Atomic, Molecular and Optical Physics Commons^™

Spectroscopic End Point Detection With An Electron Beam Evaporator, Ryan Mcgraw

University Honors Theses

Spectroscopic end point detection is a common tool used for measuring slope changes in wavelength intensity. Using algorithms able to apply this concept, coatings will be able to be dynamically measured in real time and stopped at the appropriate level to ensure process uniformity. It is currently applied to reductive processes such as etching, where the surface will start to be eaten away, creating a plasma. When the entire amount of a material on a substrate has been eaten away, the plasma will change color as it is beginning to etch a different material. Using a spectrometer, this point where …

Recent Advances In Experimental Design And Data Analysis To Characterize Prokaryotic Motility, Megan M. Dubay, Jacqueline Acres, Max Riekeles, Jay Nadeau

Physics Faculty Publications and Presentations

Bacterial motility plays a key role in important cell processes such as chemotaxis and biofilm formation, but is challenging to quantify due to the small size of the individual microorganisms and the complex interplay of biological and physical factors that influence motility phenotypes. Swimming, the first type of motility described in bacteria, still remains largely unquantified. Light microscopy has enabled qualitative characterization of swimming patterns seen in different strains, such as run and tumble, run-reverse-flick, run and slow, stop and coil, and push and pull, which has allowed for elucidation of the underlying physics. However, quantifying these behaviors (e.g., identifying …

Self-Contained Photon Coincidence Counting With Ni Myrio Ecosystem, Georges Oates Larsen, Andres H. La Rosa

University Honors Theses

Digital coincidence counting units (CCU) have made experimental verification of fundamental quantum mechanical principles financially accessible to undergraduate level teaching programs. However, recent implementations of these systems are not easily ported to National Instruments (NI) FPGAs, making them unsuitable for physics departments that have heavily invested in the NI ecosystem. Therefore, there is clear need for a detailed implementation based on an NI FPGA. We present a formal description of one such implementation, based on the NI myRIO (NI's lower-cost, student-oriented offering) which achieves 6.9 ns minimum guaranteed-distinguishable delay and 32.2 MHz peak coincidence counting rate with four input channels …

Dipole Emission Characteristics Near A Topological Insulator Sphere Coated With A Metallic Nanoshell, Huai-Yi Xie, Railing Chang, P. T. Leung

Physics Faculty Publications and Presentations

Topological insulators (TI) are quantum states of (2D/3D) matter with an insulating interior but conducting edge/surface states, with these boundary conducting states being protected topologically by time-reversal symmetry. Composite materials of heavy atoms such as Bi₂Te₃ can be fabricated to show TI properties due to the strong intrinsic spin-orbit coupling of the electrons in these materials. Among the so many intriguing physical properties of these materials, their topological magneto-electric (TME) response is unique and has been studied intensively in the literature, leading to intriguing optical effects such as Faraday and Kerr rotations of incident polarized beams at …

Analytical Results For The Three-Body Radiative Attachment Rate Coefficient, With Application To The Positive Antihydrogen Ion H̄+, Jack C. Straton

Physics Faculty Publications and Presentations

To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient αRA for producing the negative hydrogen ion H⁻ or its antimatter equivalent, the positive antihydrogen ion H¯⁺ , we found the analytic form for this integral. This procedure is useful for temperatures below 700 K, the region for which the production of H¯⁺ has potential use as an intermediate stage in the cooling of antihydrogen to ultra-cold (sub-mK) temperatures for spectroscopic studies and probing the gravitational interaction of the anti-atom. Our results, utilizing a 50-term …

Predicting Densities And Elastic Moduli Of Sio2-Based Glasses By Machine Learning, Yong-Jie Hu, Ge Zhao, Mingfei Zhang, Bin Bin, Tyler Del Rose, Qian Zhao, Qan Zu, Yang Chen, Xuekun Sun, Maarten De Jong, Multiple Additional Authors

