Optimal precursor behavior during Chemical Vapor Deposition (CVD) is crucial for reproducible synthesis of high quality thin films. Desirable precursor properties include: 1) volatility and thermal stability at <180 °C (10 - 100 millitorr vapor pressure at atmospheric pressure) 2) low decomposition temperature (350-550 °C) to metal oxide with minimal organic ligand contamination and 3) ambient stability and minimal toxicity. Optimal selection and usage of CVD precursors is implemented by synthesis and characterization studies. Additionally, precursor synthesis and characterization studies render the development of novel precursors, which are specifically engineered for the CVD process. Lead bis-tetramethylheptadione [Pb(thd)₂], lead bis-heptafluorodimethyloctadione [Pb(fod)₂], and zirconium tetrakis-tetramethylheptadione [Zr(thd)₄], which are lead and zirconium precursors for CVD of Pb(Zr_xTi_1-x)O₃ thin films, and T8- hydridospherosiloxane, which is a silica precursor, were synthesized and purified. Free ligand was the predominant impurity from the lead and zirconium precursor syntheses, and the T8 synthesis produced several byproducts including T10-hydridospherosiloxane and a polymer. The lead and zirconium precursors were purified by recrystallization from toluene, and the T8 was purified by extracting the byproducts with pentane. Purity of Pb(thd)₂, Pb(fod)₂ and Zr(thd)₄ was confirmed by melting point determination, carbon and hydrogen elemental analysis and proton nuclear magnetic resonance spectrometry (NMR). Purity of T8 was confirmed by proton NMR. Isothermal gravimetric analysis (TGA) was used to study volatility and thermal stability of the precursors. The Zr(thd)₄ isotherms ranged from 180-260 °C, the Pb(thd)₂ and Pb(fod)₂ isotherms were 80-200 °C, and the T8 isotherms were 80-140 °C. Vapor pressure was calculated from TGA data, with use of diffusion equations. Precursors exhibited vapor pressure ranging from 0.2 - 600 millitorr, over their respective vaporization temperature ranges. Enthalpy of vaporization was calculated from Arrhenius plots of vapor pressure as a function of temperature. The Zr(thd)₄ and T8 were observed to be thermally stable over the temperature ranges and durations of experiments. The Pb(thd)₂ and Pb(fod)₂ are not thermally stable over the vaporization temperatures, and undergo oligomerization when heated at high vaporization temperatures. Addition of a polyether adduct to the lead precursor was proposed to inhibit oligomer formation at high vaporization temperatures. Precursor decomposition studies were executed in sealed quartz tubes. Products of decomposition were examined by infrared spectrometry, mass spectrometry, and solid state NMR spectrometry. Metal oxide formation from decomposition of precursors was observed at; 300-350 °C for T8, 350-550 °C for Zr(thd)₄, 250-350 °C for Pb(thd)₂, and 300 °C for Pb(fod)₂. Lead fluoride became the dominant phase of Pb(fod)₂ decomposition products above 300 °C. Intermediate decomposition products of all the precursors were documented and discussed. Synthesis and/or isolation of intermediate decomposition products of Zr(thd)₄ , Zr2O(thd)₄, was proposed as a novel precursor for ZrO₂ deposition. / Master of Science

