of bare Fe atomic-width and height nanowires grown by self-
assembly at the step edges of platinum vicinal single crystal stepped surfaces such as
Pt(997) have been investigated in the past [1]. Capping such self-assembled nanowire
arrays by a few monolayers of gold is expected to change greatly the magnetic behaviour
of these systems as has been observed to occur for cobalt nanowires [2]. The self-
assembled growth of Fe nanowires on Pt(997) will be attempted and these nanowires will
be capped with an ultra-thin Au layer. Preparation of the Pt(997) surface and the growth
of these nanowires will occur in ultra-high vacuum (UHV) chambers. In UHV the growth
will be characterised by low energy electron diffraction (LEED) and Auger electron
spectroscopy (AES) and also by in-situ reflection anisotropy spectroscopy (RAS) in the
visible and near-visible regions. Upon successful growth then the capping layer prevents
oxidation upon removal from the chamber and ex-situ magnetic measurements such as
magneto-optic Kerr effect (or RAS-MOKE) measurements will measure the magnetic
hysteresis of the Au-capped Fe nanowire arrays at room temperature and at a range of
temperatures below room temperature. In addition, further ex-situ measurements by x-ray
photoemission spectroscopy (XPS) can serve to confirm the electronic structure and
metallicity of the capped Fe nanowires. It is the intention that these samples will then be
studied at synchrotron radiation sources by x-ray magnetic circular dichroism (XMCD)
techniques. The student will become skilled in many aspects of surface science, vacuum
technology, magnetic surface optical linear spectroscopy and analytical techniques.
[1] R. Cheng, K.Y. Guslienko, F.Y. Fradin, J.E. Pearson, H.F. Ding, D. Li, and S.D. Bader, Phys. Rev. B 72, 014409 (2005). [2] M.J. Duignan, J.P. Cunniffe, P.-A. Glans, E. Arenholz, C. McGuinness, and J.F. McGilp, Phys. Status Solidi B, 253, 241 (2016).
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47.
The measurement of the reflectance anisotropy spectrum (RAS) arising from penta-silicene nanoribbons formed on Ag(110) Supervisor: Cormac McGuinness Location: TCD This project is to measure for the first time the optical anisotropy due to penta-silicene
nanoribbons that can be formed on Ag(110) surfaces. It has recently been shown by
Cerda et al. that a monolayer of silicon evaporated onto Ag(110) surfaces can form a
variety of penta-silicene nanoribbons [1]. These nanoribbons form parallel to the Ag
[110] rows displacing one of the surface rows i.e. of the missing row reconstruction,
where the silicon forms a chain of distorted pentagons within the missing row troughs
(a,b). Each pentagon consists of four co-planar silicon atoms in the trough with the fifth
silicon adatom buckling the planarity of the pentagon (e). These one-dimensional silicon
surface nanostructures have been controversial. Evidence from Cerda et al [1] for both
single and double silicene penta-nanoribbon formation now gives confidence that the
above is an accurate picture.
This experimentally challenging project involves the preparation of ultra-clean Ag(110)
surfaces in ultra-high vacuum, verification of this via low energy electron diffraction
(LEED) and by Auger electron spectroscopy (AES), the calibration and evaporation of
<1ML of Si onto these surfaces (to be verified via AES). The goal being the
measurement of the anisotropic optical properties of the penta-silicene nanoribbons as
measured in situ during the penta-silicene nanoribbon formation via reflection anisotropy
spectroscopy (RAS) and subsequent structural measurement by LEED. Earlier surface
differential reflectance spectroscopy (SDRS) measurements by Borensztein et al [2]
were obtained for what should be the same system described by Cerda et al. but as of
yet no direct RAS measurement has been acquired from this penta-silicene system. The
objective is to complete such measurements. The student will become skilled in many
aspects of surface science, vacuum technology, surface optical linear spectroscopy and
analytical techniques.
[1] J. I. Cerda et al, Nature Communications, 7, 13076, 2016 10.1038/ncomms13076 [2] Y. Borensztein et al., Phys. Rev. B, 89, 245410 (2014) 10.1103/PhysRevB.89.245410
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48.
Self-consistent data analysis of x-ray magnetic circular dichroism x-ray absorption spectra of sub-monolayer cobalt nanowire arrays. (Computational/Data analysis) Supervisor: Cormac McGuiness
Location: TCD X-ray magnetic circular dichroism (XMCD) is a synchrotron radiation based x-ray
spectroscopy used to measure the magnetic moments and probe magnetic behaviour of
materials on an elementally selective basis due to the distinct binding energies of the
orbitals probed to connect with the magnetically polarised unoccupied states. XMCD
uses circularly polarised x-rays where differential x-ray absorption of a material in a
magnetic field is measured in four differing modes: +B+, -B+ , +B-, and +B-
corresponding to the two differing circular polarizations available (+, -) and the differing
applied fields parallel (B+) or anti-parallel (B-) to the direction of propagation of the x-
rays. The XMCD spectrum is computed from the difference of any pair of the x-ray
absorption spectra. For bulk materials where the underlying x-ray absorption signal is
strong, the XMCD is not susceptible to transient problems related to the measurement.
