Physics Commons^™

Effect Of Fabrication Parameters On The Ferroelectricity Of Hafnium Zirconium Oxide Films: A Statistical Study, Guillermo A. Salcedo, Ahmad E. Islam, Elizabeth Reichley, Michael Dietz, Christine M. Schubert Kabban, Kevin D. Leedy, Tyson C. Back, Weison Wang, Andrew Green, Timothy S. Wolfe, James M. Sattler

Faculty Publications

Ferroelectricity in hafnium zirconium oxide (Hf_1−xZr_xO₂) and the factors that impact it have been a popular research topic since its discovery in 2011. Although the general trends are known, the interactions between fabrication parameters and their effect on the ferroelectricity of Hf_1−xZr_xO₂ require further investigation. In this paper, we present a statistical study and a model that relates Zr concentration (x), film thickness (t_f), and annealing temperature (T_a) with the remanent polarization (P_r) in tungsten (W)-capped Hf_1−xZr_xO₂. …

Measurements Of Magnetic Field Penetration Of Materials For Superconducting Radiofrequency Cavities, Iresha Harshani Senevirathne

Physics Theses & Dissertations

Superconducting Radio Frequency (SRF) cavities used in particle accelerators are typically formed from or coated with superconducting materials. Currently high purity niobium is the material of choice for SRF cavities which have been optimized to operate near their theoretical field limits. This brings about the need for significant R&D efforts to develop next generation superconducting materials which could outperform Nb and keep up with the demands of new accelerator facilities. To achieve high quality factors and accelerating gradients, the cavity material should be able to remain in the superconducting Meissner state under high RF magnetic field without penetration of quantized …

Gamma-Ray Radiation Effects In Graphene-Based Transistors With H-Bn Nanometer Film Substrates, E. J. Cazalas, Michael R. Hogsed, S. R. Vangala, Michael R. Snure, John W. Mcclory

Faculty Publications

Radiation effects on graphene field effect transistors (GFETs) with hexagonal boron nitride (h-BN) thin film substrates are investigated using 60Co gamma-ray radiation. This study examines the radiation response using many samples with varying h-BN film thicknesses (1.6 and 20 nm thickness) and graphene channel lengths (5 and 10 μm). These samples were exposed to a total ionizing dose of approximately 1 Mrad(Si). I-V measurements were taken at fixed time intervals between irradiations and postirradiation. Dirac point voltage and current are extracted from the I-V measurements, as well as mobility, Dirac voltage hysteresis, and the total number of GFETs that remain …

Erratum: "Imaging The Three‐Dimensional Orientation And Rotational Mobility Of Fluorescent Emitters Using The Tri‐Spot Point Spread Function", Oumeng Zhang, Jin Lu, Tianben Ding, Matthew D. Lew

Electrical & Systems Engineering Publications and Presentations

In the original paper, a calibration error exists in the image-formation model used to analyze experimental images taken by our microscope, causing a bias in the orientation measurements in Figs. 2 and 3. The updated measurements are shown in Fig. E1. We have also updated the supplementary material for the original article to discuss the revised PSF model and estimation algorithms (supplementary material 2) and show the revised model and measurements (Figs. S1, S3, S7, S8, and S10–S13).

Imaging The Three-Dimensional Orientation And Rotational Mobility Of Fluorescent Emitters Using The Tri-Spot Point Spread Function, Oumeng Zhang, Jin Lu, Tianben Ding, Matthew D. Lew

Electrical & Systems Engineering Publications and Presentations

Fluorescence photons emitted by single molecules contain rich information regarding their rotational motions, but adapting single-molecule localization microscopy (SMLM) to measure their orientations and rotational mobilities with high precision remains a challenge. Inspired by dipole radiation patterns, we design and implement a Tri-spot point spread function (PSF) that simultaneously measures the three-dimensional orientation and the rotational mobility of dipole-like emitters across a large field of view. We show that the orientation measurements done using the Tri-spot PSF are sufficiently accurate to correct the anisotropy-based localization bias, from 30 nm to 7 nm, in SMLM. We further characterize the emission anisotropy …

Characterization And Analysis Of Ultrathin Cigs Films And Solar Cells Deposited By 3-Stage Process, Grace Rajan, Krishna Aryal, Shankar Karki, Puruswottam Aryal, Robert W. Collins, Sylvain Marsillac

Electrical & Computer Engineering Faculty Publications

In view of the large-scale utilization of Cu(In,Ga)Se₂ (CIGS) solar cells for photovoltaic application, it is of interest not only to enhance the conversion efficiency but also to reduce the thickness of the CIGS absorber layer in order to reduce the cost and improve the solar cell manufacturing throughput. In situ and real-time spectroscopic ellipsometry (RTSE) has been used conjointly with ex situ characterizations to understand the properties of ultrathin CIGS films. This enables monitoring the growth process, analyzing the optical properties of the CIGS films during deposition, and extracting composition, film thickness, grain size, and surface roughness which …

