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Full-Text Articles in Physics

A Radial Velocity Survey Of Embedded Sources In The Rho Ophiuchi Cluster, Bruce Wilking, Timothy Sullivan, Thomas Greene, Lindsey Lisalda, Erika Gibb, Chemeda Ejeta Jul 2019

A Radial Velocity Survey Of Embedded Sources In The Rho Ophiuchi Cluster, Bruce Wilking, Timothy Sullivan, Thomas Greene, Lindsey Lisalda, Erika Gibb, Chemeda Ejeta

UMSL Faculty Works

We present the results of a radial velocity survey of young stellar objects (YSOs) in early stages of evolution in the core of the L1688 molecular cloud. New and archival spectra obtained with four high-resolution infrared spectrographs were analyzed using Markov chain Monte Carlo techniques that simultaneously fit for the radial velocity, T eff, v sin i, and veiling by comparison with synthetic spectra. The radial velocity distribution for 32 objects, most with Class I or flat-spectrum spectral energy distributions, is marginally Gaussian, with a higher dispersion relative to optical surveys at the 2σ level. When comparing the results from ...


Status Of The Los Alamos Room Temperature Neutorn Electric Dipole Moment Search, Robert W. Pattie Jr. Apr 2019

Status Of The Los Alamos Room Temperature Neutorn Electric Dipole Moment Search, Robert W. Pattie Jr.

ETSU Faculty Works

A discovery of the neutron's permanent electric dipole moment larger than the standard model prediction of dn ≈ 10-31 e·cm would signal a new source of CP-violation and help explain the matter-antimatter asymmetry in the universe. Tightening the limits on dn constrain extensions to the standard model in a complementary fashion to the atomic and electron EDM searches. The recent upgrade of the Los Alamos ultracold neutron source makes it possible for a new room temperature search with the statistical reach to improve upon current limits by a factor of 10 or more. During the 2018 ...


Nanoscale Thermal Transport In Thermally Isolated Nanostructures, Brian G. Green Jan 2019

Nanoscale Thermal Transport In Thermally Isolated Nanostructures, Brian G. Green

Electronic Theses and Dissertations

Experiments with nanoscale structures, designed to measure some of their thermal and optical properties, are the subjects of this dissertation. We studied the transport of thermal energy in systems of nanoparticles, and used the method of transient thermoreflectance to monitor those dynamics, and assess whether thermal transport features special to nanoscale systems emerged. This same method was also used to study the thermal transport of a single system of layered membranes. Optical properties were investigated using computational simulations of a nanoparticle system, using the method of finite-difference time-domain simulation.

In nanoparticle studies, there are two features of interest special to ...


Quantitative Aspects Of Interface Remodeling During Germband Extension, Timothy E. Vanderleest Jan 2019

Quantitative Aspects Of Interface Remodeling During Germband Extension, Timothy E. Vanderleest

Electronic Theses and Dissertations

Oriented cell intercalation is an essential developmental process that shapes tissue morphologies through the directional insertion of cells between their neighbors. Intercalary behaviors in the early Drosophila embryo occur through a remodeling of cell topologies, with cells contracting shared AP interfaces to a single point, followed by newly juxtaposed DV cells constructing horizontally-oriented interfaces between them. Previous research has focused on properties of cell-cell interfaces, and led to a model in which actomyosin networks mediate higher line tensions at AP interfaces to direct contraction. However, the contribution of tricellular vertices to tissue elongation remains unclear. This study shows that cell ...


Coupling Of Light's Orbital Angular Momentum To A Quantum Dot Ensemble, Alaa A. Bahamran Jan 2019

Coupling Of Light's Orbital Angular Momentum To A Quantum Dot Ensemble, Alaa A. Bahamran

Electronic Theses and Dissertations

We theoretically and experimentally investigate the transfer of orbital angular momentum from light to an ensemble of semiconductor-based nanostructures composed of lead sulfide quantum dots. Using an ensemble of quantum dots offers a higher cross-section and more absorption of twisted light fields compared to experimentally challenging single-nanostructure measurements. However, each quantum dot (except for on-center) sees a displaced light beam parallel to its own axis of symmetry. The transition matrix elements for the light-matter interaction are calculated by expressing the displaced light beam in terms of the appropriate light field centered on the nanoparticles. The resulting transition rate induced by ...


