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An automated ellipsometer was used to study field-induced optical anisotropy in anodic niobium oxide films. The oxide films were found to change from the optically isotropic state to the optically anisotropic state when an electric field was applied normal to the film surface. The anisotropic refractive indices of the oxide films decreased quadratically while the thickness of the films increased quadratically with the applied field. The quadratic electro-optic coefficients were determined. The changes in refractive indices and in thickness of the oxide films were found to be independent of time. Field recrystallization of the anodic niobium oxide films was investigated using a scanning electron microscope. The results are compared with those reported for anodic tantalum oxide films in the published literature. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This investigation is a theoretical study of the influence of defects of finite volume on the electrical conductivity in the quantum size effect regime. Correction terms to existing equations are derived, and a physical explanation of the results is given. Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable to the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In very thin films, scattering from surfaces, phonons, and crystal defects plays an increasingly important role. In this investigation the influence of scattering centers (defects) in semimetal films on the electrical conductivity is explored by extending existing work to include scattering centers of finite range. The purpose of this study is to determine the overall change in the conductivity and the alteration of the amplitude of the oscillations. The Boltzmann transport equation is the starting point for the calculation. An equation for the vector mean free path is derived, and a solution is obtained by the iterative process. The relaxation approximation need not be made since the vector mean free path is determined. The sample is a thin slab that is infinite in two dimensions. The assumption is made that the electron wave function is zero at the walls of the sample. It is further assumed that there is a known number of randomly located defects within the slab. The noninteracting electrons are considered free except in the vicinity of the scattering centers. The defects are characterized by a potential that is constant within a small cube and zero outside of it. This approach allows the potential matrix elements to be evaluated by expanding in a power series. The electrical conductivity is calculated for three defect sizes, and a comparison is made to 3-function (infinitely small) scattering centers. An overall decrease in the conductivity is found in each case, and the absolute magnitude of the oscillations is decreased. The percentage of oscillation, however, is increased. The general conductivity decrease is attributed to the increase in the scattering range. The change in the amplitude of the oscillations is explained by analyzing the transition probabilities to available energy states at critical film thicknesses. The oscillations are found to be a result of transitions from states with large energies in the plane of the film to states with small energies in the plane of the film. The number of electrons occupying the various states is determined at critical film thicknesses, and a comparison with the conductivity equation shows excellent agreement.

Fatigue and electrical degradation including low voltage breakdown of ferroelectric lead zirconate titanate Pb(Zr_xTi₁)O₃ (i.e. PZT) thin films are the major limitations for commercial memory applications of these films. It is noted that the presence of oxygen vacancies and their entrapment at the electrode-ferroelectric interfaces are the sources of the degradation phenomena. Attempts were made in this study to solve these problems: 1) by minimizing oxygen vacancy entrapment at the interfaces by employing RuO₂ electrodes; 2) by lowering the oxygen vacancy concentration in PZT films using donor doping (e.g. La³⁺ at Pb²⁺ site and Nb⁵⁺ at Ti/Zr⁴⁺ site). For this study, PZT thin films were prepared by a sol-gel method and deposited on both Pt/Ti/SiO₂/Si and RuO₂/SiO₂/Si substrates. The microstructure and electrical properties, such as hysteresis properties, fatigue, leakage current, time-dependent dielectric breakdown (TDDB), and retention, were studied with regard to the Zr/Ti ratio, the excess lead, the annealing temperature, the electrode material, and the doping amount. Furthermore, the pyrochlore to perovskite phase transformation of PZT on RuO₂ electrodes was also investigated. It was shown that PZT films (Zr/Ti=50/50) with 10 at.