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Student Projects Post-Graduate Projects Project: Chalcogenide glasses as phase-change materials for solid-state optical and memory applications Supervisor: Mark Ridgway Description: Chalcogenide materials are of tremendous importance for optical data storage and improved nonvolatile memory devices as they can be readily switched between a high resistance / non-reflective amorphous state and a low resistance / reflective crystalline state. This phenomenon is now exploited in rewritable compact discs (CD-RW) and digital versatile discs (DVD-RW) even though the structural changes behind the transformation are yet to be clarified. For this project, we propose a study of the technologically relevant Ge-As-Se and Ge-Sb-Te alloys in both amorphous and crystalline forms, including the application of ion irradiation for the introduction of defects and / or dopants to controllably modify the phase transformation. X-ray absorption spectroscopy (XAS) will be used to characterise the structural and vibrational properties of both phases and results will be correlated with optical measurements performed in conjunction with the ANU Laser Physics Centre. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for XAS measurements.   Project: Charge storage and dissipation in dielectrics containing nanocrystals Supervisor: Robert G Elliman Description: Growth in the use of portable electronic devices and embedded electronic systems has resulted in an increased demand for low-power, high-density non-volatile memory (NVM). However, the scaling of these devices to smaller dimensions is approaching fundamental physical limits and future advances will depend on the use of new materials and greater understanding of limiting processes. A new technique in which the memory is encoded by charged nanocrystals embedded in a high-dielectric constant (high-k) insulating film holds great promise in this regard. This project aims to understand the physical processes underpinning this approach.   Project: Charge transport and trapping in high-k dielectric thin-films Supervisor: Robert G Elliman Description: Dielectric materials with high dielectric constant (high-k dielectrics) are needed as replacements for SiO2 in future integrated circuits, including low-power, high-density non-volatile memory (NVM) devices. Critical to such applications is an understanding of charge transport and trapping in such materials. This includes an understanding of transport through extremely thin films, such as direct and field-induced (Fowler-Nordheim (FN)) tunnelling and a range of trap-assisted tunnelling processes, as well as field-induced breakdown of such films. This project will examine such processes in an important class of high-k dielectrics based on hafnium oxide its alloys.   Project: Dopant-defect complexes in semiconductors studied with x-ray absorption spectroscopy Supervisor: Mark Ridgway Description: Using the synchrotron-radiation based technique of extended x-ray absorption fine structure (EXAFS) spectroscopy, the atomic-scale environment of dopants in semiconductors can be determined and the causes of electrical inactivation can be deduced. This project combines a variety of semiconductor processing methods including ion implantation, thermal annealing and chemical etching with the characterisation techniques of EXAFS, Rutherford backscattering and electrical measurements to study dopants in Si and Ge. Examples include As and Sb clustering and precipitation following ion implantation and thermally-induced solid-phase epitaxy. The combination of very-high photon flux and advanced fluorescence detection at the state-of-the-art EXAFS beamline of the Australian Synchrotron is ideally suited for such a study and the student will make extensive use of this new national facility.   Project: Growth and Characterisation of Semiconductor Nanostructures Supervisor: Chennupati Jagadish Description: The synthesis and study of materials having at least two dimensions with nanometer scale size (i.e. so called 1D materials) such as nanotubes and nanowires has attracted intense interest due to their potential applications in electronics and photonics. Semiconductor nanowires have drawn considerable interest due to the potential of using conventional processes such as doping, junction formation, growth of heterostructures and superlattices during growth of nanowires. We are growing these nanowires by the so-called vapor-liquid-solid process in the Metalorganic Chemical Vapour Deposition (MOCVD) reactor. In addition we are also using ordered alumina porous membranes to create nano scale ordered gold patterns as nucleation sites for the growth of nanowires that could be used for fabrication of 3-D photonic crystals. On a separate but parallel study, we are investigating the growth of inverted opal III-V structures by MOCVD where the starting template of regularly stacked silica spheres are being infiltrated by III-V materials.   Project: Growth of Novel Semiconductor Materials Supervisor: Chennupati Jagadish Description: Novel (In,Ga)SbN compound semiconductors are of great interest for a wide range of device applications in the mid- to long-wavelength infrared spectral region. Due to the huge negative bandgap bowing effect from N, the emission/absorption wavelength of InGaSb and InSb can respectively be extended to mid- and long-wavelength infrared spectral range by adding a few percent of N. The wavelength can be fine-tuned by controlling the N content. This project aims to develop such a novel (In,Ga)SbN material system for a new generation of mid- to long-wavelength infrared optoelectronic devices using MOCVD that could lead to the development of advanced applications in thermal imaging, environmental monitoring, biological and chemical sensing, disease diagnosis and treatments.   