Lee, Kin Hang = (La₀.₆₇Sr₀.₃₃MnO₃/La₀.₄₀Ca₀.₆₀MnO₃)多層薄膜的磁致電阻特性 / 李建恆. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Lee, Kin Hang = (La₀.₆₇Sr₀.₃₃MnO₃/La₀.₄₀Ca₀.₆₀MnO₃) duo ceng bo mo de ci zhi dian zu te xing / Li Jianheng. / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Review of Magnetoresistance --- p.1 / Chapter 1.2 --- Giant magnetoresistance (GMR) --- p.4 / Chapter 1.3 --- Colossal magnetoresistance (CMR) and rare earth manganites --- p.6 / Chapter 1.3.1 --- Tolerance factor in perovskite structure --- p.8 / Chapter 1.3.2 --- Electronic structure and magnetic exchange mechanism --- p.10 / Chapter 1.3.3 --- Jahn-Teller (JT) distortion --- p.13 / Chapter 1.3.4 --- Magnetic and electronic phase diagram --- p.15 / Chapter 1.3.5 --- Charge ordering (CO) effect --- p.18 / Chapter 1.3.6 --- Percolation in a phase-separated state --- p.19 / Chapter 1.4 --- Phase separation at the interfaces in thin films --- p.24 / Chapter 1.5 --- Our motivation --- p.26 / Chapter 1.6 --- Review of manganite multilayer system --- p.27 / Chapter 1.7 --- Scope of this thesis --- p.34 / References --- p.35 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thin film deposition --- p.39 / Chapter 2.1.1 --- Facing target sputtering (FTS) --- p.40 / Chapter 2.1.2 --- Vacuum system --- p.43 / Chapter 2.2 --- Characterization --- p.45 / Chapter 2.2.1 --- α-step profilometer --- p.45 / Chapter 2.2.2 --- X-ray diffraction (XRD) --- p.45 / Chapter 2.2.3 --- Resistance measurement --- p.48 / Reference --- p.50 / Chapter Chapter 3 --- Epitaxial growth and characterization of single layer thin films / Chapter 3.1 --- Introduction --- p.51 / Chapter 3.2 --- Fabrication of the sputtering targets --- p.51 / Chapter 3.3 --- Epitaxial growth of single layer thin films --- p.52 / Chapter 3.3.1 --- Substrate materials --- p.52 / Chapter 3.3.2 --- Review of deposition conditions of our group with FTS system --- p.54 / Chapter 3.3.3 --- Substrate temperature --- p.57 / Chapter 3.3.4. --- Target-to-target distance and sputtering power --- p.58 / Chapter 3.3.5 --- Deposition procedures --- p.59 / Chapter 3.3 --- Characterization of single layer thin films --- p.60 / References --- p.64 / Chapter Chapter 4 --- La0.67Sr0.33MnO3/La0.40Ca0.60MnO3 multilayers / Chapter 4.1 --- Sample preparation --- p.65 / Chapter 4.2 --- As-grown multilayers --- p.69 / Chapter 4.2.1 --- Structural characterization of as-grown samples --- p.69 / Chapter 4.2.2 --- Transport properties of as-grown samples --- p.80 / Chapter 4.2.2.1 --- The effect of ts for fixed tc and the effect of tc for fixed ts --- p.83 / Chapter 4.2.2.2 --- The effect of thin La0.40Ca0.60MnO3 spacer layers --- p.92 / Chapter 4.2.2.3 --- The effect of fixed bilayer thickness --- p.94 / Chapter 4.2.2.4 --- The effect of ts for fixed volume fraction (tc / ts) --- p.97 / Chapter 4.2.2.5 --- The sample without M-I transition --- p.101 / Chapter 4.3 --- Discussion --- p.103 / References --- p.108 / Chapter Chapter 5 --- Conclusion --- p.110 / Chapter 5.1 --- Conclusion --- p.110 / Chapter 5.2 --- Future outlook --- p.112 / References --- p.114