% excess lead annealed at 650°C for 30 min possessed the best electrical properties for ferroelectric memory application. In confirmation with earlier theoretical and experimental results, no polarization loss was observed up to 10¹¹ switching cycles for the PZT films deposited on RuO₂ electrodes. However, the low Schottky barrier at the interfaces between RuO₂ and PZT films resulted in a higher leakage current at a high electric fields. Donor doping of PZT films decreased carrier concentrations in PZT films, and thus, decreased the leakage current to acceptable limits. In addition, it was also noted that the pyrochlore to perovskite phase transformation of PZT on RuO₂ was similar to that of PZT on Pt electrodes. It can be concluded that the combination of RuO₂ electrodes and donor doping produced PZT films with high fatigue endurance and low leakage currents which are suitable for memory applications. / Master of Science

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: In this investigation the formation of thin film manganites and their electrical characteristics is studied. In order to see the effect of oxidation states on magneto-resistivity, 80% of Mn is replaced by Fe. Pulsed laser deposition (3 J/cm2), carried out in oxygen partial pressures ranging from 0.01 mbar to 1.00 mbar was used to fabricate the thin films from two target compositions, namely La2CaMn2.94Feo.0609 and La2CaMno.6Fe2.409. Films were deposited on Si< 100 >, MgO< 100 >, SrTi03< 100 > and LaAl03< 100 > single crystal substrates. Samples were characterized by RBS, AFM, SEM, and XRD. Electrical measurements were also carried out. One of the main characterization techniques in this investigation is Rutherford Backscattering Spectrometry (RBS). It has been shown that RBS is a very powerful characterization technique when used in conjunction with the RUMP simulation program. The effect of various parameters can be determined beforehand by RUMP simulation of the thin film structures to be investigated. Simulation shows that RBS is an excellent characterization tool for determining film thickness and stoichiometry. The role of oxygen uptake in La2CaMn3_xFexOg was investigated as the oxidation states of elements in manganite materials have a large effect on their magnetoresistive properties. The height of the La signal can be used as a measure of the oxygen content. RBS spectra of films deposited on single crystal silicon substrates at different ambient pressures show that the fit between simulated and measured RBS spectra improves with higher oxygen pressures, thereby indicating better quality manganite material. The RBS spectra also show that the films have good stoichiometry. Atomic force microscopy was used to determine the roughness of the thin films. The annealed film (average roughness 4.5 nm) shows a surface smoother than the non-annealed film (average roughness 5.3 nm). SEM measurements show that in the case of samples having a high Fe content, the crystallite size varies between about 0.04 11m and 0.10 11m, while for samples with high manganese content, the crystallinity varies between 0.03 jJ,m and 0.06jLm. Manganites were analyzed using Bragg-Brentano (28) X-ray diffraction. Measurements show that manganite films cannot be grown epitaxially on Si< 100 > and MgO< 100 > single crystals due to a large lattice mismatch. In the case of SrTi03 and LaAl03 several reflections and sharp peaks from the film can be seen, indicating reasonable epitaxial growth. SEM measurements of the samples however show polycrystallinity. Complete epitaxy has thus not occurred, but many grains have an epitaxial orientation. Resistance versus temperature (the room temperature to about 100 K) in zero magnetic field was measured for a La2CaMno.06Fe2.409 thin film and maximum resistance corresponding to about 108 K was found. At higher temperatures the resistance decreases as temperature increases. The manganite thin film therefore shows semiconductor behaviour. Resistance measurements carried out at different magnetic fields (0 - 1 T) show a small positive magnetoresistance of 0.83 %. Usually the magnetoresistance phenomenon is measured at higher magnetic fields and this could be the reason for our low value as well as the fact that the iron content could be too high. / AFRIKAANSE OPSOMMING: In hierdie ondersoek is die formasie en karakterisering van dunlagie manganiete ondersoek. Om die effek van oksidasie-toestand op magnetoresistiwiteit te bepaal, is 80% van die Mn verplaas deur Fe. Pulseerde laser deposissie(3 J/cm2), is uitgevoer by 'n parsiële suurstof druk tussen 0.10 en 1.00 mbar deur gebruik te maak van