However in the case of very small x-ray absorption signals due to small amounts of
material, e.g. sub-monolayer coverages of the material being probed, transient problems
(noise as well as differing spectral backgrounds due to variable flux from the x-ray
monochromator or machine issues) from each separate measurement have an untoward
effect on the ability to compute XMCD. This project envisages the development of a
robust self-consistent data analysis method whereby a quartet of spectra (or octet of
spectra), known to be probing the same amount of material, are treated to obtain reliable
XMCD spectra. XMCD data previously obtained at synchrotrons in Sweden (MAX-lab)
and the US (ALS) are available for this project. This data arises from gold-capped cobalt
nanowire arrays self-assembled on vicinal regularly stepped platinum substrates such as
Au(4-7ML)/Co(0.39-0.78ML)/Pt(997) investigated by us in the recent past [1,2].
[1] J. P. Cunniffe, D. E. McNally, M. Liberati, E. Arenholz, C. McGuinness, and J. F. McGilp, Phys. Status Solidi B, 247, 2108 (2010) [2] M.J. Duignan, J.P. Cunniffe, P.-A. Glans, E. Arenholz, C. McGuinness, and J.F. McGilp, Phys. Status Solidi B, 253, 241 (2016).
49. Project removed from list.
50.
The packing structure of disordered platelet suspensions
Supervisor: Professor Matthias Möbius
Location: TCD
Microscopic platelet particles naturally occur in clays, for example. More recently 2D
nanoparticles such as graphene and many others can be produced. Suspensions of
these nano-sheets are often used to make films for battery electrodes or can be used as
fillers to enhance the mechanical properties in nanocomposites. One important quantity
is the volume fraction at which these particles form a stress bearing network and its
dependence on particle aspect ratio. You will investigate this experimentally by studying
a system of sheets suspended in a fluid and compare your results with theoretical
predictions. Furthermore you will study the disordered structure using a CT scanner.
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51.
Droplet splashing of 2D nanosuspensions
Supervisor: Professor Matthias Möbius
Location: TCD
Beyond a critical impact velocity liquid droplets splash on a solid surfaces. This
phenomenon is important in the context of printed electronics, where nanoparticle inks
are used to print circuits on substrates. As splashing limits the resolution of feature
sizes, it is important to understand it for nanoparticle suspensions which exhibit a
different flow behaviour than ordinary liquids. In this project you will measure the onset
of splashing for a 2D nano-suspension, such as aqueous graphene oxide, and the
influence of particle concentration, which is unknown. This experimental project involves
using a high speed camera to probe the dynamics of the splashing process.
52.
Integrated Optical-Electrical Modelling and Characterisation for Light Trapping
Effect in Thin Film Organic Photovoltaic Cells
Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll
Location: TCD
Solar cells absorb solar light energy and convert it to electricity directly by the
optoelectronic reaction known as photovoltaic effect. Organic photovoltaic (OPV) cells has
been studied for decades as potential candidates to replace the silicon solar cells because
of the advantages such as light weight, thin film, flexible shape, simple fabrication, etc.
Recent new materials have developed the power conversion efficiency to 14% in
experimental condition, which close to the commercial silicon products’. This project will
use electromagnetic and electrical modelling methods to study the working mechanism of
OPV cells, from photon absorption, exciton excitation, exciton diffusion, carrier transport
and collection. Also, current-voltage measurement of the OPV cells will be taken to verify
the modelling results.
53.
Light Extraction and Beam Steering Effect in Organic Light Emitting Diode with
Nano Patterned Encapsulation Thin Film.
Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll
Location: TCD
Plastic organic light emitting diodes (P-OLEDs) are being used widely because of their
thinness, shape flexibility, and low pixilation. P-OLEDs typically exhibit homogeneous
luminance density so that no preferred angular emission direction. Also, because of the
instability of organic polymer materials, an encapsulation thin film is normally placed on
the device to isolate the ambient environment. Here, electromagnetic simulations are used
to design nanostructures on the encapsulation layer of the OLED and to quantify the extent
to which the light illuminance directions and intensities will be changed, followed by the
fabrication process by using photo lithography and plasma etching. Light emission angular
characterisation is probably involved in this project as well by doing the quantum yield
measurement.
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54.
Quantum Efficiency Enhancement in Organic Light Emitting Diode with Plasmonic
Metasurfaces for Different Coloured Light Emission
Supervisor: Dr. Chenguang Wang and Professor Deirdre O’Carroll
Location: TCD
Plastic organic LEDs (P-OLEDs) are being used widely because of their thinness, shape
flexibility, and low pixilation. However, the phosphorescent P-OLED emitters are unstable
due to long emission lifetimes, excited-state quenching, and large band gap. These
drawbacks will lead to the energy waste and heat generation of the OLED by non-radiative
recombination. This project theoretically and experimentally investigates the use of silver
plasmonic metasurface structures to increase the light extraction efficiency, radiative
decay rate and stability of inverted P-OLED devices. Electromagnetic simulations are
used to design silver metasurfaces and to quantify the extent to which they increase
radiative decay rate of OLED emissive layers. Nano imprint lithography technique is used
to fabricate the silver metasurface and experimental measurement works will be included
to test the performance of OLEDs with designed metasurface structures.
55.
