Third Year Special Projects - Applied and Plasma Physics 2002

 

1.9 The electrical conductivity of metallic and metal nitride thin films-a problem in percolation theory and nanotechnology

Supervisors: Dr Bee K. Gan, Dr Paul Swift (UTS), Professor David McKenzie, Professor Marcela Bilek

In this project we plan to study the growth properties of thin metallic and metal nitride films, in particular the nature of a film, from being discontinuous island-like when a film is first being deposited, to continuous and optically smooth when a critical thickness is reached. This project is related to the percolation problem, a classical problem in physics. When the connectedness of a conducting medium in an insulating matrix is increased gradually, there is a point at which a pathway can be found through the conducting medium from one side to the other. At this point the percolation threshold is reached, at a critical mass per unit area of material. One method of determining the critical thickness is by measuring the electrical conductivity of thin films in-situ during deposition. The knowledge of the critical thickness is important as it enables us to fabricate ultra-thin multilayer stacks which have applications as wear-resistant hard coatings. A major research initiative is underway in the School to study these systems as an application of Nanotechnology. Various metals and their nitrides will be studied, including Ti, Al, Cr and V. New pulsed cathodic arc sources, one at the University of Sydney and one at the UTS will be employed as the main deposition technique to study and compare the electrical properties of these films. Additional characterisation will then be performed using ellipsometry, scanning electron and atomic force microscopy. Ellipsometry will be used to quantify the nitride colour changes from gold to red that occur when metal nitrides are mixed.

 

1.4 Molecular Dynamics Study of Real Processes-1. Crystallisation of Titanium Nitride

Supervisors: Dr Nigel Marks, Professor David McKenzie and Professor Marcela Bilek

The problem with the study of real processes in molecular dynamics is the timescale problem. Accurate descriptions are possible of the interactions between atoms using the density functional theory of quantum mechanics, for which Walter Kohn was recently awarded a Nobel prize. However, a system containing enough atoms to be interesting can only be described for short times, of the order of a few picoseconds. Some real processes we would like to study such as crystallisation require somewhat longer owing to the need for some relatively rare events to occur. Normally, the quenching of a liquid in a few picoseconds will produce an amorphous or glassy material. For a crystal to form, the quench rate needs to be reduced. We have developed a strategy for modifying the cooling protocol in a liquid quench in such a way that the rare events in crystallisation have the best chance of happening on a short timescale. The project will use the national computing facility, APAC, on which we have been granted time for this work. We will use the strategy on titanium nitride, an important material for commercial applications as a wear resistant coating. Our partner company Sutton Tools is producing titanium nitride as one of the wear resistant coatings in their range.

 

1.5 Molecular Dynamics Study of Real Processes-2 Simulated Deposition of Nano-crystalline Silicon

Supervisors: Dr Nigel Marks, Professor Marcela Bilek, Professor David McKenzie

Magnetron sputtering has been proposed as a low temperature process for depositing silicon nanocrystals onto soft materials such as plastics. If such a process can be developed, it could be used for many applications such as flexible displays and photocopy drums. We have a collaboration with a Korean colleague who has a link with Samsung, the Korean electronics company. This project will use molecular dynamics simulation to explore the factors which control crystal nucleation and epitaxial growth. Epitaxy is the phenomenon whereby one crystal can be used as a substrate for the growth of another. The simulations will explicitly include the relevant physics of the deposition apparatus, and thus will enable a virtual experiment in which the experimental control parameters such as beam energy, voltage bias and substrate temperature are simulation inputs. The project will use the in-house simulation package EDIP which has a good compromise of accuracy and simulation efficiency. The project will generate Quicktime animation video sequences to show what is happening.

 

1.6 The physics of stress generation in thin films - is the thermal spike real?

Supervisors: Mr R.N. Tarrant, Professor M.M. Bilek, Professor D.R. McKenzie

The thermal spike is believed to occur when an energetic atom or ion hits a surface. The thermal spike has been implicated in both the generation and the relief of stress in thin films grown from energetic beams. Stress can be a major problem for applications of thin films and ways of reducing or eliminating it are therefore very important. In this project we will examine one of the key predictions of the thermal spike theory of stress generation, that is that low energy thermal spikes are quickly quenched and freeze in stress, whereas high energy thermal spikes relieve stress by creating a molten volume that quenches slowly enough to relieve stress. We have studied high energy thermal spikes and shown that the stress relieving effect obeys the thermal spike theory in that the stress relief effect is proportional to the volume of thermal spikes created. We will now test quantitative predictions of thermal spike theory by probing the stress created by impacts in the energy region below 1keV where the transition from stress relief to stress generation should occur. The work will be mainly experimental research using newly commissioned equipment in the School for depositing films with energetic impacts. The results will be interpreted using analytic theoretical predictions which may be refined further during the project.

