Physical Sciences and Mathematics Commons^™

A New Technique For Whole-Wafer Etch-Pit Density Mapping In Gaas, David C. Look, D. C. Walters, J. S. Sewell, S. C. Dudley, M. G. Mier, J. S. Sizelove

Physics Faculty Publications

The pits formed on an etched GaAs surface, due to the anisotropic etching around dislocations, are efficient light scatterers, and thus reduce transmission. We have derived a quantitative relationship between the fractional transmission and the etch‐pit density (EPD) and have shown that the same absorption apparatus which is commonly used to obtain a whole‐wafer [EL2] map can also be used to generate an EPD map. The technique is verified by comparing the fractional transmission with the actual EPD count at 166 points on a three‐inch, low‐pressure, liquid‐encapsulated Czochralski wafer. Also, [EL2] and EPD maps, with more than 3500 points each, …

Measured Spectra Of The Hygroscopic Fraction Of Atmospheric Aerosol Particles, Darryl J. Alofs, Donald E. Hagen, Max B. Trueblood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The relation between dry diameter (X₀) and critical supersaturation (S_c) for atmospheric submicron aerosol particles is investigated using a long term air sampling program at Rolla, Missouri. The particles are passed through an electrostatic aerosol size classifier, and then through an isothermal haze chamber. Results are reported in terms of an apparent volume fraction of soluble material, ε_v defined such that for particles composed only of ammonium sulfate and water insoluble compounds, ε_v is the actual volume fraction of soluble material. The probability distribution of ε_v is found to be approximately Gaussian in …

Elastic Angular Differential Cross Sections For Quasi-Oneelectron Collision Systems At Intermediate Energies: (Na+, Li+)+H And (Mg+, Be+)+He, J. L. Peacher, E. Redd, D. G. Seely, Timothy J. Gay, D. M. Blakenship, J. T. Park

Timothy J. Gay Publications

Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na⁺+H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li⁺+H collisions at energies of 19.44 and 43.75 keV, for Mg⁺+He collisions at energies of 30, 66.7, and 150 keV, and for Be⁺+He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …

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.

Elastic Angular Differential Cross Sections For Quasi-One-Electron Collision Systems At Intermediate Energies: (Na⁺, Li⁺)+H And (Mg⁺, Be⁺)+He, Jerry Peacher, E. Redd, Denver G. Seely, Timothy Gay, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na⁺+H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li⁺+H collisions at energies of 19.44 and 43.75 keV, for Mg⁺+He collisions at energies of 30, 66.7, and 150 keV, and for Be⁺+He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …

Non-Debye Enhancements In The Mie Scattering Of Light From A Single Water Droplet, James A. Lock, Judith R. Woodruff

Physics Faculty Publications

The glare spots usually seen on a single water droplet which has been illuminated by a plane wave are produced by geometrical rays which correspond to the different terms of the Debye series expansion of the Mie scattered field. Recently other glare spot enhancements have been predicted which correspond to scattering resonances coupling to the orbiting rays associated with high-order geometrical rainbows. We observed the non-Debye enhancement of the eleventh-order rainbow glare spot at an observation angle of 90° on a 3.5-mm water droplet illuminated by polarized He-Ne laser light.

The 157 Nm Photodissociation Of Ocs, C. E. Strauss, George C. Mcbane, P. L. Houston, I. Burak, J. W. Hepburn

Peer Reviewed Articles

The photodissociation of OCS at 157 nm has been investigated by using tunable vacuum ultraviolet radiation to probe the CO and S photoproducts. Sulfur is produced almost entirely in the ¹S state, while CO is produced in its ground electronic state and in vibrational levels from v=0-3 in the appropriate ratio (v=0):(v=1):(v=2):(v=3) = (1.0):(1.0):(0.5):(0.3). The rotational distribution for each vibrational level is found to be near Boltzmann, with temperatures that decrease from 1350 K for v=0 to 780 K for v=3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from …

Low-Energy Features Of The E--H(N=2) System Exhibited In Fast H- Detachment Collisions, Chih-Ray Liu, Anthony F. Starace

Anthony F. Starace Publications

Quantitative predictions for the doubly differential detachment collisions, 0.5-MeV H^-+He→H(n=2)+He*+e^-, are provided by use of hyperspherical wave functions for the H-e^- system. Individual H-e^- hyperspherical channels are identified as producing distinct "cusp," "shape resonance," and/or "shoulder" features in the laboratory-frame cross sections. Moreover, the first quantitative predictions of the expected Gailitis-Damburg dipole-field-induced oscillations in the cross sections above the H(n=2) threshold are presented and distinguished from ¹P∘ shape resonance effects.