Quantum-mechanical simulation of magneto-optical spectroscopy
Supervisor: Professor David O’Regan
Location: TCD
Certain materials exhibit the phenomenon of rotating linearly-polarised light passing
through them, an effect known as optical activity or magneto-optical response. The
related spectroscopic techniques, in particular, electronic circular dichroism (ECD) and
optical rotatory dispersion (ORD) directly probe the chirality of the material in question.
These techniques are particularly important for characterising similar molecules or
nanostructures with different chirality, whose absorption spectra may be identical but
whose magneto-optical may differ enormously. ECD also plays a role in the study of
magnetic materials with a strong orbital component to magnetism. Experimental ECD
signals are often very clear, but can be difficult to understand without some prior
knowledge of the crystal structure. This is why a theoretical description, necessarily
quantum-mechanical, is an essential, but hitherto almost entirely absent, companion to
experimental magneto-optical spectroscopy. Up to now, relatively very few first-
principles quantum calculations of magneto-optical spectra have been carried out, and
code for carrying them out is not very widely available. The proposed project first entails
a study of the rather interesting and under-developed quantum-mechanical theory of
angular momentum and related magneto-optical response, and how they can be
computed using the output of computer simulations using the widely used atomistic
simulation method known as density-functional theory (DFT), and its linear-scaling
generalisation. This project aims to bring to completion research carried out by summer
interns, involving abstract theory and its software implementation in parallelised code for
high-performance computing architectures.
See https://arxiv.org/abs/1703.05056
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56.
Developing empirical rules for correcting density-functional theory: how best to
simulate entangled electronic states using pure ones?
Supervisor: Professor David O’Regan
Location: TCD
The computer simulation of molecules and materials using density-functional theory is
beset by a number of well understood, but difficult to correct, systematic errors. As a
result, it yields very inaccurate predictions in a wide range of systems. An established
route to addressing one of the main problems is by adding a correction involving a
parameter known as the Hubbard U. Adding a parameter to the theory is undesirable,
and a number of recipes have been developed for calculating an optimal value for U,
whereby the theory again becomes parameter-free. We will investigate a new such
recipe, testing it systematically on series of small molecules comprising transition metals
across the periodic table. With this, we may also be able to establish empirical rules for
how the U parameter should vary with atomic number, charge, spin, and bond-length.
We will also look at trends in the Hund’s J parameter, which can help to correct strong
’static correlation’ errors that occur in density-functional theory calculations when strong
multi-reference or entanglement effects arise, since these calculations need to work with
a pure state one. This will be particularly helpful to the simulation of systems where
bonds break (e.g., in catalysis for water splitting or CO2 reduction), and in multiple-
valence degenerate systems (transition metal oxides used to store lithium ions in high-
performance batteries).
See and https://arxiv.org/abs/1704.08076 and Phys. Rev. B 94, 220104(R) (2016).
57.
Methodology for efficient computational screening for photovoltaic active layer
materials
Supervisor: Professor David O’Regan
Location: TCD
Photovoltaic solar cells are leading candidates for the energy needs of remote,
personally wearable, and autonomous (Internet-of-Things type) off-grid devices. For the
large-scale roll out of small format cells, requirements include low economic and
environmental cost, flexibility, durability, and ease of manufacture. Organic and polymer
cells are clear candidates, but they suffer from poor efficiencies in simpler, single-layer
cell geometries, limiting their market share. Dramatic improvements to the efficiently of
these materials can be yielded when multi-exciton generation effects are harnessed,
particularly rapid fission of singlets into multiple excitations, via dark and charge-transfer
(CT) states, reactions which can even be endothermic if entropy driven. Theory and
simulation are beginning to offer valuable insights into these optically dark but important
processes, including work in the School demonstrating a new ‘constrained DFT’ code for
large, disordered systems. In this project, we will explore a new, inexpensive technique
for simulating singlet, triplet, and CT excitations with minimal prior physical assumptions,
including their polarons, migration barriers, exciton binding, spin-flip conversion
constants, and oscillator strengths. In particular, we will concentrate on the singlet-
fission effect in pentacene, classifying its low-lying excitations with this new
methodology.
See Phys. Rev. B 93, 165102 (2016) and https://arxiv.org/abs/1802.01669 . For wider context,
see Nature Physics 13, 114–115 (2017); 13, 176–181 (2017); 13, 182–188 (2017).
35
58.
Many-body theory of exciplexes for OLED devices
Supervisor: C. H. Patterson
Location: TCD
Some optical excitations in matter result in transfer of an electron between two distinct
parts of a molecule or from one molecule to a neighbouring molecule. These are known
as charge transfer (CT) excitations. When a CT excitation occurs between two
molecules there is a coulombic attraction between the negatively charged acceptor
molecule and the positively charged donor molecule. The donor and acceptor molecules
are unbound in the ground state but become bound in the excited state. This is known
as an exciplex. Exciplexes are finding applications as light emitters for organic LEDs
(OLEDs) because of this delocalised nature of the excited state. Optical excitations exist
as spin-parallel or anti-parallel excited states called triplets and singlets. When excited
states are formed by optical pumping (or by injecting electrons and holes as in an OLED)
there are three triplet excited states formed for every singlet. However, only the singlet
states fluoresce readily (photon emission). Exciplexes are important for OLED emitters
as the delocalised nature of the CT excited state means that singlet and triplet excited
states have similar energies. This allows thermal interconversion of triplets to singlets
and an increase in the theoretical efficiency from 25% to 100%. This project will use
many-body quantum methods to calculate properties of exciplexes.
