Zinc Oxide (ZnO) has great potential for applications on ultraviolet/blue light emitting devices because of high exciton binding energy and low cost. This research use low lattice-mismatched £^-LiAlO2 (LAO) substrate to grow ZnO epitaxial films by chemical vapor deposition (CVD). The first part of the present study deals with effect of processing parameters including temperature of Zinc procuser, sample position and growth temperature on ZnO epilayer. High the precuser temperature and long distance between sample and center of CVD furnace resulted in high growth rates. When growth rate was low, (10 0) ZnO (m-ZnO) was obtained and its crystallinity and luminescence property were poor. After increasing the growth rate to a certain extent, the surface of epilayer was flat and the crystallinity was improved. A further increase of growth rate resulted in a mixture of m-ZnO and c-plane in the ZnO epilayer. Based on the first part of study, the second part was focused on examining the effect of a nanosized buffer layer on inhibiting the nucleation of c-plane ZnO. Results showed that the nucleation of c-plane ZnO was indeed inhibited at low growth temperature. Finally, the crystallinity the optical property of the epilayer were improved by introducing a thick and flat buffer layer of ~170 nm in thickness.

¡@In this thesis, we have studied the growth of M-plane GaN thin film on LiGaO2 (100) substrate by Plasma-Assisted Molecular Beam Epitaxy. We found that the growth of GaN thin films on as-received LiGaO2 substrates is poly-crystalline by analysis of X-ray diffraction, and these of GaN thin films were peeled off after thin film process. Using atomic force microscopy (AFM) to scan the surface of as-received LiGaO2 substrate, we found that many particles which are Ga2O3 existed on the surface of as-received LiGaO2. The annealing ambient for LiGaO2 substrates in vacuum and air ambient has been studied in order to improve the surface of LiGaO2. The scanning results of AFM shows that the crystal quality and stress of M-plane GaN grown on LiGaO2 (100) substrate pre-annealed in air ambient is significantly improved. We conclude that the reason of GaN peeling off from LiGaO2 substrate is attributed to stress between GaN/ LiGaO2. The measurement of polarization-dependent PL shows that the luminescence intensity of growing sample increases and reaches a maximum at £p = 90¢X (E¡æc), which indicates the growing samples is M-plane GaN as well. The microstructure of growing samples was characterized by transmission electron microscopy. We found that the formation of stacking fault in GaN is attributed to the growth of GaN on cubic-Ga2O3 nano-particles. The formation of Ga2O3 nano-particles can be suppressed by pre-annealing LiGaO2 substrate in air. It revealed that the thermal annealing LiGaO2 substrate in air ambient can improve the surface of LiGaO2 substrate effectively, and then one can grow a high quality M-plane GaN thin film on the LiGaO2 substrate.

The focus of this research is the development of high strength, high conductivity copper films. Pure copper is soft and traditional strengthening mechanisms cause substantial decrease in conductivity. To address the challenge, epitaxial nanotwinned copper films are synthesized on HF etched Si (110) substrates. These films show high hardness (~ 2.8 GPa) due to high density of coherent twin boundaries (CTBs) which effectively block the motion of dislocations similar to grain boundaries (GBs). Resistivity of CTBs is calculated to be an order of magnitude lower than that of GBs. Hence, conductivity of nanotwinned copper is still comparable to that of pure copper. In addition, it is shown that average twin spacing can be controlled by adjusting deposition rate. Analytical studies together with experimental evidence show that nanotwins can improve the strength-to-resistivity ratio significantly in copper. In general, nanocrystalline metals suffer from low ductility. To study plastic deformation via rolling, thick polycrystalline nanotwinned copper foils are sputtered on SiO2 and then peeled off the substrate. Despite the high strength, room temperature rolling experiments show that nanotwinned copper films exhibit stable plastic flow with no shear localization or fracture even at thickness reduction of over 50%. Postdeformation studies of microstructure reveals that the plastic deformation is facilitated by the migration of CTBs normal to the twin boundary plane due to the glide of twinning dislocations in the twin plane. X-ray pole figure measurements show insignificant out of plane rotation as a result of 50% rolling thickness reduction. Thermal stability of nanocrystalline metals is also a concern. Free standing nanotwinned polycrystalline copper films show remarkable thermal stability after annealing at 800 degrees C. The driving force for twin growth is much lower than that for grain coarsening because the energy stored in CTBs is an order of magnitude lower than that of GBs. As a result, the average twin spacing stays below 20 nm after annealing. Such high thermal stability of nanotwins leads to the retention of hardness of 2.2 GPa. Low energy twin boundary may provide a unique way to achieve both high strength and high temperature thermal stability in certain metallic materials.

In the past several years, epitaxial graphene on silicon carbide has been transformed from an academic curiosity of social scientists to a leading candidate material to replace silicon in post-CMOS electronics. This has come with rapid development of growth technologies, improved understanding of epitaxial graphene on the polar faces of silicon carbide, and new device fabrication techniques. The contributions of this thesis include refinement and improved understanding of graphene growth on the silicon- and carbon-faces in the context of managed local silicon partial pressure, high-throughput epitaxial graphene thickness measurement and uniformity characterization by ellipsometry, observations of nearly ideal graphene band structures on rotationally stacked carbon-face multilayer epitaxial graphene, presentation of initial experiments on localized in situ chemical modification of epitaxial graphene for an alternate path to semiconducting behavior, and novel device fabrication methods to exploit the crystal structure of the silicon carbide substrate. The latter is a particularly exciting foray into three dimensional patterning of the substrate that may eliminate the critical problem of edge roughness in graphene nanoribbons.

In der vorliegenden Arbeit wurden Röntgentechniken benutzt um die Struktur von dünnen (etwa 40 nm) CrSi2-Schichten, die unter UHV-Bedingungen mittels reaktive Koabscheidung und template-Verfahren auf Si(001) hergestellt wurden, zu charakterisieren. Die Ergebnisse wurden mit TEM-, SEM- und RBS-Untersuchungen korreliert und ergänzt. Die XRD-Analysen zeigen, dass die beiden Abscheideverfahren immer zur Bildung der CrSi2-Phase führen, wobei die Kristallite mit einer bevorzugten Orientierungsbeziehung CrSi2(001)[100] || Si(001)[110] wachsen. Im ersten Teil der Arbeit wurde die Cr-Si-Koabscheidung benutzt um die Prozessparameter zu bestimmen, die zum Wachstum epitaktischer Schichten führen können. Die Strukturuntersuchungen zeigen, dass nur bei einer Substrattemperatur von 700°C nahezu geschlossene Schichten mit Kristalliten, welche lateral eine Größe bis zu 300 nm haben und neben der bevorzugten noch andere Orientierungen zum Substrat aufweisen, entstehen. Als zweite Herstellungsmethode wurde das template-Verfahren verwendet, wo die Cr-Si-Koabscheidung auf ein vorher in-situ präpariertes ultradünnes CrSi2-template erfolgt. Die Morphologie und die Stärke der bevorzugten Orientierung der CrSi2-Schichten sind stark von der template-Dicke abhängig. Die Abscheidung auf CrSi2-templates, welche aus einer Cr-Schicht mit nominaler Dicker von 0,35 nm bis 0,52 nm entstehen, führt zum Wachstum weitgehend geschlossener, homogener und epitaktischer CrSi2-Schichten. Ein Modell, das den Einfluss der template-Dicke auf die Qualität der CrSi2-Schichten erklären kann, wird vorgeschlagen.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 80-84). Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 97-104).

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 95-100).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 105 p. : ill. Includes abstract. Includes bibliographical references (p. 100-105).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.