Engineering Commons^™

Development Of Metal Halide Perovskites For Radiation Detection, Ryan Tan

Doctoral Dissertations

Metal halide perovskite (MHP) semiconductors have attracted significant interest in recent years within photovoltaic and radiation detection communities due to their inexpensive solution growths, high effective atomic number for gamma and X-ray sensing, suitable bandgap, large resistivity, and moderate mobility-lifetime products. The MHP stoichiometry can also be tuned as needed to achieve desired physical and electronic properties. Moreover, the hybrid or organometallic halide perovskite (OMHP) variants contain a large atomic fraction of hydrogen for fast neutron sensing. These qualities make MHPs an attractive low-cost option for meeting detector needs within nuclear security and imaging applications. This work presents the development …

Brain Inspired Organic Electronic Devices And Systems For Adaptive Signal Processing, Memory, And Learning., Subhadeep Koner

Doctoral Dissertations

A new class of electronic device has emerged which bear the potential for low powered brain like adaptive signal processing, memory, and learning. It is a non-linear resistor with memory coined as memristor. A memristor is a two-terminal electrical device which simultaneously changes its resistance (processing information) and store the resistance state pertaining to the applied power (memory). Therefore, it can collocate memory and processing much like our brain synapse which can save time and energy for information processing. Leveraging stored memory, it can thereby help future engineered systems to learn autonomously from past experiences. There has been a growing …

Cmos Compatible Carbonization Of Polymer For Elctrochemical Sensors, Mohammad Aminul Haque

Doctoral Dissertations

Carbon-based electrodes that are integrable with CMOS readout electrodes possess great potential in a wide range of cutting-edge applications. The primary scientific contribution is the development of a processing sequence which can be implemented on CMOS chips to fabricate pyrolyzed carbon microelectrodes from 3D printed polymer microstructures to develop lab-on-CMOS monolithic electrochemical sensor systems. Specifically, optimized processing conditions to convert 3D printed polymer micro- and nano-structures to carbonized electrodes have been explored in order to obtain sensing electrodes for lab-on- CMOS electrochemical systems. Processing conditions have been identified, including a sequel of oxidative and inert atmosphere anneals to form pyrolyzed …

Development Of Codoped Cesium Iodide Scintillators For Medical Imaging Applications, Everett M. Cavanaugh

Masters Theses

Cesium iodide has a rich history of use as a scintillating material. CsI finds use in a variety of fields, but it is primarily used in radiography, tomography, and geological exploration. Of the three common variants of CsI, thallium doped CsI is by far the most widely used among these applications. It possesses favorable physical characteristics like a high density and high effective Z and exhibits high light output at room temperature. Despite how great CsI scintillators may be on paper, they have an Achilles heel: afterglow. CsI:Tl has significant afterglow which leads to imaging artifacts that can be difficult …

Combinatorial Cuni Alloy Thin Film Catalysts For Layer Number Regulation In Cvd Grown Graphene, Sumeer Khanna

Masters Theses

In this work, synthesis of combinatorial library of Cu_xNi_1-x (copper nickel) alloy thin films via co-sputtering from Cu (copper) and Ni (nickel) targets as catalysts for chemical vapor deposition (CVD) growth of graphene is reported. The gradient alloy morphology, composition and microstructure were characterized via scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD), respectively. Subsequently, the Cu_xNi_1-x alloy thin films were used to grow graphene in a CH₄-Ar-H₂ (methane-argon-hydrogen) ambient in thermal CVD tube furnace. The underlying rationale is to adjust the Cu_xNi_{1-x …}

Radiation Effects On Lithium Indium Diselenide Semiconductors As Neutron Imaging Detectors, Robert M. Golduber

Masters Theses

The studies presented in this work aim to improve upon the knowledge base of lithium indium diselenide (LISe) semiconductors to understand how the material behaves in high radiation environments and refine the process of turning it into a neutron detector. LISe has great potential as neutron imaging detector because of the high neutron absorption efficiency of its enriched ⁶Li component and its ability to discriminate between gamma-rays and neutrons. Its ability to remain functional after being irradiated with large amounts of neutron fluence has been tested and the change in its electro-optical properties with relation to fluence has been …