Project: Integrated Optoelectronic Devices Supervisor: Chennupati Jagadish Description: Monolithic integration of optoelectronic devices is desirable for practical applications, as this would lead to low loss, high speed modules and operating at lower currents. To achieve this, the in-plane band-gap tuning is required. Our research in this area involves the investigation of three different techniques to achieve the lateral band-gap control: (i) ion implantation induced intermixing (ii) impurity free induced disordering (using a dielectric cap) (iii) selective area epitaxy (of quantum dots)   Project: Ion-irradiation-induced porosity in elemental and compound semiconductors Supervisor: Mark Ridgway Description: Energetic ions interact with a solid through elastic and inelastic processes. The former can result in the ballistic displacement of substrate atoms while the latter can yield excitation and ionisation of substrate atoms. The relative magnitude of these two energy loss mechanisms is governed by the ion velocity and the atomic numbers of the incident ion and substrate atom. We have previously investigated porosity induced in semiconductors by low energy ions (elastic processes) including GaSb and InSb. (For example, see Kluth et al., Appl.Phys.Lett. 86 (2005) 131920.) Recently, we have observed porosity in amorphous Ge induced by very high energy ions (inelastic processes). For this project, we propose a study of irradiation-induced porosity via both elastic and inelastic interactions utilising a variety of analytical techniques including x-ray absorption spectroscopy (XAS) to measure the inter-atomic distance distributions of substrate atoms and identify the defect configurations that trigger porous layer formation plus scanning and transmission electron microscopies coupled with small angle x-ray scattering (SAXS) to quantify the evolution of porosity. Furthermore, positron annihilation spectroscopy will be performed in conjunction with the ANU Centre for Antimatter-Matter Studies to characterise vacancy-related defect configurations associated with the continuous-to-porous transformation. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for XAS and SAXS measurements.   Project: Metal nanoparticle formation by ion implantation and elongation by swift heavy-ion irradiation Supervisor: Mark Ridgway Description: Metal nanoparticles embedded in a silica matrix have a variety of optical device applications and are readily formed by ion implantation and thermal annealing. Subsequent to formation, spherical nanoparticles can be transformed to rod-like structures via swift heavy-ion irradiation yielding nanorods aligned with the incident ion beam direction. While we have previously studied the formation of metal nanoparticles including Co, Cu, Pt and Au (for example, see Giulian et al., Appl.Phys.Lett. 91 (2007) 93115), we now seek to include metals of lower melting temperature such as Sn and Ag. Swift heavy-ion irradiation of such nanoparticles should elucidate the shape transformation mechanism. We will use x-ray absorption spectroscopy (XAS) to measure the inter-atomic distance distribution of metal nanoparticle atoms and identify finite-size effects including a capillary-pressure-governed bond-length contraction. Transmission electron microscopy and small angle x-ray scattering (SAXS) measurements will be performed to determine the distributions of nanoparticle dimensions for insight on the science driving this novel irradiation-induced change in shape. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for XAS and SAXS measurements.   Project: Probing liquid- and solid-state phase changes in amorphous semiconductors with swift heavy-ion irrad Supervisor: Mark Ridgway Description: We propose a novel study of amorphous semiconductors to probe fundamental properties such as the glass transition as achieved through a unique combination of processing and characterisation techniques. Glass formation is considered the resolidification of an undercooled melt in the absence of recrystallisation. Upon cooling through the glass transition temperature, the disordered structure of the liquid is frozen into the solid state yielding an isotropic amorphous solid with a density comparable to the liquid from which it was formed. Historically, amorphous Si was not considered a glass given the absence of a low density liquid Si phase linking the well known low density amorphous Si solid and the high density liquid Si melt. Though simulations predicted a first-order liquid-liquid phase transition from high to low density liquid Si, only recently has a glass transition in amorphous Si been definitively proven through the application of swift heavy-ion irradiation to produce a molten ion track. For this project, we seek to identify comparable phase transformations in Ge and the compound semiconductors, determine glass transition temperatures and assess the validity of theoretical predictions. Swift heavy-ion irradiations will be performed by the student at both the ANU and GSI (Germany), the latter in conjunction with Germany collaborators.   