[1] Exciplex: an intermolecular charge-transfer approach for TADF, M. Sarma and K.-T. Wong,
ACS Appl. Mater. Interfaces 10, 19279 (2018).
59.
Reflectance anisotropy of the SrTiO3(110) surface
Supervisor: C.H. Patterson
Location: TCD
Two dimensional electron gases form at oxide heterostructures such as LaAlO3/SrTiO3.
These 2DEG systems have interesting properties including superconductivity. The (110)
surface of SrTiO3 has been shown to have an anisotropic 2DEG [1] using angle
resolved photoemission experiments. The surface has also been studied in TCD using
reflectance anisotropy [2]. The aim of this project is to model the effects of oxygen
vacancies at this surface on the optical anisotropy spectrum using density functional
theory. TCD experimentalists found that annealing this surface in vacuum at high
temperature resulted in a new feature in the optical anisotropy of SrTiO3(110) around
1 eV photon energy, well below the oxide bulk band gap of 3.7 eV. They attributed the
low energy feature to oxygen vacancies at the surface. In this project you will model
oxygen vacancies at this surface and calculate the optical anisotropy using methods
described in Ref. [3].
[1] Anisotropic two-dimensional electron gas at SrTiO3(110), Z. Wang et al, PNAS 111, 3933
(2014)
[2] Optical anisotropy of SrTiO3(110) for different surface terminations, K. Fleischer et al. Phys.
Stat. Sol. B 255, 1700459 (2018)
[3] Reflectance anisotropy of the anatase TiO2(001)-(4x1) surface, P. Kumar and
C. H. Patterson, J. Phys. Condens. Matter 26, 445006 (2014)
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60.
Reflectance Anisotropy of the Ag(110) surface
Supervisor: C. H. Patterson
Location: TCD
Reflectance anisotropy spectroscopy (RAS) offers a method for probing electronic
optical transitions for electrons confined to the outer atomic layers of materials. It
requires the surface atomic layers to have reduced lateral symmetry (a surface
anisotropy) and the underlying bulk material to have isotropy. This is the case for the
(110) faces of close packed metals such as the Ag(110) surface. This project will be to
calculate the RAS spectrum for Ag(110), to identify which electronic transitions are
responsible for the RAS signal and to compare to available experimental data [1].
Through the project you will learn about electronic structure of surfaces, density
functional theory and high performance computing. To learn more about RAS and its
applications to surface states [2].
[1] Martin et al. Phys. Rev. B 76, 115403 (2007).
[2] Jorgji et al. Phys. Rev. B 87, 195304 (2013).
61.
Electron scattering from bilayer islands in graphene
Supervisor: Dr Stephen Power
Location: TCD
Figure 3: Bilayer islands surrounding by single layer graphene during CVD growth
(from Luo et al, J. Mat. Chem C. 4, 7464 (2016))
Graphene has an unusual electronic properties that are well-described using the
relativistic Dirac equation in place of the more standard Schrodinger equation. The
electronic properties of graphene are strongly dependent on the number of atomic
layers, with electrons in a system of two layers (bilayer graphene) behaving very
different to the single layer case.
This project will simulate how electrons in single layer graphene scatter from bilayer
regions, which commonly form during some growth processes (see Figure 1). The aim is
to determine whether this scattering can be controlled by applying an electric field. The
project will also determine if such a setup has potential valleytronic applications. The
student will:
• Learn the tight-binding and Dirac spinor representations of electrons in single
layer and bilayer graphene
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• Examine how barrier and spherically-symmetric scattering geometries can be
solved using the Dirac approach for simple potential terms
• Solve the full scattering problem for a range of realistic parameters, and calculate
the valley-splitting efficiencies of these systems.
62.
Machine-learning prediction of edge-state magnetism in graphene
Supervisor: Dr Stephen Power
Location: TCD
Figure 4: Section of a graphene ribbon with mixed edges grown using chemical "bottom-up" techniques (from Ruffieux et al, Nature 531, 489 (2016))
Graphene is a two-dimensional hexagonal lattice of carbon atoms whose ground-
breaking physical and electronic properties have been investigated in great detail over
the last decade. Recent experimental techniques allow graphene to be produced both at
very large scales for industrial purposes, and at the nanometre scale required for
investigating fundamental physics.
The latter approach allows for a high-degree of control over the edge geometries of finite
flakes or narrow ribbons of graphene. This is particularly exciting because, although
carbon is generally considered nonmagnetic, local magnetism can arise near edges with
particular geometries. Magnetic edge features have received much attention from
theorists, and recent experiments show convincing signatures of their presence.
Although the expected magnetic behaviour of small scale or periodic systems can be
easily predicted, the computational power required increases rapidly when larger or
disorder systems (with a mix of different edge types) are considered. This project aims to
solve some of these problems by training a machine-learning algorithm to predict the
magnetic properties of arbitrary graphene systems using only their geometry and a
knowledge of the properties of similar structures.
The student(s) will
• Learn tight-binding methods required describe non-magnetic graphene samples
• Implement a self-consistent procedure to calculate magnetic profiles
• Generate a training set and develop a suitable descriptor to capture its important
features
• Train machine-learning algorithms to predict the magnetic profiles of unseen
samples using its knowledge of the training set.