The objective of this dissertation is to develop amorphous metal thin films (AMTFs) for two-terminal electrical device and nanolaminate applications. Two AMTFs, ZrCuAlNi and TiAl, are investigated in both two-terminal electrical device and nanolaminate applications. Material properties including composition, atomic order, surface morphology, surface potential, and electrical resistivity are explored. Application of AMTFs as electrodes in tunneling MIM diodes leverages the ultra-smooth AMTF surface morphology which results from the amorphous atomic order of AMTFs. Analysis methodologies using tunneling MIM diode I-V characteristics are described. A methodology used to estimate potential barrier heights is applied to tunneling MIM diode with differing lower electrode material, upper electrode material and upper electrode deposition technique. A second methodology used to estimate relative tunneling MIM diode insulator thickness is also presented. The presented I-V characteristic analysis methodologies illustrate that tunneling MIM diodes fabricated with AMTF lower electrodes possess tunable I-V characteristics. Nanolaminates are layered materials fabricated with alternating dissimilar thin-film layers. The flexibility of AMTF nanolaminates is illustrated through the presentation of amorphous metal/oxide nanolaminates fabricated with differing AMTFs and aqueous solution deposited oxides. TEM and XPS depth profile analysis of realized nanolaminates are presented. The optical dielectric response of ZrCuAlNi/aluminum phosphate oxide (AlPO) and TiAl/AlPO nanolaminates are evaluated through polarized reflectance measurements and effective medium theory. The optical dielectric response of the nanolaminates differ from the optical dielectric response of the component layers. ZrCuAlNi/AlPO and TiAl/AlPO nanolaminates therefore satisfy the definition of metamaterials. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from May 9, 2012 - May 9, 2013

In this thesis, I present studies in the field of terahertz (THz) spectroscopy. These studies are divided into three areas: Development of a narrowband THz source, the study of carrier transport in metal thin films, and the exploration of coherent dynamics of quasi-particles in semiconductor nanostructures with both broadband and narrowband THz sources. The narrowband THz source makes use of type II difference frequency generation (DFG) in a nonlinear crystal to generate THz waves. By using two linearly chirped, orthogonally polarized optical pulses to drive the DFG, we were able to produce a tunable source of strong, narrowband THz radiation. The broadband source makes use of optical rectification of an ultra-short optical pulse in a nonlinear crystal to generate a single-cycle THz pulse. Linear spectroscopic measurements were taken on NiTi-alloy thin films of various thicknesses and titanium concentrations with broadband THz pulses as well as THz power transmission measurements. By applying a combination of the Drude model and Fresnel thin-film coefficients, we were able to extract the DC resistivity of the NiTi-alloy thin films. Using the narrowband source of THz radiation, we explored the exciton dynamics of semiconductor quantum wells. These dynamics were made sense of by observing time-resolved transmission measurements and comparing them to theoretical calculations. By tuning the THz photon energy near exciton transition energies, we were able to observe extreme nonlinear optical transients including the onset of Rabi oscillations. Furthermore, we applied the broadband THz waves to quantum wells embedded in a microcavity, and time-resolved reflectivity measurements were taken. Many interesting nonlinear optical transients were observed, including interference effects between the modulated polariton states in the sample. / Graduation date: 2012

xv, 101 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries under the call number: KNIGHT QC176.84.E5 P47 2007 / Silver films with nanoscale to mesoscale thicknesses were produced by chemical reduction onto silica substrates and their physical and electrical properties were investigated and characterized. The method of silver deposition was developed in the context of this research and uses a single step reaction to produce consistent silver films on both flat silica coverslips and silica nanospheres of 250-1000 nm. Both the structure and the electrical properties of the silver films are found to differ significantly from those produced by vacuum deposition. Chemically deposited (CD) silver is not uniformly smooth, but rather is granular and porous with a network-like structure. By quantitatively accounting for the differences in scale, geometry, and microstructure of the CD films, it is found that the same models used to describe the resistivity of vacuum deposited films may be applied to CD films. A critical point in the analysis that allows this relation involves the definition of a geometric parameter, g, which replaces the thickness, t, as the critical length that influences the electrical properties of the film. The temperature dependent properties of electrical transport were also investigated and related to the microstructure of the CD films. A detailed characterization of CD silver as shells on silica spheres is also presented including physical and optical properties. In spite of the rough and porous morphology of the shells, the plasmon resonance of the core-shell structure is determined by the overall spherical shell structure and is tunable through variations in the shell thickness. Preliminary investigations into the electrical transport properties of aggregates of silver coated spheres suggest similarities in the influence scale, geometry, and microstructure to silver films on flat substrates. The aggregates of shells also exhibit pressure related resistance behavior due to the composite structure. / Adviser: Miriam Deutsch

