Physics Commons^™

Mitigation Of Water Vapor Interference For Infrared Polarization-Modulated Gas Filter Correlation Radiometry, David K. Lockwood

Electrical & Computer Engineering Theses & Dissertations

Gas filter correlation radiometry (GFCR) is a high-resolution, high-specificity technique for sensing gaseous species. A variation of absorption spectroscopy, GFCR has a long-proven record on orbital platforms for quantitative measurements of atmospheric constituents, as well as common usage in ground-based sensing applications. PMGFCR (Polarization-modulated GFCR) is a recent refinement of the technique with several advantages over the traditional method, including reducing the number of photodetectors required, increased sensitivity, and elimination of moving parts.

To date, no infrared remote sensors have successfully measured nitric oxide (NO) in vehicle exhaust due to spectral overlap by strong water vapor (H₂O_{v …}

Concept Of Local Polaritons And Optical Properties Of Mixed Polar Crystals, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

The concept of local polaritons is used to describe the optical properties of mixed crystals in the frequency region of their restrahlen band. It is shown that this concept allows for a physically transparent explanation of the presence of weak features in the spectra of so-called one-mode crystals and for one-two mode behavior. The previous models Were able to explain these features only with the use of many fitting parameters. We show that under certain Conditions new impurity-induced polariton modes may arise within the restrahlen of the host crystals, and study their dispersion laws and density of states. Particularly, we …

Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B. V. Vayner, D. C. Ferguson, W. A. Degroot, C. D. Thomson, John R. Dennison, R. E. Davies

All Physics Faculty Publications

Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant …

Use Of Diffuse Reflectance Spectroscopy To Determine Desorption Coefficients Of Trichioroethylene From Powdered Soils, Jay H. Foil

Theses and Dissertations

This laboratory thesis investigated the applicability of reflectance spectroscopy as a tool to measure desorption rates by directly observing the change in trichloroethylene bound to surface sites. Diffuse reflectance spectroscopy holds the promise of being a faster technique with minimal sample preparation time. Reflectance spectroscopy's dependence on the surface of the sample is its greatest advantage, as well as its greatest disadvantage. Both high and low resolution scans were made of different soil samples contaminated by trichloroethylene. After the technique of spectral subtraction was used, potential TCE signals were observed from the dolomitic limestone sample. Unfortunately, due to the low …

Analysis Of Scanning Tunneling Optical Spectroscopy Applied To Narrow Gap Semiconductors, James D. Patterson, James G. Mantovani

Aerospace, Physics, and Space Science Faculty Publications

Homogeneous II-VI narrow gap semiconducting alloys are of interest because of their use in infrared detectors. These compound semiconductor materials are inherently difficult to grow in bulk due to gravity induced convective flows. A microgravity growth environment has therefore been considered. In order to evaluate the quality of crystals grown in space compared to those grown on the ground, it is necessary to characterize both. One important aspect of this characterization is the study of stoichiometry, x. A characterization scheme using scanning tunneling optical spectroscopy (STOS) involves determining the spectral response of the photoexcited tunneling current for a semiconductor. By …

Spectroscopy Of Atoms Confined To The Single Node Of A Standing Wave In A Parallel-Plate Cavity, V. Sandoghar, C. I. Sukenik, S. Haroche, E. A. Hinds

Physics Faculty Publications

We have performed spectroscopy on sodium atoms that are optically channeled in the single node of a laser standing wave set up across a parallel-plate cavity. Using this technique we have extended our previous measurement of the Lennard-Jones van der Waals energy-level shift [Sandoghdar et al., Phys. Rev. Lett. 68, 3432 (1992)] down to a cavity width of ~500 nm. We discuss the applications of this technique to the precise measurement of atom-surface distances.

Basic Astronomy Labs, Terry L. Smith, Michael D. Reynolds, Jay S. Huebner

Physics Faculty Research and Scholarship

Providing the tools and know-how to apply the principles of astronomy first-hand, these 43 laboratory exercises each contain an introduction that clearly shows budding astronomers why the particular topic of that lab is of interest and relevant to astronomy. About one-third of the exercises are devoted solely to observation, and no mathematics is required beyond simple high school algebra and trigonometry.Organizes exercises into six major topics—sky, optics and spectroscopy, celestial mechanics, solar system, stellar properties, and exploration and other topics—providing clear outlines of what is involved in the exercise, its purpose, and what procedures and apparatus are to be used. …

Visible Luminescence From Single Crystal‐Silicon Quantum Wells, Peter N. Saeta, A. C. Gallagher

All HMC Faculty Publications and Research

Single crystal‐silicon quantum wells with SiO₂ barriers have been grown from SIMOX silicon‐on‐insulator substrates. Photoluminescence in the red and near‐infrared is observed for average well width <8 >nm, with peak signal for 2‐nm average width. The luminescence spectrum is independent of well width for SiO₂ barriers, but shifts 0.3 eV to higher energy upon removal of the upper oxide layer with HF. Both results suggest the importance of radiation from surface states.