Polycrystalline silicon (pc-Si, grain size > 1??m, no amorphous tissue) on glass is an interesting material for thin-film solar cells due to the low costs, the abundance and the non-toxic character of Si, and the properties of pc-Si like long-term stability and lateral conductance. Glass as supporting material significantly complicates the fabrication process as it limits the thermal budget and the maximum temperature. In this work, the feasibility of forming large-grained pc-Si thin-film solar cells on glass by ion-assisted deposition (IAD) on aluminium-induced crystallisation (AIC) seed layers (ALICIA solar cells) is investigated. IAD allows epitaxial growth at high rate, and being based on evaporation, is of low cost (high source material usage, no toxic gases involved). High-quality epitaxy on (100)-oriented Si wafer substrates is demonstrated in a non{UHV environment, to further increase its industrial appli- cability. High{rate growth and a sacrificial protective layer control contamination problems associated with the non-UHV environment. The process is then trans- ferred to AIC-seeded glass and optimised, with particular focus on the influence of the glass. Using high-temperature rapid thermal annealing and hydrogenation as post-deposition treatments, ALICIA solar cells with a 1-Sun open-circuit voltage of 420 mV are achieved. Moreover, two novel characterisation techniques are presented. One allows the fast and non-destructive assessment of the structural quality of pc-Si films using opti- cal measurements. Furthermore, `impedance analysis', a novel capacitance-voltage measurement technique based on impedance spectroscopy, is presented. It allows the reliable determination of the absorber layer doping density and the built{in potential of non-ideal p-n junction solar cells. The latter is used to investigate the influence of post{deposition treatments on the n-type absorber layer doping of ALICIA solar cells. It is found, using temperature dependent impedance analysis, that unintentional doping and defects have a strong influence on the absorber layer doping. A maximum in the short-circuit current density of ALICIA solar cells is found for phosphorus concentrations in the absorber of 1??1017 cm??3. For such ALI- CIA cells a base difusion length in the range 600 - 950nm, a short{circuit current density in the range 10 - 13.5 mA/cm2 and an energy conversion efficiency of 2.2% are obtained.

No description available.

��-SiC is a semiconductor for high temperature devices, which exhibits several outstanding properties such as high thermal stability, good chemical stability and wide band gap. There is a possibility of fabricating a crack-free ultrathin SiC film on silicon wafers by pyrolysis of polymethylsilane (PMS) film. This study looks into the possibility, as the first phase, to modify the surface of silicon and graft PMS onto the surface. A new technique reported in this thesis consists of a surface modification with trimethoxysilylpropene (TSP) followed by the surface attachment of dichloromethylsilane (DMS) in the presence of a platinum catalyst, which acts as the first unit for grafting PMS molecules by the sodium polycondensation of additional DMS monomers. The grafted PMS polymers would serve as the pyrolytic precursor to be converted into thin layers of SiC. Surface analysis of these films on silicon wafers by X-ray photoelectron spectroscopy (XPS) indicated that the silicon surface was successfully modified with TSP, attached with DMS, and finally grafted with PMS. It was also confirmed by powder X-ray diffraction (XRD) that PMS formed simultaneously in the bulk solution was converted into SiC by pyrolysis at temperatures above 1100��C under Ar atmosphere. Extended studies showed that the PMS-derived coatings, formed in an Ar stream containing 1% H��� at 400��C, were significantly oxidized, and further heating to 700��C yielded a Si0��� layer with graphitic carbon. The intensity of the graphite peak decreased with an increase in the pyrolysis temperature. Based on these preliminary studies towards the second phase, i.e. the pyrolysis of PMS to SiC, the need for further research to eliminate the oxidation source(s) is strongly suggested. / Graduation date: 2001

