Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, 2000. / Includes bibliographical references.

La thèse est une étude des propriétés photophysiques et photochimiques de systèmes contenant la molécule sulfonylcalix[4]arène, membre de la famille des thiacalixarènes. Une série d'études dans notre laboratoire a révélé qu'un complexe agrégat tétranucléaire de manganèse(II) avec le ligand para-tert-butylsulfonylcalix[4]arène (thiaSO2) montrait une forte émission rouge sous l'action de lumière bleu. Cette découverte surprenante est la base de cette étude doctorale.Le premier chapitre est une revue de la littérature concernant les thiacalixarènes et leurs complexes métalliques. La synthèse et les modifications de ces molécules seront décrites, ansi que leurs propriétés fondamentales.La deuxième partie se concentre sur les propriétés de luminescence. Afin de proposer une explication mécanistique, la réponse de l'émission provenant du complexe (K)[Mn4(thiaSO2)2F] (2) a été étudiée sous des conditions variables de pression, température, pression d'O2 … L'hypothèse que ces systèmes sont capables de produire l'oxygène singulet sera faite.Le troisième chapitre concerne les photoréactions de systèmes en solution des complexes de manganèse(II). La photo-oxydation des ions Mn2+ en Mn3+ a été étudiée et les divers facteurs contribuants à ce processus seront discutés. Le rôle important de l'oxygène et sa transformation en espèces réactives, l'effet du solvant et du pH du milieu de réaction, et l'importance des matériaux de départ, sont confirmés ; nous proposons un mécanisme réactionnel basé sur ces données et la photoréactivité du composé organique calculée par une méthode théorique.La dernière partie montrera la préparation et la caractérisation d'espèces hybrides organique-inorganique par l'insertion d'agrégats [Mn4(thiaSO2)2F]- dans des matériaux LDH (« Hydroxyde Double Lamellaires »). Ces hybrides sont réalisés par des méthodes de chimie douce. Les études préliminaires sur la structure, la luminescence, et la photoréactivité des produits ont été faites. Finalement, un essai a été fait afin de tester la capacité des matériaux hybrides à agir comme photocatalyseur pour l'oxydation de molécules simples / This thesis is a study of the photophysical and photochemical properties of systems containing the molecule sulfonylcalix[4]arene, a member of the thaicalixarene family. A series of studies in our laboratory revealed that a tetranuclear cluster complex of manganese(II) with the ligand para-tert-butylsulfonylcalix[4]arene (thiaSO2) displayed strong red emission under the action of blue light. This surprising discovery became the basis for this doctoral study.The first chapter is a review of the literature concerning thiacalixarenes and their metal complexes. The syntheses and modifications of these compounds will be described, as well as their fundamental properties.The second part is dedicated to the properties of luminescence. In order to propose a mechanistic explanation, the response of the emission arising from the complex (K)[Mn4(thiaSO2)2F] (2) has been studied under varying conditions of pressure, temperature, O2 partial pressure … The hypothesis that these systems are capable of producing singlet oxygen will be made.The third chapter is concerned with photoreactions of these systems in solution. The photo-oxidation of Mn2+ ions into Mn3+ ions was investigated and the various contributing factors to this process will be discussed. The important role of oxygen and its transformation into reactive species, the effect of the solvent and the pH of the reaction medium, and the importance of the starting material, are all confirmed; we will propose a reaction mechanism based on both these data and the photoreactivity inherent to the organic compound calculated by a theoretical method.The final part will show the preparation and characterisation of organic-inorganic hybrid species by the insertion of [Mn4(thiaSO2)2F]- aggregates into LDH (“Layered Double Hydroxide”) materials. These hybrids were obtained by soft chemistry methods. Preliminary investigations of the structure, the luminescence, and the photoreactivity of these products have been made. Finally, an attempt was carried out to test the capacity of these hybrid materials to act as photocatalysts for the oxidation of simple molecules

In this research, Ni–NiOx–Cr and Ni–NiOx–ZnO–Cr metal-insulator-metal (MIM) junction based tunnel diodes have been investigated for the purpose of a wide-band detector. An MIM diode has a multitude of applications such as harmonic mixers, rectifiers, millimeter wave and infrared detectors. Femtosecond-fast electron transport in MIM tunnel diodes also makes them attractive for energy-harvesting devices. These applications require the tunnel diodes to have high current-asymmetry and non-linear current-voltage behavior at low applied voltages and high frequencies. Asymmetric and non-linear characteristics of Ni–NiOx-Cr MIM tunnel diodes were enhanced in this research by the addition of ZnO as a second insulator layer in the MIM junction to form metal-insulator-insulator-metal (MIIM) structure. Electrical characteristics were studied in a voltage range of for the single-insulator Ni–NiOx–Cr and double-insulator Ni–NiOx–ZnO–Cr tunnel diodes. Since the electrical characteristics of the diode are sensitive to material selection, material arrangement, thickness, deposition techniques and conditions, understanding the diode behavior with respect to these factors is crucial to developing a robust diode structure. Thus, ZnO insulator layer in MIIM junction was deposited by two different techniques: sputtering and atomic layer deposition (ALD). Also, the optical properties were characterized for the sputter deposited NiOx insulator layers by ellipsometry and the impact of annealing was explored for the NiOx optical properties. The Ni–NiOx–Cr MIM tunnel diodes provide low resistance but exhibit a low (~1) current-asymmetry. Asymmetry increased by an order of magnitude in case of Ni–NiOx–ZnO–Cr MIIM tunnel diode. The sensitivity of the MIM and MIIM diodes was 11 V-1 and 16 V-1, respectively. The results suggest that the MIIM diode can provide improved asymmetry at low voltages. The tunneling behavior of the device was also demonstrated in the 4-298K temperature range. It is hypothesized that the improved performance of the bilayer insulator diode is due to resonant tunneling enabled by the second insulator. Finally, the MIM and MIIM devices were investigated for wide-band detection up to 50GHz (RF) and 0.3THz (optical).

