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MSc, Faculty of Science, University of the Witswatersrand, 2011 / The objective of this project is to understand the details of the electronic transport in low dimensional carbon structures at low temperatures as well as high magnetic fields. The emphasis is on the quasi-2 dimensional thin grain boundary regions of nanodiamond films and one dimensional carbon nanotubes. As such nitrogen “doped” and undoped nanodiamond films were synthesized by the hot filament chemical vapor deposition method (HFCVD). The films were micro-structurally and electrically characterized using several techniques such as Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and magnetoresistance (MR) measurements. The electronic transport properties were compared to the films deposited by microwave plasma enhanced chemical vapour deposition (MWCVD). The conductivity revealed a typical semiconducting and semi-metallic behavior for the HFCVD films depending on the nitrogen percentage in the chamber. The dephasing time of the electronic wave function was found to be weakly temperature dependant i.e. τ T-p with p < 1, a behavior reported in artificial superlattices. These results show potential application of these materials in novel nano-electronic devices. Previously the transport mechanism in nanodiamond films has been attributed to hopping conduction in the grain boundaries which is predominately disordered sp2 phases. Our studies on nanodiamond films have however shown different mechanisms in these films. We observed very little contribution from hopping and pronounced weak localization contributions in nanodiamond films. We thus establish the significance of tunneling transport in nanodiamond films. We also studied the electronic transport in films of metal filled multiwalled carbon nanotubes which show significant contribution from the hopping mechanism and a negative magnetoresistance at low fields that crosses over into positive MR at high magnetic fields.

Chan Lai To = 硏究巨磁阻自旋閥磁記錄頭的靈敏度與溫度之關係 / 陳麗圖. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 80-83). / Text in English; abstracts in English and Chinese. / Chan Lai To = Yan jiu ju ci zu zi xuan fa ci ji lu tou de ling min du yu wen du zhi guan xi / Chen Litu. / Abstracts --- p.ii / 論文摘要 --- p.iii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / Abbreviations --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- History of Data Storage in Computers --- p.1 / Chapter 1.2 --- Structure and Working Principle of the Recording Head of a Magnetic Disk Storage device --- p.2 / Chapter 1.2.1 --- Structure of a Current Magnetic Recording Head --- p.2 / Chapter 1.2.2 --- Principle of Recording --- p.6 / Chapter 1.2.2.1 --- General Operating Principle of a Magnetic Recording Head --- p.7 / Chapter 1.2.2.2 --- Principle of Recording using AMR Elements --- p.9 / Chapter 1.2.2.3 --- Principle of Recording using GMR Elements --- p.14 / Chapter 1.3 --- Reliability of Magnetic Recording Heads --- p.23 / Chapter 1.3.1 --- Importance in the Determination of Reliability of Magnetic Recording Heads --- p.23 / Chapter 1.3.2 --- Current Relevant Reliability Issues in the Field --- p.23 / Chapter 1.4 --- Objectives of the Thesis Work --- p.24 / Chapter Chapter 2 --- Methodology --- p.25 / Chapter 2.1 --- Sample Preparation --- p.25 / Chapter 2.2 --- Principle of Amplitude Thermal Robustness Measurements --- p.28 / Chapter 2.2.1 --- Black's Equation --- p.28 / Chapter 2.2.2 --- Thermal Coefficient (TC) or Temperature Resistivity Coefficient Test --- p.29 / Chapter 2.2.3 --- Temperature Rise (TR) --- p.31 / Chapter 2.2.4 --- Thermal Electrical (TE) Stress Test (Accelerated Test) --- p.34 / Chapter 2.2.5 --- Maximum MR Resistance for Normal Device Operation --- p.38 / Chapter 2.3 --- Magnetic Field Effects Induced by the Biasing Current in an ATR Measurement --- p.40 / Chapter Chapter 3 --- Experimental Results and Data Analysis --- p.41 / Chapter 3.1 --- Results of the ATR Measurement --- p.43 / Chapter 3.1.1 --- Thermal Coefficient (TC) Test Result --- p.43 / Chapter 3.1.2 --- Temperature Rise (TR) Results --- p.48 / Chapter 3.1.3 --- Thermal Electrical (TE) Stress Test Result --- p.51 / Chapter 3.1.4 --- Maximum MR Resistance for Normal Device Operation --- p.60 / Chapter 3.2 --- Preliminary Data from the Magnetic Field Effects Induced by the Biasing Current in an ATR Measurement --- p.61 / Chapter Chapter 4 --- Discussion of Results and Failure Mechanisms --- p.62 / Chapter 4.1 --- Summary of the ATR characteristics of GMR heads --- p.62 / Chapter 4.2 --- "Comparison of ATR characteristics of AMR and GMR, and Discussion of Failure Mechanisms" --- p.63 / Chapter 4.2.1 --- ATR characteristics and Failure Mechanisms of AMR --- p.63 / Chapter 4.2.1.1 --- Summary of ATR characteristics of AMR heads --- p.63 / Chapter 4.2.1.2 --- Electromigration (EM) Induced Failure in AMR --- p.65 / Chapter 4.2.1.3 --- Diffusion Induced Failure in AMR --- p.67 / Chapter 4.2.2 --- Possibility of Diffusion Induced Failure in GMR --- p.68 / Chapter 4.2.3 --- Possibility of EM Induced Failure in GMR --- p.69 / Chapter 4.3 --- Magnetic-field Dependent ATR characteristics of GMR --- p.69 / Chapter 4.3.1 --- Temperature Dependence of the Exchange Coupling Field --- p.70 / Chapter 4.3.2 --- Rotation or Reversal of Magnetic Moments of the Pinned Layer --- p.75 / Chapter 4.3.3 --- Relaxation of the Magnetization of the Pinning Layer --- p.77 / Chapter Chapter 5 --- Conclusions and Suggestions for Future Work --- p.78 / References --- p.80

by Leung Chi Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Leung Chi Hung. / Acknowledgments --- p.i / Abstract --- p.ii-iii / Table of Contents --- p.iv-v / Figures Caption --- p.vi-xii / Tables Caption --- p.xiii / Chapter 1. --- Introduction / Chapter 1.1 --- "Magnetoresistance (MR),Giant Magnetoresistance (GMR),Colossal Magnetoresistance (CMR) and Their Applications" --- p.1-1 / Chapter 1.2 --- Colossalmagnetoresistance Effect in LCMO --- p.1-5 / Chapter 1.3 --- Significance of Ultra-Sharp Metal-Semiconductor Transition LCMO Thin Film --- p.1-12 / Chapter 1.4 --- The Use of Silver in the YBCO --- p.1-14 / Chapter 1.5 --- Previews --- p.1-15 / Chapter 1.6 --- References --- p.1-17 / Chapter 2. --- Epitixial Growth of Single-Crystal LCMO Thin Film by FTS method / Chapter 2.1 --- Facing-Target Sputtering Method --- p.2-1 / Chapter 2.2 --- Fabrication of LCMO Targets --- p.2-4 / Chapter 2.3 --- Deposition of the LCMO Thin Film / Chapter 2.3.1 --- Deposition Condition --- p.2-6 / Chapter 2.3.2 --- Deposition Process --- p.2-9 / Chapter 2.4 --- X-ray Diffraction Studies and Surface Morphology --- p.2-11 / Chapter 2.5 --- M-S Transition of LCMO Thm Film --- p.2-15 / Chapter 2.6 --- Discussions --- p.2-19 / Chapter 3. --- The Role of Silver in LCMO / Chapter 3.1 --- Reaction between Ag and LCMO --- p.3-1 / Chapter 3.2 --- Grain Size and Transition Temperature in Bulk LCMO --- p.3-9 / Chapter 3.3 --- Improving the Sharpness of Metal - Semiconductor Transition and Crystallinity of LCMO Film --- p.3-15 / Chapter 3.4 --- Stabilization of the LCMO Structure --- p.3-21 / Chapter 3.5 --- Discussions --- p.3-25 / Chapter 4 --- Epitaxial Growth of the Ultra-Sharp