Non-equilibrium photocarriers in multilayer WSe2 injected by femtosecond laser pulses exhibit extraordinary nonlinear dynamics in the presence of intense THz fields. The THz absorption in optically excited WSe2 rises rapidly in the low THz field regime and gradually ramp up at high intensities. The strong THz pulses drive the photocarriers...
Cell signaling under external stimulation is a critical mechanism that governs many biological processes such as cell proliferation, cell migration, and cell apoptosis, etc. For multicellular organisms, the ability to synchronize heterogeneous individual cellular responses through intercellular communication is crucial to maintain normal functionality. However, even though the biological pathways...
Quantum mechanics is increasingly being taught with a spins-first approach where instructors use simple spin systems to introduce the principles of quantum mechanics rather than systems with wavefunctions. One of the defining characteristics of a spins-first approach is that systems studied have discrete bases, whereas systems with wavefunctions have continuous...
Transparent conductive oxides (TCO) are at the forefront of technology with their uses in
touch screen phones and televisions, solar cells and more. Titanium dioxide and tin dioxide are two TCOs that have been studied in depth on their own, so to further explore these TCOs, this project focuses on...
Physicists solve problems and communicate their work using many external representations, such as equations, words, diagrams, graphs, sketches, pictures, and more. To learn physics, then, students must learn to use external representations. In this dissertation, I present three manuscripts. Each manuscript discusses how upper-division Paradigms in Physics students use multiple...
Given the recent advancements in the field of pulsar timing pertaining to the detection of a stochastic gravitational wave background (GWB), it is now the perfect time to perform tests of gravity via exploration of the correlation signature between the timing data of pairs of pulsars induced by the polarization...
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is an international collaboration that seeks to use perturbations in the time of arrivals of pulsar signals to detect gravitational waves in the nanohertz range of frequencies. The 15-year data set will be released as of June 2023. It is a...
Crystals are solid materials with periodic and symmetric molecular patterns. The structure of a crystalline solid determines its properties, making it essential to study its structures. From the principle of minimum energy, a crystal will choose a structure with the lowest free energy F = U – TS. At low...
Brownian motion is the movement of a particle in a fluid resulting from collisions with surrounding molecules. It has modern applications in simulating fluid dynamics and the motion of proteins in biophysics. Brownian motion simulations generally evolve the initial state by applying Newton’s second law to every particle. These simulations...
Semiconductors serve an integral role in our technologies today. However, with new advancements in ultra-fast electronics, we are approaching the fundamental speed limits of traditional silicon-based semiconductors. Silicon-based semiconductors typically exhibit photocarrier dynamics in nanosecond timescales. Transition metal dichalcogenides (TMDs) are 2D materials shown to exhibit photocarrier dynamics in picosecond...
Organic semiconductors are a promising alternative to the traditional inorganic semiconductors, such as silicon. Organics are solution-processable, low-cost, sustainable, and have interesting optoelectronic properties. One such property is the formation of exciton-polaritons, quantum quasi-particles formed by an electron-hole pair in the semiconductor and a photon. This process can be induced...
I examine the strong co-variability between the surface divergence and vorticity and how it varies with latitude in the Pacific Ocean using surface vector winds from reanalysis and satellite scatterometer observations. This analysis was motivated in part by a significant correlation between divergence and vorticity over the global oceans that...
I had to write again. My research lay in science, and it was a science of three parts. The first part made a careful, introductory chapter, begged for by things that were lacking. It summarizes the von Neumann measurement model, derived from the Stern-Gerlach experiment, and it explains how weak...
We present a classical density functional to model the soft, repulsive potential of a Weeks-Chandler-Andersen (WCA) fluid using Soft Fundamental Measure Theory (SFMT) with temperature-dependent parameters inspired by the Barker-Henderson method. Our functional uses soft spheres to model the soft-sphere WCA potential, and gives results that are in good agreement...
I led a collaborative project involving a search for an evidence of a gravitational wave background (GWB) with all the spatial correlations allowed by general metric theories of gravity using NANOGrav’s 12.5 year data set. The search found no substantial evidence in favor of the existence of such correlations.
The...
Computational statistical mechanics leans heavily on the class of Markov Chain Monte Carlo Algorithms. Many such algorithms exist, and simulations can run for several weeks, making the selection of algorithms a difficult, but critical task. In this work, we introduce a benchmark system of two quadratic wells with an analytical...