Pitch Of Complex Tones With Many High‐Order Harmonics, Adrianus J. M. Houtsma, J. Smurzynski

Jacek Smurzynski

Eigenvalues And Retardation Effects In The N=10 States Of Helium, Gordon W. F. Drake

Physics Publications

High-precision variational eigenvalues are obtained for the 10D, 10F, 10G and 10H states of helium by the application of multiple basis set methods. The accuracy is sufficient to provide the first definitive test of asymptotic expansion methods extensively developed by Drachmann (1982-8) for Rydberg states of high angular momentum. The results are also compared with recent high-precision measurements for the 10G-10H and 10F-10G transition frequencies, and interpreted in terms of predicted long-range retardation corrections. Bethe logarithms are calculated and Lamb shift corrections included. Small residual discrepancies persist which could be explained by uncalculated radiative shifts.

Predicted Energy Shifts For Paronic Helium, Gordon W. F. Drake

Physics Publications

It has been shown recently that one can construct a local relativistic quantum field theory which admits small violations of the Pauli exclusion principle by introducing paronic states which obey para-Fermi statistics of order 2. Paronic shifts are calculated for the low-lying states of helium to aid in the design of experiments either to detect paronic helium, or place upper limits on its possible existence. © 1989 The American Physical Society.

Application Of The Linear Muffin-Tin-Orbital Band-Structure Method To Calculate Optical Properties Of Solids, R. Zemach, J. Ashkenazi, E. Ehrenfreund

Physics Articles and Papers

Optical matrix elements have been derived for crystals by applying the theory of optical transitions within the formalism of the linear muffin-tin-orbital band-structure method and using Racah algebra. A Brillouin-zone integration by the tetrahedron method allows straightforward numerical computation of the optical function ε₂(ω) [or σ(ω)]. Other optical functions may be derived by using a Kramers-Kronig analysis.

Calculation Of Optical Properties Of Trans-Polyacetylene By The Linear Muffin-Tin-Orbital Method, R. Zemach, J. Ashkenazi, E. Ehrenfreund

Physics Articles and Papers

The basic optical properties of trans-(CH)_x in the P2₁/n and the P2₁/a space groups are derived from first principles. The relevant optical matrix elements are calculated within the self-consistent linear muffin-tin-orbital band-structure method. The derived optical response functions are compared with the results from a variety of optical as well as electron-energy-loss experimental studies. It is shown that the measured optical constants are consistent with the P2₁/n structure.

Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Ashkenazi Et Al. Reply, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

Ashkenazi et al. reply to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters 62, 2016 (1989).

Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Errata, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

Errata to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters, 62, 2016 (1989).

Ground State Of Trans-Polyacetylene And The Peierls Mechanism, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

It is shown formally that the Peierls expression is inadequate for studying the instabilities of a physically realizable one-dimensional chain of atoms, due to the long-range nature of the Coulomb interaction. Detailed total-energy studies of trans-polyacetylene, for both suggested crystal structures (P2₁/n,P2₁/a) and for the one-dimensional chain, establish that no appreciable total-energy minimum occurs for nonzero dimerization amplitude within the local-density approximation. The measured dimerization is discussed within the context of recent models of electron correlation.

Excitations In A Nearly Half-Filled Hubbard Model With U=∞, S. E. Barnes

Physics Articles and Papers

It is shown that, even near half filling, the elementary excitations of the large-U Hubbard model form wide bands of width ∼t, the intersite hopping integral, and that the slave-boson-based mean-field approximation is qualitatively wrong in the relevant limit. This large-U limit has no Kondo-type divergences.

