The major objective of this thesis was to evaluate electrically the damage caused by a low energy (< 4keV) Ar⁺ bombardment on n-GaAs(100) surfaces. Electrical measurements were performed on Schottlky diodes formed on the virgin and the ion-etched surfaces. The l-V measurements show deterioration of diode parameters by ion etching. The ion etched diodes have a strong component of surface leakage current. The high frequency capacitance of ion-etched diodes is less than that of the virgin diodes. The low frequency capacitance of ion-etched diodes was found to be frequency dispersive. The extent of frequency dispersion diminishes at low temperatures and at low reverse biases. Virgin diode capacitance, on the other hand, was found to be independent of frequency. The electrical characteristics of ion-etched diodes are explained by means of an amorphous layer and a donor-like damaged layer formed as a result of ion etching. The depth of the top amorphous layer increases with etch energy. The damaged layer containing the ion induced traps superimposes over the amorphous layer and extends deep into the bulk semi-conductor. The density of such traps is very bias sensitive and also temperature dependent. A possible equivalent circuit model for the ion-etched material is proposed. Low temperature isochronal annealing (< 450°C, 10mins.) was not found effective in causing complete recovery of the ion-damaged surface. / Master of Science

No description available.

Thesis: M.S., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1978 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Materials Science and Engineering

The bombardment of surfaces by ions can lead to the spontaneous formation of nano-structures. Depending on the irradiation conditions, smoothening or roughening mechanisms can be the leading order in pattern formation which can result in the creation of dots, ripples or ultra-smoothening effects. Because ion bombardment is already ubiquitous in industrial settings, and is relatively inexpensive compared to other surface processing techniques, self-organized patterning by ion bombardment could enable a simple, economical means of inducing well-defined nanoscale structures in a variety of settings. Understanding the fundamental behavior of surfaces during ion bombardment is therefore a vital goal; however, a complete understanding of physical processes governing surface pattern formation has not been reached yet. In order to address this issue, my thesis research has utilized three primary approaches. First, I have done real-time non-coherent X-ray scattering experiments at Cornell High Energy Synchrotron Source (CHESS) for studying kinetics of structure formation of Silicon undergoing Ar⁺ bombardment over a range of wavenumbers 4-5 times larger than has previously been obtained. From our data, we were able to extract values of the angle-dependent thickness of the amorphous layer that forms under ion bombardment, the ion-enhanced fluidity within that film, the magnitude of the stress being generated by the ion beam, and the strength of prompt atomic displacement mechanisms. Second, to further deepen our knowledge of surface dynamics, I have performed coherent X-ray studies of Ar⁺ bombardment of SiO₂ at the Advanced Photon Source (APS) for investigating the dynamics more profoundly than can be done with traditional time-resolved experiments. When using a focused ion beam, an inhomogeneous ripple motion was generated, this phenomenon reflected as an oscillatory behavior in the two-time and corresponding g₂(t) correlation functions. By fitting the oscillations in the g₂(t) correlation function, we have determined the surface ripple velocity on SiO₂ driven by Ar⁺ sputter erosion. Finally, to support the results of coherent X-ray experiments, simulations of growth models such as linear Kuramoto-Sivashinsky (KS) and Kardar-Parisi-Zhang (KPZ) have been carried out in order to compare the simulated temporal correlation functions of the scattered intensity with those obtained from the coherent x-ray scattering experiments.