Metal-Semiconductor Transition LCMO Thin Film / Chapter 4.1 --- Synthesis Process of the Ultra-Sharp Metal-Semiconductor Transition LCMO Thin Films --- p.4-1 / Chapter 4.2 --- Resistivity and Magnetoresistance --- p.4-6 / Chapter 4.3 --- Thermal Annealing Effects / Chapter 4.3.1 --- Oxygen Annealing Effect --- p.4-15 / Chapter 4.3.1 --- High Pressure Annealing Effect --- p.4-20 / Chapter 4.3.2 --- Vacuum Annealing Effect --- p.4-23 / Chapter 4.4 --- Surface Morphology and Characterization --- p.4-27 / Chapter 4.5 --- Discussions --- p.4-37

by Chan Hing Nam = 壓力對La₀.₆₇Ca₀.₃₃MnO₃薄膜的導電能的效應 / 陳慶楠. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Chan Hing Nam = Ya li dui La₀.₆₇Ca₀.₃₃MnO₃ bo mo de dao dian neng de xiao ying / Chen Qingnan. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of contents --- p.iv / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction to colossal magnetoresistance --- p.1-1 / Chapter 1.2 --- Effects of chemical pressure and strain on LCMO thin films --- p.1-7 / Chapter 1.3 --- Review of pressure effects on bulk LCMO --- p.1-11 / Chapter Chapter 2 --- Instrumentation and Characterization / Chapter 2.1 --- Preparation of LCMO thin films --- p.2-1 / Chapter 2.2 --- X-ray diffraction (XRD) --- p.2-3 / Chapter 2.3 --- Self-clamping pressure cell --- p.2-5 / Chapter 2.3.1 --- Electrical feedthroughs --- p.2-5 / Chapter 2.3.2 --- Teflon cell --- p.2-8 / Chapter 2.3.3 --- Pressure variations in the pressure-transmitting medium --- p.2-9 / Chapter Chapter 3 --- Pressure effect on LCMO thin films grown on different substrates / Chapter 3.1 --- Annealing effect --- p.3-1 / Chapter 3.2 --- Thickness effect --- p.3-4 / Chapter 3.3 --- Lattice effect and pressure effect --- p.3-5 / Chapter 3.4 --- Crystallinity effect --- p.3-13 / Chapter Chapter 4 --- Activation energy of small polaron in LCMO thin films / Chapter 4.1 --- Motivation --- p.4-1 / Chapter 4.2 --- Basic theory --- p.4-2 / Chapter 4.3 --- Activation energy --- p.4-4 / Chapter Chapter 5 --- Conclusion --- p.5-1

Yeung Chun Fai = 厚度和眞空熱處理對單晶 La0.67Ca0.33MnO3 薄膜特性之影響 / 楊進輝. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Yeung Chun Fai = Hou du he zhen kong re chu li dui dan jing La0.67Ca0.33MnO3 bo mo te xing zhi ying xiang / Yang Jinhui. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iv / Table of contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xiii / Chapter Chapter I --- Introduction / Chapter 1.1 --- Development of magnetoresistance materials --- p.1-1 / Chapter 1.1.1 --- Magnetoresistance (MR) --- p.1-1 / Chapter 1.1.2 --- Anisotropy magnetoresistance (AMR) --- p.1-1 / Chapter 1.1.3 --- Giant magnetoresistance (GMR) --- p.1-2 / Chapter 1.1.4 --- Colossal magnetoresistance (CMR) in rare-earth manganites --- p.1-3 / Chapter 1.1.5 --- Possible origin of CMR in rare-earth manganites --- p.1-4 / Chapter 1.1.5.1 --- Double exchange mechanism --- p.1-4 / Chapter 1.1.5.2 --- Jahn-teller effect --- p.1-6 / Chapter 1.1.5.3 --- Other mechanisms --- p.1-7 / Chapter 1.1.6 --- Possible origins of CMR in Thallium manganite pyrochlores (TI2Mn207) --- p.1-7 / Chapter 1.2 --- New developments in manganite materials --- p.1-8 / Chapter 1.3 --- Our approach --- p.1-8 / Chapter 1.3.1 --- Why choose La0 .67Ca0.33Mn03 material? --- p.1-8 / Chapter 1.3.2 --- The role of oxygen content in manganite materials --- p.1-9 / Chapter 1.4 --- The scope of this thesis work --- p.1-11 / References --- p.1-12 / Chapter Chapter II --- Instrumentation / Chapter 2.1 --- Thin film deposition --- p.2-1 / Chapter 2.1.1 --- Introduction --- p.2-1 / Chapter 2.1.2 --- Facing-target sputtering (FTS) --- p.2-3 / Chapter 2.1.3 --- Deposition profile calculation for sputtering with FTS --- p.2-4 / Chapter 2.1.4 --- Vacuum system --- p.2-7 / Chapter 2.2 --- Characterization --- p.2-8 / Chapter 2.2.1 --- Profilometer --- p.2-8 / Chapter 2.2.2 --- Atomic force microscopy (AFM) --- p.2-8 / Chapter 2.2.3 --- X-ray diffraction (XRD) --- p.2-8 / Chapter 2.2.4 --- Resistance and magnetoresistance measurement --- p.2-10 / Chapter 2.2.5 --- Hall effect measurement --- p.2-11 / References --- p.2-13 / Chapter Chapter III --- Epitaxial growth of La0.67Ca0.33 Mn03 thin films / Chapter 3.1 --- Introduction --- p.3-1 / Chapter 3.2 --- Fabrication and characteristics of LCMO target --- p.3-1 / Chapter 3.3 --- Substrate materials --- p.3-5 / Chapter 3.4 --- Deposition --- p.3-10 / Chapter 3.4.1 --- Sample preparation --- p.3-10 / Chapter 3.4.2 --- Substrate temperature --- p.3-10 / Chapter 3.4.3 --- Deposition process --- p.3-17 / Chapter 3.5 --- Post-annealing effect --- p.3-18 / Chapter 3.6 --- Film composition analysis --- p.3-22 / Chapter 3.7 --- Epitaxial growth examination --- p.3-22 / References --- p.3-27 / Chapter Chapter IV --- Thickness effect in single-crystal LCMO thin films grown on NGO and STO / Chapter 4.1 --- Motivation --- p.4-1 / Chapter 4.2 --- Resistance measurement --- p.4-2 / Chapter 4.3 --- Magnetoresistance (MR) --- p.4-8 / Chapter 4.4 --- Crystal structure --- p.4-12 / Chapter 4.5 --- Surface morphology --- p.4-16 / Chapter 4.6 --- Hall effect measurement --- p.4-19 / Chapter 4.6.1 --- Basic principle --- p.4-19 / Chapter 4.6.2 --- Experiment --- p.4-20 / Chapter 4.6.3 --- Carrier concentration & mobility --- p.4-20 / Chapter 4.7 --- Discussions --- p.4-25 / References --- p.4-27 / Chapter Chapter V --- Strain dependent vacuum annealing effectin single-crystal La0.67Ga0.33MnO3 thin films / Chapter 5.1 --- Motivation --- p.5-1 / Chapter 5.2 --- Sample description --- p.5-1 / Chapter 5.3 --- Vacuum annealing process --- p.5-2 / Chapter 5.4 --- Crystal structure --- p.5-2 / Chapter 5.5 --- Resistance measurement --- p.5-6 / Chapter 5.6 --- Discussions --- p.5-8 / Chapter 5.6.1 --- Lattice expansion --- p.5-8 / Chapter 5.6.2 --- Determination of oxygen content --- p.5-9 / References --- p.5-11 / Chapter Chapter VI --- Activation energy of small polaron in La0.67Ca0.33MnO3 thin films / Chapter 6.1 --- Motivation --- p.6-1 / Chapter 6.2 --- Basic theory --- p.6-1 / Chapter 6.2.1 --- Variable range hopping --- p.6-1 / Chapter 6.2.2 --- Semiconduction --- p.6-2 / Chapter 6.2.3 --- Nearest-neighbor hoping of small polarons --- p.6-2 / Chapter 6.3 --- Sample description --- p.6-3 / Chapter 6.4 --- Resistance measurement --- p.6-4 / Chapter 6.5 --- Activation energy --- p.6-4 / Chapter 6.6 --- Discussions --- p.6-5 / References --- p.6-12 / Chapter Chapter VII --- Conclusions --- p.7-1

by Lee Koon Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Lee Koon Ho. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.ix / Chapter Chapter I --- Introduction / Chapter 1.1 --- Review of magnetoresistance --- p.1 -1 / Chapter 1.1.1 --- Colossal magnetoresistance in rare earth manganites --- p.1 -2 / Chapter 1.1.2 --- Review of manganite multilayer system --- p.1-10 / Chapter 1.2 --- Research motivation --- p.1-12 / Chapter 1.2.1 --- Scope of the thesis --- p.1-14 / Reference --- p.1-15 / Chapter Chapter II --- Instrumentation --- p.2-1 / Chapter 2.1 --- Facing target sputtering system --- p.2-1 / Chapter 2.1.1 --- Preparation of LCMO/PCMO multilayer thin film --- p.2-3 / Chapter 2.2 --- Annealing system --- p.2-5 / Chapter 2.2.1 --- Oxygen post-annealing system --- p.2-5 / Chapter 