Ng Ka Shun = La₀.₄Ca₀.₆MnO₃/La₀.₈Ca₀.₂MnO₃多層薄膜之龐磁阻 / 吳家信. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Ng Ka Shun = La₀.₄Ca₀.₆MnO₃/La₀.₈Ca₀.₂MnO₃ duo ceng bo mo zhi pang ci zu / Wu Jiaxin. / 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.viii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Review of magnetresistance --- p.1-1 / Chapter 1.2 --- Colossal magnetoresistance (CMR) --- p.1-4 / Chapter 1.3 --- Possible mechanism of CMR --- p.1-7 / Chapter 1.3.1 --- Double exchange --- p.1-7 / Chapter 1.3.2 --- Phase separation and percolation theory --- p.1-9 / Chapter 1.3.3 --- Current carrier density collapse --- p.1-12 / Chapter 1.4 --- Our motivation --- p.1-14 / Chapter 1.5 --- Brief review of several manganite multilayer systems --- p.1-15 / Chapter 1.6 --- Scope of this thesis work --- p.1-16 / References --- p.1-17 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thin film deposition --- p.2-1 / Chapter 2.1.1 --- Facing target sputtering (FTS) --- p.2-1 / Chapter 2.1.2 --- Connection of heating wires and thermocouple --- p.2-5 / Chapter 2.1.3 --- Vacuum system --- p.2-7 / Chapter 2.2 --- Annealing system --- p.2-9 / Chapter 2.3 --- Characterization --- p.2-11 / Chapter 2.3.1 --- X-ray diffraction (XRD) --- p.2-11 / Chapter 2.3.2 --- Resistance measurement --- p.2-13 / Chapter 2.3.3 --- Thickness estimation --- p.2-15 / References --- p.2-15 / Chapter Chapter 3 --- Growth and characterization of LCMO single layer thin film --- p.3-1 / Chapter 3.1 --- Fabrication and characterization of LCMO targets --- p.3-1 / Chapter 3.2 --- Preparation of LCMO thin film --- p.3-5 / Chapter 3.2.1 --- Deposition conditions --- p.3-5 / Chapter 3.2.2 --- Depostion procedure --- p.3-8 / Chapter 3.2.3 --- Characterization of single layer film --- p.3-9 / References --- p.3-12 / Chapter Chapter 4 --- La0.4Ca0.6MnO3 / La0.8Ca0.2MnO3 multilayers / Chapter 4.1 --- Sample preparation --- p.4-1 / Chapter 4.2 --- Results and discussion --- p.4-4 / Chapter 4.2.1 --- Structural characterization --- p.4-4 / Chapter 4.2.2 --- Transport properties --- p.4-10 / Chapter 4.3 --- Oxygen post-annealing of multilayer thin films --- p.4-13 / Chapter 4.3.1 --- Introduction --- p.4-13 / Chapter 4.3.2 --- Oxygen post-annealing conditions --- p.4-14 / Chapter 4.3.3 --- Results and discussion --- p.4-16 / Chapter 4.4 --- Conclusion --- p.4-26 / References --- p.4-27 / Chapter Chapter 5 --- Conclusion