A typical electronic or photonic device may consist of several materials each one potentially meeting at an interface or terminating with a free-surface boundary. As modern device dimensions reach deeper into the nanoscale regime, interfaces and boundaries become increasingly influential to both electrical and thermal energy transport. While a large majority of the device community focuses on the former, we focus here on the latter issue of thermal transport which is of great importance in implementing nanoscale devices as well as developing solutions for on-chip heat removal and waste heat scavenging. In this document we will discuss how modern performance enhancing techniques (strain, nanostructuring, alloying, etc.) affect thermal transport at boundaries and across interfaces through the avenue of three case studies. We use first-principles Density Functional Perturbation Theory to obtain the phonon spectrum of the materials of interest and then use the dispersion data as input to a phonon Boltzmann Transport model. First, we investigate the combined effects of strain and boundary scattering on the in-plane and cross-plane thermal conductivity of thin-film silicon and germanium. Second, we review a recently developed model for cross-dimensional (2D-3D) phonon transport and apply it to 3D-2D-3D stacked interfaces involving graphene and molybdenum disulfide 2D-layers. Third, we combine relevant models from earlier Chapters to study extrinsic effects, such as line edge roughness and substrate effects, on in-plane and through-plane thermal transport in 1H-phase transition metal dichalcogenide (TMD) alloys. Through these investigations we show that: (1) biaxial strain in Si and Ge thin-films can modulate cross-plane conductivity due to strong boundary scattering, (2) the thermal boundary conductance between 2D-3D materials can be enhanced in the presence of an encapsulating layer, and (3) the thermal conductivity of 1H-phase TMDs can be reduced by an order of magnitude through the combination of nanostructuring, alloying, and substrate effects.

Graphene electronics represent a developing field where many material properties and devices characteristics are still unknown. Researching several possible fabrication processes creates a fabrication process using resources found at Cal Poly a local industry sponsor. The project attempts to produce a graphene network in the shape of a fractal Sierpinski carpet. The fractal geometry proves that PDMS microfluidic channels produce the fine feature dimensions desired during graphene oxide deposit. Thermal reduction then reduces the graphene oxide into a purified state of graphene. Issues arise during thermal reduction because of excessive oxygen content in the furnace. The excess oxygen results in devices burning and additional oxidation of the gate contacts that prevents good electrical contact to the gates. Zero bias testing shows that the graphene oxide resistance decreases after thermal reduction, proving that thermal reduction of the devices occurs. Testing confirms a fabrication process producing graphene electronics; however, revision of processing steps, especially thermal reduction, should greatly improve the yield and functionality of the devices.

In this dissertation, I am presenting my research on the fabrication and simulation of the optical properties of 3D photonic crystals and 2D graded photonic super-crystals. The 3D photonic crystals were fabricated using holographic lithography with a single, custom-built reflective optical element (ROE) and single exposure from a visible light laser. Fully 3D photonic crystals with 4-fold, 5- fold, and 6-fold symmetries were fabricated using the flexible, 3D printed ROE. In addition, novel 2D graded photonic super-crystals were fabricated using a spatial light modulator (SLM) in a 4f setup for pixel-by-pixel phase engineering. The SLM was used to control the phase and intensity of sets of beams to fabricate the 2D photonic crystals in a single exposure. The 2D photonic crystals integrate super-cell periodicities with 4-fold, 5-fold, and 6-fold symmetries and a graded fill fraction. The simulations of the 2D graded photonic super-crystals show extraordinary properties such as full photonic band gaps and cavity modes with Q-factors of ~106. This research could help in the development of organic light emitting diodes, high-efficiency solar cells, and other devices.