Mathematics and Statistics Faculty Publications and Presentations

Chemical design of SiO2-based glasses with high elastic moduli and low weight is of great interest. However, it is difficult to find a universal expression to predict the elastic moduli according to the glass composition before synthesis since the elastic moduli are a complex function of interatomic bonds and their ordering at different length scales. Here we show that the densities and elastic moduli of SiO2-based glasses can be efficiently predicted by machine learning (ML) techniques across a complex compositional space with multiple (>10) types of additive oxides besides SiO2. Our machine learning approach relies on a training set …

Enhancing Final Image Contrast In Off-Axis Digital Holography Using Residual Fringes, Manuel Bedrossian, Kent Wallace, Eugene Serabyn, Chris Lindensmith, Jay Nadeau

Physics Faculty Publications and Presentations

We show that background fringe-pattern subtraction is a useful technique for removing static noise from off-axis holographic reconstructions and can enhance image contrast in volumetric reconstructions by an order of magnitude in the case for instruments with relatively stable fringes. We demonstrate the fundamental principle of this technique and introduce some practical considerations that must be made when implementing this scheme, such as quantifying fringe stability. This work also shows an experimental verification of the background fringe subtraction scheme using various biological samples.

Polarization In The Production Of The Antihydrogen Ion, Casey A. Yazejian, Jack C. Straton

Physics Faculty Publications and Presentations

We provide estimates of both the cross section and rate coefficient for the radiative attachment of a second positron to create the H̅+ ion, H̅(1s)+e+→H̅+(1s2 1Se)+ℏω, for which the polarization of the initial state H̅(1s) is taken into account. We show how to analytically integrate the resulting six-dimensional, three-body integrals for wave functions composed of explicitly correlated exponentials, a result that may be extended to Hylleraas wave functions. We extend Bhatia’s polarization results for the equivalent matter problem down to the low temperatures required for the Gravitational Behaviour of Antihydrogen …

Photoemission Electron Microscopy To Characterize Slow Light In A Photonic Crystal Line Defect, Theodore Stedmark, Rolf Könenkamp

Physics Faculty Publications and Presentations

Using femtosecond nonlinear photoemission electron microscopy (PEEM) we provide a detailed characterization of slow light in a small-size asymmetric photonic crystal structure. We show that PEEM is capable of providing a unique description of the light propagation in such structures by direct imaging of the guided mode. This noninvasive characterization technique allows modal properties such as effective index, phase velocities, and group velocities to be determined. Combining experimental results with finite element method simulation calculations, we study slow light phenomena in a photonic crystal defect mode, and we produce a comprehensive picture of the mechanisms behind it. Our results illustrate …

Imaging Technologies And Strategies For Detection Of Extant Extraterrestrial Microorganisms, Jay Nadeau, Manuel Bedrossian, Chris Lindensmith

Physics Faculty Publications and Presentations

There is no reductionist definition of life, so the way organisms look, behave, and move is the most definitive way to identify extraterrestrial life. Life elsewhere in the Solar System is likely to be microbial, but no microscope capable of imaging prokaryotic life has ever flown on a lander mission to a habitable planet. Nonetheless, high-resolution microscopes have been developed that are appropriate for planetary exploration. Traditional light microscopy, interferometric microscopy, light-field microscopy, scanning probe microscopy, and electron microscopy are all possible techniques for the detection of extant micro-organisms on Mars and the moons of Jupiter and Saturn. This article …

High-Performance Self-Powered Uv Detector Based On Sno2-Tio2 Nanomace Arrays, Duo Chen, Lin Wei, Lingpan Meng, Yanxue Chen, Yufeng Tian, Shishen Yan, Liangmo Mei, Jun Jiao

Physics Faculty Publications and Presentations

Photoelectrochemical cell-typed self-powered UV detectors have attracted intensive research interest due to their low cost, simple fabrication process, and fast response. In this paper, SnO2-TiO2 nanomace arrays composed of SnO2 nanotube trunk and TiO2 nanobranches were prepared using soft chemical methods, and an environment-friendly self-powered UV photodetector using this nanostructure as the photoanode was assembled. Due to the synergistic effect of greatly accelerated electron-hole separation, enhanced surface area, and reduced charge recombination provided by SnO2-TiO2 nanomace array, the nanostructured detector displays an excellent performance over that based on bare SnO2 arrays. The impact of the growing time of TiO2 branches …