Nanostructure Evolution Of Magnetron Sputtered Hydrogenated Silicon Thin Films, Dipendra Adhikari, Maxwell M. Junda, Sylvain X. Marsillac, Robert W. Collins, Nikolas J. Podraza

Electrical & Computer Engineering Faculty Publications

Hydrogenated silicon (Si:H) thin films have been prepared by radio frequency (RF) magnetron sputtering. The effect of hydrogen gas concentration during sputtering on the resultant film structural and optical properties has been investigated by real time spectroscopic ellipsometry (RTSE) and grazing incidence x-ray diffraction (GIXRD). The analysis of in-situ RTSE data collected during sputter deposition tracks the evolution of surface roughness and film bulk layer thickness with time. Growth evolution diagrams depicting amorphous, nanocrystalline and mixed-phase regions for low and high deposition rate Si:H are constructed and the effects of process parameter (hydrogen gas concentration, total pressure and RF power) …

Properties Of Cu(In,Ga,Al)Se² Thin Films Fabricated By Magnetron Sputtering, Talaat A. Hameed, Wei Cao, Bahiga A. Mansour, Inas K. Elzawaway, El-Metwally M. Abdelrazek, Hani E. Elsayed-Ali

Applied Research Center Publications

Cu (In,Ga,Al)Se₂ (CIGAS) thin films were studied as an alternative absorber layer material to Cu(In_xGa_1-x)Se₂. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350 °C, followed by postdeposition annealing at 520 °C for 5 h in vacuum. The film composition was measured by an electron probe microanalyzer while the elemental depth profiles were determined by secondary ion mass spectrometry. X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2θ …

Polarization Of Bi2te3 Thin Film In A Floating-Gate Capacitor Structure, Hui Yuan, Kai Zhang, Haitao Li, Hao Zhu, John E. Bonevich, Helmut Baumgart, Curt A. Richter, Qiliang Li

Electrical & Computer Engineering Faculty Publications

Metal-Oxide-Semiconductor (MOS) capacitors with Bi₂Te₃ thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi₂Te₃ thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi₂Te₃, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent …

Physical Analysis Of Vo2 Films Grown By Atomic Layer Deposition And Rf Magnetron Sputtering, Madhavi Tangirala, Kai Zhang, David Nminibapiel, Venkateswara Pallem, Christian Dussarrat, Wei Cao, Thomas N. Adam, Corbet S. Johnson, Hani E. Elsayed-Ali, Helmut Baumgart

Electrical & Computer Engineering Faculty Publications

Among the many vanadium suboxides and different stoichiometries, VO₂ has received considerable attention due to its remarkable metal-insulator transition (MIT) behavior, which causes a significant reversible change in its electrical and optical properties occurring across the phase transition at 67°C. The initially amorphous VO₂ thin films were fabricated by the emerging, Atomic Layer Deposition (ALD) technique with (tetrakis[ethylmethylamino]vanadium) {V(NEtMe)₄} as precursor and H₂O vapor as oxidation agent. For benchmarking we have also used the RF Magnetron Sputtering technique to deposit metallic vanadium thin films, which were later oxidized during furnace annealing. Post annealing of …

The Impact Of Growth Conditions On Cubic Znmgo Ultraviolet Sensors, Ryan Boutwell

Electronic Theses and Dissertations

Cubic Zn1-xMgxO (c-Zn1-xMgxO) thin films have opened the deep ultraviolet (DUV) spectrum to exploration by oxide optoelectronic devices. These extraordinary films are readily wet-etch-able, have inversion symmetric lattices, and are made of common and safe constituents. They also host a number of new exciting experimental and theoretical challenges. Here, the relation between growth conditions of the c-Zn1-xMgxO film and performance of fabricated ultraviolet (UV) sensors is investigated. Plasma-Enhanced Molecular Beam Epitaxy was used to grow Zn1-xMgxO thin films and formation conditions were explored by varying the growth temperature, Mg source flux, oxygen flow rate, and radio-frequency (RF) power coupled into …

Structural, Optical And Electrical Properties Of Yttrium-Doped Hafnium Oxide Nanocrystalline Thin Films, Abhilash Kongu