2.2.2 --- Vacuum annealing system --- p.2-7 / Chapter 2.3 --- X-ray diffraction (XRD) --- p.2-9 / Reference --- p.2-11 / Chapter Chapter III --- Annealing of LCMO/PCMO multilayer thin films --- p.3-1 / Chapter 3.1 --- Oxygen post-annealing of LCMO/PCMO multilayer thin film --- p.3-1 / Chapter 3.1.1 --- Introduction to post-annealing of managanites oxides --- p.3-1 / Chapter 3.1.2 --- LCMO and PCMO Single Layer Films Description --- p.3-1 / Chapter 3.1.3 --- Selection of PCMO --- p.3-5 / Chapter 3.1.4 --- La2/3Ca1/3MnO3/ Pr2/3Ca1/3MnO3 Multilayer Description --- p.3-5 / Chapter 3.1.5 --- Oxygen post-annealing condition --- p.3-9 / Chapter 3.1.6 --- Oxygen post annealing of P100 --- p.3-9 / Chapter 3.1.7 --- Conclusion --- p.3-16 / Chapter 3.2 --- Vacuum annealing of LCMO/PCMO multilayer thin films --- p.3-19 / Chapter 3.2.1 --- Introduction --- p.3-19 / Chapter 3.2.2 --- Sample description --- p.3-20 / Chapter 3.2.3 --- Vacuum annealing condition --- p.3-21 / Chapter 3.2.4 --- Vacuum Annealing of LCMO and PCMO --- p.3-23 / Chapter 3.2.5 --- Vacuum Annealing of LCMO/PCMO multilayer thin films --- p.3-29 / Chapter 3.2.6 --- Conclusion --- p.3-49 / References --- p.3-50 / Chapter Chapter IV --- Activation energy of small polaron in LCMO/PCMO multilayer thin films --- p.4-1 / Chapter 4.1 --- Introduction to small lattice polarons --- p.4-1 / Chapter 4.2 --- Theory of small polarons --- p.4-2 / Chapter 4.3 --- Activation energy of small polaron --- p.4-3 / Chapter 4.4 --- Discussion --- p.4-7 / References --- p.4-8 / Chapter Chapter V --- Conclusions --- p.5-1

Magnetoresistance (MR) and doping effects have been investigated in a poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic light emitting diodes. In single device of fixed composition (Au/P3HT/Al as spun and processed in air), the measured MR strongly depends on the drive conditions. The magnetoconductance (MC) varies from negative to positive (-0.4% ≤ MC ≤ 0.4%) with increasing current density, depending on which microscopic mechanism dominates. The negative MC is due to bipolaron based interactions and the positive MC to triplet-polaron based interactions (as confirmed by light emission). Oxygen doping is prevalent in P3HT devices processed in air and the effect of de-doping (by annealing above the glass transition temperature) is investigated on the MC of an Au/P3HT/Al diode. De-doping reduces the current through the device under forward bias by ~3 orders of magnitude, but increases the negative (low current) MC from a maximum of -0.5% pre-annealing to -3% post-annealing. This increased negative MC is consistent with bipolaron theory predictions based on Fermi level shifts and density of states (DoS) changes due to de-doping. The decrease in current density is explained by increased injection barriers at both electrodes also resulting from de-doping. Deliberate chemical doping of P3HT is carried out using pentacene as a hole trap centre. The trapping effect of pentacene is confirmed by reproducible and significant hole mobility-pentacene concentration behaviour, as measured by dark injection (DI) transient measurements. The enhanced carrier injection resulting from the pentacene doping also leads to increased electroluminescence (EL). The resultant MC in pentacene doped devices is strongly dependent on carrier injection and can be significantly enhanced by doping, for example from -0.2% to -0.6% depending on device and drive conditions. Throughout this thesis Lorentzian and non-Lorentzian function fitting is carried out on the measured MC, although the underlying microscopic mechanisms cannot always be discerned.