Project: Quantum Dot Optoelectronic Devices Supervisor: Chennupati Jagadish Description: Self-assembled semiconductor quantum dots (QDs) grown in the Stranski-Krastanow growth mode have found application in a multitude of optoelectronic devices such as lasers, modulators and photodetectors. Improved characteristics are predicted for these devices due to the unique electrical and optical properties provided by the quantum dots as a result of their 3-dimensional carrier confinement and delta function like density of states. Research in the areas of QD lasers involves the growth of In(Ga)As(N) QDs laser structures on GaAs or InP substrates and investigating the properties of the devices such as gain saturation, the built-in electric field and the strain effects arising from the QDs. The concept of using the intersubband absorption of infrared radiation has led to the development of quantum well infrared photodetectors (QWIPs) in the past decades. Quantum dot infrared photodetectors (QDIPs) are expected to show improved performance over their quantum well counterpart in detecting infrared signal due to the localized states in quantum dots and they respond to normal incidence photoexcitation. We fabricate and characterize QDIP devices grown by MOCVD and also investigate the various schemes that can be used to improve device performance and tunability (such as dots-in-a-well structure and intermixing).   Project: Rare-earth doping and waveguiding in HfO2 and its alloys Supervisor: Robert G Elliman Description: Hafnium oxide is of great interest as a replacement for silicon dioxide in microelectronic devices due to its high dielectric constant (high-k). It is also of interest for optical and photonic applications due to its high refractive index (n > 2) and low optical loss. These properties make hafnium oxide and its alloys potential candidates for the fabrication of integrated planar waveguide devices or structures that combine electronic and photonic functionality on a single chip. This study will examine rare-earth doping of HfO2 films as a means of making optically active photonic structures, including waveguides.   Project: Self-assembled growth and doping of optically active silica nanowires Supervisor: Robert G Elliman Description: There has been an explosion of interest in the synthesis, structure, properties and applications of nanostructures in recent years. This stems from the fact that materials confined in one or more dimension can exhibit novel properties as well as providing the basis for new devices and structures. We have recently been exploring the optical properties of self-assembled silica nanowires grown via a vapour-liquid-solid mechanism and doped with erbium. (Er is a particularly important dopant for many telecommunication-based applications as it emits light at 1.5m, the wavelength of minimum loss in silica-based optical fibres.) This project builds on our preliminary experiments to understand the synthesis, structure, properties and application of these optically active silica nanowires.   Project: Semiconductor Photonic Crystals Supervisor: Chennupati Jagadish Description: Photonic crystals are poised to be the dominant driving force behind the technical innovation of new optoelectronic devices due to their ability to guide and control light propagation. By controlling their feature size and periodicity, they may be used as notch filters where their transmission peaks can be tuned. Couple this to a quantum dot infrared photodetector would not only enhance the detector’s performance but the device will now detect a narrow band around the desired frequency. This project aims to integrate these two components to achieve multi-colour detectivity.   Project: Semiconductor THz Emitters and Detectors Supervisor: Chennupati Jagadish Description: The generation and detection of THz radiation using semiconductors depend strongly on the material from which the device is fabricated. Material dependent carrier trapping and recombination times play an essential role in photoconductive receiver device performance. Specifically, long carrier lifetimes will permit the reception of large amounts of noise and short carrier lifetimes will reduce the signal level and accuracy. The use of ion implantation to modify the material properties (such as the carrier trapping times) of the semiconductors are investigated. This project is in collaboration with Oxford University   Project: Soft x-ray absorption spectroscopy of amorphised semiconductors Supervisor: Mark Ridgway Description: We seek to use soft x-ray absorption spectroscopy (XAS) to complement previous studies of amorphised semiconductors in the hard x-ray range to elucidate the structural and vibrational properties of these technologically relevant materials. For example, while we have quantified the fraction of In-In homopolar bonding in amorphous InP (see Schnohr et al., Phys.Rev. B 77 (2008) 073204), P-P bonding has thus far not been accessible. Similarly, amorphous Si, SiC, SixGe1-x and ZnO remain to be probed. We will utilise the Australian Synchrotron (Melbourne) for XAS measurements in both the soft and hard x-ray regimes to study the formation, relaxation and vibration of the amorphous phase. The student will gain experience with a variety of semiconductor processing techniques including deposition methods and ion implantation plus additional characterisation techniques beyond XAS including transmission electron microscopy and Raman spectroscopy.   