We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl3, CoCl2, CuCl2, and MnCl2. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have considerable internal strain, resulting in clearly visible lattice distortions in bright and dark-field transmission electron micrographs. Photo and electroluminescence studies indicate that the strain-induced defects strongly dominate any dopant-related effects. However, annealing at moderate temperature as well as laser annealing induces strain relaxation and leads to dopant activation. Hence, the optical and electrical properties of the nanowires significantly improve, allowing these nanowires to become feasible for use in the fabrication of solar cell and LED devices. In addition, the magnetic impurities incorporated into our ZnO nanowires show superparamagnetic behavior at room-temperature, while Al-doped and undoped ZnO nanowires show no magnetic behavior. The electroluminescence (EL) is achieved from a vertical hybrid p-n junction LED arrangement consisting of a hole-conducting polymer and n-type ZnO nanowires, our group was the first to report this vertical nanowire-based LED in Könenkamp et al., 2004 [12]. The observed EL spectra show an ultraviolet excitonic emission peak and a broad defect-related emission band in the visible range. After annealing at 380° C, the defect related EL peak exhibits a characteristic shift to higher wavelengths, where the magnitude of the shift is dependent on the dopant type. Aluminum incorporation exhibited the most improved exciton related-emission, leading to the emergence of a narrow excitonic luminescence peak around 390 nm, which is close to the bandgap of ZnO. The comparison of spectra obtained from temperature-dependent photoluminescence (PL) measurements, before and after thermal annealing, also indicates that the optical activity of impurities changes noticeably upon annealing. The internal quantum efficiency for PL is measured to be as high as 16 percent for Al-doped samples annealed at 380° C. The PL measurements also show that the excitonic luminescence is preferentially guided, while the defect related emission is more isotropically emitted. The nanostructured heterojunction solar cell is designed such that thin CdSe quantum dot films are embedded between a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and an efficient collection of photogenerated carriers. Here, we present a detailed analysis of the pyridine solution and 1,2- ethanedithiol ligand exchange processes of the quantum dots, deposition processes of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal annealing process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous poly-crystalline film, with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the CdSe layer. The combination of the solution and ligand exchange of CdSe quantum dots, as well as the deposition and optimized annealing processes of this quantum dot layer, resulted in solar cells with an open-circuit voltage up to 0.6 V, a short circuit current of ~15 mA/cm2, an external quantum efficiency of 70 percent, and an energy conversion efficiency of 3.4 percent. This 3.4 percent efficiency is presently one of the best efficiencies obtained for this type of device.

Quantum dots show great potential for use as spectral converters in solar cells, lighting applications, and biological imaging. These applications require precise control of quantum dot size to maximize performance. The quality, size, and fluorescence of quantum dots depend on parameters that are difficult to control using traditional batch synthesis processes. An alternative, high precision process was developed for the synthesis of cadmium-selenide quantum dots using a microfluidic reactor and fluorescence flow cell. The process required creating separate cadmium and selenium precursors that were then mixed in a nitrogen environment at 17°C. Using an NE-300® syringe pump, the solution was pumped through a microfluidic reactor submerged in a 240°C oil bath. The reactor then fed through a water quench bath at 25°C to terminate the nucleation and growth reaction. The fluorescence profiles of the quantum dot solutions were then characterized with an in-line fluorescence flow cell used in conjunction with an Ocean Optics® USB4000® spectrometer and a ThorLabs® LED UV light source. Flow rates through the reactor were varied from 0.05ml/min to 2ml/min. A central peak wavelength was registered in the fluorescence profiles for each flow rate. Monodisperse Cd-Se quantum dot solutions were synthesized across a broad spectrum of wavelengths ranging from 490nm to 620nm. An empirical relationship between flow rate and center wavelength was determined.

The design and implementation of a micro-force displacement system was completed to test the force-displacement characteristics of square silicon diaphragms with side lengths of 4mm, 5mm, and 7mm with a thickness of 10um. The system utilizes a World Precision Instruments Fort 10g force transducer attached to a World Precession Instruments TBM4M amplifier. A Keithley 2400 source meter provided data acquisition of the force component of the system. A micro prober tip was utilized as the testing probe attached to the force transducer with a tip radius of 5um. The displacement of samples was measured using a Newport M433 linear stage driven by a Newport ESP300 motion controller (force readings at constant displacement intervals). An additional 3 linear stages were used to provide X and Y-axis positioning of samples beneath the probe tip. The system components were mounted to an optical bench to provide stability during testing. C# was used to deliver the code to the individual components of the system. In addition the software provides a graphic user interface for future users that includes a calibration utility (both X/Y and force calibration), live force-displacement graph, motion control, and a live video feed for sample alignment. Calibration of the force transducer was accomplished using an Adam Equipment PGW153e precision balance to assign force values to the voltage data produced from the transducer. Displacement calibration involved the use of a microscope calibration micrometer. The system was characterized with an equipment variability of ±1.02mg at 1.75um, and ±1.86mg at 3.5um with the ability to characterize samples with stiffness less than 279 mg/um. The displacement resolution of the system was determined to be 35 nm per step of the linear stages. The diaphragms created to test the machine were fabricated from 10um thick device layer SOI wafers. An etch consisting of 38g/l silicic acid, 7g/l ammonium persulfate, and 5% TMAH was used to reduce the formation of hillocks, and provide a consistent etch rate. A Gage R&R study was performed on the fabricated diaphragms, indicating that the deflection produced by the 4mm, 5mm, and 7mm diaphragms was resolvable by the machine. A model was developed to correlate theoretical results to the observed measured values.