High Resolution Electron Energy Loss Spectroscopy Of Plasmonic Nanostructures, Grace Pakeltis

Doctoral Dissertations

This dissertation discusses developing fabrication techniques to study the plasmonic phenomena of nanostructures utilizing high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron. While standard lithography has been widely used to create planar nanostructures, investigation into 3-dimensional nanostructures is lacking. A robust synthesis approach utilizing focused electron beam induced deposition, atomic layer deposition, and thin film sputter deposition to fabricate complex 3D plasmonic architectures is described and characterization of single nanoresonators is presented. Additionally, this dissertation discusses the use of high-resolution electron energy loss spectroscopy to investigate the hybridization of gold nanorod oligomers. Experiment and simulation resolve magnetic …

Spin Effects Of Excited States In Organic Semiconductors And Hybrid Perovskites For Optoelectronics And Spintronics, Miaosheng Wang

Doctoral Dissertations

Organic semiconductors and organic-inorganic hybrid perovskites have demonstrated versatile functionalities for optoelectronic and spintronic applications. Research in this dissertation focuses on the spin effects of excited states in emerging organic semiconductor and hybrid perovskite systems to understand the fundamental working principle. The investigation on the spin effects in excited states can provide insightful guidance for the development of the next-generation organic and hybrid perovskite optoelectronics and spintronics.

In organic semiconductors, the excited states, namely, excitons can be characterized by the total spin angular momentum S=S_e+S_h of the constituent electron and hole, which determines the …

Chemico-Physical Interactions In Metal Halide Perovskites, Yongtao Liu

Doctoral Dissertations

Metal halide perovskite (MHP) has attracted tremendous attention due to its success in optoelectronics, largely due to outstanding photovoltaic performance. A wide variety of characterization approaches have been used to explore the fundamentals behind the outstanding optoelectronic properties of MHP, which has yet to be unambiguously established despite considerable efforts to do so. Given the high ionic mobility in MHP, when physical phenomena are coupled with chemical changes, all behaviors will become very complex due to the strong ion migration. Therefore, chemico-physical interactions in MHP can no longer be ignored, which will be the focus of the researches in this …

Exploration Of Thin Films For Neuromorphic, Electrofluidic, And Magneto-Plasmonic Applications, Walker L. Boldman University Of Tennessee Knoxville

Doctoral Dissertations

Due to the limit in computing power arising from the Von Neumann bottleneck, computational devices are being developed that mimic neuro-biological processing in the brain by correlating the device characteristics with the synaptic weight of neurons. We demonstrate a platform that combines ionic liquid gating of amorphous indium gallium zinc oxide (aIGZO) thin film transistors and electrowetting for programmable placement/connectivity of the of the ionic liquid. In this platform, both short term potentiation (STP) and long-term potentiation (LTP) are realized via electrostatic and electrochemical doping of the aIGZO, respectively, and pulsed bias measurements are demonstrated for low power considerations. Using …

Optics Of Two-Dimensional Materials Used As Substrates For Nanoparticle-Based Devices, Reagan Newman

Chancellor’s Honors Program Projects

No abstract provided.

Tixzr(1-X)N Thin Films For Advanced Plasmonic Materials, Susan R. Schickling, Codi Ferree, Amy Godfrey, Andre Hillsman, Hannah Robinson

Chancellor’s Honors Program Projects

No abstract provided.

An Examination Of The Au-Ni Phase Diagram For Magneto-Plasmonic Applications, Christopher C. Walker, John Carothers, Michael Roulier, Brandon Rowell

Chancellor’s Honors Program Projects

No abstract provided.