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63.
Machine-learning force fields for phase diagram predictions
Supervisor: S. Sanvito
Location: TCD
Machine learning is rapidly becoming a powerful tool to discover patterns in apparently uncorrelated data [1]. It comprises a range of computational methods, which underpin the most diverse applications, going from image recognition to natural language processing, to complex optimisation and classification problems. The use of machine learning in materials science instead is in its infancy [2], mostly because of the relatively poor availability of data. This issue is, however, mitigated by the access to large databases of computed properties [3], so that machine learning algorithms can serve the purpose of replacing numerically costly computational methods. One particular use of machine learning in materials science is related to the construction of highly accurate atomic potentials [4]. These can describe the interaction between atoms at a level of accuracy comparable to that of the much more demanding first principles methods at a fraction of their computational cost. In this project we will explore how such machine-learning force fields can predict the phase diagram of binary compounds. In particular we will study of the force fields can describe compounds presenting different stoichiometry and different structure. The student will:
1. Learn the basics of machine learning 2. Construct a machine-learning force field for a binary phase diagram 3. Extract elementary properties with the machine learning force field
References [1] T. Hastie, R. Tibshirani and J. Friedman, The elements of statistical learning, Springer. [2] R. Ramprasad, R. Batra, G. Pilania, A. Mannodi-Kanakkithodi and C. Kim, Machine learning in materials informatics: recent applications and prospects, npj Comp. Mat. 3, 54 (2017). [3] S. Curtarolo, G.L.W. Hart, M.B. Nardelli, N. Mingo, S. Sanvito and O. Levy, The high- throughput highway to computational materials design, Nature Materials 12, 191-201 (2013). [4] V. Botu , R. Batra, J. Chapman and R. Ramprasad, Machine Learning Force Fields: Construction, Validation, and Outlook, . Phys. Chem. C 121, 511 (2017).
64.
Use of Generative Adversarial Networks in physics
Supervisor: S. Sanvito
Location: TCD
Generative Adversarial Networks (GANs) belong to a class of machine learning algorithms, where two neural networks compete with each other [1]. These have widespread applications in several fields, with the most celebrated success being in image processing/recognition. A classical example of how GANs work is that of picture generation. In this case a first neural network (call it “Alice") generates pictures (for example, human faces), which are included in a database of images of real people. Then a second neural network (call it “Bob") sort the real images of people from the computer-generated ones. Bob and Alice then play against each other, namely Alice generates more and more realistic pictures and Bob refines its discrimination ability. The game ends when Bob is no longer able to distinguish the real images from the computer-generated ones. At this point Alice’s ability is to generate pictures of people indistinguishable from those of real people. An example of this scheme at work can be found at https://thispersondoesnotexist.com/. Similar methods have been used to generate characters of Anime cartoons [2] or to age people in photographs [3] In this project we will attempt to use GANs for solving physics problems that require sampling a vast distribution of configurations [4]. This, for instance, is the case when calculating phase transitions of quantum models (e.g. the Ising model), or in general for extracting temperature-dependent properties. In this project the student will:
39
1. Learn the basics of machine learning 2. Construct a simple GAN model 3. Extract finite-temperature properties of a simple quantum model
References [1] I. Goodfellow, J. Pouget-Abadie, M. Mirza, B. Xu, D. Warde-Farley, S. Ozair, A. Courville, Y. Bengio, Generative Adversarial Networks, arXiv:1406.2661 (2014). [2] Y. Jin, J. Zhang, M. Li, Y. Tian, H. Zhu and Z. Fang, Towards the Automatic Anime Characters Creation with Generative Adversarial Networks, arXiv:1708.05509 (2017). [3] G. Antipov, M. Baccouche and J.-L. Dugelay, Face Aging With Conditional Generative Adversarial Networks, arXiv:1702.01983 (2017). [4] Z. Liu, S.P. Rodrigues and W. Cai, Simulating the Ising Model with a Deep Convolutional Generative Adversarial Network, arXiv:1710.04987 (2017).
65.
Electronic structure simulations of spin-phonon coupling in molecular materials
Supervisor: S. Sanvito
Location: TCD
Magnetic materials represent the conventional way to store information in hard drives. This is done by orienting the magnetization of a material along one spatial direction with either positive (the bit has value 0) or negative (the bit has value 1) polarization. Molecular magnetic materials represent the smallest units that can be used to store information but they usually have a very low working temperature [1]. This limitation mainly comes from the interaction between the molecular spin, that generates the magnetic moment, and molecular phonons [2]. In order to optimize the production of these materials a deep understanding of the physical principles governing the spin- phonon interaction is needed. In this context, electronic structure theory can be used to simulate magnetic proprieties of materials and get access to the correlation between the chemical nature of molecules and their magnetic properties. In this project we will exploit electronic structure methods to explore the effect of different chemical environments on molecular magnetic anisotropy and its coupling with molecular vibrations. The student will:
1. Learn the basics of electronic structure theory 2. Learn how to calculate magnetic anisotropy in molecular compounds 3. Extract elementary correlations between magnetism and structural parameters
References [1] Bogani L. and Wernsdorfer W., Molecular spintronics using single-molecule magnets, Nat. Mater. 7, 179-186 (2008). [2] Lunghi A., Totti F., Sessoli R. and Sanvito S., The role of anharmonic phonons in under-barrier spin relaxation in single molecule magnets, Nat. Commun. 8, 14620 (2017).
