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No description available.

Graduation date: 2002

The objective of the research presented in this thesis is to develop, implement, and demonstrate the utility of an n-sheet, state-space alternating-current thin-film electroluminescent (ACTFEL) device model. In this model, the phosphor layer is discretized into n + 1 layers, with band-to-band impact ionization, space charge creation/ annihilation, and luminescent impurity excitation/do-excitation occurring only at n sheets between the n + 1 layers. The state-space technique is a structured approach in which the ACTFEL device physics implementation is separated from the ACTFEL measurement circuit electrical response, resulting in a set of coupled, first-order differential equations which are numerically evaluated. The device physics implementation begins with electron injection from phosphor/insulator interfaces and band-to-band impact ionization. Phosphor layer space charge generation via band-to-band impact ionization and subsequent hole trapping, trap-to-band impact ionization, and shallow donor trap emission are then added to the model. Finally, impact excitation and radiative relaxation are added to the model to account for ACTFEL device optical properties. The utility of the n-sheet, state-space ACTFEL device model is demonstrated in simulations which verify hypotheses regarding ACTFEL device measured characteristics. The role of phosphor layer hole trapping and subsequent thermionic emission in SrS:Cu ACTFEL device EL thermal quenching is verified via simulation. Leaky ACTFEL device insulators are shown to produce high luminance but low efficiency. A novel space charge estimation technique using a single transferred charge curve is presented and verified via simulation. Hole trapping and trap-to-band impact ionization are shown to produce realistic overshoot in C-V curves, and each results in a different phosphor layer space charge distribution. DC coupling of the sense capacitor used in the measurement circuit to the applied voltage source is required for the generation of ACTFEL device electrical offset, as verified by simulation. Shallow donors are identified as a probable SrS:Ce ACTFEL device leakage charge mechanism. A field-independent emission rate time constant model is shown to yield realistic ZnS:Mn ACTFEL device leakage charge trends. / Graduation date: 2001

The goal of this thesis study is to develop an activated reactive evaporation (ARE) system and to demonstrate its utility by fabricating-alternating current thin-film electroluminescent (ACTFEL) oxide phosphor devices. ARE entails evaporation in an activated gas. The main ARE system components are three thermal evaporation sources, a microwave power supply, an electron cyclotron resonance plasma (ECR) source, a substrate heater/controller, a film thickness monitor, and a leak valve for gas flow control. Ga���0���:Eu ACTFEL devices are fabricated using the ARE system. The maximum Ga���O: deposition rate is approximately 2 nm/s. As-deposited films are transparent, insulating, and amorphous with an index of refraction of 1.68 and an optical bandgap of 4.25-4.9 eV. Ga���O��� films are typically amorphous until annealed above 1000��C in a furnace or by rapid thermal annealing. However, when hydrothermal annealing is employed, Ga���O��� films crystalize at temperatures as low as 450��C. Electrical and optical characterization indicates that the Ga���O���:Eu ACTFEL devices have very little charge transfer and emit very dim, orange-red electroluminescence with an emission peak of about 615 nm. / Graduation date: 2001

With the given information that dendrimers have precisely controlled their sizes and spherical structures in the molecular level, the aim of this study is to show that dendrimer particles can become ordered into a self-assembled regular structure due to the nature of their regular sizes and shapes. For this project, melamine based generation 3 dendrimer was used for solution cast of thin films from the dendrimer-chloroform solutions with different casting conditions, i.e. various solution concentrations, casting temperatures, and substrates. As a result of these experiments, unique phenomena of highly ordered uniform 2-D contraction separations were observed during the solvent evaporation from the dendrimer films. The cast films from the concentration of 0.8 wt% and higher exhibit regular 2-D separation contraction patterns and make well-developed regularly arrayed structures due to the interaction between the contraction stresses and adhesion strength between films and substrates. From the DSC tests, both powder and cast film samples of a dendrimer show similar melting behaviors with different areas under the melting peaks. The results of these tests show that dendrimers, when they are in a descent environment that provides dendrimers with molecular mobility due to surface ionic bonding strength, can make a structural order and regularity in their macroscopic structures.

Graduation date: 1993

Mn12-acetate single-molecule magnets (SMMs) are nano-scale magnets showing a strong magnetic anisotropy, slow relaxation and stepwise magnetic hysteresis curves. Possible applications of Mn12-acetate, e.g. for ultra high density magnetic information storage device, quantum computation, and magnetic molecular electronics, have been suggested due to the unusual magnetic behavior. It is an important prerequisite for the applications to develop a reliable technique to organize the molecules on a surface and to detect the magnetic signals of the molecules. A solution evaporation technique combined with conventional lithography is a simple but reliable method to create Mn12-acetate thin film patterns on the micro/nano-scale. The method is demonstrated with a series of analysis. A superconducting quantum interference device (SQUID) shows a non-linear I-V (Current vs. Voltage) characteristic that is modulated by a magnetic flux inside the loop, allowing one to sense and analyze an extremely weak magnetic field. The miniaturized SQUID is appropriate for sensing the magnetic flux from the film structure of the molecular magnets. Theoretical ideas, fabrication, and a measurement technique of the device are presented. A new interesting system, the so-called superconductor/SMM hybrid, results from the experimental configuration. Understanding this new type of hybrid system is important not only because of the expectation of new phenomena affecting the functionality of superconducting devices, but also because the two coupled substances are fundamentally incompatible phases. The first experimental attempt to investigate the interaction between an aluminum superconducting film and Mn12-acetate SMMs will be discussed.

Stress induced wavelength shift of thin film filter (TFF) were investigated. The substrate thickness of the TFF were greatly reduced by lapping to enhance the effects of stress. For CWDM TFF, no significant wavelength shift was observed by reducing their substrate thickness from 300 £gm to 70 £gm. Further, thermal stress caused by direct heating the thin TFF to 100¢J shows no effective changes of their optical characteristics. On the other hand, wavelength shifts induced by mechanical stress after reducing the substrate thickness of the DWDM TFF were observed. The maximum wavelength shift 3.8 nm was measured by lapping the substrate from 1mm to 120 £gm. Additional wavelength shifts of 3.5 nm were observed from the thin DWDM TFF if a lens fiber was brought into close contact with the thin DWDM TFF and was pushed forward for a distance of 45 £gm.

Zinc selenide is a wide bandgap II-VI semiconductor. The minimum bandgap at £F point (zone center) is direct and has a room temperature value of 2.67eV, corresponding to the blue region of the visible spectrum (464nm). Molecular beam epitaxy (MBE) is an ultra high vacuum technique used for the growth of semiconductors. The molecular beam epitaxy system used for the growth of semiconductors . The molecular beam epitaxy system used for growth of the II-VI semiconductor layers is described in detail in Chapter 2. Chapter 3 describes the substrate preparation procedure and growth of ZnSe epitaxial layers. Last, information from characterization technique has been used to analysis the quality of the layers and hence determine referred growth conditions.