by Lee, Chun-Sing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 98-105). / Abstracts in English and Chinese. / Acknowledgements --- p.2 / Abstract --- p.3 / Table of Contents --- p.7 / List of Figures --- p.10 / List of Tables --- p.13 / Chapter Chapter 1 --- Introduction --- p.14 / Chapter 1.1. --- Ion implantation --- p.14 / Chapter 1.2. --- Scope of the thesis --- p.15 / Chapter Chapter 2 --- Background Theory --- p.17 / Chapter 2.1. --- Ion stopping --- p.17 / Chapter 2.2. --- The energy-loss process --- p.17 / Chapter 2.3. --- Kinematics of binary elastic collision --- p.20 / Chapter 2.4. --- Nuclear and electronic stopping --- p.21 / Chapter 2.5. --- Radiation Damage --- p.22 / Chapter 2.6. --- Spikes --- p.24 / Chapter 2.7. --- Topography of ion bombarded surface --- p.26 / Chapter Chapter 3 --- Equipment Reviews --- p.31 / Chapter 3.1. --- Metal Vapour Vacuum Arc Ion Source Implanter --- p.31 / Chapter 3.2. --- Atomic Force Microscopy --- p.34 / Chapter 3.3. --- Rutherford Backscattering Spectrometry --- p.37 / Chapter 3.4. --- X-ray Diffraction --- p.40 / Chapter Chapter 4 --- Study of Ion Beam Implanted Germanium by Atomic Force Microscopy and Rutherford Backscattering Spectrometry --- p.43 / Chapter 4.1. --- Introduction --- p.43 / Chapter 4.2. --- Experiments --- p.45 / Chapter 4.3. --- Results and discussion --- p.47 / Chapter 4.3.1. --- AFM --- p.47 / Chapter 4.3.2. --- RBS and ion channeling --- p.64 / Chapter 4.4. --- Conclusions --- p.71 / Chapter Chapter 5 --- Ion Beam Synthesised Cobalt Germanide Alloy by Metal Vapour Vacuum Arc Implantation --- p.73 / Chapter 5.1. --- Introduction --- p.73 / Chapter 5.2. --- Experiments --- p.74 / Chapter 5.3. --- Results and discussion --- p.74 / Chapter 5.3.1. --- XRD --- p.74 / Chapter 5.3.2. --- AFM --- p.78 / Chapter 5.3.3. --- RBS and ion channeling --- p.82 / Chapter 5.4. --- Conclusions --- p.87 / Chapter Chapter 6 --- Tip Artifacts in Atomic Force Microscope Imaging of Ion Bombarded Nanostructures on Germanium Surfaces --- p.89 / Chapter 6.1. --- Introduction --- p.89 / Chapter 6.2. --- Experiments --- p.90 / Chapter 6.3. --- Results and discussion --- p.90 / Chapter 6.4. --- Conclusions --- p.95 / Chapter Chapter 7 --- Conclusions --- p.96 / Bibliography --- p.98 / Publications --- p.105

"May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Yuen Yung Hui. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / Yuen Yung Hui.

Drift time ion mobility spectrometry (DTIMS) is a rapid post ionization gas-phase separation technique that distinguishes between compounds based on their differences in reduced mass, charge and collisional cross-section while under a weak, time-invariant electric field. Standalone DTIMS is currently employed throughout the world for the detection of explosives, drugs and chemical-warfare agents. The coupling of IMS to MS (IM-MS) has enabled the performance of time-nested multidimensional separations with high sample throughput and enhanced peak capacity, allowing for the separation of ions not only based on their mass/charge (m/z) ratios, but also their shape. This allows for the elucidation of valuable structural information that can be utilized for determining gas phase ion conformation and differentiation between closely related ionic species. Over the past decade, these advances have transformed IM-MS applications and instrumental designs into one of the most rapidly growing areas of mass spectrometry. The work presented in this thesis is aimed at the development and subsequent characterization of a novel high-resolution resistive-glass atmospheric pressure DTIMS, and the application of this prototype DTIMS to the detection of environmentally relevant compounds. A review of the different types of ion mobility spectrometers, their principles of operation, and the advantages and disadvantages of each type are presented in Chapter 1. Chapter 2 describes the design and development of our prototype resistive glass DTIMS. A detailed description of the IMS hardware, including the ion sources, custom-built control computer, pulsing electronics, data acquisition system, and the timing schemes developed to operate the instrument in standalone DTIMS, multiplexed DTIMS, and IM-MS mode, are presented. Chapter 3 presents an initial characterization of the performance of a prototype resistive glass DTIMS under a wide range of instrumental parameters and also characterizes the radial ion distribution of the ions in the drift region of the spectrometer. Chapter 4 addresses the lack of sensitivity in DTIMS and explores ion trapping and multiplexing methods, introduces the principles of multiplexing and describes an extended multiplexing approach that encompasses arbitrary binary ion injection waveforms with variable duty cycles. Chapter 5 presents a detailed theoretical and experimental study of the separation power of our DTIMS and presents an evaluation of the field homogeneity and the performance of the ion gate.