Mesostructure Of Photoluminescent Porous Silicon, David D. Allred, F. Ruiz, C. Vázquez-López, Jesus González-Hernández, G. Romero-Paredes, R. Peña-Sierra, G. Torres-Delgado

Faculty Publications

Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to characterize the microstructure of photoluminescent porous silicon (PS) layers formed by the anodic etching (HF:H2O:ethanol), at various current densities, of p-type (100) silicon wafers possessing resitivity in the range 1-2 Ω cm. Existing models for the origin of luminescence in PS are not supported by our observations. Cross-sectional as well as surface atomic force micrographs show the material to be clumpy rather than columnar; rodlike structures are not observed down to a scale of 40 nm. A three-dimensional model of the mesostructure of porous silicon is discussed. Room-temperature …

Self-Consistent Determination Of Electronic Structure And Elementary Excitations Of Finite Modulation-Doped Superlattices, Roger H. Yu

All Faculty Scholarship for the College of the Sciences

A self-consistent framework for the study of the electronic level structure of finite superlattices has been proposed. One of the surface states (Tamm states) found in our calculation crosses the Fermi energy in the energy gap when the depletion effect near the surface increases. We have shown the existence of low-energy Tamm states in our calculation when the surface barrier is lower than that of the interior. The electronic excitations of the superlattice have been studied via the electron-energy-loss function within the random-phase approximation. Two plasmon modes (well above the phonon response frequency) due to the Tamm states have also …

Extension Of The Metal Light Pipe Infrared Spectroscopy Technique: Applications To Surface Adsorption And High Tc Superconductors, Torsten Will

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The development of an infrared instrument for the study of surface adsorption and high T_c superconductors is presented and its applicability is discussed. The use of and theoretical background for the metal light pipe multiple-reflection technique are discussed in comparison to other infrared devices. Measurements are carried out to determine its limitations with powdered substrates as well as its sensitivity limitation for thin films. The results of the two test measurements, adsorption of CO on MgO and investigation of the energy gap of high T_c superconductors, are presented. Comparisons of the spectra with the experimental and theoretical literature …

Nature Of Carbon-Carbon Bonding In Evaporated And Ion-Sputtered (Diamondlike) Amorphous Carbon From (E, 2e) Spectroscopy, Chao Gao, Yun Yu Wang, A. L. Ritter, John R. Dennison

All Physics Faculty Publications

The local carbon-carbon bonding in evaporated (e-C) and ion-sputtered (i-C) amorphous carbon has been investigated by transmission electron-energy-loss spectroscopy (EELS) and by (e, 2e) spectroscopy. The EELS data indicate that the e-C is graphiclike and the i-C is diamondlike. The (e, 2e) data demonstrate that the concentration of sp² bonding is ∼100% in both materials (0.85≤c_sp²≤1.0) for e-C and 0.75≤c_sp²≤1.0 for i-C). There is significant rehybridization of the π orbital in i-C.

Spectral Momentum Density From Graphite From Spectroscopy: Comparison With First Principles Calculations, Chao Gao, A. L. Ritter, John R. Dennison, N. A. Holzwarth

All Physics Faculty Publications

We have measured the spectral momentum density ρ(E,q) of graphite by (e,2e) spectroscopy for momentum parallel and perpendicular to the crystal c axis. In the independent-electron approximation, ρ(E,q)=Σ_G‖U_k(G)‖² δ(q-k-G)δ(E-E(k)) where the one-electron wave function is Ψ_k(r)=e^ik⋅rΣ_GU_k(G)e^iG⋅r) and G is a reciprocal-lattice vector. The measurements covered a range of momentum parallel to the c axis equal to 0≤‖q‖≤1.84 Å^-1 and a range of momentum perpendicular to the c axis equal to 0≤‖q‖≤2.35 Å^-1. The energy range spanned the valence band of graphite from …

The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, John R. Dennison, R. Jones

All Physics Faculty Publications

The spectral momentum density of the valence band of an amorphous carbon film has been measured by (e, 2e) spectroscopy. Two "bands," energy as a function of momentum, are resolved. One extends from 23 eV below the Fermi energy to about 10 eV below E_F. The other, ∼ 9 eV below E_F, does not disperse significantly. Although the existence of diamond bonding in the film cannot be ruled out, the bands are more suggestive of the graphite band structure.