Crystallochemical Characterization Of Magnetic Spinels Prepared From Aqueous Solution, Stephen Mann, Nicholas H.C. Sparks, Suzanne B. Couling, Miranda C. Larcombe, Richard B. Frankel

Physics

The crystallochemical characterization of magnetic spinels prepared from aqueous solution has been studied primarily by electron microscopy and ⁵⁷Fe Mossbauer spectroscopy. Two synthetic routes have been investigated : method 1 ; partial oxidation of Fe" solutions in the presence of NO; at 100 C , and method 2; reaction of hydrated Ferrr oxide (ferrihydrite) with Fe" ions at room temperature, pH = 7, 8 and 9. Both routes gave small (10-60 nm) irregular magnetite (Fe,O,) particles that were readily oxidised to maghemite (y-Fe,O,). The reaction proceeded via a green-rust intermediate and anions such as inorganic phosphate (Pi) and SO,,- …

On The Size Distribution Of Newly Formed Grains In Red Supergiant Atmospheres, C Gregory Seab, Theodore P. Snow

Physics Faculty Publications

Theoretical ultraviolet extinction curves have been calculated for comparison with observed curves for circumstellar dust in M supergiants. The theoretical curves assumed a silicate grain composition, because silicate grains are expected in the oxygen-rich environments that are observed. Calculations were performed with and without the inclusion of scattering into the beam, with largely similar results. A comparison of the computed curves with the observed ultraviolet extinction curve for circumstellar dust in Scorpii indicates that the size distribution of the circumstellar grains must cut off near 800 Å that is, there are few or no grains smaller than this. Our conclusion …

Predicting Peculiar Interstellar Extinction From Gaseous Abundances, Charles L. Joseph, Theodore P. Snow, C Gregory Seab

Physics Faculty Publications

Molecular and atomic abundances are examined for 19 lines of sight through dense clouds, each with a peculiar selective extinction curve. The interstellar clouds in the present study appear to fall into two distinct categories: CN-rich, with relatively small amounts of neutral iron, or CN-poor, with large amounts of neutral iron. Lines of sight, having a CN/(Fe i) abundance ratio about two (~ 0.3 dex) or greater, are found to have a shallow (2.57 ± 0.55 mag) 2175 Å feature relative to the underlying extinction, while the strength of the bump is 3.60 ± 0.36 for the other dense clouds …

A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab

Physics Faculty Publications

It has recently been suggested that the diffuse interstellar bands may be formed by ionized polyhedral carbon molecules such as C60(+). While specific laboratory measurements of absorption bands of this molecular ion have not been made, a feature due to the neutral molecule C60 has been discovered at 3860A. Examination of spectra of several reddened stars, as well as one star known to have circumstellar carbonaceous dust, shows no sign of the feature, leading to upper limits of the order of 10 to the 14th/sq cm for the column density of C60. These limits are not yet sensitive enough to …

The Exchange Potential In Path Integral Studies: Analytical Justification, Randall W. Hall

Collected Faculty and Staff Scholarship

We present analytical justification for our previously described exchange pseudopotential. We show how the fermi quantum partition function can be constructed from the Boltzmann (distinguishable particle) wave functions if the states that correspond to like‐spin electrons occupying the same quantum state are excluded. A class of weighting functions that satisfy this constraint approximately is discussed. Our previous pseudopotential falls under this class. Essentially, our pseudopotential forces the unwanted states to have high energy and, hence, to make negligible contribution to the partition function. Exchange potentials of the form discussed in this article should be useful for studying systems where the …

Track “Core” Effects In Heavy Ion Radiolysis, Robert Katz, Guo-Rong Huang

Robert Katz Publications

By assuming that HO₂^● radical production in water and H₂ production in benzene are 2 hit processes, and applying the concepts of track physics, we are able to obtain a parametric fit to the yields of these reactions by heavy ion radiolysis from knowledge of the radial dose distribution about a heavy ion’s path. We make no use of the concept of a track core, for no clearly definable track core appears in our calculations of the radial dose distribution. Instead we calculate an action cross section σ from the assumed 2 hit response to γ-rays. The …

Perspectives On The Development Of Track Physics, Robert Katz

Robert Katz Publications

Let me thank all of you for being here, Tony Starace, for having conceived this meeting, and Bob Wood and Matesh Varma, for over 20 years of support without which there would have been no track physics. There are many others to thank: the students, postdoctorates, and senior visitors who actually did all the work, and the many investigators around the world who made measurements that proved to be essential to developing and testing the notions of particle tracks.