A low pressure halide transport chemical vapor deposition (HTCVD) system to grow ZnS:Mn electroluminescent phosphors is characterized. Reactor parameters such as gas composition, gas flow rate, and source and substrate temperature are investigated. Crystal structure is investigated using x-ray diffraction, electron spin resonance, and transmission electron microscopy. Chemical characterization includes electron microprobe and Auger electron spectroscopy. Double-insulating alternating current thin film electroluminescent devices are constructed around the HTCVD phosphors. The devices are studied using electroluminescence (brightness-voltage), photoluminescence and electrical characterization. The luminescent properties of films with a (002) preferred orientation are studied. A maximum electroluminescent brightness of 1475 cd/m�� is achieved. The photoluminescence (PL) of ZnS:Mn films grown at different substrate temperatures is compared. The intensity correlates to Mn concentration. Red emission is seen in films grown at lower substrate temperature which have low Mn concentration. Mechanisms proposed in the literature cannot explain the red emission. A blue PL ZnS film intentionally doped with chlorine is achieved. This blue emission is associated with self-activated (SA) emission. Hexagonal and cubic thin-film ZnS:Mn electroluminescent phosphors are grown by HTCVD. Processing conditions, most notably introduction of a H���S ambient, lead to a change in the preferred orientation and phase of the polycrystalline thin film. In addition to the commonly reported growth along the closest packed plane [(111) for cubic crystal structure or (002) for hexagonal], thin films have been grown along the less dense cubic (311) direction. The electrical characterization of ZnS:Mn ACTFEL devices with phosphors having different structure and preferred orientation is studied. A comparison of different preferred orientations and structures on conduction charge, obtained by internal charge-phosphor field (Q-F[subscript]p), is performed. When grown in the (311) direction, the conduction charge of a ZnS:Mn ACTFEL device increases from 2.3 ��C/cm�� to 5.0 ��C/cm��. Moreover, the leakage charge, Q[subscript]l[subscript]e[subscript]a[subscript]k, of the (311) HTCVD films is small compared to other devices. / Graduation date: 1998

Recent superconducting thin films studies have attempted to create pure metal layer films of Niobium and Titanium with the same properties of superconducting NbTi wire used in industry. These studies have all reported depression of the superconducting properties of the pure metal films which has been attributed to the proximity effect. The purpose of this research project was to construct several NbTi films composed of alloyed layers to overcome the proximity depression of superconducting properties. These films are unique in that they are the only films with both alloyed Nb/Ti superconducting and normal layers reported in the literature. Films with several different compositions and bilayer geometries were designed, constructed and their superconducting properties characterized. The films were created by the RF sputtering of alloyed targets at ambient temperatures. Characterization of the composition of the films was performed by microprobe analysis at two different electron beam voltages. A simulation of the electron beam excitation volume of the microprobe was performed to determine the difference in the two analyses and to determine whether the substrate would be found upon microprobe examination. X-ray diffraction was utilized to determine the bilayer spacing and to give a qualitative understanding of the alignment of the film microstructures. The critical temperature and upper critical magnetic field were measured to determine the superconducting properties and the extent of the proximity effect in the films. The microprobe analysis found most films to be very pure alloys except for films 6001, 6002, 6003(1) in which there were between 1-8 wt% of impurities. All films contained compositional variations on the order of 10 wt% from the design values. X-ray diffraction indicated agreement with the designed bilayer spacing in all films but 6003(2), 6005(1), and 6005(2) which had bilayer periods larger than originally designed. The proximity effect was not observed in any of the film's superconducting properties examined. T[subscript]c and H[subscript]c��� properties for the films without impurities had properties equal to that of bulk Nb/47wt% Ti. Films 6001, 6003(1) had depressed T[subscript]c and H[subscript]c��� values which were attributed to their impurity contamination. The low Ti composition in many of the films points to the inaccuracy of the deposition parameters when the films were first processed. The lack of T[subscript]c and H[subscript]c��� depression normally seen in other film studies with bilayer periods between 10-30 nm demonstrates that alloyed layers should be used to overcome the proximity effect in multilayer thin film superconductor studies. Overcoming the proximity effect should translate into a better understanding of flux pinning mechanisms in the material and increased superconducting critical currents in these films. / Graduation date: 1999

Graduation date: 1997

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, June 1999. / Includes bibliographical references. Also available on the Internet.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.