Multidimensional Spectroscopy Of Mixed-Cation Perovskite Thin Films, Geoffrey Michael Diederich Jan 2019

Multidimensional Spectroscopy Of Mixed-Cation Perovskite Thin Films, Geoffrey Michael Diederich

Electronic Theses and Dissertations

Metal halide perovskite (MHP) thin films are currently undergoing an intense re- search thrust due to the excellent performance of MHP based photovoltaic (PV) devices, which have the potential to revolutionize the worlds energy production via a unique combination of low-cost fabrication and high power conversion efficiency (PCE). However, the vast majority of research is currently aimed at incremental improvements in device PCE, resulting in a body of work without the foundational understanding of the charge-carrier dynamics of the system upon photoexcitation.

This thesis begins with the development of a phase-modulated multidimensional coherent spectroscopy (PM-MDCS) experiment. PM-MDCS is an ultrafast ...


Monte Carlo Of Trapped Ultracold Neutrons In The Ucnτ Trap, Nathan Callahan, Chen-Yu Liu, Fransisco Gonzalez, Evan Adamek, James D. Bowman, Leah J. Broussard, S. M. Clayton, S. Currie, C. Cude-Woods, E. B. Dees, X. Ding, E. M. Egnel, D. Fellers, W. Fox, Peter Geltenbort, Kevin P. Hickerson, M. A. Hoffbauer, A. T. Holley, A. Komives, S. W.T. Macdonald, Marc Makela, C. L. Morris, J. D. Ortiz, Robert W. Pattie Jr., J. Ramsey, D. J. Salvat, A. Saunders, Susan J. Seestrom, E. I. Sharapov, Sky L. Sjue, Z. Tang, J. Vanderwerp, B. Vogelaar, P. L. Walstrom, Z. Wang, H. Weaver, W. Wei, J. Wexler, A. R. Young, B. A. Zeck Oct 2018

Monte Carlo Of Trapped Ultracold Neutrons In The Ucnτ Trap, Nathan Callahan, Chen-Yu Liu, Fransisco Gonzalez, Evan Adamek, James D. Bowman, Leah J. Broussard, S. M. Clayton, S. Currie, C. Cude-Woods, E. B. Dees, X. Ding, E. M. Egnel, D. Fellers, W. Fox, Peter Geltenbort, Kevin P. Hickerson, M. A. Hoffbauer, A. T. Holley, A. Komives, S. W.T. Macdonald, Marc Makela, C. L. Morris, J. D. Ortiz, Robert W. Pattie Jr., J. Ramsey, D. J. Salvat, A. Saunders, Susan J. Seestrom, E. I. Sharapov, Sky L. Sjue, Z. Tang, J. Vanderwerp, B. Vogelaar, P. L. Walstrom, Z. Wang, H. Weaver, W. Wei, J. Wexler, A. R. Young, B. A. Zeck

ETSU Faculty Works

In the UCNτ experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth’s gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN—whose dynamics can be described by Hamiltonian mechanics—do not exhibit ...


Developing A Femtosecond Stimulated Raman Spectroscopy Experiment For Solid State Materials, Daniel Hammerland Aug 2018

Developing A Femtosecond Stimulated Raman Spectroscopy Experiment For Solid State Materials, Daniel Hammerland

Electronic Theses and Dissertations

Femtosecond Stimulated Raman Spectroscopy (FSRS) is a ultrafast spectroscopy technique first implemented by chemists to understand isomerization and other ultrafast molecular morphology changes by resolving vibrational dynamics[1, 2, 3]. FSRS has an unparalleled temporal and spectral resolution [4, 1, 5, 6] that arises as a result of a clever combination of picosecond and femtosecond pulses. However, despite this capability, FSRS has yet to be applied to modern materials in condensed matter physics. This thesis explores the design and implementation of FSRS to study two-dimensional materials in order to measure their quantum confined vibrational dynamics on utlrafast time scales.