In this thesis, we explore a general method for constructing path sums in a discrete spacetime using a jump amplitude matrix. This is accomplished by deriving a composition law that relates jump amplitudes to the propagator. Then properties of causal sets are used to average this relationship over sprinklings. This...
Fast neutron detection is important to the detection of illicit nuclear materials and can help prevent those materials from being used or transported without discovery. Previous research has shown that Heavy Oxide Inorganic Scintillator crystals can be used to detect fast neutrons by capitalizing on their high inelastic scattering cross...
TiO₂ typically crystallizes into three polymorphs: brookite, rutile, and anatase. The phase selection problem in TiO₂ is the lack of understanding what conditions cause amorphous TiO₂ to crystallize into one of its three polymorphs during an annealing process. It has been recently shown that phase selection in TiO₂ is highly...
Future quantum technologies will require high-efficiency, on-demand sources of entangled photons. A possible route to building such light sources employs two-dimensional (2D) semiconductors interfaced with a source of Cooper pairs. To investigate the possibility of such devices, we are testing methods to make high transparency n-type contacts, p-type contacts, and...
I am a physics education researcher. My ‘laboratory’ is a year-long Introductory Algebrabased Physics sequence taught at Oregon State University (OSU). While not technically a hybrid class, it has most of the aspects of a hybrid learning environment, as the course is “flipped,” and includes a combination of pre-lecture online...
This thesis conveys the key technical features and scientific applications of a particle-particle ballistic simulation tool (SpaceLab) as well as a high level overview of experiments it was designed for and executed on. SpaceLab simulates spherical particle interactions under any combination of self-gravity, sliding friction, rolling friction, Van-Der-Waals (VDW) cohesion...
Electrostatic gating of nanomaterials allows researchers to control carrier density and shape potential barriers that confine carriers. Lithographic patterning followed by metal deposition is the standard technique to define electrostatic gates; however, the methods of fabricating these devices often involve harsh processing. For example, taking a material to high temperatures...
Organic semiconductors have attracted considerable attention due to their applications in low-cost, solution-processable (opto)electronic devices. An important class of high-performance organic semiconductors is pentacene derivatives, which exhibit high charger carrier mobilities in field-effect transistors and ultrafast singlet fission in photovoltaic devices. These derivatives have served as benchmark materials for systematic...
Taking long-term electrical measurements of a large number of neurons simultaneously is required for many modern neuroscience experiments. However, such experiments are currently limited by the shortcomings of traditional neurosensing technology. For example, there is a significant mechanical mismatch between rigid silicon probes and soft biological tissues. This mismatch can...
At the intersection of basic science research and clinical relevance, cancer metastasis and cell invasion is a multifaceted problem that has been investigated for the past several decades. Importantly, cancer cell plasticity, the ability of a single cell to change its phenotype without genetic mutations in response to environmental cues,...
Gamma Ray Bursts (GRBs) are the most energetic explosions in the Universe, producing up to $\sim10^{53}$ ergs of energy in the first few seconds of their emission -- the so-called prompt phase that is dominated by high energy X-ray and $\gamma$-ray photons. The very large luminosities released in these events...
Fluorescent proteins have emerged as an essential toolset for bioimaging, creating a demand for engineering proteins with new and improved fluorescent properties. In this thesis, I explore the atomistic structure of REX-GECO1, a newly engineered protein biosensor that has unique optical properties. Since this protein has no available crystal structure,...
Carbon nanotube (CNT) photodiodes are a promising system for high-efficiency photocurrent generation due to the strong Coulomb interactions that can drive carrier multiplication. If the Coulomb interactions are too strong, however, exciton formation can hamper photocurrent generation. Here, we explore, experimentally and theoretically, the effect of the environmental dielectric constant...
In this work, we systematically explore the effectiveness of optical aberration correction over a wide range of optical depths using the Segmented and Zernike Polynomial bases. We manufacture a set of 16 optical phantom samples consisting of a clear polyester resin substrate embedded with varying concentrations of aluminum oxide (Al₂O₃)...
Solutions to Einstein's equations are usually found by considering ideal, simplified models. However, if the real world always matched ideal physics models, then farmers would milk black and white spheres. To combat this, Regge calculus was developed as a numerical approximation scheme for general relativity. In Regge calculus curved manifolds...
Different models show the effects of environmental decoherence on a quantum system
due to various environments of interest. One important quantity within these models is
the decoherence time, which tells us how quickly environments wash away the coherence of
local measurements. We can describe this effect as the quantum system...