Project: Structural investigation of latent ion tracks in semiconductors and insulators Supervisor: Patrick Kluth Description: Irradiation of a solid with very high energy ions can leave a trail of permanent damage along the ion path, a so-called latent track. The formation of such tracks is governed by the interaction of the projectile ions with the target electrons when the electronic energy deposition exceeds a critical value. Ion tracks can be observed in various crystalline and amorphous materials including semiconductors, insulators and metals and are of both fundamental and technological interest with a potential use in nanofabrication/nanoscale material modification. Although their formation was first observed nearly five decades ago, the study of the damage profile within isolated tracks still remains a challenge given their small dimensions of only a few nanometers in diameter. We have recently performed the first successful measurements of latent ion tracks in SiO2 using synchrotron based small-angle x-ray scattering (SAXS) experiments. These reveal a previously unresolved fine structure in the track radial density distribution. The PhD candidate will utilize this method to systematically study ion-track properties in a variety of materials with the aim of verifying the underlying mechanism(s) and the validity of existing models for track formation. This will involve a further development of the SAXS experimental protocol including sample preparation, data analysis and modeling. SAXS experiments will be carried out at synchrotron facilities overseas as well as the new Australian synchrotron. High energy ion irradiation will be carried out on-site at the ANU heavy ion accelerator facility. Specific tasks involve semiconductor materials processing and characterization methods, including ion implantation and irradiation, small angle x-ray scattering, Rutherford backscattering spectroscopy and transmission electron microscopy. Requirements: Background or interest in materials science/solid-state physics, semiconductor materials processing and characterization, and synchrotron-based techniques.   Project: Switching mechanisms in nonvolatile resistive memory using high-k dielectrics Supervisor: Robert G Elliman Description: Reversible resistivity changes can be induced in thin metal oxides by the application of an electric field and control of the current density flowing through the film. This switching behaviour has a great promise for nonvolatile memory applications but the mechanisms underpinning the resistivity changes remain speculative. This project will examine these mechanisms in high-k dielectrics based on hafnium oxide and study two new methods for controlling the switching behaviour.   Project: ZnO for next generation UV/visible Optoelectronics Supervisor: Chennupati Jagadish Description: Zinc oxide is a future material which is very attractive for a range of optoelectronic devices due to its wide band gap of 3.4 eV and large exciton binding energy of 60 meV at room temperature. To be able to fabricate devices, a p-n junction is usually required. However for ZnO, p-type doping is still an unresolved issue. Ion implantation is a very well established technique to selectively dope semiconductor layers. However for this technique to be successful we need to understand damage accumulation, recrystallization processes and thermal stability of ion-implanted ZnO. A new pulsed laser deposition system will be used to grow ZnO epitaxial layers, quantum wells, p-type doped layers to explore this material system for optoelectronic devices operating in the visible and UV region of the electromagnetic spectrum.   Honours Projects Project: Growth and advanced characterisation of embedded GaAs nanoparticles Supervisor: Leandro Langie Araujo Description: Unlike bulk crystalline or amorphous semiconductors, semiconductor nanocrystals (NCs) exhibit quantum confinement effects that lead to light emission and carrier multiplication, making them highly suited for the development of new technological devices. Such effects are intrinsically linked to the high surface-to-volume ratio characteristic of nanoscale structures and thus the properties of semiconductor NCs are highly dependent on their composition, shape, size and surface termination. Such contributions must be evaluated in detail to achieve an insightful understanding of their effects on the quantum confinement features of the NCs and thus maximize their efficiency in a variety of applications. This project aims at determining, at the atomic level, the structural, thermal and vibrational properties of Gallium arsenide (GaAs) NCs produced in SiO2 films by ion implantation. GaAs NCs are chosen since they are promising candidates for making improved microwave frequency integrated circuits (MMICs), infrared light-emitting diodes and solar cells, for example. Carrying out this project will involve performing: - Ion implantation of molecular GaAs- ions into 500 nm SiO2 layers to form the NCs (at the ANU) - Transmission electron microscopy measurements to verify the NCs morphology (at the ANU) - Raman spectroscopy measurements to confirm the NCs crystallinity degree and the presence of quantum confinement effects (at Geoscience Australia) - X-ray absorption spectroscopy measurements to determine the structural, thermal and vibrational properties of GaAs NCs at the atomic level (at the ANBF - Photon Factory synchrotron facility in Japan)   Project: Chalcogenide glasses as phase-change materials for solid-state optical and memory applications Supervisor: Mark Ridgway Description: Chalcogenide materials are of tremendous importance for optical data storage and improved nonvolatile memory devices as they can be readily switched between a high resistance / non-reflective amorphous state and a low resistance / reflective crystalline state. This phenomenon is now exploited in rewritable compact discs (CD-RW) and digital versatile discs (DVD-RW) even though the structural changes behind the transformation are yet to be clarified. For this project, we propose a study of the technologically relevant Ge-As-Se alloys in both amorphous and crystalline forms. X-ray absorption spectroscopy (XAS) will be used to characterise the structural and vibrational properties of both phases and results will be correlated with optical measurements performed in conjunction with the ANU Laser Physics Centre. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for XAS measurements.   Project: Ion implantation in silicon carbide Supervisor: Jennifer Wong-Leung Description: Silicon carbide is the semiconductor of choice for devices operating at high power, high frequency and high temperature. Ion implantation has been a real success story in silicon microelectronics and currently 15 out of 100 processing steps leading to the silicon chip fabrication are ion implantation. Most dopants have comparatively much lower diffusion lengths in silicon carbide than in silicon. Hence, ion implantation is the only viable processing step for the controlled incorporation of dopants both laterally and in depth. Ion implantation results in the formation of defects and defect engineering and control over defect formation are important prerequesites to the application of ion implantation processing to devices. The projects in this area will study defect formation and evolution of these defects in silicon carbide, from point defects to extended defects. Suitable characterisation techniques will include electrical characterisation of point defects (deep level transient spectroscopy) and structural characterisation of extended defects (transmission electron microscopy).   Project: Ion Irradiation effects on GaSb Supervisor: Patrick Kluth Description: GaSb is a semiconductor suitable for fabricating high-frequency electronic and optoelectronic devices. Ion implantation, commonly used for introduction of electrically-active impurities (“doping”) in semiconductor materials, can lead to the damage/amorphization of such materials. In addition appropriate implant conditions will render GaSb porous leading to fascinating network structures and surface features. Such structures were observed after irradiation with ions of keV energies where the ions elastically displace substrate atoms, so called “ballistic interactions”. At very high ion irradiation energies (tens of MeV) the ballistic processes become negligible, however, large amounts of energy are deposited due to inelastic interactions of the incoming ion with the electrons of the material, so called “electronic interactions”. This project investigates effects of ion irradiation on the morphology and structure of GaSb at both energy regimes with the aim to identify the underlying mechanism(s) of the crystalline to amorphous/porous transformation. In particular the effect of high energy irradiation has not yet been studied in detail for GaSb. The project will include a variety of processing and characterisation techniques common to the semiconductor industry and participation in X-ray absorption spectroscopy measurements at the newly opened Australian Synchrotron in Melbourne. The project will include: Ion irradiation (keV – range) to amorphise/induce porosity into GaSb (ANU), ion irradiation (MeV - range) of crystalline/amorphous/porous GaSb (at ANU), scanning and transmission electron microscopy to characterise changes in the topology of the material structure (at ANU), rutherford backscattering spectroscopy to measure the damage profile in the GaSb (at ANU), X-ray absorption spectroscopy to measure the evolution of the inter-atomic distance distribution within the irradiated GaSb (at the Australian Synchrotron, Melbourne)   Project: Ion-irradiation-induced porosity in amorphous Ge Supervisor: Mark Ridgway Description: Energetic ions interact with a solid through elastic and inelastic processes. The former can result in the ballistic displacement of substrate atoms while the latter can yield excitation and ionisation of substrate atoms. The relative magnitude of these two energy loss mechanisms is governed by the ion velocity and the atomic numbers of the incident ion and substrate atom. We have previously investigated porosity induced in semiconductors by low energy ions (elastic processes) including GaSb and InSb. (For example, see Kluth et al., Appl.Phys.Lett. 86 (2005) 131920.) Recently, we have observed porosity in amorphous Ge induced by very high energy ions (inelastic processes). For this project, we propose a study of irradiation-induced porosity in amorphous Ge via both elastic and inelastic interactions utilising a variety of analytical techniques including scanning and transmission electron microscopies coupled with small angle x-ray scattering (SAXS) to quantify the evolution of porosity. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for SAXS measurements.   