Low Energy Recoil Simulations In Mgo, Linbo3, And Litao3 Using Ab Initio Molecular Dynamics, Benjamin Aaron Petersen

Doctoral Dissertations

Ab initio molecular dynamics (AIMD) was utilized to test a series of materials, MgO, LiNbO₃ , and LiTaO₃ , to determine defect structures produced due to low energy recoil events . The kinetic energy required to displace an atom from its lattice site, the threshold displacement energy, was calculated for an array of directions in each material, based on symmetry and complexity of the structure. MgO having a simple rock salt structure provided a model material for demonstrating computational techniques used later on LiTaO₃ and LiNbO₃ . The minimum values for displacing an atom were at …

The Development Of Cesium Calcium Bromo-Iodide Scintillator For X-Ray And Gamma Ray Detection, Matthew Starr Loyd

Masters Theses

CsCaI₃:Eu [cesium calcium iodide doped with europium] is a promising scintillator material that can be grown from the melt, but undergoes a tetragonal to orthorhombic phase transition upon cooling at 255 °C [degrees Celsius], causing twinning and cloudiness. The purpose of this work is to suppress this solid to solid phase transition in the CsCaI₃:Eu scintillator, which has a light yield of ~40000 ph/Mev and energy resolution at 662keV of ~4%, by halide replacement to form the compound CsCaBr_xI_3-x:Eu [cesium calcium bromo-iodide doped with europium]. Crystals 8 cm³ [cubic centimeters] in …

Advanced Purification And Direct-Write 3d Nanoprinting Via Focused Electron Beam Induced Deposition, Brett Bloxton Lewis

Doctoral Dissertations

This dissertation addresses three difficulties with focused electron beam induced deposition preventing broader application; purity, spatial control, and mechanical characterization.

Focused electron beam induced deposition (FEBID) has many advantages as a nanoscale fabrication tool. It is compatible for implementation into current lithographic techniques and has the potential to direct-write in a single step nanostructures of a high degree of complexity. FEBID is a very versatile tool capable of fabricating structures of many different compositions ranging from insulating oxides to conducting metals.

Due to the complexity of the technique and the difficulty in directly measuring many important variables, FEBID has remained …

Dewetting Properties Of Ag-Ni Alloy Thin Films, Benjamin Scott Wolf

Masters Theses

In this study, pulsed laser induced dewetting of both patterned and continuous Nickel (Ni)-Silver(Ag) thin films was investigated extensively as a novel way to perform directed assembly of nano-particles. First, continuous Ni-Ag thin film dewetting was studied on both bulk and TEM (Transmission electron microscope) membrane substrates at a variety of compositions to better understand the dewetting dynamics of the Ni-Ag system. Then, patterned Ni-Ag thin film dewetting was studied on both bulk and TEM membrane substrates to understand how different patterns and thin film configurations effect nano-particle distribution and formation. All of this work was done in anticipation of …

Strategies For Controlling Bulk Heterojunction Morphology, Zach Daniel Seibers

Doctoral Dissertations

Organic photovoltaic devices have been extensively studied as a means to produce sustainable energy. However, the performance of organic-photovoltaic (OPV) devices is dependent upon a number of factors including the morphology of the active layer, device architecture, and processing conditions. Recent research has indicated that fullerenes in the bulk heterojunction are entropically driven to the silicon and air interfaces upon crystallization of P3HT, which occurs during thermal annealing. The first chapter of this research focuses on investigating the structure and function of end-tethered poly(3-hexylthiophene) chains to a transparent electrode as an anode buffer layer. Neutron reactivity reveals that these P3HT …

Material And Process Engineering For Bulk Single Crystal Growth Of High Performance Scintillator Potassium Calcium Iodide, Adam Coleman Lindsey

Doctoral Dissertations

Protection against threats of nuclear terrorism relies on the deployment of an enormous number of radiation detection devices with energy resolution to differentiate the radiological signatures of special nuclear materials amongst naturally occurring radiation and other nuisance sources. The capabilities of these devices rely upon the availability of high performance scintillator and semiconductor materials which provide useful responses in the presence of radiation. So far, few materials have been developed to a level that can supplant the use of underperforming NaI:Tl [thallium doped sodium iodide] crystals in the field due to their high cost and/or low yields of production. KCaI …