Solution processed circuits are expected to be the main components to achieve low cost, large area, flexible electronics. However, the commercialization of solution processed flexible electronics face several challenges. The passive component such as capacitors are limited in frequency range and operating voltage. The active component such as transistors suffer from low mobility ultimately leading to limited current-carrying capacity. Just as in traditional silicon technology, the fabrication process and material choices significantly impact the performance of the fabricated devices. My thesis focuses on the optimization of the performance of printed capacitors and transistors through investigation of several aspects of the device structure and fabrication process. The first part of this work focuses on the optimization of printed nanoparticle/polymer composite capacitors. Thin film metal oxide nanoparticle/polymer composites have enormous potential to achieve printable high-k dielectrics. The combination of high-k ceramic nanoparticle and polymer enables room temperature deposition of high dielectric constant film without the need of high temperature sintering process. The polymer matrix host fills the packing voids left behind by the nanoparticles resulting to higher effective dielectric permittivity as a system and suppresses surface states leading to reduced dielectric loss. Such composite systems have been employed in a number of flexible electronic applications such as the dielectrics in capacitors and thin film transistors. One of the most important properties of thin film capacitors is the breakdown field. In a typical capacitor system, the breakdown process leads to catastrophic failure that destroys the capacitor; however, in a nanoparticle/polymer composite system with self-healing property, the point of breakdown is not well-defined. The breakdown of the dielectric or electrodes in the system limits the leakage observed. It is possible, however, to define a voltage/field tolerance. Field tolerance is defined as the highest practical field at which the device stays operational with low failure rate by qualifying the devices with defined leakage current density. In my work, the optimization of the field tolerance of (Ba,Sr)TiO₃ (BST)/parylene-C composite capacitors is achieved by studying the influence of the electromigration parameter on leakage and field strength through the inherit asymmetrical structure of the fabricated capacitors. One approach to creating these composites is to use a spin-coated nanoparticle film together with vapor deposited polymers, which can yield high performance, but also forms a structurally asymmetric device. The performance of a nanoparticle BST/parylene-C composite capacitor is compared to that of a nanoparticle BST capacitor without the polymer layer under both directions of bias. The composite device shows a five orders of magnitude improvement in the leakage current under positive bias of the bottom electrode relative to the pure-particle device, and four orders of magnitude improvement when the top electrode is positively biased. The voltage tolerance of the device is also improved, and it is asymmetric (44 V vs. 28 V in bottom and top positive bias, respectively). This study demonstrates the advantage of this class of composite device construction, but also shows that proper application of the device bias in this type of asymmetrical system can yield an additional benefit. The dependence of the field tolerance of nanoparticle/polymer composite capacitors on the electromigration parameter of the electrodes is investigated using the symmetrical dielectric system. The breakdown is suppressed by selecting the polarity used in nanoparticle (Ba,Sr)TiO₃/parylene-C composite film-based capacitors. Metals including gold, silver, copper, chromium, and aluminum with comparable surface conditions were examined as the electrodes. The asymmetric silver, aluminum, gold, copper, and chromium electrode devices show a 64 %, 29 %, 28 %, 17 %, 33 %, improvement in the effective maximum operating field, respectively, when comparing bias polarity. The field at which filament formation is observed shows a clear dependence on the electromigration properties of the electrode material and demonstrates that use of electromigration resistant metal electrodes offers an additional route to improving the performance of capacitors using this nanoparticle/polymer composite architecture. The second part of my thesis focuses on the novel pneumatic printing process that enables manipulation of the crystal growth of the organic semiconductors to achieve oriented crystal with high mobility. Small molecule organic semiconductors are attracting immense attention as the active material for the large-area flexible electronics due to their solution processability, mechanical flexibility, and potential for high performance. However, the ability to rapidly pattern and deposit multiple materials and control the thin-film morphology are significant challenges facing industrial scale production. A novel and simple pneumatic nozzle printing approach is developed to control the crystallization of organic thin-films and deposit multiple materials with wide range of viscosity including on the same substrate. Pneumatic printing uses capillary action between the nozzle and substrate combined with control of air pressure to dispense the solution from a dispense tip with a reservoir. Orientation and size of the crystals is controlled by tuning the printing direction, speed, and the temperature of the substrate. The main advantages of pneumatic printing technique are 1) simple setup and process, 2) multi-material layered deposition applicable to wide range of solution viscosity, 3) control over crystal growth. The manipulation of crystal growth will be discussed in the next chapter. This method for performance optimization and patterning has great potential for advancing printed electronics. The dependence of the mobility of printed thin film 6,13-bis(triisopropylsilylethynyl) pentacene [TIPS-pentacene] and C8-BTBT on printing conditions is investigated, and the result indicates that the formation of well-ordered crystals occurs at an optimal head translation speed. A maximum mobility of 0.75 cm²/(Vs) is achieved with 0.3 mm/s printing speed and 1.3 cm²/(Vs) with 0.3 mm/s printing speed at 50C for TIPS-pentacene and C8-BTBT respectively. In summary, pneumatic printing technique can be an attractive route to industrial scale large area flexible electronics fabrication.