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66. Quasi-classical spin dynamics in compensated ferrimagnetic systems – a 1D/2D approach to understanding pinning and nucleation of domain walls and skyrmions (theory/computation) Supervisor: Dr. Plamen Stamenov Location: TCD
The project will involve the theoretical and computational modelling of spin dynamics in a relatively new class of magnetic materials – the Zero-Moment Half-Metals (ZMHM). ZMHMs are posing a challenge to understand and exploit a rather unique for spin electronics combination of high bulk spin polarisation, stray field immunity and intrinsically high resonance and switching frequencies, effectively limited by the exchange energy in the system. Nano-scale ultrafast and non-volatile MRAM elements and terahertz oscillators are only two examples of applications, which could benefit hugely from the utilisation of ZMHMs. The complete theoretical (ab initio) modelling of these materials is rather challenging, for the incomplete knowledge of their intrinsic and extrinsic disorder and the fine details of the effective interactions in the system, including higher order exchange and spin-orbit torques. Here a divide and conquer approach will be used to theoretically and computationally model within an effective spin Hamiltonian approach the dynamics of domain walls and other topological objects, such as skyrmions, which become possible with the inclusion of Dzyaloshinskii-Moriya interactions. The influence of magnetic field, electric current and local pinning on the mobility and dissipation within these objects will be clarified. The work will start with an existing 1D code for quasi-classical spin simulation and transition it into a 2D version towards the end of the project, looking for phenomena that cannot be mapped-down successfully in 1D. Sz1e-2Sz0.5e-2Sz0.0e-22e-22Sz4e-2Sz5e-2Sz6e-222
Figure 1. Time-evolution of a 1D skyrmion in a two-lattice compensated ferrimagnet, at different
values of the applied magnetic field, for a chain of 100 spins, with DM interactions included.
Sz
1e-2
Sz
0.5e-2
Sz
0.0e-2 2e-2
Sz
3e-2
Sz
Sz
4e-2
Sz
5e-2
Sz
6e-2
Sz
7e-2
Sz
8e-2
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67.
High-Power Broadband Ferromagnetic Resonance in Thin Magnetic Films and Microstructures Using Δmz – SQUID-based Detection at Low Temperatures (experiment) Supervisor: Dr. Plamen Stamenov Location: TCD
FerroMagnetic Resonance (FMR) has been instrumental in characterising the
magnetisation and the effective anisotropy fields in a large number of bulk materials and
some repetitive microstructures. Conventional FMR relies on narrow band inductive
excitation and detection of the precessional motion of the local magnetisation averaged
over some volume – typically of the order of mm3. The superb sensitivity of modern
SQUID-based magnetometers allows for a different approach towards the FMR
measurement problem – direct measurement of the precession cone angle as a function
of frequency, applied magnetic field and temperature, by detecting the mz component of
the magnetisation and the small decrease in its value upon microwave excitation Δmz.
This can, in principle, allow for the continuous broadband tracking of the FMR modes in
a broad range of the applied magnetic field and thus permit direct comparisons with
theory and micromagnetic modelling.
The project will involve the preparation of magnetic thin films of novel magnetic materials
(Co/Pt multilayers, CoFeB), their lateral patterning and comparative FMR study by both
SQUID-based and conventional inductive techniques. Within this study, an in-house-
developed probe will be utilized and a new high-power broadband amplifier will be
developed, pushing the envelope of precession cone angles that can be investigated. A
success in this will inform the design of high power microwave circulators and filters for
the 5G networks of the near future.
Figure 1. The principle of resonance detection via SQUID magnetometry in one diagram, the
high-power SFMR measurement assembly (rod), which fits into the bore of a commercial
Quantum Design MPMS 5 magnetometer, and data on the magneto-static resonance modes of
an YIG sphere, with their corresponding indexes.
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68.
Anisotropy of the Conductivity and Hall Effect in Zero-Moment Half-Metallic Systems Supervisor: Dr. Plamen Stamenov (experiment) Location: TCD
The project will involve the experimental investigation of a relatively new class of
magnetic materials – the Zero-Moment Half-Metals (ZMHM), using their prototype Mn2-
xRuxGa, in a thin film form. ZMHMs have the potential to offer the rather unique for spin
electronics combination of high bulk spin polarisation, stray field immunity and
intrinsically high resonance and switching frequencies. Nano-scale memory elements
and terahertz oscillators are only two examples of possible applications.
Highly oriented and/or epitaxial films prepared by sputtering at different conditions
(temperature, Ru-target current, etc.) will be used to determine the anisotropy of the
conductivity and Hall effect tensor in these, typically tetragonally-distorted ZMHMs. The
measurements will be executed at both low-temperature and room-temperature, in
magnetic fields of up to 14 T, in order to discern the influence of the two ferrimagnetic
sub-lattices. Fitting models and visualization software will be prepared, taking into
account the magnetic space-group and general symmetries of the crystalline films, which
will allow for the quantitative interpretation of the anisotropy and correspondingly the
strength of the various spin-orbit and exchange interactions in the system. The
information gained will be critical for the development of prototype magnetic devices
working in the high-GHz and low-THz regions.