Interaction Between Charge-Transfer States Studied By Magnetic Field Effects, Mingxing Li

Doctoral Dissertations

Organic semiconducting materials, consisting mostly of carbon and hydrogen atoms, provide remarkable promise for electronic applications due to their easy processing, chemical tenability, low costs and environmental-friendly characteristics. For realizing electronic applications such as light emitting diodes and photovoltaic cells, charge-transfer states act as an important intermediate state for recombination and dissociation. Interestingly, magnetic field effects on semiconducting materials have been realized based on the suppression of spin mixing in the charge-transfer states. Although lots of studies have been carried out on investigating the properties of charge-transfer states, little has been done to consider the interaction between them. This thesis …

Exploring Thermoelectric Effect Based On Multi-Layer Conductor/Organic/Conductor Devices, Qing Liu

Doctoral Dissertations

Thermoelectric phenomena involve the simultaneous presence of both electrical and thermal currents. The entropy has been heavily used as the driving force to diffuse charge carriers between high and low temperature surfaces towards the development of Seebeck effects in thermoelectric devices. However, this driving force from entropy difference can cause an inverse relationship between Seebeck coefficient and electrical conductivity in the thermoelectric developments. Increasing the charge density can decrease the entropy difference to diffuse the charge carriers at a given temperature difference and lead to a decrease on the Seebeck coefficient developed by the entropy difference. Therefore, it is necessary …

Fluorochlorozirconate Glass Ceramics For Computed Radiography, Adam Wesley Evans

Masters Theses

Heat treating fluorochlorozirconate (FCZ) glasses nucleates nanocrystals in the glass matrix, resulting in a glass ceramic that has optical properties suitable for use as a medical imaging plate. As the temperature of heat treatment rises, the resulting FCZ glass-ceramic becomes increasingly more opaque as the size of the orthorhombic phase BaCl­₂[barium chloride] nanocrystals grow within the glass matrix. This opaqueness negatively affects imaging. The effect of adding Fe³⁺[iron] on the valence state of zirconium and overall glass quality was investigated.

Samples were synthesized and characterized with differential scanning calorimetry to determine the temperature of the orthorhombic …

Symbiotic Plasmonic Nanomaterials: Synthesis And Properties, Abhinav Malasi

Doctoral Dissertations

Metal particles of the dimensions of the order of 1 to 100's of nanometers show unique properties that are not clearly evident in their bulk state. These nanoparticles are highly reactive and sensitive to the changes in the vicinity of the particle surface and hence find applications in the field of sensing of chemical and biological agents, catalysis, energy harvesting, data storage and many more. By synthesizing bimetallic nanoparticles, a single nanoparticle can show multifunctional characteristics. The focus of this thesis is to detail the synthesis and understand the properties of bimetallic nanomaterial systems that show interesting optical, chemical, and …

Magnetic, Optical And Electrical Properties Of Electron-Hole Pairs In Polymer And Organo-Metal Halide Perovskite Photovoltaic Cells, Yu-Che Hsiao

Doctoral Dissertations

Organic polymer and organo-metal halide perovskite (OMHP) materials have attracted extensive attention during the past decade due to their various applications, like solar cells, light emitting diode, even lasing action (OMHP). Especially, the organo-metal halide perovskite solar cell shows a remarkable power conversion efficiency of about 20%, which is comparable to the amorphous silicon solar cell. Therefore, OMHP solar cell had been considered as a promising substitution for the next generation of renewable energy source. The OMHP materials contain both advantages of organic and inorganic semiconductors, like solution processable thin film fabrication, long-range ambipolar transport characteristics, high dielectric constants, low …

Thermal Characteristics Of Lithium Indium Diselenide And Lithium Indium Gallium Diselenide Neutron Detection Crystals, Dustin Carroll Giltnane