The work described in this thesis is an analysis of the Plasma Source Ion Implantation (PSII) process. A metal target is placed within a plasma, and pulsed to a high negative potential (10 - 50 kV). The electrons in the plasma close to the target are then repelled very rapidly, leaving an area of uniform positive charge. This causes an electric field to be set up between the plasma and the metal target. The ions close to the target are then accelerated towards the target by the electric field. The ions reach the target at high velocities, and implant deeply into the metal (-5 x 10-8 m), and form nitrides, which pin dislocations within the metal's atomic structure. The strength of the metal is therefore increased, and other properties such as the corrosion resistance of the metal are also improved. Metals that have undergone the PSII process have widely diverse applications. For example, in the motor industry, ion implanted metal punches last much longer than nitrided punches, while in the medical industry ion implanted metals are used for artificial limbs. A combination of a number of different analytic, numerical and simulation models are used to describe the PSII process, including the plasma behaviour and final nitrogen implantation profile in the metal target after the application of the voltage pulse. In all cases, a specific attempt has been made to realistically describe as closely as possible, the actual experimental arrangement at the University of Natal. For example: a waveform with a fast rise time, short plateau and exponential decay was used; the nitrogen plasma was more realistically described by a two species fluid to account for the measured N+, N; mix; and finally, the actual atomic composition for 304 stainless steel was used in the TAMIX particle simulation. This work thus models the whole PSII process, and could form the basis of future studies for the optimisation of the process. / Thesis (M.Sc.)-University of Natal, 1993.

Graphene is a promising material for many technological applications. To realize these applications, new fabrication techniques that allow precise control of the physical properties, as well as large scale integration between single devices are needed. In this work, a series of studies are performed in order to develop graphene based devices. First, using MD simulations we study the effects of irradiating graphene with a carbon ion atom at several positions and energies from 0.1 eV to 100 keV. The simulations show four types of processes adsorption, reflection, transmission, and vacancy formation. At energies below 10 eV the dominant process is reflection, between 10 and 100 eV is adsorption, and between 100 eV and 100 keV the dominant process is transmission. Vacancy formation is a low rate process that takes place at energies above 30 eV. Three types of defects were found: adatom, single vacancy, and 5-8-5 defect formed from a double vacancy defect. Also a bottom-up fabrication method is studied, in this method, the controlled folding of graphene structures, driven by molecular interactions with water nanodroplets, is analyzed considering the interactions with substrates such as SiO2, HMDS and IPA on SiO2. When the graphene is supported on SiO2, the attraction between graphene and the substrate prevents graphene from folding but if the substrate has HMDS or IPA, the interaction between graphene and the substrate is weak, and depending on the geometry of the graphene structure, folding is possible. Finally, to evaluate the characteristics of graphene based devices, we model the vibrational bending modes of graphene ribbons with different dimensions. The resonant frequencies of the ribbons and relations between the size of the ribbon and their resonant frequencies are calculated. The interaction of a graphene vibronic device with water and IPA molecules are simulated and demonstrate that this device can be used as a sensitive vibronic molecular sensor that is able to distinguish the chemical nature of the detected molecule. Also, the electrical properties of the graphene vibronic with armchair and zigzag border are calculated; the latter has the potential to generate THz electrical signals as demonstrated in this work.