La2Ca Mn2.94Feo.o609 en La2CaMno.6Fe2.409 teiken skywe. Dunlagies was gedeponeer op Si<IOO>, MgO<IOO>, SrTi03<100> en LaAl03<100> enkelkristal substrate. Die dunlagies is daarna ge-karakteriseer met behulp van Rutherford terugverstrooing (RBS), atoom krag mikroskopie(AFM), skandeer elektronmikroskopie (SEM) en xstraal diffraksie(XRD). Elektriese metings is ook uitgevoer. Een van die hoof tegnieke wat gebruik is in hierdie ondersoek is Rutherford terugverstrooing (RBS) van 2 Mev alfa-deeltjies. In hierdie navorsing is aangetoon dat RBS saam met spektra simulasie(RUMP), 'n besondere kragtige metode is om die stoichiometrie en dikte van manganiet lagies te bepaal. Die rol van die opname van suurstof in die dunlagies was ondersoek, aangesien die oksidasie toestand van manganiet lagies 'n groot effek het op hulle magnetoresistiwiteit. Die hoogte van die La sein is gebruik as 'n maatstaf van suurstof inhoud. RBS spektra van dunlagies gevorm op enkelkristal silikon substrate by verskillende parsiële suurstof drukke wys dat die passing tussen gemete en gesimuleerde spektra verbeter by hoër suurstof drukke, wat beter kwaliteit manganiet materiaal aandui. Die RBS spektra het ook aangetoon dat die stoichiometrie van die lagies uitstekend is. Atoom krag mikroskopie(AFM) is gebruik om die grofheid van die oppervlaktes van die dunlagies te bepaal. Lagies wat by 750 grade celsius uitgegloei is ( gemiddelde gladheid van 4.5 nm) was gladder as films wat nie na ablasie uitgegloei is nie (gemiddelde gladheid van 5.3 nm). SEM metings toon ook dat dunlagies met 'n hoë Fe inhoud 'n kristalliet deursnit het van 0.04 tot 0.10 mikrometer en die met 'n hoë mangaan inhoud 'n poli-kristalliniteit het van tussen 0.03 en 0.06 mikrometer het. Bragg-Brentano(twee-theta) X-straal diffraksie meting wys dat manganiet films nie epitaksieël op Si<IOO> en MgO<IOO> enkelkristal substrate gevorm kan word nie, weens 'n groot verskil in die kristal-rooster parameters. SEM metings van die monsters wys polikristalliniteit. Algehele epitaksie het dus nie plaasgevind nie, maar verskeie kristalliete het 'n epitaksiële orientasie. Weerstand metings is gemaak by temperature so laag as 100 Kelvin vir La2CaMno.o6Fe2.409dunlagies en 'n maksimum weerstand is by 108 Kelvin gevind. By hoër temperature het die weerstand afgeneem soos die temperatuur toeneem, wat halfgeleier gedrag aandui. Weerstand metings by verskillende magneetvelde (0 tot I Tesla) wys 'n klein magnetoresistiwiteits effek van 0.83%. Gewoonlik word magnetoresistiwiteit gemeet by hoë magneet velde (ongeveer 6 Tesla). Dit, sowel as die hoë Fe samestelling van die monsters kan die rede wees vir die lae magnetoresistiwiteit wat waargeneem word.

by Fung Chi Keung = 採用脈衝直流電源對靶濺射技術製備銦錫氧化物薄膜的硏究 / 馮志強. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Fung Chi Keung = Cai yong mai chong zhi liu dian yuan dui ba jian she ji shu zhi bei yin xi yang hua wu bo mo de yan jiu / Feng Zhiqiang. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of contents --- p.iv / List of figures --- p.viii / List of tables --- p.xii / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1 --- Genesis --- p.1-1 / Chapter 1.2 --- Aims and Objectives --- p.1-1 / Chapter 1.3 --- Layout of Thesis --- p.1-3 / References --- p.1-4 / Chapter Chapter 2 --- Literature Review --- p.2-1 / Chapter 2.1 --- Introduction to transparent conducting oxides (TCOs) --- p.2-1 / Chapter 2.2 --- Indium tin oxide (ITO) --- p.2-2 / Chapter 2.2.1 --- Use of ITO --- p.2-2 / Chapter 2.2.2 --- Structure and properties of ITO --- p.2-3 / Chapter 2.3 --- Properties of ITO films deposited by different growth techniques --- p.2-8 / Chapter 2.3.1 --- Sputtering --- p.2-9 / Chapter 2.3.2 --- Vacuum evaporation --- p.2-11 / Chapter 2.3.3 --- Spray pyrolysis --- p.2-11 / Chapter 2.3.4 --- Chemical vapor deposition (CVD) --- p.2-12 / Chapter 2.3.5 --- Reactive ion plating --- p.2-12 / Chapter 2.4 --- Contradictions in existing literature --- p.2-13 / References --- p.2-15 / Chapter Chapter 3 --- Thin Film Fabrication and Process --- p.3-1 / Chapter 3.1 --- Facing-target sputtering (FTS) --- p.3-1 / Chapter 3.2 --- Asymmetric bipolar pulsed DC power source --- p.3-3 / Chapter 3.2.1 --- Target poisoning --- p.3-3 / Chapter 3.2.2 --- Preferential sputtering --- p.3-4 / Chapter 3.2.3 --- Discussion --- p.3-4 / Chapter 3.3 --- Substrates --- p.3-6 / Chapter 3.3.1 --- Microscopic glass --- p.3-7 / Chapter 3.3.2 --- Corning 7059 glass --- p.3-8 / Chapter 3.3.3 --- Epitaxial growth --- p.3-8 / Chapter 3.3.3.1 --- Epitaxial lattice matching --- p.3-8 / Chapter 3.3.3.2 --- Yttrium stabilized zirconia (YSZ) --- p.3-9 / Chapter 3.3.3.3 --- Sapphire --- p.3-9 / Chapter 3.3.3.4 --- Silicon wafer --- p.3-11 / Chapter 3.3.4 --- Substrate cleaning --- p.3-11 / Chapter 3.4 --- Targets for the reactive sputtering of ITO films --- p.3-13 / Chapter 3.4.1 --- Indium Tin Oxide target (90wt% ln203 : 10wt% Sn04) --- p.3-14 / Chapter 3.4.2 --- Indium Tin alloy target (90wt% In : 10wt% Sn) --- p.3-14 / Chapter 3.5 --- Deposition conditions --- p.3-16 / Chapter 3.5.1 --- Sputter atmosphere --- p.3-16 / Chapter 3.5.2 --- Deposition pressure --- p.3-16 / Chapter 3.5.3 --- Deposition power --- p.3-17 / Chapter 3.5.4 --- Target to substrate distance --- p.3-17 / Chapter 3.5.5 --- Pulse frequency and pulse width --- p.3-17 / Chapter 3.6 --- Deposition --- p.3-17 / References --- p.3-19 / Chapter Chapter 4 --- Measurement and Analysis Techniques --- p.4-1 / Chapter 4.1 --- Resistivity measurement --- p.4-1 / Chapter 4.2 --- "Transmittance, reflectivity and absorption measurements" --- p.4-3 / Chapter 4.3 --- Thickness measurement --- p.4-4 / Chapter 4.4 --- "Crystal structure, surface morphology and roughness measurements" --- p.4-4 / Chapter 4.5 --- Photolithography --- p.4-7 / Chapter 4.6 --- Hall effect measurements --- p.4-8 / References --- p.4-10 / Chapter Chapter 5 --- Experimental results and discussions --- p.5-1 / Chapter 5.1 --- Effect of O2 partial pressure --- p.5-1 / Chapter 5.1.1 --- Deposition rate --- p.5-2 / Chapter 5.1.2 --- Electrical and optical properties --- p.5-4 / Chapter 5.1.3 --- Structure and orientation --- p.5-16 / Chapter 5.1.4 --- Surface morphology and roughness --- p.5-22 / Chapter 5.1.5 --- Conclusion --- p.5-29 / Chapter 5.2 --- Effect of substrate temperature --- p.5-29 / Chapter 5.2.1 --- Electrical and optical properties --- p.5-29 / Chapter 5.2.2 --- Structure and orientation --- p.5-44 / Chapter 5.2.3 --- Surface morphology and roughness --- p.5-49 / Chapter 5.2.4 --- Conclusion --- p.5-54 / Chapter 5.3 --- Effect of vacuum annealing --- p.5-54 / Chapter 5.3.1 --- Electrical and optical properties --- p.5-54 / Chapter 5.3.2 --- Conclusion --- p.5-59 / Chapter 5.4 --- Effect of different substrates --- p.5-59 / Chapter 5.4.1 --- Comparison of heteroepitaxial and polycrystalline ITO films --- p.5-60 / Chapter 5.4.2 --- Conclusion --- p.5-63 / Chapter 5.5 --- Effect of film thickness --- p.5-64 / Chapter 5.5.1 --- Film thickness calibration --- p.5-64 / Chapter 5.5.2 --- Electrical properties --- p.5-64 / Chapter 5.5.3 --- Conclusion --- p.5-67 / Chapter 5.6 --- Effect of deposition pressure --- p.5-68 / Chapter 5.6.1 --- Deposition rate --- p.5-68 / Chapter 5.6.2 --- Electrical properties --- p.5-70 / Chapter 5.6.3 --- Conclusion --- p.5-70 / Chapter 5.7 --- Effect of target pre-conditioning --- p.5-72 / Chapter 5.8 --- Conclusion --- p.5-72 / References --- p.5-74 / Chapter Chapter 6 --- Further works --- p.6-1 / Appendix I

The isolation of monolayer graphene by Andre Geim and Konstantin Novoselov in 2004 created an explosion of layered materials research in the fields of condensed matter physics, material science, electrical engineering, chemistry, and nanobiology, to name a few. The applications have been broad from enhancing electrode performance in batteries to gas sensing to high-frequency analog flexible electronics. For several years and still to this day, graphene has provided a fertile ground for research due to its superior properties. However, failed efforts to engineer a substantial bandgap, a requirement for digital electronics, led researchers to look elsewhere in the periodic table for other layered materials with rich physics and an even broader application space. Fortunately, the technical expertise developed in the graphene system could, for the most part, be leveraged and modified in these new material systems. This thesis presents a brief history of the field of two-dimensional electronics. The rediscovery - and it can only really be characterized as such since most of these materials were studied in the bulk form going back to the 1960s - of these two-dimensional materials with properties ranging from superconductivity, piezoelectricity, optical and electrical anisotropy, and large magnetoresistivity required the development of new characterization techniques to address the perturbations that accompanied the “thinning” of layers. Several characterization techniques were developed and are presented in this thesis. Moreover, in an effort to push these materials closer towards technological viability, synthesis techniques were developed that enabled the systematic study of a prototypical material system, molybdenum disulfide (MoS₂), in order to address the challenges that accompany scalability and determine the structure-property-function relationship.