 

1.12 A comparative study of some macro-environmental impacts of conventionally and organically grown food

Supervisors: Manfred Lenzen, Christopher Dey, Applied Physics

Student: Richard Wood

The proposed study aims at quantifying some macro-environmental impacts of organic farming, and comparing the results with those obtained for conventional farming. These environmental impacts are determined in terms of energy consumption, greenhouse gas emissions, land use/disturbance, and water use. Also including some social and economic impacts in terms of employment generated, income generated, and imports.In contrast to existing audit-type assessments of the environmental impact of agriculture (see for example Cederberg and Mattsson 2000), this projects seeks to quantify indirect, off-site effects. Off-site land disturbance occurs for example, through the purchase of agricultural machinery, which requires steel to be made, and iron ore to be mined, which in turn disturbs land. The neglection of off-site effects in life-cycle and environmental impact assessments (LCA, EIA) can lead to serious systematic errors that can be in the order of 50%, and moreover lead to erroneous conclusions in decision-making (Lenzen and Treloar 2002).

 

1.11 Atmospheric pressure plasma processing

Supervisors: Dr Kerrie Balla, Professor David McKenzie, Professor Marcela Bilek , Dr Ian Brown, Lawrence Berkeley Laboratory

The small dimensions, in the sub micron range, obtainable with plasma processing, makes it an invaluable technique in the microelectronics industry, and also for optical and biomedical applications. In industrial applications such as improving corrosion resistance or metal hardness, very large area plasma systems are often required. To avoid the necessity of expensive, large vacuum systems, a new technique of using higher pressure plasmas, ultimately at atmospheric pressure has been proposed. If high deposition and etch rates are possible, room pressure plasma processing would be economical compared to conventional vacuum based processing. There is a scaling law for plasmas, such that the product of gas pressure and plasma dimension equals a constant. So, in order to use atmospheric pressure plasmas, the distance between the electrodes must be around 0.3 mm, instead of the several centimetres or more used at low pressures. Atmospheric pressure reactors can be made on a substrate, and these are called microplanar reactors. We have designed and fabricated a microplanar reactor ready for this project. We hope to use this technique in the future for depositing films by plasma enhanced chemical vapour deposition, (PECVD) beginning with the deposition of amorphous carbon films from methane. In this project we will study the current and voltage characteristics of the microplanar reactor beginning with a helium plasma. Then the deposition rate of carbon films will be studied as a function of applied voltage, gas pressure, and flow rate.

 

1.7 Identification of light photon responsible for the photo-stimulated desorption of gases in vacuum glazing

Supervisors: Dr Nelson Ng and Ms L.C. So

Vacuum glazing consists of two glass sheets separated by vacuum space (0.2 mm) with a leak free seal around the edges. If vacuum glazing is manufactured in a low temperature evacuation and bakeout process (150C), the internal pressure of the device will increase when it is exposed to sunlight. In this project, we will perform a degradation experiment using optical filters to find out the bands of wavelength responsible for optical vacuum degradation in various samples of vacuum glazing. This will be done by covering samples of vacuum glazing with band-pass filters and then exposing them to sunlight. The experiment will involve measuring optical transmittance profiles of different glass filters in order to identify the specific ranges of wavelengths responsible for optical vacuum degradation. Measurements will also be done to determine the time dependence of pressure increases in the samples.

 

1.8 Thermal conductance measurement of vacuum glazing

Supervisors: Dr Nelson Ng and Ms L.C. So

A new method has been developed for measuring the thermal conductance of vacuum glazing. Vacuum glazing consists of two glass sheets separated by vacuum space (0.2 mm) with a leak free seal around the edges. The introduction of the method will significantly reduce the cooling time in an industrial production line. The method involves the measurement of the cooling rate of vacuum glazing after the device was sealed in a high temperature process. In this project, we will carry out investigations of this method on different types of vacuum glazing in order to provide accurate calibration data for the method. The project will involve assembling samples of vacuum glazing with fine thermocouple wires (0.3 mm) in different locations, temperature measurements and calibrating the measured thermal conductance of samples against conductance measured by other methods.