Mixing Times Of Organic Molecules Within Secondary Organic Aerosol Particles: A Global Planetary Boundary Layer Perspective, Adrian M. Maclean, Christopher L. Butenhoff, James W. Grayson, Kelley Barsanti, Jose L. Jimenez, Allan K. Bertram

Physics Faculty Publications and Presentations

When simulating the formation and life cycle of secondary organic aerosol (SOA) with chemical transport models, it is often assumed that organic molecules are well mixed within SOA particles on the timescale of 1 h. While this assumption has been debated vigorously in the literature, the issue remains unresolved in part due to a lack of information on the mixing times within SOA particles as a function of both temperature and relative humidity. Using laboratory data, meteorological fields, and a chemical transport model, we estimated how often mixing times are < 1 h within SOA in the planetary boundary layer (PBL), the region of the atmosphere where SOA concentrations are on average the highest. First, a parameterization for viscosity as a function of temperature and RH was developed for α-pinene SOA using room-temperature and low-temperature viscosity data for α-pinene SOA generated in the laboratory using mass concentrations of ∼ 1000 µg m−3. Based on this parameterization, the mixing times within α-pinene SOA are < 1 h for 98.5 % and 99.9 % of the occurrences in the PBL during January and July, respectively, when concentrations are significant (total organic aerosol concentrations are > 0.5 µg m−3 at the surface). Next, as a starting …

Quasi-Optical Measurement For Low Loss Material Characterization In Submillimeter Wave Range, Ha Khiem Tran, Thanh Ngoc Dan Le, Branimir Pejcinovic

Student Research Symposium

An accurate knowledge of dielectric constant of materials is required in many sub-millimeter wave applications. Free-space measurement of materials has always been one of the first choices due to their non-destructive nature and relatively simple sample preparation. However, free-space measurement systems at sub-millimeter frequency range suffer from two main problems: high loss because of divergent beam pattern and diffraction when the beam waist of the radiated beam is relatively large compared to the size of the sample under tests. In order to mitigate these issues, we set up a quasi-optical system using off-axis parabolic mirrors, which enhance the dynamic range …

Atomic Layer Growth Of Inse And Sb₂Se₃ Layered Semiconductors And Their Heterostructure, Robert Browning, Neal Kuperman, Bill Moon, Raj Solanki

Physics Faculty Publications and Presentations

Metal chalcogenides based on the C–M–M–C (C = chalcogen, M = metal) structure possess several attractive properties that can be utilized in both electrical and optical devices. We have shown that specular, large area films of ^_y-InSe and Sb₂Se₃ can be grown via atomic layer deposition (ALD) at relatively low temperatures. Optical (absorption, Raman), crystalline (X-ray diffraction), and composition (XPS) properties of these films have been measured and compared to those reported for exfoliated films and have been found to be similar. Heterostructures composed of a layer of y-InSe (intrinsically n-type) followed by a layer of …

Synthesis And Characterization Of The 2-Dimensional Transition Metal Dichalcogenides, Robert Browning

Dissertations and Theses

In the last 50 years, the semiconductor industry has been scaling the silicon transistor to achieve faster devices, lower power consumption, and improve device performance. Transistor gate dimensions have become so small that short channel effects and gate leakage have become a significant problem. To address these issues, performance enhancement techniques such as strained silicon are used to improve mobility, while new high-k gate dielectric materials replace silicon oxide to reduce gate leakage. At some point the fundamental limit of silicon will be reached and the semiconductor industry will need to find an alternate solution. The advent of graphene led …

Modeling The Optical Response To A Near-Field Probe Tip From A Generalized Multilayer Thin Film, A.J. Lawrence

Dissertations and Theses

The contrast mechanism in Kerr imaging is the apparent angle through which the plane of polarization is rotated upon reflection from a magnetic surface. This can be calculated for a well characterized surface given the polarization state of the incident light. As in traditional optical microscopy, the spatial resolution is limited by diffraction to roughly half the wavelength of the illumination light.