Figure 1. Top-left to bottom right: spontaneous hall effect loops and their corresponding torque
fits for field applied perpendicular to the film plane (MRG), in-plane rotational scan showing the 4-
th order anisotropy, in-plane and out-of plane field scans and their fits, using a combination of a
torque model and an analytical hysteronic distribution.
0 15 30 45 60 75 90
-1.0
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0.0
0.5
1.0
0 60 120 180 240 300 360-1.0
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0.0
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0 60 120 180 240 300 360
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0.93
0.94
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0.96
0.97
0.98
0.99
-15 -10 -5 0 5 10 15-1.0
-0.5
0.0
0.5
1.0
0 60 120 180 240 300 360-1.0
-0.5
0.0
0.5
1.0
xy/
N xy
()
Data 1 T
Data 2 T
Data 14 T
Fit 1 T
Fit 2 T
Fit 14 Txy/
N xy
()
Data 1 T
Data 2 T
Data 14 T
()
()
xy/
N xy
Data
Fit
Data
Data
Fit
Fit
xy/
N xy
()
xy/
N xy
Data
Data
Fit
Fit
43
69.
Tailoring the nonlinear optical performances of sulphur-based transition metal
dichalcogenide by defect engineering
Supervisor: Jun Wang
Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of
Sciences, Shanghai 201800, China
This project focuses on investigation of the nonlinear optical performances of sulphur-
based transition metal dichalcogenides (TMDs) by defect engineering. We need to
characterize the morphology, structure, and optical properties of the sulphur-based
TMDs before and after defect engineering and investigate the influence of defects on the
nonlinear optical performance of the TMDs using the Z-scan technique with femtosecond
pulses ranging from visible to infrared. The optical nonlinear parameters such as
absorption coefficients, third-order susceptibility and damage threshold need to be
obtained. The defect dependence of the nonlinear optical behaviour should be studied
systematically. The intrinsic mechanisms of the optical nonlinearity are to be clarified.
(See our previous work: Tailoring the nonlinear optical performance of two-dimensional
MoS2 nanofilms via defect engineering. Nanoscale 10, 17924-17932 (2018))
70.
Investigation of the nonlinear refractive index dispersion in layered transition
metal dichalcogenides
Supervisor: Jun Wang
Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of
Sciences, Shanghai 201800, China
Third-order optical nonlinearity, concerning both nonlinear absorption (NLA) and
nonlinear refraction (NLR), is becoming an important parameter to evaluate the potential
applications of materials in a number of fields, such as integrated optics, optical
switching devices, and optical signal processing. Therefore, the exploitation of materials
with higher nonlinear refractive index and nonlinear absorption coefficient has great
practical application values. Transition metal dichalcogenides (TMDs) have attracted
tremendous attention owing to their superior nonlinear responses. Our previous work
revealed a dispersion of nonlinear refractive index in the WS2 films that translated from
44
positive in the monolayer to negative in bulk material. However, the values are not
identical with the calculation results via the Kramers-kronig (KK) relation. This project will
focus on the study of NLA and NLR properties in TMD films. We need to characterize
the morphology, structure and optical properties of TMDs. Investigate the layer number
and excitation wavelength dependence of the NLA and NLR performances of mono- and
few-layer TMDs (like WS2 and MoS2, etc.) using the Z-scan technique with femtosecond
pulses ranging from visible to infrared. The intrinsic mechanisms of NLR dispersion are
to be clarified.
(See our previous work: Dispersion of nonlinear refractive index in layered WS2 and
WSe2 semiconductor films induced by two-photon absorption. Opt. Lett. 41(17), 3937
(2016))
71.
Stimulated Brillouin scattering in bulk polymer composites and polymer fibers
containing 2D nanoparticles
Supervisor: Jun Wang
Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of
Sciences, Shanghai 201800, China
The goal is to perform a Stimulated Brillouin scattering (SBS) intensity control in optical
fibres with the help of dispersed nonlinear absorbing 2D nanoparticles. The particles
deemed perspective to study are graphene, tellurium, -antimonene, hexagonal boron
nitride and others, one of them can be chosen for one project. The project comprises
polymer composite preparation, its characterization with absorption and Raman spectra
and measurements of SBS with 1064 nm nanosecond laser. The project strategy will be,
at first, to disperse nanoparticles in a polymer composition cautious to fit immersion
composition to minimize the light scattering in it. At second, to obtain SBS and energy
measurements in pure polymer composition and in the 2D-doped composite to
determine the Brillouin gain factor change. The third step will be to introduce the polymer
composite into a capillary to simulate optical fibre and obtain SBS in it, making the same
comparative energy measurements.
The goal will be achieved when SBS control will be demonstrated in the fibre geometry
and its intensity characteristic will be measured depending on the nanoparticle
concentration. The project is the development of work published in
https://doi.org/10.1364/OE.26.034346 and https://doi.org/10.1364/OE.27.011029.
45
72.