In the last decade, the emerging classes of two-dimensional (2D) materials have been studied as potential candidates for various sensing technologies, including magnetic and optoelectronic detectors. Within the quickly growing portfolio of 2D materials, graphene and semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive candidates for various sensor applications because of their unique properties such as extreme thickness, excellent electrical and optical properties. In this thesis, I have exploited the unique properties of graphene and TMDs materials to develop 2D detectors based on field effect transistors for sensing magnetic field and light. In the first part of this thesis I have shown how the sensitivity of the properties of 2D materials to their surrounding environment can be turned into a feature useful to create new types of magnetic field sensors. The first experimental demonstration of this concept involved the use of graphene deposited on hexagonal Boron Nitride (h-BN), where the inevitable contaminations occurring at the interface of the two materials was used to generate a large magnetoresistance (MR) for a magnetic field sensor. Specifically, I have demonstrated that the contaminations generate an inhomogeneity in the carrier mobility throughout the channel, which is a required ingredient for magnetic field sensing based on linear magnetoresistance (LMR). Another approach I used to make a LMR sensor was by exploiting the large dependence of the mobility in graphene on the Fermi level position. This concept was used to generate two parallel electron gases with different mobility by tuning the Fermi level with an electrical field employing a field effect transistor. The second part of the thesis is focussed on strategies to reduce the impact of the surrounding environment on the properties of 2D materials in order to improve their performance. In particular, I used a 2D heterostructure encapsulated in an ionic polymer to makeii a highly responsive graphene-TMD photodetector. In this device, the ionic polymer covering the heterostructure was employed to screen the long-lived charge traps that limit the speed of such detectors, resulting in a drastic improvement of the detector responsivity properties. Finally, some of the 2D materials properties are very sensitive to the configuration of the electronics measurement setup. For example, effects behind spintronic and valleytronic concepts require non-local electrical transport measurement. We built a novel circuit that enables the detection of such effects without concern about the spurious contributions.

by Xianting Zeng. / Publication date from spine. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 165-173). / ABSTRACT --- p.iii / ACKNOWLEDGEMENT --- p.v / TABLE OF CONTENTS --- p.vii / LIST OF FIGURES --- p.x / LIST OF TABLES --- p.xiv / Chapter I. --- Introduction --- p.1 / Chapter 1.1 --- Previous research on magnetoresistance --- p.1 / Chapter 1.2 --- Preparation methods --- p.12 / Chapter 1.3 --- Application prospects and existing problems of GMR materials --- p.15 / Chapter 1.4 --- Main contents in this thesis --- p.17 / Chapter II. --- The facing-target sputtering technique --- p.20 / Chapter 2.1 --- Brief description of FTS method --- p.20 / Chapter 2.2 --- Considerations and studies about the deposition conditions of La-Ca-Mn-O thin films --- p.26 / Chapter 2.2.1 --- Substrate materials --- p.26 / Chapter 2.2.1.1 --- Mismatch of lattice constant --- p.26 / Chapter 2.2.1.2 --- Thermal expansion coefficient --- p.31 / Chapter 2.2.1.3 --- Cleaning and surface treatment --- p.33 / Chapter 2.2.2 --- Substrate temperature --- p.35 / Chapter 2.2.3 --- Discharge pressure and sputtering power --- p.36 / Chapter 2.2.4 --- Oxygen content and critical thickness --- p.36 / Chapter 2.3 --- Fabrication and characteristics of La-Ca-Mn-O target materials --- p.42 / Chapter 3.2.1 --- Fabrication process --- p.42 / Chapter 2.3.2 --- Characterizations --- p.46 / Chapter 2.3.2.1 --- Structural parameters --- p.46 / Chapter 2.3.2.2 --- Electrical and magnetic properties --- p.51 / Chapter III. --- Growth of La-Ca-Mn-O thin films with c-axis orientation --- p.53 / Chapter 3.1 --- Thin film deposition --- p.53 / Chapter 3.2 --- Characterization methods --- p.53 / Chapter 3.2.1 --- XRD --- p.54 / Chapter 3.2.2 --- SEM/EDX --- p.54 / Chapter 3.2.3 --- VSM --- p.57 / Chapter 3.3 --- Results and discussions --- p.58 / Chapter 3.3.1 --- Structures of the films grown on (100) MgO --- p.58 / Chapter 3.3.2 --- Resistance and magnetoresistance --- p.62 / Chapter 3.3.3 --- Annealing effect --- p.69 / Chapter 3.4.3.4 --- Magnetization --- p.71 / Chapter 3.4 --- Conclusion --- p.75 / Chapter IV. --- Epitaxial growth of single crystal LCMO thin films with a-axis orientation --- p.77 / Chapter 4.1 --- Motivation and thin film deposition --- p.77 / Chapter 4.2 --- Characterizations --- p.79 / Chapter 4.2.1 --- DCD/GID --- p.79 / Chapter 4.2.2 --- Laue diffractometry --- p.84 / Chapter 4.3 --- Results and discussions --- p.85 / Chapter 4.4 --- Conclusion --- p.91 / Chapter V. --- Crystal growth mechanisms in the deposition of LCMO thin films --- p.93 / Chapter 5.1 --- Introduction --- p.93 / Chapter 5.2 --- AFM/STM --- p.96 / Chapter 5.3 --- Step-flow growth --- p.100 / Chapter 5.4 --- Roughening growth --- p.107 / Chapter 5.5 --- 3-D growth --- p.111 / Chapter 5.6 --- Conclusion --- p.119 / Chapter VI. --- Anisotropy properties of epitaxial LCMO thin films and colossal low field magnetoresistance --- p.122 / Chapter 6.1 --- Introduction --- p.122 / Chapter 6.2 --- Experiments --- p.124 / Chapter 6.3 --- Results and discussions --- p.125 / Chapter 6.3.1 --- Morphology --- p.125 / Chapter 6.3.2 --- Transport properties --- p.125 / Chapter 6.4 --- Conclusion --- p.134 / Chapter VII. --- Optical response of epitaxial LCMO thin films --- p.135 / Chapter 7.1 --- Introduction --- p.135 / Chapter 7.2 --- Experimental procedures --- p.138 / Chapter 7.2.1 --- Sample preparation --- p.138 / Chapter 7.2.2 --- Measurements of the optical spectra --- p.140 / Chapter 7.2.3 --- Measurements of the optical response --- p.140 / Chapter 7.3 --- Experimental results and discussions --- p.142 / Chapter 7.3.1 --- Optical spectra --- p.142 / Chapter 7.3.2 --- Optical response characteristics --- p.145 / Chapter 7.3.3 --- 1/f noise in LCMO materials --- p.148 / Chapter 7.4 --- Potential applications --- p.154 / Chapter 7.5 --- Conclusion --- p.156 / Chapter VIII. --- Conclusion and further studies --- p.158 / Chapter 8.1 --- Conclusion --- p.158 / Chapter 8.2 --- Further studies --- p.161 / References --- p.165

