The extended-Lifshitz-Kosevitch formalism (ELK) unifies the treatment of
the de Haas-van Alphen (dHvA) effect, allowing it to transcend its traditional roles
of mapping Fermi surfaces and measuring effective masses. Here we exploit the
capabilities of dHvA as a probe of many-body effects to examine heavy-fermion su-
perconductivity. ELK successfully describes...
In this thesis I studied several THz components that can be used for potential THz
technology. THz waves were generated in nonlinear medium via optical rectification
of femtosecond optical pulses. Utilizing the phase matching condition between the
optical and THz waves in a ZnTe crystal, single-cycle broad-band THz pulses were...
This dissertation concerns a broad range of unique phenomena related to the light propagation at nano- and micro-scales. To access the nano-domain, we introduce anisotropy-based waveguides with positive- and negative-index modes. These novel structures allow energy propagation in subwavelength regions and, in contrast to surface waves, have the mode structure...
A new, reproducible method of using electromigration to form
metallic nano-conductors is developed using gold and a tin-silver alloy.
Measurements revealed a quantization of the electrical conductance
consistent with the theory of quantum conductance. The theory of
quantum conductance is applied to show that a nano-conductor with a
cross-section of...
Gallium arsenide shows excellent promise for terahertz generation using mid infrared.
This is for two reasons. First, the indices of refraction for the terahertz (nTHz=3.61 at 1 THz) and mid infrared (nopt=3.431 at 2 μm) are close allowing a long interaction length.
Second, the linear absorption is low at terahertz...
This thesis deals with applications of uniaxial anisotropic crystals for microcavity resonators with partially chaotic underlying ray dynamics. We develop an implementation of the scattering matrix formalism, and relate the eigenvalues and eigenvectors of the scattering matrix to the field distribution of inside the system. Using the developed technique, we...
This work comprises two main parts: creating and shaping narrowband, pulsed THz radiation in a table-top optical setup; and applying THz pulses to semiconductor nanostructures to study electron dynamics.
I developed a scheme to shape the THz output of a fanned-out periodically poled lithium niobate (PPLN) crystal. The pulses are...
Total electronic energies are calculated numerically for
free and singly-ionized He, Li, C, and Ne atoms using density
functional theory. Immersion energies are calculated for a single
C impurity atom embedded or absorbed into a charge-neutral system
composed of a free-electron gas with uniform positive background,
also called 'jellium'. Nonspherical...
The main result of this written dissertation is a mathematical solution to the problem of multiplex recording for high performance tandem time-of-flight mass spectrometry. The prescription is to use a time-lag accelerator in the second stage to match the ion optical properties of the decay fragments to the requirements of...
Aquifer recharge is generally driven by fluids that move from the Earth’s surface to groundwater through the unsaturated zone, also known as the vadose zone. When the vadose zone is fractured, fluids, which may include contaminants, can move through the fracture network as well as the porous matrix. Such a...
Theories predict that making a dilute magnetic semiconductor strongly p -type would allow it to remain ferromagnetic at room temperature. This is of intrest as a ferromagnetic semiconductor would allow for a great many applications in the field of spintronics. Neutron scattering experiments were undertaken to better understand the antiferromagnetic...
In this dissertation we study the electromagnetic properties of planar waveguides
with non-magnetic strongly anisotropic dielectric cores. We develop an analytical
description of the mode propagation in these systems and show that the index
of refraction can be either positive or negative depending on the specific material
parameters. Propagating modes...
The results of an investigation into carrier dynamics in several novel functionalized and solution-processable pentacene and anthradithiophene derivatives are reported. Measurements were made of real-time photoresponse of polycrystalline thin films of these materials to ultrafast laser pulses, on picosecond to microsecond time-scales, as well as measurements of dark current and...
The ability to interpret graphical information is a prime concern in physics as
graphs are widely used to give quick summaries of data sets, for pattern recognition, and for analysis of information. While visual graphs have been developed so that their content can be readily and concisely discerned, there is...
In this dissertation we study the electromagnetic properties of plasmonic metamaterials. We develop an analytical description to solve the fundamental problem of free-space scattering in planar plasmonic systems by utilizing anisotropic metamaterials. We show with exact numerical simulations that these manufactured materials do completely eliminate the scattering, and even in...
The authors demonstrate a flexible terahertz pulse-shaping technique, manipulating spatially dispersed multifrequency components generated by optical rectification in a fanned-out periodically poled lithium niobate crystal. Spatial masks of low pass, high pass, and double slit in front of the crystal manipulate the spatial pattern of the optical excitation beam on...
The authors demonstrate the generation of multicycle narrow-bandwidth terahertz pulses in periodically inverted GaAs structures using optical rectification of 2 μm, 100 fs pump pulses. Three different types of orientation-inverted samples are employed: optically contacted multilayer, orientation-patterned, and diffusion-bonded GaAs. The terahertz pulses are characterized by two-color (pump at 2...