The purpose of this project is to verify scattering mechanisms in semiconductors by measuring transport properties and producing data that reflects existing research. The Hall effect is utilized to measure the resistivity, mobility and charge carrier concentration of the semiconductors: indium tin oxide (ITO), p-type silicon, and n-type silicon. By...
A new class at Oregon State, PH 317: Experimental Physics, is designed to simulate a traditional laboratory research experience for undergraduate students. Several weeks of the class is devoted to Brownian motion experiments. Although this is a common topic for undergraduate lab classes, the experiment still needed some basic exploration...
Detecting gravitational waves is a topic at the forefront of physics. The first gravitational wave was detected by LIGO in 2015. This wave had a frequency in the 10s of Hz. This project is focused on detecting gravitational waves on the nanohertz spectrum using a pulsar timing array. This array...
Gravitational wave (GW) astronomy is a key ingredient in confirming Einstein’s theory of General Relativity and showing how the universe sends ripples through spacetime, distorting distances between two points. The confirmation of high-frequency GWs observed by The Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 was a breakthrough in our understanding...
Impedance spectroscopy is a method of modeling materials with equivalent circuits to determine electrical properties, such as the resistivity and the dielectric constant. We explore impedance spectroscopy, both theoretically and experimentally through applying the method to samples of BaCuS1-xSexF. Grain boundary effects were dominant in the results, and although they...
This study used SCOUT optical modelling software to create models of the reflectance and transmittance spectra generated by mixtures of titanium dioxide (TiO2) and tin oxide (SnO2). These models enabled identification of how altering the ratio of a mixture changes the optical response. By being able to identify how altering...
Terahertz (THz) frequencies of the electromagnetic spectrum have been underutilized when compared to neighboring microwave and infrared frequencies, largely due to the difficulties controlling and detecting these fields. In a step toward gaining control over THz frequencies, my advisor Dr. Yun-Shik Lee’s group experimentally demonstrated optical-pulse THz-control over a plasmonic...
Organic semiconducting materials have emerged in the last few decades as viable alternatives to inorganics in broad applications from field effect transistors to LEDs to solar cells. Organics provide many benefits over inorganics such as flexibility, sustainability, and reduced cost. However, these materials are more susceptible to degradation in the...
Cell division, arguably the most important event during the life cycle of the eukaryotic cell, is achieved through a complicated yet beautiful machinery. The mitotic spindle — a microtubule-based bipolar structure—is the cellular machinery responsible for the correct segregation of the genetic material, chromosomes. The protein-based nanomachines termed molecular motors...
Type I collagen fibers, the connective tissue that makes up the human breast, can be easily manipulated by cells or other outside factors. In previous studies, the alignment of collagen has been associated with the beginning of metastatic cancer, possibly influencing cancerous cells to migrate from the tumor. In this...
The motor protein dynein is responsible for cellular processes such as axonal transport and cell division by delivering vital information along the microtubule track. A failed delivery can cause severe damage to the cell’s functionality and lead to neurological diseases. Despite dynein’s rich history in cellular research, the mechanism of...
Physics problems that require integration, such as finding the center of mass of an object or finding the electric field from a continuous distribution of charge, are one type of problem that is difficult for introductory physics students to solve. These problems require students to define a coordinate system in...
Physicists who study semiconductor devices are fascinated by the fundamental limits of device performance. From the sub-threshold swing of transistors to the power conversion efficiency of photocells, performance is limited by the electronic structure of the materials used to build them. To surpass traditional device limits, we must turn to...
Understanding the impact of inter-molecular orientation on the optical proper-ties of organic semiconductors is important for designing next-generation organic (opto)electronic and photonic devices. However, fundamental aspects of how various features of molecular packing in crystalline systems determine the nature and dynamics of excitons have been a subject of debate. Toward...
The discovery of GW170817 provided the first empirical evidence that merging binary neutron star systems are both progenitors of short gamma-ray bursts, as well as the primary sites of the nucleosynthetic rapid-neutron capture process. Initially detected as gravitational wave (GW) and gamma-ray burst (GRB) triggers, GW170817 was well-localized and follow-up...
One of the biggest open questions in physics is the prevalence of matter over anti-matter in the present universe. One of possible answers lies in the violation of charge and parity symmetry in the lepton sector that would favor matter over anti-matter so that the universe becomes dominated by matter...