by Yueng Hiu Wa. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaf 56). / Text in English; abstracts in English and Chinese. / by Yueng Hiu Wa. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of contents --- p.iv / List of Figures --- p.v / List of Tables --- p.vi / Chapter Chapter I --- Introduction / Chapter 1.1 --- Development of magnetoresistance materials --- p.1 / Chapter 1.1.1 --- Magnetoresistance (MR) --- p.1 / Chapter 1.1.2 --- Giant magnetoresistance (GMR) --- p.1 / Chapter 1.1.3 --- Colossal magnetoresistance (CMR) in rare-earth manganites ..… --- p.4 / Chapter 1.2 --- Our research motivation --- p.5 / Chapter 1.2.1 --- Scope of this thesis --- p.7 / Chapter Chapter II --- Instrumentation / Chapter 2.1 --- Vacuum annealing system --- p.8 / Chapter 2.2 --- X-ray diffraction (XRD) --- p.11 / Chapter 2.3 --- Rutherford backscattering spectroscopy --- p.13 / Chapter Chapter III --- Oxygen diffusion / Chapter 3.1 --- Introduction --- p.15 / Chapter 3.2 --- Theory --- p.16 / Chapter 3.3 --- Experimental --- p.21 / Chapter 3.4 --- Result and discussion --- p.24 / Chapter Chapter IV --- Vacuum annealing effect in La0.67Ca0.33Mn03 thin films / Chapter 4.1 --- Introduction --- p.31 / Chapter 4.2 --- Principles of resonant RBS and ion channeling --- p.32 / Chapter 4.2.1 --- Resonant RBS and its application / Chapter 4.2.2 --- Ion channeling and its application / Chapter 4.3 --- Experimental --- p.39 / Chapter 4.4 --- Data analysis and discussion --- p.48 / Chapter 4.5 --- Conclusion --- p.50 / Chapter Chapter V --- Conclusion