We report on a novel class of semiconductor metamaterials that employ a strongly anisotropic dielectric function to achieve negative refraction in the midinfrared region of the spectrum, ~8.5–13 μm. We present two types of metamaterials, layered highly doped/undoped heterostructures and quantum well superlattices that are highly anisotropic. Contrary to other...
BaCuQF (Q=S,Se) materials, candidate transparent p-type conductors, were prepared by solid-state reaction, and their bulk electrical and optical properties were evaluated. The room-temperature Seebeck coefficient and electrical conductivity of undoped BaCuQF pellets were +56 μV/K and 0.088 S/cm, respectively, for the sulfide fluoride, and +32 μV/K and 0.061 S/cm, respectively,...
Radioactive In has been incorporated into oriented thin films of YBa₂Cu₃O₇₋δ during a thermal coevaporation process. The hyperfme technique of perturbed γγ-angular correlation spectroscopy shows that 60% of the indium substitutes at a single site in the superconductor. We obtain spectra with reasonable statistics from 2 mCi of starting material,...
High electron mobility thin films of In₂₋ₓWₓO₃₊y(0≤x≤0.075) were prepared on amorphous SiO₂ and single-crystal yttria-stablized zirconia (001) substrates by pulsed laser deposition. Mobilities ranged between 66 and 112 cm² /Vs depending on the substrate type and deposition conditions, and the highest mobility was observed at a W-dopant concentration of x~0.03....
We analyze the performance of a planar lens based on realistic negative index material in a generalized geometry. We demonstrate that the conventional superlens design (where the lens is centered between the object and the image) is not optimal from the resolution point of view, develop an analytical expression for...
We derive an approach to determine the causal direction of wavevectors of modes in optical metamaterials, which, in turn, determines signs of refractive index and impedance as a function of real and imaginary parts of dielectric permittivity and magnetic permeability. We use the developed technique to demonstrate that the interplay...
We demonstrate color shifting from the yellow to the red in the electroluminescence from (ZnGa)S:Mn films. We observe threshold voltages down to about 35 V, extremely low for such devices. We discuss the materials characteristics of the phosphor films, and the potential for improvement of the luminous intensity of the...
We report on the effect of various guest molecules added to a functionalized anthradithiophene (ADT) host on photoexcited charge carrier dynamics in solution-deposited thin films, from ~100 ps to >100 μs after photoexcitation with 100 fs laser pulses. An addition of 2 and 5 wt % of C60 to a...
The authors demonstrate an efficient room temperature source of terahertz radiation using femtosecond laser pulses as a pump and GaAs structures with periodically inverted crystalline orientation, such as diffusion-bonded stacked GaAs and epitaxially grown orientation-patterned GaAs, as a nonlinear optical medium. By changing the GaAs orientation-reversal period (504–1277 μm), or...
We demonstrate a technique for terahertz pulse shaping via optical rectification in the pre-engineered domain structure of poled lithium niobate crystals. The terahertz wave forms coincide with the crystal domain structures. The one-dimensional nonlinear wave equation simulates the experimental results with a good qualitative agreement.
We employ two different methods to generate controllable elliptical polarization of teraherz (THz) pulses. First, THz pulses are generated via optical rectification in nonlinear crystals using a pair of temporally separated and perpendicularly polarized optical pulses. The THz ellipticity is controlled by adjusting the relative time delay and polarization of...
Electron avalanche due to intraband optical absorption is discussed as a mechanism responsible for laser induced damage in certain insulating crystals.
The authors study perspectives of nanowire metamaterials for negative-refraction waveguides, high-performance polarizers, and polarization-sensitive biosensors. They demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of...
The authors analyze electromagnetic modes in multilayered nanocomposites and demonstrate that the response of a majority of realistic layered structures is strongly affected by the nonlocal effects originating from strong field oscillations across the system, and is not described by conventional effective-medium theories. They develop the analytical description of the...
Transparent films of CuScO₂₊ₓ have been prepared which show p-type electrical conductivity. The temperature dependence of the conductivity indicates semiconducting behavior with an apparent room temperature activation energy of 0.11 eV. The highest room temperature conductivity observed was 30 S cm⁻1. Films 110 nm thick show 40% transparency in most...
Electronic structure calculations for free and immersed atoms are performed in the context of unrestricted Hartree-Fock Theory. Spherical symmetry is broken, lifting de-generacies in electronic configurations involving the magnetic quantum number m. Basis sets, produced from density functional theory, are then explored for completeness. Com-parison to spectroscopic data is done...
Quantum mechanics provides a conventional theory of scattering that is limited in
at least two ways: it focuses exclusively on the asymptotic regime and, in a more general
sense characteristic of all quantum descriptions, provides no concrete account of individual
particle evolution in spacetime. This is particularly true during the...
We construct a quantum interchange walk, related to classical walks with memory. This gives us a coinless discrete walk, while the origin in classical walks with memory offers the promise of use of existing tools from classical memoried walks. This approach readily reproduces all standard approaches. We briefly discuss its...