This thesis focuses on improving the adhesion of electroless metal layers plated to pit contacts in interdigitated, backside buried contact (IBBC) solar cells. In an electrolessly plated, pit contact IBBC cell, the contact grooves are replaced with lines of pits which are interconnected by the plated metal. It is shown, however, that electroless metal layers, plated by the standard IBBC plating sequence, are not adherent on pit contact IBBC solar cells. The cause of this adhesion problem is investigated by examining the adhesive properties of each of the metal layers in the electroless metallization sequence on planar test structures. This investigation reveals that Pd activation of heavily P diffused Si impedes Ni silicide growth and that, in the absence of a silicide at the Ni/Si interface, an electrolessly plated Cu layer will cause the underlying Ni layer to peel away from the substrate. It is also found that the Ni silicidation process itself intermittently causes the unreacted Ni to spontaneously peel away from the substrate. An electroless metallization sequence that results in thick, adhesive Cu deposits on planar &lt 100&gt surfaces is developed in this thesis. It is shown that this process leads to the formation of a Ni silicide on both n- and p- type, heavily diffused surfaces. Fully plated, pit contact IBBC solar cells were not able to be fabricated during the course of this work but it is reasonable to expect that the modified plating sequence developed in this work will result in the metal layers being adhesive on these cells.

The objective of the present dissertation is to advance the science and engineering of metal-dielectric thin-film structures for ultrafast all-optical applications. The research presented consists of three parts: first, the linear and nonlinear optical (NLO) properties of Au and Ag/Au bilayer metallic thin films are comprehensively studied; then the design and properties of a novel nonlinear device structure are presented and finally an ultrafast all-optical shutter is developed and applications are discussed. In the first part, this study describes the linear and NLO properties of bilayer metallic films and shows that they can be tuned by controlling the mass-thickness ratio between Au and Ag. The combined properties of these bilayers are attractive for active plasmonic applications and nonlinear optical filters. Detailed physical models describing the linear and NLO response of Au and Ag/Au bilayers are presented and compared with experiments. In the second part, these models are used to optimize the NLO response of a novel Au-based NLO device. With only four layers, this novel device strongly amplifies the NLO response of the component Au thin film. NLO devices with broad spectral and angular bandwidths in the visible spectral region are demonstrated. The narrow band dependent NLO response of the NLO device is shown to lead to all-optical controls of high peak-power optical signal pulses. Finally, the NLO device technology is integrated into a novel ultrafast all-optical shutter, which allows temporal opening windows (the time shutter remains open) as short as a few ps. Ultrafast all-optical shutter potentially can temporally shape high peak-power nanosecond optical pulses, which could benefit biomedical and micromachining applications. Other possible optical applications such as short electron, X-ray pulse generations, ultrafast photography, and biomedical imaging will also be discussed.

