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The frontier orbitals of organic semiconductors at interfaces as they relate to organic electronic device applications, both relative energy and possible relative orientations, are the focus of this work. Heterojunctions between perylenetetracarboxylicdianhydride (PTCDA) or N,N'-di-n-butylperylene bis(dicarboximide) (C4-PTCDI) and metal centered phthalocyanines, including chloroaluminum, chloroindium, zinc, and copper phthalocyanine, have been characterized with ultraviolet photoelectron spectroscopy (UPS).Organic semiconductors heterojunctions clearly demonstrate that they cannot be treated as insulators, that vacuum level shifts occur at many organic semiconductor heterojunctions, and that Fermi level alignment is achieved but the individual nature of the organic Fermi levels must considered. UPS shows that the n-type semiconductors PTCDA and C4-PTCDI have organic Fermi levels pinned at the lower edge of the LUMO. Phthalocyanines have organic Fermi levels approximately midway between the HOMO and LUMO. The same Fermi levels are applicable for organic semiconductors at interfaces with gold as with other organic semiconductors. Further, heterojunctions of the organic semiconductors on gold show that although the alignment farther from the interface is determined by Fermi level alignment, at the immediate interface the interface dipole is determined by different factors as described by the additive model of interface dipole formation which includes factors for metal surface dipole, charge transfer, and molecular dipole moments. This model and the role of the molecular dipolar have been well characterized with alkanethiol and fluorinated alkanethiol self-assembled monolayers on gold, leading to the conclusions that the effective work function of the gold surface could be modified over a range of ca. 1.5eV with the SAM dipole and that the gold-sulfur bond is largely covalent.Fluorescence spectroscopy of phthalocyanine heterojunctions with PTCDA and C4-PTCDI was able to determine favored interfacial exciton dissociation pathways, and that charge transfer dissociation to form mobile charges is favored at PTCDA heterojunctions but energy transfer to create phthalocyanine excitons dominates at C4-PTCDI heterojunctions. The wavelength and progression of fluorescence emission from monomer phthalocyanines and aggregated phthalocyanine structures was also able to characterize thin film growth and the resultant polymorphs created by vacuum deposition of phthalocyanines on KCl (100) surfaces and on PTCDA and C4-PTCDI thin films.