This enterprise began when I undertook to rewrite an introductory physics text by Henry Semat to adapt it to a calculus-based …

A Simple Monochromatic Spark Discharge Light-Source, Chin Oi Hoong

Chin Oi Hoong

Spark light illumination has been used in high-speed photog-raphy since the beginning ofthe century and various designs ofthe spark discharge light source have since been reportedr with spark duration ranging from nanoseconds to millisec-onds. We report here a simple and easy to build spark dis-charge tube for operation as a monochromatic point light source. The design and construction ofthe spark discharge tube is shown in Fig. 1. The sharp-tip solid cone anode is made of stainless steel which is screwed onto a brass rod connected A compact spark discharge tube operated as a monochromatic light source at 587.5 nm is …

Specific Heat Of Pure And Thoriated Ube13 At Low Temperatures In High Magnetic Fields, M. J. Graf, Nathanael A. Fortune, J. S. Brooks, J. L. Smith, Z. Fisk

Physics: Faculty Publications

We have measured the specific heat of pure and thoriated (3.3% thorium) UBe13 in the temperature interval 0.3 1.8 K in applied magnetic fields up to 20 T, and find striking qualitative differences between the two systems. For pure UBe13 the electronic coefficient of specific heat el(=Cel(T)/T) is noticeably suppressed by a field of 20 T at 1.8 K; below 1 K, however, this reduction from the low-field, normal-state value tends to zero. For the 3.3% thoriated sample, the high-temperature value of el is relatively insensitive to strong magnetic fields, but at lower temperatures the suppression of el becomes much …

Snow And Avalanche Physics: Physical Analysis Of Factors Affecting The Stability Of A Seasonal Continental Snowpack, James Frankenfield

All Graduate Plan B and other Reports, Spring 1920 to Spring 2023

Each section in this paper is intended to be as independent as possible. An attempt has been made to avoid references to other sections, and in particular to equations previously used. Hopefully the reader will not find it necessary to page back and forth very much. Figures and footnotes are numbered separately for each section.

A glossary has been included to assist the reader who is unfamiliar with some of the terms used. It includes entries of a qualitative nature (e.g. 'rime', 'graupel') as well as technical terms (e.g. 'Strouhal number').

The text was prepared using Wordperfect 4.1. Certain symbols …

Magnetospheric Plasma Pressures In The Midnight Meridian: Observations From 2.5 To 35 Re, Harlan E. Spence, M. G. Kivelson, R. J. Walker, D. J. Mccomas

Physics & Astronomy

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) were statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12–35 RE) magnetotail plasma sheet. The observed plasma pressure, assumed isotropic, was mapped along model magnetic field flux tubes (obtained from the Tsyganenko and Usmanov [1982] model) to the magnetic equator, sorted according to magnetic activity, and binned according to the mapped equatorial location. In regions (L ≳ 12 RE) where the bulk of the plasma pressure was contributed by particles in the energy range of the FPE (70 …

Inverse Ac Josephson Effect At Terahertz Frequencies, W C. Danchi, William Golightly, E C. Sutton

Physics and Astronomy

The inverse ac Josephson effect occurs when a Josephson junction driven by a microwave source of frequency  f  produces constant‐voltage steps at integer multiples of h f/2e. For low‐leakage current hysteretic junctions driven at microwave frequencies below about 100 GHz, some of these steps can cross the zero dc bias current axis. These zero‐crossing steps allow modern series array voltage standards to operate without individually biasing the junctions in the array. We reexamine the theory behind these steps and show that they can exist at frequencies much higher than thought previously. The Riedel singularity in the supercurrent …

A Nonlinear Eigenvalue Problem In Astrophysical Magnetohydrodynamics: Some Properties Of The Spectrum, John A. Adam

Mathematics & Statistics Faculty Publications

The equations of ideal magnetohydrodynamics (MHD) with an external gravitational potential—a ‘‘magnetoatmosphere’’—are examined in detail as a singular nonlinear eigenvalue problem. Properties of the spectrum are discussed with specific emphasis on two systems relevant to solar magnetohydrodynamics. In the absence of a gravitational potential, the system reduces to that of importance in MHD and plasma physics, albeit in a different geometry. This further reduces to a form isomorphic to that derived in the study of plasma oscillations in a cold plasma, Alfvén wave propagation in an inhomogeneous medium, and MHD waves in a sheet pinch. In cylindrical geometry, the relevant …