Project: Metal nanoparticle formation by ion implantation Supervisor: Mark Ridgway Description: Metal nanoparticles embedded in a silica matrix have a variety of optical device applications and are readily formed by ion implantation and thermal annealing. While we have previously studied the formation of metal nanoparticles including Co, Cu, Pt and Au (for example, see Giulian et al., Appl.Phys.Lett. 91 (2007) 93115), we now seek to include metals of lower melting temperature such as Sn and Ag. We will use x-ray absorption spectroscopy (XAS) to measure the inter-atomic distance distribution of metal nanoparticle atoms and identify finite-size effects including a capillary-pressure-governed bond-length contraction. Transmission electron microscopy and small angle x-ray scattering (SAXS) measurements will be performed to determine the distributions of nanoparticle size. The student will gain experience with a variety of semiconductor processing and characterisation techniques and will utilise the Australian Synchrotron (Melbourne) for XAS and SAXS measurements.   Project: Structural characterisation of amorphous/porous Ge using synchrotron-based (and other) methods Supervisor: Leandro Langie Araujo Description: The fabrication of electronic semiconductor devices involves “doping” by ion implantation to introduce electrically-active impurities into crystalline Si, Ge or GaAs substrates. When these wafers are subjected to implantation with ions of keV energies they are rendered amorphous as incident ions elastically displace substrate atoms and long-range crystalline order is progressively destroyed. We have recently observed the transformation of an amorphised Ge layer from continuous to sponge-like or porous when subsequently irradiated with very-high-energy (185 MeV), heavy (197Au) ions. At this energy, the probability of displacing lattice atoms is now negligible and instead the incident ion loses energy through inelastic interactions with substrate electrons. For this project, we will study the transformation as functions of the heavy-ion irradiation energy and dose with the aim of identifying the underlying science and mechanism(s) governing these dramatic changes. Our interest in porous Ge stems from the novel potential applications of this material in micro-electronic devices, micro-electro-mechanical systems (MEMS) and chemical sensors. The student will be introduced to a variety of processing and characterisation techniques common to the semiconductor industry and also participate in X-ray absorption spectroscopy measurements at the newly opened Australian Synchrotron in Melbourne. The project will include: Sputter deposition of crystalline and amorphous Ge (at ANU), Ion implantation (74Ge at 500 keV) to amorphise crystalline Ge (at ANU), Ion irradiation (197Au at 25-200 MeV) to induce porosity in amorphised Ge (at ANU), Scanning and transmission electron microscopy to characterise changes in the topology of the porous structure (at ANU), Surface profilometry to measure swelling of the porous layer (at ANU) and X-ray absorption spectroscopy to measure the evolution of the inter-atomic distance distribution within the porous structure (at the Australian Synchrotron, Melbourne). Background requirements: An interest in materials science or engineering, solid-state physics, semiconductor materials processing, materials characterisation or synchrotron-based analytical methods. More information: Leandro Araujo (leandro.araujo@anu.edu.au / 6125 0358) or Mark Ridgway (mark.ridgway@anu.edu.au / 6125 0519).   Project: Structure and thermal properties of Sn nanocrystals Supervisor: Patrick Kluth Description: Extensive world-wide effort is focused on exploiting the unique properties of nano-materials. Metallic nanocrystals embedded in SiO2 show interesting optical properties with a high potential for application in optical filters, memories or switching devices. The nanocrystals can be fabricated by a process called ion implantation (ions are accelerated in a strong electrical field and subsequently penetrate into a target material of choice). Ion implantation is a well established technique in microelectronic materials engineering. The crystallographic structure of such nanocrystals, which contain only about a few hundred atoms, can differ dramatically from this of corresponding bulk material (containing in the order of 10e23 atoms) and is far from being fully understood. Sn nanocrystals are of particular interest as they show peculiar thermal properties. The project will study structural and thermal aspects of Sn nanocrystals with the aim of verifying and understanding such peculiarities. The student will be introduced into a variety of processing and characterisation techniques common to the semiconductor industry and participate in X-ray absorption spectroscopy at a synchrotron facility in Japan. Particular aspects of the project are: Ion implantation to form Sn nanocrystals in SiO2, Rutherford backscattering spectroscopy to verify the implantation profile, transmission electron microscopy to image the nanocrystals and X-ray absorption spectroscopy to measure the evolution of the inter-atomic distance distribution as a function of measurement temperature. Background requirements: An interest in materials science or engineering, solid-state physics, nanotechnology, materials characterisation and synchrotron-based analytical methods   Project: The development of a molecular ion source for ion irradiation studies Supervisor: Mark Ridgway Description: The Cs-sputter-type sources used on the high-energy ion accelerator in this department readily extract negative monomer ions. The extraction and acceleration of molecular ions, such as C or Au clusters, would extend our capabilities and be advantageous for ion irradiation studies. This project involves a literature search to assess the most appropriate elemental candidates followed by experimental determinations of molecular ion output and abundance following acceleration as a function of the accelerator operating parameters.