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Jiao Yang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 85-87). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Table of Content --- p.iv / List of Figures --- p.ix / List of Tables --- p.xiv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Background of the Pseudo One-dimensional Si Crystal Growth --- p.5 / Chapter 2.1 --- Vapor-liquid-solid (VLS) Mechanism --- p.5 / Chapter 2.2 --- Oxide-assisted-growth (OAG) Mechanism --- p.8 / Chapter 2.3 --- Solid-liquid-solid Mechanism --- p.10 / Chapter Chapter 3 --- Instrumentation --- p.12 / Chapter 3.1 --- Deposition Apparatus --- p.12 / Chapter 3.2 --- Scanning Electron Microscope (SEM) --- p.14 / Chapter 3.2.1 --- Principle of SEM --- p.14 / Chapter 3.2.2 --- Electron-specimen Interactions in SEM --- p.14 / Chapter 3.2.3 --- Imaging by Secondary Electron --- p.15 / Chapter 3.2.4 --- Elemental Analysis by Energy Dispersive X-ray --- p.16 / Chapter 3.3 --- Transmission Electron Microscope (TEM) --- p.18 / Chapter 3.3.1 --- Principle of the TEM --- p.18 / Chapter 3.3.2 --- Electron Specimen Interaction in TEM --- p.18 / Chapter 3.3.3 --- Electron Diffraction --- p.19 / Chapter 3.3.4 --- Contrast --- p.20 / Chapter 3.3.5 --- X-ray Microanalysis --- p.22 / Chapter 3.3.6 --- Energy-loss Spectrum and Element Distribution Image (elemental mapping) --- p.22 / Chapter 3.4 --- Scanning TEM (STEM) --- p.23 / Chapter Chapter 4 --- Synthesis of SiNWs Using Si Wafer and H2 --- p.31 / Chapter 4.1 --- Experiment --- p.31 / Chapter 4.2 --- Morphologies and Microstructures of the As-synthesized Nanowires --- p.32 / Chapter 4.2.1 --- Morphologies and Microstructures of the Nanowires Synthesized Using SiO Powder as the Starting Material (control experiment) --- p.32 / Chapter 4.2.2 --- Morphologies and Microstructures of the Nanowires Synthesized Using Smashed Si Wafers as the Source Material --- p.34 / Chapter 4.3 --- Discussions --- p.36 / Chapter 4.3.1 --- Growth Mechanism of the Modified SiNW Synthesis Method (use smashed Si wafer) --- p.36 / Chapter 4.3.1.1 --- Comparison with the OAG --- p.36 / Chapter 4.3.1.2 --- Yield Dependence on the Surface Area of the Si Wafer --- p.37 / Chapter 4.3.1.3 --- The Importance of H2 --- p.37 / Chapter 4.3.2 --- Advantages of the Modified Method --- p.38 / Chapter 4.3.2.1 --- Stable and Low Supersaturation Level (in comparison with the conventional OAG method using SiO powder) --- p.38 / Chapter 4.3.2.2 --- A Possible Method to Achieve SiNW Doping --- p.39 / Chapter Chapter 5 --- One-dimensional Au-Si Heterojunctions ´ؤ Microstructure and Phase Evolution under Electron Beam Irradiation --- p.48 / Chapter 5.1 --- Experiment --- p.48 / Chapter 5.2 --- Microstructure Analysis of the As-synthesized One-dimensional Au-Si Heterojunctions --- p.49 / Chapter 5.3 --- The Au Flow and Phase Evolution of the Au-Si Heteroj unctions under the Electron Beam Irradiation --- p.51 / Chapter 5.3.1 --- The Phenomenon --- p.51 / Chapter 5.3.2 --- The Mechanisms --- p.52 / Chapter 5.4 --- Conclusions --- p.55 / Chapter Chapter 6 --- A General Route to Fabricate One-dimensional Metal-Si Heteroj unctions --- p.65 / Chapter 6.1 --- Experiment --- p.65 / Chapter 6.2 --- Common Morphology Descriptions (SEM) --- p.66 / Chapter 6.3 --- 1D Au-Si Heterojunctions --- p.66 / Chapter 6.3.1 --- General Morphologies --- p.66 / Chapter 6.3.2 --- Effect of the Au Film Thickness on the Yield and Diameter of the Nanowire Products --- p.68 / Chapter 6.4 --- 1D Cu-Si Heterojunctions --- p.68 / Chapter 6.5 --- 1D Au-SiO2 Heterojunctions --- p.69 / Chapter 6.6 --- 1D Zn-SiO2 Heterojunctions --- p.70 / Chapter 6.7 --- Result of the Control Experiments --- p.70 / Chapter 6.8 --- Discussions --- p.70 / Chapter 6.8.1 --- General Mechanism of the 1D Si-metal Heterojunction Formation --- p.70 / Chapter 6.8.2 --- Source of the Si (vapor source and supersaturation control) --- p.71 / Chapter 6.8.3 --- Source of Metal --- p.72 / Chapter 6.8.4 --- Effect of the Reductive Atmosphere --- p.73 / Chapter Chapter 7 --- Conclusions --- p.83 / Reference --- p.85

<p>An <em>isotype heterojunction</em> is a junction between two layers of dissimilar semiconductors both of which are doped either n-type or p-type. These semiconductor structures are found in a variety of optoelectronic devices, such as solar cells, semiconductor lasers, and detectors. Motivated by the structure of third generation inorganic solar cells, this thesis concentrates on the analytical modelling of isotype heterojunctions and its application to the design optimization of these devices. The main development of this work is the introduction of an analytical expression for the current density across an isotype heterojunction valid for arbitrary doping concentration ratios. This result generalizes the standard expression found in the literature, which is limited by the assumption that the doping concentration ratio between the two sides of the heterojunction is equal to one. The generalization is developed by employing the Lambert W function in the solution of the electrostatic boundary condition associated with the heterojunction interface. As done in the derivation of the standard expression found in the literature, the generalization only considers thermionic emission, but the same method can readily be applied for other transport mechanisms. A key feature of this generalized result is that it mathematically contains the expression for the current density across a metal-semiconductor Schottky contact as a limiting case, thereby unifying the treatment of these two heterointerfaces into a single general analytical description. This latter find is particularly significant from a theoretical perspective, considering that the two heterointerfaces are traditionally described as separate topics in the presentation of semiconductor device theory.</p> / Master of Applied Science (MASc)

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