Masters Theses

Tracking special nuclear materials (SNM) has never been more important than in the 21^st century where information is transferred rapidly around the globe. Tracking SNM is important to nuclear power, weapons, medicine, and science. Neutron and gamma ray detection are the primary methods of detecting SNM. Increased movement and availability of SNM have increased the demand for radiation detection systems beyond the capacity of traditional neutron detection technologies (³He) [Helium three]. Many alternative neutron detection materials are being considered, including ⁶LiInSe₂ [Lithium Indium Diselenide grown with lithium enriched in lithium six] and its derivative ^{6 …}

Study Of Magneto-Optical Behaviors At A Ferromagnetic/Organic Semiconductor Interface, Jeremy Tyler Tisdale

Masters Theses

Organic materials have been widely studied for the last 20 years to use for photovoltaic applications. Organic photovoltaic materials have shown promising properties for solar cells, such as very low cost, flexibility, easy fabrication methods, etc. Although power conversion efficiencies for organic-based solar cells have exponentially grown in the last decade, up to about 13% in early 2016, it is still optimal to increase these efficiencies. In order to raise efficiencies, it is important to study the fundamental mechanisms inside organic materials that lead to photovoltaic properties. This thesis reports the magneto-optical effects on the p-type organic semiconductor, tetracene, from …

Interface And Morphology Engineering In Solution-Processed Electronic And Optoelectronic Devices, Sanjib Das

Doctoral Dissertations

The first part of this dissertation focuses on interface and morphology engineering in polymer- and small molecule-based organic solar cells. High-performance devices were fabricated, and the device performance was correlated with nanoscale structures using various electrical, spectroscopic and microscopic characterization techniques, providing guidelines for high-efficiency cell design.

The second part focuses on perovskite solar cells (PSCs), an emerging photovoltaic technology with skyrocketing rise in power conversion efficiency (PCE) and currently showing comparable PCEs with those of existing thin film photovoltaic technologies such as CIGS and CdTe. Fabrication of large-area PSCs without compromising reproducibility and device PCE requires formation of dense, …

Incorporation Of High-K Hfo2 Thin Films In A-Igzo Thin Film Transistor Devices, Aaron Hamilton Bales

Masters Theses

In this study, HfO2 [hafnium oxide] thin films are investigated extensively as part of indium gallium zinc oxide (IGZO) thin film transistor (TFT) devices. They are incorporated into the TFTs, both as a gate insulator and a passivation layer. First, the HfO2 [hafnium oxide] films themselves are investigated through an annealing study and through I-V and C-V measurements. Then, HfO2 [hafnium oxide] is suggested as a replacement for commonly used SiO2 [silicon dioxide] gate insulator, as it has a dielectric constant that is 4 – 6 times higher. This higher dielectric constant allows for comparable TFT performance at a lower …

Ion Irradiation Induced Damage And Dynamic Recovery In Single Crystal Silicon Carbide And Strontium Titanate, Haizhou Xue

Doctoral Dissertations

The objective of this thesis work is to gain better understanding of ion-solid interaction in the energy regime where electronic and nuclear energy loss are comparable. Such responses of materials to ion irradiations are of fundamental importance for micro-electronics and nuclear applications. The ion irradiation induced modification for the crystal structure, the physical and chemical properties etc. may strongly affect the performance of functional materials that needs to be better understood.

Experimentally, ion irradiation induced damage accumulation and dynamic recovery in SiC [silicon carbide] and SrTiO₃ [strontium titanate] were studied in this dissertation project. Five chapters are presented: Firstly, …

Bulk Heterojunctions In Photovoltaic Devices, Ondrej Edward Dyck

Doctoral Dissertations

Current solar cells, on the market today, have little room for improved efficiency or cost reduction. Part of this is due to the costly manufacture of high purity silicon and the current fabrication methods for solar cells. Solution processable solar cells would mark a great stride forward to cost reduction. If such cells can be demonstrated to be efficient enough and stable enough it would be a turning point in history. However, solution processable devices still need much work before they can compete in the market. This text addresses characterization problems in the TEM, covers a study dealing with optimization …