Saturable absorption of 2D nanoparticles in 1D photonic crystal
Supervisor: Jun Wang
Location: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of
Sciences, Shanghai 201800, China
The goal is to construct a saturable absorber based on periodic structure of polymer
layers (blue and red in the figure) containing dispersion of 2D nanoparticles with strong
saturable absorption (SA) behaviour. The absorber is a dielectric mirror with the minimal
transmission at selected wavelengths (photonic crystal bandgaps) enhancing light
electric field at these wavelengths and the SA of the 2D structure.
Perspective 2D material which are graphene, tellurium, -antimonene, black phosphorus
can be chosen to perform the project. The project comprises nanoparticle dispersion
preparation, its characterization with absorption and Raman spectra, preparation of the
multilayer structure and its characterization with absorption spectra and femtosecond Z-
scan at different wavelengths. The project strategy: 1) dissolve polymers having different
refractive indices (PVA and PVK as an example), 2) suspend 2D nanoparticle in one of
the polymer solutions, 3) spin-coat alternating layers on the substrate, 4) characterize
the structure with absorption spectra and AFM profiles, 5) perform Z-scan measurement
of the samples at wavelengths inside the photonic crystal bandgaps. The goal will be
achieved when an enhancement of SA properties of nanostructure will be demonstrated
as compared to the bulk polymer composite film. The project is the development of work
archived in https://arxiv.org/abs/1808.07668
73.
Helium-ion beam for nanofabrication
Supervisor: Hongzhou Zhang
Location: TCD
The precise creation of surface structure is crucial to the future of the nanotechnology.
High resolution Ion beam machining is one of the key enabling methodologies allowing
for the creation of 10nm fine structures [1]. However as the demands for finer structures
begin to approach the maximum capabilities of current machinery alternatives must be
investigated. The Helium-ion Microscope with its sub nm spot size and milling
capabilities shows excellent promise in this area. The milling rate of the HIM is a factor
of a hundred times slower than the commonly used Focused-ion beam system. This low
removal rate allows for more controlled amounts of material to be removed resulting in
finer etching, while beam damage and contamination must be evaluated. In this project,
we will mainly use SRIM (software packages for simulating the transport of ions in matter
[2]) to study the interaction of the ion beam with a range of specimens with an objective
of understanding its capability and limitation in nanoscale fabrication.
References:
Fox, D., et.al. Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer
Helium Ion Beam. Nano Lett 15 (8), 5307 (2015).
46
SRIM: http://www.srim.org/
74.
Understanding the origins of luminescence tuning in ZnO nanostructures via ion
irradiation
Supervisor: Hongzhou Zhang
Location: TCD
ZnO nanostructure is one of the most-intensively-investigated materials in recent years
because of its extraordinary properties and remarkable potential applications. The
ultimate goal of this project is to tune the photoemission of ZnO nanowires via site-
specific defect and strain engineering utilising focused-ion beam irradiation. The He+
beam induced surface sputtering, lattice damage and strain field will adjust the
dimensions, surface roughness, and refractive index of the ZnO sample. Our preliminary
experimental results show that the position of the wavelengths of the Whispering Gallery
Mode (WGM) in a ZnO microrod [1] exhibit a ion-dose-dependent shift, while the
success of effective tuning relies on the knowledge of localised defect generation and
the origin of the light emission. To gain such knowledge, this summer project will focus
on understanding the shift of the WGMs. The student will develop a COMSOL model [1]
and simulate the light emission of ZnO microrod to identify the defects that are
responsible for the luminescence tuning and hence optimise the strategy of ion
irradiation. This project also involves cutting-edge charged-particle microscopy, e.g. Cs-
correct scanning transmission electron microscopy (STEM), nanobeam diffraction,
electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and helium ion
microscopy (HIM). The student will have the opportunity to gain knowledge and skills in
advanced materials characterisation.
References:
Czekalla, C., et al., Whispering gallery modes in zinc oxide micro- and nanowires. Physica Status
Solidi B-Basic Solid State Physics, 2010. 247(6): p. 1282-1293.
COMSOL: https://www.comsol.com/
75.
Photoelectron spectroscopy elucidates energy-level alignment at functional
organic-inorganic interfaces
Supervisor: Steffen Duhm
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website: http://funsom.suda.edu.cn/funsomen/c4/0c/c3002a50188/page.htm
76.
Fabrication of perovskite micro/nano crystals for the high-performance
optoelectronic devices
Supervisor: Jiansheng Jie
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website: http://www.jjs-group.com/
47
77.
Nanoelectronic characterization of layered dielectrics using conductive atomic
force microscopy.
Supervisor: Mario Lanza
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website: http://lanzalab.com
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Design and Synthesis of Emerging Perovskite Nanocrystals for Photovoltaic
Application
Supervisor: Wanli Ma
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website: http://funsom.suda.edu.cn/funsomen/c3/fc/c3002a50172/page.htm
79
Self-powered sensing system based on triboelectric nanogenerator
Supervisor: Xuhui Sun
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website: http://funsom.suda.edu.cn/funsomen/c4/a0/c3002a50336/page.htm
80
Synergistic Device Architecture for Highly-Efficient Flexible Perovskite Light-
Emitting Diodes
Supervisor: Jianxin Tang
Location: Functional Nano & Soft Materials Laboratory (FUNSOM) at Soochow
University, China
More details can be obtained once a student expresses an interest.
Supervisor Website http://funsom.suda.edu.cn/funsomen/c3/f7/c3002a50167/page.htm