by Xu Mingsheng. / "October 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. / 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.

Over the last 5 decades, the semiconductor industry has been well served by Si based technology due to its abundant availability, lower manufacturing cost, large wafer sizes and less complexity in fabrication. Over this period, electronic devices and integrated systems have been miniaturized by downscaling of the transistors. The miniaturization has been guided by the Moore's law where the numbers of transistors have doubled over every two years. However, the trend of transistor miniaturization is fast approaching its limit. Hence, alternate and innovative solutions are necessary to tackle this problem and this propels the research for finding novel materials with unique properties. The isolation of graphene, a single layer of graphite in 2004 had dramatically pioneered a new regime of research and investigation as a potential material to replace traditional Si. Graphene is the most widely studied two dimensional (2D) material exhibiting fascinating electronic, optoelectronic and electrochemical properties. Room temperature graphene has very high carrier mobility, a hundred times larger than that of Si, but it lacks a bandgap preventing its application in digital electronics. However, the advent of graphene initiated exploration of other 2D materials as a possible replacement for Si for future generation of electronic devices. Other 2D layered materials include transition metal dichalcogenides (TMDs), other layered metal chalcogenides, black phosphorus (BP), boron nitride (BN) etc which are also attractive due to fascinating electronic band structure and layer dependent properties that have demonstrated potential applications in optoelectronics and semiconductor devices. Metal chalcogenides are among the well-studied layered materials that have been isolated as high-quality and two-dimensional crystals. Among the 2D layered metal chalcogenide materials is tin selenide (SnSe), which belongs to group IV--VI that has attracted considerable attention due to its interesting structural and optical properties, hence it has potential applications in optoelectronics, photovoltaics, memory, energy storage, and catalysis. To date, SnSe films have been produced by exfoliation or chemical vapor deposition that produces flaky films. In this research, uniform, smooth and high quality SnSe thin films were grown over large area (5cm x 5cm) Si/SiO2 substrates using Atomic Layer Deposition (ALD). Films were grown over a temperature range of 350°C to 450°C, which exhibit p- type semiconductor characteristics. ALD is perfect for the growth of layered materials due to its precise controllability of film composition and thickness as the growth proceeds layer by layer. Structural and optical properties of the as-grown films were investigated using X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). These analyses show growth of 2 dimensional, orthorhombic phase films. Magnetic analysis shows a paramagnetic behavior. Back-gated transistors were fabricated for electrical characterization which showed p-type conductance, with an average hole mobility of 10 cm2/V.s and Ion/Ioff ratio of ~105.

CuGaSe���/CuInSe��� tandem junction solar cell is currently being pursued to be a low cost and high efficiency renewable energy source. A reported theoretical efficiency of 33.9% solar cells has been the motivation to fabricate CuGaSe��� films in a simple and low cost method. Electrodeposition is a potentially suitable method to obtain the CuGaSe��� films. A better understanding of the electrodeposition process is required to optimize the process. Focusing on the manufacture of CuGaSe��� film, the reaction accompanying the electrodeposition of CuGaSe��� using rotating disk electrode from cupric sulfate, selenious acid and gallium chloride solution in sulphate medium were studied by voltammetry. Cyclic and rotating disk voltammetry in pure and binary systems were performed in order to understand the complexity of Cu + Ga + Se systems. Diffusion coefficients of Cu(II) and Se(IV) were determined using Levich equation to be 6.93x 10������ cm��/s and 9.69x 10������ cm��/s, respectively. The correlations between supporting electrolytes, flux ratios, working electrodes and films were investigated experimentally. The deposited films were characterized by Induced Couple Plasma Spectrometry, X-Ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-Ray. CuGaSe��� is formed via the reaction of CuSe compound reduction and Ga(III) and higher gallium concentration will favor the formation of CGS film. The incorporation of gallium is highly depending on the pH (higher is better). An impinging flow electrochemical reactor was built as an alternative approach for electrochemical deposition method. Preliminary experiments of copper and copper selenide electrodeposition were conducted, and the results were comparable to the rotated disk voltammetry. / Graduation date: 2004