by Li Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Li Ho. / Abstract --- p.i / 論文摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.viii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Magnetoresistance --- p.1 / Chapter 1.1.1 --- Giant magnetoresistance (GMR) --- p.3 / Chapter 1.1.2 --- Colossal magnetoresistance (CMR) in perovskite manganites --- p.5 / Chapter 1.1.2.1 --- Perovskite-type structure --- p.5 / Chapter 1.1.2.2 --- Metal-insulator transition --- p.7 / Chapter 1.1.2.3 --- Possible origin of CMR --- p.11 / Chapter 1.2 --- Low field magnetoresistance in CMR materials --- p.12 / Chapter 1.2.1 --- Single crystal and polycrystalline perovskite manganites --- p.12 / Chapter 1.2.2 --- Manganite trilayer junctions --- p.13 / Chapter 1.2.3 --- Possible mechanism of low field MR --- p.15 / Chapter 1.3 --- Our motivation --- p.15 / Chapter 1.3.1 --- Brief review of several manganite multilayer systems --- p.16 / Chapter 1.3.2 --- Scope of this thesis work --- p.18 / Reference --- p.19 / Chapter Chapter 2 --- Preparation and characterization of manganite thin films / Chapter 2.1 --- Thin film deposition --- p.22 / Chapter 2.1.1 --- Facing-target sputtering (FTS) --- p.22 / Chapter 2.1.2 --- Vacuum system --- p.25 / Chapter 2.2 --- Fabrication and characterization of PCMO and LCMO targets --- p.27 / Chapter 2.3 --- Epitaxial growth of LCMO thin films --- p.31 / Chapter 2.3.1 --- Substrate materials --- p.31 / Chapter 2.3.2 --- Deposition conditions --- p.32 / Chapter 2.3.3 --- Deposition procedure --- p.33 / Chapter 2.3.4 --- Results and discussions --- p.34 / Chapter 2.3.4.1 --- Morphology --- p.35 / Chapter 2.3.4.2 --- Structure --- p.39 / Chapter 2.3.4.3 --- Transport properties --- p.42 / Chapter 2.3.4.4 --- Conclusion --- p.48 / Chapter 2.4 --- Epitaxial growth of PCMO thin films --- p.49 / References --- p.51 / Chapter Chapter 3 --- LCMO/PCMO multilayer / Chapter 3.1 --- Sample preparation --- p.53 / Chapter 3.2 --- Results and discussion --- p.53 / Chapter 3.2.1 --- Structure characterization --- p.55 / Chapter 3.2.2 --- Transport properties --- p.59 / Chapter 3.2.3 --- Low-field magnetoresistance --- p.55 / Chapter 3.2.4 --- Magnetization --- p.73 / Chapter 3.3 --- Conclusion --- p.76 / References --- p.77 / Chapter Chapter 4 --- Conclusions --- p.78

No description available.

The low-field magnetoresistance of colossal magnetic thin film can be enhanced by proton implantation. Compare with the as grown sample, the implantation samples has lower transition temperature and higher resistivity. By the hall measurement, we can get the carrier type and carrier concentration. The hall magnetoresistance (MRH) is much greater than the longitude magnetoresistance (MR). Chapter 1. Introduce experiment purpose and expected results. Chapter 2. Introduce the basic theorem of colossal magnetic materials. Chapter 3. The steps of experiment. Chapter 4. Results and discussion. Chapter 5. The conclusion.

The electrical conductivity of InN, group III-V semiconductor, is measured by four point measurement at low temperatures and high magnetic fields. From Resistance Vs temperature measurements (done in the absence of magnetic field) there is a transition from semiconducting state to superconducting state at 2.5K. This superconducting state disappears when the measurements are repeated but at a magnetic field of 0.1 Tesla. Mover the Hall voltage is not proportional to the magnetic field.

No description available.

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