BaCuChF (Ch = S, Se, Te) materials are chalcogen-based transparent conductors with wide optical band gaps (2.9 – 3.5 eV) and a high concentration of free holes (10¹⁸ – 10²⁰ cm⁻³) caused by the presence of copper vacancies. Chalcogen vacancies compensate copper vacancies in these materials, setting the Fermi level...
The process of de-excitation of the actinides is a very important question in both pure and applied science. In this dissertation the process was studied using the neutrons emitted in coincidence with fission induced by the bombardment of ²³⁸U with 14.85 MeV deuterons. Neutrons can be emitted at multiple stages...
Intraexciton transitions in semiconductor quantum wells are modulated by strong and tunable few-cycle terahertz pulses. Time-resolved terahertz-pump and optical-probe measurements demonstrate that the 1s heavy-hole and light-hole exciton resonances undergo large-amplitude spectral modulations when the terahertz radiation is tuned near the 1s–2p intraexciton transition. The strong nonlinear optical transients exhibit...
The effect of a pulse produced by an acoustic or electromagnetic
line source oriented parallel to the edge of a perfectly conducting
half plane is considered. The Green's functions for the modified
Helmholtz equation are found by solving for the Green's functions
for a cylinder of sectorial cross-section, then allowing...
This dissertation concerns several problems in the fields of light interaction with nanostructured media, metamaterials, and plasmonics. We present a technique capable of extending operational bandwidth of hyperbolic metamaterials based on interleaved highly-doped InGaAs and undoped AlInAs multilayer stacks. The experimental results confirm theoretical predictions, exhibiting broadband negative refraction response...
Nonlinear optical processes can be described as multiphoton scattering events in terms of high order perturbation theory. The standard procedure for quantitative calculation of high order terms is to impose a steady state condition on the perturbative radiation fields. In the present work, this condition will be lifted, and explicit...
Semiconducting materials which can be ambipolarly doped are highly desirable in many electronics applications, including use as solar cell materials. SnZrS₃ is being investigated for the possibility of ambipolar doping, with potential applications as a solar cell absorber layer. This dissertation covers the synthesis of SnZrS₃ and the related compound...
An investigation was made to determine teacher facilitation techniques in large lecture physics classrooms that foster small group discussion. Video recordings of an introductory calculus-based physics class were taken for the 2008-2009 academic year at Oregon State University. These videos were analyzed to determine student participation in small group discussion...
A method for bandgap energy determination using di use re ection is presented and compared to the traditional integrating sphere method. We have found the bandgap energies of ZnO, TiO₂, Cu₂O, Si, SnZrS₃, SnZrSe₃, Sn₂S₃, and BiCuOSe powders with both methods and found they agree within 0.03 eV. We have...
As electronics reach nanometer size scales, new avenues of integrating biology and electronics become available. For example, nanoscale field-effect transistors have been integrated with single neurons to detect neural activity. Researchers have also used nanoscale materials to build electronic ears and noses. Another exciting development is the use of nanoscale...
Crystals of CdF₂:In and CdF₂:Ga reduced in a cadmium vapor exhibit unusual
metastable properties that can be explained by a "negative U" model. This work
uses NMR to investigate this model for CdF₂:Ga and CdF₂:Ga,Y and compare the
results to optical measurements. Temperature dependent relaxation measurements
were done on ¹¹³Cd...
We used two temporally separated femtosecond pulses to manipulate the waveforms of multi-cycle THz pulses through optical rectification in periodically-poled lithium mobate (PPLN). The relative phase of the THz pulses was controlled by the relative time delay between the optical pulses. This phase adjustability combined with the frequency tunability of...
The Seebeck coefficient is examined in the high temperature limit, using an approach based on a grand partition function containing Hubbard Hamiltonian interaction terms. Although the carriers of interest occupy localized Wannier states, this work is prefaced by the case of delocalized Bloch states, which is examined using Boltzmann transport,...
Zinc tin oxide (ZTO) films deposited by pulsed laser deposition (PLD) are
investigated as a channel layers for transparent thin-film transistors (TTFTs).
Films are deposited on glass for characterization, and transistor channel layers are
deposited onto aluminum oxide-titanium oxide/tin doped indium oxide/glass
substrates (ATO/ITO/glass) to produce TTFTs.
UV-visible spectroscopy on...
Bulk properties of CuSc₁₋ₓMgₓO₂, CuSc₁₋ₓMgₓO₂₊y, BaCu₂S₂, Bai₁₋ₓKCu₂S₂, BaCu₂Se₂
and Bai₁₋ₓKₓCu₂Se₂ are investigated supporting the search for highly conductive p-type
thin films. Mg is an efficient dopant in CuScO₂ with conductivity up to l.5.10⁻² S/cm.
Oxidation of CuScO₂:Mg leads to further increase in conductivity up to 0.5 S/cm. The
amount of...