Open Access Theses & Dissertations

Hafnium oxide (HfO2) has emerged as the most promising high-k dielectric for Metal-Oxide-Semiconductor (MOS) devices and has been highlighted as the most suitable dielectric materials to replace silicon oxide because of its comprehensive performance. In the present research, yttrium-doped HfO2 (YDH) thin films were fabricated using RF magnetron sputter deposition onto Si (100) and quartz with a variable thickness. Cross-sectional scanning electron microscopy coupled with Filmetrics revealed that film thickness values range from 700 A° to 7500 A°. Electrical properties such as AC Resistivity and current-voltage (I-V) characteristics of YDH films were studied. YDH films that were relatively thin (<1500 A°) crystallized in monoclinic phase while thicker films crystallized in cubic phase. The band gap (Eg) of the films was calculated from the optical measurements. The band gap was found to be ∼5.60 eV for monoclinic while it is ∼6.05 eV for cubic phase of YDH films. Frequency dependence of the electrical resistivity (ρac) and the total conductivity of the films were measured. Resistivity decreased (by three orders of magnitude) with increasing frequency from 100 Hz to 1 MHz, attributed due to the hopping mechanism in YDH films. Whereas, while ρac∼1Ω-m at low frequencies (100 Hz), it decreased to ∼ 104 Ω-cm at higher frequencies (1 MHz). Aluminum (Al) metal electrodes were deposited to fabricate a thin film capacitor with YDH layer as dielectric film thereby employing Al-YDH-Si capacitor structure. The results indicate that the capacitance of the films decrease with increasing film thickness. A detailed analysis of the electrical characteristics of YDH films is presented.

Investigation Of Nbnx Thin Films And Nanoparticles Grown By Pulsed Laser Deposition And Thermal Diffusion, Ashraf Hassan Farha

Electrical & Computer Engineering Theses & Dissertations

Niobium nitride films (NbNx) were grown on Nb and Si (100) substrates using pulsed laser deposition (PLD), laser heating, and thermal diffusion methods. Niobium nitride films were deposited on Nb substrates using PLD with a Q-switched Nd: YAG laser (λ = 1064 nm, 40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, different nitrogen background pressures and deposition temperatures. The effect of changing PLD parameters for films done by PLD was studied. The seen observations establish guidelines for adjusting the laser parameters to achieve the desired morphology and phase of the grown NbNx films.

When the …

Plasmonic And Photonic Designs For Light Trapping In Thin Film Solar Cells, Liming Ji

Graduate Theses and Dissertations

Thin film solar cells are promising to realize cheap solar energy. Compared to conventional wafer cells, they can reduce the use of semiconductor material by 90%. The efficiency of thin film solar cells, however, is limited due to insufficient light absorption. Sufficient light absorption at the bandgap of semiconductor requires a light path more than 10x the thickness of the semiconductor. Advanced designs for light trapping are necessary for solar cells to absorb sufficient light within a limited volume of semiconductor. The goal is to convert the incident light into a trapped mode in the semiconductor layer.

In this dissertation, …

Self-Assembly Of Ge Quantum Dots On Si(100)- 2×1 By Pulsed Laser Deposition, M. S. Hegazy, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Self-assembled Ge quantum dots are grown on Si(100)- 2×1 by pulsed laser deposition. The growth is studied by in situ reflection high-energy electron diffraction and postdeposition atomic force microscopy. After the completion of the wetting layer, transient hut clusters, faceted by different planes, are observed. When the height of these clusters exceeded a certain value, the facets developed into {305} planes. Some of these huts become {305}-faceted pyramids as the film mean thickness was increased. With further thickness increase, dome clusters developed on the expense of these pyramids. © 2005 American Institute of Physics. [DOI: 10.1063/1.1949285]

Cuin1-Xalxse2 Thin Films And Solar Cells, P. D. Paulson, M. W. Haimbodi, S. Marsillac, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

CuIn[sub 1-x]Al[sub x]Se[sub 2] thin films are investigated for their application as the absorber layer material for high efficiency solar cells. Single-phase CuIn[sub 1-x]Al[sub x]Se[sub 2] films were deposited by four source elemental evaporation with a composition range of 0≤x≤0.6. All these films demonstrate a normalized subband gap transmission >85% with 2 µm film thickness. Band gaps obtained from spectroscopic ellipsometry show an increase with the Al content in the CuIn[sub 1-x]Al[sub x]Se[sub 2] film with a bowing parameter of 0.62. The structural properties investigated using x-ray diffraction measurements show a decrease in lattice spacing as the Al content increases. …

Reflection High-Energy Electron-Diffraction Study Of Melting And Solidification Of Pb On Graphite, Z. H. Zhang, P. Kulatunga, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The melting and solidification of Pb thin films on pyrolytic graphite are investigated in situ by reflection high-energy electron diffraction. Thin films with thicknesses of 4-150 monolayers are investigated. The surface morphology of the thin films were studied by scanning electron microscopy. Superheating of the Pb thin films by 4±2 to 12±2 K is observed from diffraction intensity measurements. Upon cooling the substrate, the Pb on graphite is seen to supercool by ∼69±4 K.

Low‐Cost Technique For Preparing N‐Sb2S3/P‐Si Heterojunction Solar Cells, O. Savadogo, K. C. Mandal

Faculty Publications

No abstract provided.