Micro– and subsequently nano–scale fabrication techniques have reshaped our world more drastically than almost any other development of the last half-century. Spurred by the invention of the transistor at Bell Labs in 1947, monolithic integrated circuits—or microchips in the colloquial lexicon—were developed in ’59, kickstarting the modern digital age as we know it. More recently, the maturation of classical computing technology and significant advancements in materials science have led to a boom of interest in and progress by the quantum sector on both computation and communication fronts. The explosive growth currently underway in the field of quantum information science (QIS) marks the dawning of a new age, which will undoubtedly transform our world in ways we have yet to imagine. This dissertation seeks to leverage advanced nanofabrication approaches, atomically thin materials, and state of the art microscopy techniques to develop room-temperature single photon sources for QIS applications. A basic overview of 2D materials is provided in Chapter 1. Particular emphasis is placed on the optical properties of tungsten diselenide (WSe2), which is followed by a brief discussion of quantum emitters in 2D and other material systems. Chapter 2 describes the scanning near-field optical microscopy (SNOM) technique we use to investigate the photoluminescence (PL) response of strained WSe₂ with resolution well below the classical diffraction limit. The third chapter is dedicated to the various fabrication methods explored and developed to produce the plasmonic substrates necessary for near-field optical studies. The first section focuses on the creation of extremely flat metallic surfaces, while the second deals with extremely sharp metallic stressors. These two platforms enable the investigations of nanobubbles—touched upon in Chapter 2—and nanowrinkles, which are the subject of discussion in Chapter 4. The strain confinement provided by these wrinkles leads to highly localized quantum dot-like states that exhibit excitation power saturation at room temperature. Together, these studies lay the groundwork for achieving high-temperature quantum emission in atomically thin semiconducting van der Waals materials.

A new approach to the discovery of high absorbing semiconductors for solar cells was taken by working under a set of design principles and taking a systemic methodology. Three transition metal chalcogenides at varying states of development were evaluated within this framework. Iron pyrite (FeS���) is well known to demonstrate excellent absorption, but the coexistence with metallic iron sulfides was found to disrupt its semiconducting properties. Manganese diselenide (MnSe���), a material heavily researched for its magnetic properties, is proposed as a high absorbing alternative to iron pyrite that lacks destructive impurity phases. For the first time, a MnSe��� thin film was synthesized and the optical properties were characterized. Finally, CuTaS���, a known but never characterized material, is also proposed as a high absorbing semiconductor based on the design principles and experimental results. / Graduation date: 2013

The thesis consists of two parts. Part 1 deals with the preparation of thin films and sub-micron powders of complex metal oxides by nebulized spray pyrolysis (NSP) and Part 2 consists of Brillouin scattering studies of solid materials exhibiting interesting phase transitions. The simple technique of NSP has been employed to prepare thin films of A12O3, PbTiO3, Pb(Zr0.5Ti0.5)O3 (PZT) and PbZrO3 on single crystal substrate. The films were characterized by various techniques for their composition, structure, morphology and dielectric properties. Ferroelectric (FE) films of the configuration FE/LaNiO3/SiO2/Si (FE = PbTiO3 and PZT), wherein the LaNiO3 barrier electrode was also deposited on the SiO2/Si substrate by NSP, have been investigated. The films exhibit satisfactory ferroelectric properties. PbZrO3 films deposited on LaNiO3/SiO2/Si substrates show good features, including a reversible AFE ↔ FE transition. Sub-micron particles of TiO2, ZrO2, Pb(Zr0.5Ti0.5)O3, Al2O3, S1O2 and mullite have been prepared by NSP and characterized by various techniques. Brillouin scattering has been used, for the first time, not only to characterize the Peierls transition but also the incommensurate to commensurate transition in the one-dimensional blue bronze, K0.3M0O3. The charge density wave transition in NbSe2 has also been investigated by Brillouin scattering. The charge ordering and antiferromag-netic transitions in single crystals of the rare earth manganates, Nd0.5Ca0.5MnO3 and Pr0.63Ca 0.37MnO3, have been investigated by Brillouin scattering. It is noteworthy that the temperature variation of the Brillouin shift and intensity parallel to that of the magnetization, thereby throwing light on magnetic excitations in charge-ordered state. Brillouin scattering investigations of C60 and C70 films have yielded values of the elastic moduli.