The diffraction limit can be circumvented through the use of near-field scanning optical microscopy, in which the illumination source is an evanescent field at the tip of a tapered optical fiber. A novel probe design for near-field optical …

Predicting The Optical Response Of A Generalized Multilayer Thin Film, A.J. Lawrence, Erik J. Sánchez

Student Research Symposium

The contrast mechanism in Kerr imaging is the apparent angle through which the plane of polarization is rotated upon reflection from a magnetic surface, and this can be calculated for a well characterized surface given the polarization state of the incident light. As in traditional optical microscopy, the spatial resolution is limited by diffraction to roughly half the wavelength of the illumination light. The diffraction limit can be circumvented through the use of near-field scanning optical microscopy, in which the illumination source is an evanescent field at the tip of a tapered optical fiber. The complication in merging these two …

Pinhole Neutral Atom Microscopy, Philip James Witham

Dissertations and Theses

This work presents a new form of microscopy, the instrument constructed to demonstrate it, the images produced and the image contrast mechanisms seen for the first time. Some of its future scientific potential is described and finally, recent work towards advancing the method is discussed.

Many forms of microscopy exist, each with unique advantages. Of several broad categories that they could be grouped into, those that use particle beams have proven very generally useful for micro and nano-scale imaging, including Scanning Electron, Transmission Electron, and Ion Beam microscopes. These have the disadvantage, however, of implanting electric charges into the sample, …

Crystallographic Image Processing With Unambiguous 2d Bravais Lattice Identification On The Basis Of A Geometric Akaike Information Criterion, Taylor Thomas Bilyeu

Dissertations and Theses

Crystallographic image processing (CIP) is a technique first used to aid in the structure determination of periodic organic complexes imaged with a high-resolution transmission electron microscope (TEM). The technique has subsequently been utilized for TEM images of inorganic crystals, scanning TEM images, and even scanning probe microscope (SPM) images of two-dimensional periodic arrays. We have written software specialized for use on such SPM images. A key step in the CIP process requires that an experimental image be classified as one of only 17 possible mathematical plane symmetry groups. The current methods used for making this symmetry determination are not entirely …

Development And Implementation Of Acoustic Feedback Control For Scanning Probe Microscopy, Rodolfo Fernandez Rodriguez

Dissertations and Theses

A remote-sensing acoustic method for implementing position control feedback in Scanning Probe Microscopy (SPM) is presented. The capabilities of this feedback control using the new Whispering Gallery Acoustic Sensing (WGAS) method is demonstrated in a Shear-force Scanning Probe Microscope that uses a sharp probe attached to a piezoelectric Quartz Tuning Fork (QTF) firmly mounted on the microscope's frame. As the QTF is electrically driven its mechanical response reaches the SPM frame which then acts as a resonant cavity producing acoustic modes measured with an acoustic sensor strategically placed on the SPM head. The novelty of the WGAS resides in using …

Fermiology And Superconductivity At High Magnetic Fields In A Completely Organic Cation Radical Salt, J. S. Brooks, V. Williams, E. Choi, D. Graf, M. Tokumoto, S. Uji, F. Zuo, J. Wosnitza, J. A. Schlueter, H. David, Rolf Walter Winter, Gary L. Gard, K. Storr

Chemistry Faculty Publications and Presentations

We report specialized interplane magnetoresistance (MR) measurements on the organic superconducting compound β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailedAMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from …

Enhanced Magnetic Quantum Oscillations In The Mixed State Of A Two-Dimensional Organic Superconductor, J. Wosnitza, J. Hagel, P. J. Meeson, D. Bintley, J. A. Schlueter, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard

Chemistry Faculty Publications and Presentations

We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing the field-modulation technique and torque magnetometry. At low temperatures (30 mK), the dHvA signal persists down to 1.4 T well below the upper critical field Bc2≈3.6T. Contrary to most theoretical predictions and previous experimental findings, no additional damping of the dHvA-oscillation amplitude, but a reduced damping of the dHvA signal is found. This highly unusual effect might indicate a reduced quasiparticle scattering rate or an additional oscillatory contribution in the superconducting state.

Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter

Chemistry Faculty Publications and Presentations

The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.

Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and calorimetry data on cubic Na_xC₆₀(1<x60, e.g., T_m(x=1.3)=325 K. The ordered phases are the same as in pure C₆₀: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C₆₀ molecules and and Na ions which we calculate from the local charge density of C₆₀.

Formation Of Positronium In E+ + H- Collisions, Jack C. Straton, Richard J. Drachman

Physics Faculty Publications and Presentations

Cross sections for positronium formation by capture from the negative hydrogen ion are given. Orthogonalization corrections to the Coulomb (first-order) Born approximation (CBA) differential and total cross sections are calculated using approximate H- wave functions of both Löwdin [Phys. Rev. 90, 123 (1953)] and Chandrasekhar [Astrophys. J. 100, 176 (1944)]. The present calculation of the CBA cross sections using the post interaction for Löwdin’s wave function (LCBAPS) disagrees with the calculation of Choudhury, Mukherjee, and Sural (CMS) [Phys. Rev. A 33, 2358 (1986)], whereas our results using the prior interaction agree. Thus, where CMS found an order …

Fock-Tani Hamiltonian For Reactions Involving Two-Electron Atoms, Jack C. Straton

Physics Faculty Publications and Presentations

The Fock-Tani Hamiltonian is found for scattering processes involving up to two ions and two electrons. Possible bound-state species include one or two electrons bound on an ion fixed at the origin, and a one-electron projectile atom. A diagrammatic technique is illustrated that simplifies the algebra of the transformation. Coulomb- or plane-wave states are automatically generated by the same asymptotic Hamiltonian for all arrangement channels.

Double Excitation Of Helium By Fast Particles Of Charge Z, James H. Mcguire, Jack C. Straton

Physics Faculty Publications and Presentations

Results of calculations of double excitation of helium to n=2 states for fast projectiles of charge Z are presented. Nonzero Z³ contributions for single and double excitation occur only when time-ordering contributions from the second-order amplitude are nonzero. For double excitation, electron correlation must also be nonzero to obtain Z³ terms. The time-ordering effects arise from virtual off-energy-shell intermediate states. As with second-order amplitudes for Thomas singularities in electron capture, the energy-nonconserving amplitude is connected to the second-order energy-conserving amplitude by a dispersion relation. Comparison is made with experiment.

First-Order Amplitude For General State-To-State Transitions In Hydrogen By Projectile Impact, Jack C. Straton

Physics Faculty Publications and Presentations

The closed analytic form for bound-state transitions due to projectile impact is found in the intermediate representation. The coordinate integral is obtained by evaluating the remaining two integrals in the general multicenter integral derived previously [J.C. Straton, Phys. Rev. A 41, 71 (1990)]. Evaluating the remaining time integral depends upon relating a sum of modified Bessel functions of the second kind K_N+1/2(z) to a simple polynomial in 1/z. The results of Van Den Bos and De Heer [Physica 34, 333 (1967)] are shown to be missing a phase factor of (-i)^(l′+l)

Reduced Form For Coulomb-Wave Multicenter Integrals, Jack C. Straton

Physics Faculty Publications and Presentations

In a previous paper [J. C. Straton, Phys. Rev. A 41, 71 (1990)] an integro-differential transform was introduced and utilized to obtain the analytically reduced form for multicenter integrals composed of general-state hydrogenic orbitals, Yukawa or Coulomb potentials, and plane waves. The present paper extends this result to include Coulomb waves.

Reduced Form For The General-State Multicenter Integral From An Integro-Differential Transform, Jack C. Straton

Physics Faculty Publications and Presentations

In a previous paper Gaussian transforms were utilized to obtain the analytically reduced form for the class of multicenter integrals containing a product of hydrogenic orbitals for s states, Yukawa or Coulomb potentials, and plane waves. In the present paper a related transformation is developed for nonspherical functions, leading to the reduced form for multicenter integrals that include hydrogenic orbitals representing states of arbitrary angular momentum.