Learning From Disorder And Noise In Physical Biology, Taylor Emil Firman Jan 2018

Learning From Disorder And Noise In Physical Biology, Taylor Emil Firman

Electronic Theses and Dissertations

Stochasticity, disorder, and noise play crucial roles in the functioning of many biological systems over many different length scales. On the molecular scale, most proteins are envisioned as pristinely folded structures, but intrinsically disordered proteins (IDPs) have no such folded state and still serve distinct purposes within the cell. At the scale of gene regulation, realistic in vivo conditions produce stochastic fluctuations in gene expression that can lead to advantageous bet-hedging strategies, but can be difficult to characterize using a deterministic framework. Even at the organismal scale, germband extension (GBE) in Drosophila melanogaster embryos systematically elongates the epithelial tissue using ...


Heat, Charge And Spin Transport Of Thin Film Nanostructures, Devin John Wesenberg Jan 2018

Heat, Charge And Spin Transport Of Thin Film Nanostructures, Devin John Wesenberg

Electronic Theses and Dissertations

Understanding of fundamental physics of transport properties in thin film nanostructures is crucial for application in spintronic, spin caloritronics and thermoelectric applications. Much of the difficulty in the understanding stems from the measurement itself. In this dissertation I present our thermal isolation platform that is primarily used for detection of thermally induced effects in a wide variety of materials. We can accurately and precisely produce in-plane thermal gradients in these membranes, allowing for thin film measurements on 2-D structures. First, we look at thermoelectric enhancements of doped semiconducting single-walled carbon nanotube thin films. We use the Wiedemann-Franz law to calculate ...


Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho Jun 2017

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho

Gary Tuttle

A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.


"Blinded By The Lines: Mid-Ir Spectra Of Mira Variables Taken With Spitzer", Dana Baylis-Aguirre, Michelle J. Creech-Eakman, Donald G. Luttermoser, Tina Gueth Sep 2016

"Blinded By The Lines: Mid-Ir Spectra Of Mira Variables Taken With Spitzer", Dana Baylis-Aguirre, Michelle J. Creech-Eakman, Donald G. Luttermoser, Tina Gueth

ETSU Faculty Works

We present preliminary analysis of mid-infrared spectra of M-type and C-type Mira variables. Due to the brightness of this sample, it is straightforward to monitor changes with phase in the infrared spectral features of these regular pulsators. We have spectra of 25 Mira variables, taken with phase, using the Spitzer Infrared Spectrograph (IRS) high-resolution module. Each star has multiple spectra obtained over a one-year period from 2008-09. This is a rich, unique data set due to multiple observations of each star and the high signal-to-noise ratio from quick exposure times to prevent saturation of the IRS instrument. This paper focuses ...


First-Principles Calculated Decomposition Pathways For Libh4 Nanoclusters, Zhi-Quan Huang, Wei-Chih Chen, Feng-Chuan Chuang, Eric Majzoub, Vidvuds Ozoliņš Sep 2016

First-Principles Calculated Decomposition Pathways For Libh4 Nanoclusters, Zhi-Quan Huang, Wei-Chih Chen, Feng-Chuan Chuang, Eric Majzoub, Vidvuds Ozoliņš

UMSL Faculty Works

We analyze thermodynamic stability and decomposition pathways of LiBH4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4. While experiments ...


Photoinduced Femtosecond Relaxation Of Antiferromagnetic Orders In The Iron Pnictides Revealed By Ultrafast Laser Ellipsometry, Aaron E. Patz, Tianqi Li, Sheng Ran, Sergey L. Bud'ko, Paul C. Canfield, Jigang Wang Mar 2016

Photoinduced Femtosecond Relaxation Of Antiferromagnetic Orders In The Iron Pnictides Revealed By Ultrafast Laser Ellipsometry, Aaron E. Patz, Tianqi Li, Sheng Ran, Sergey L. Bud'ko, Paul C. Canfield, Jigang Wang

Jigang Wang

We report ultrafast softening of the antiferromagnetic order, ~150fs after the electron thermalization, which follows a two-step recovery pathway to reveal a distinct interplay of magnetism and the nematic order in iron pnictides.


Molecular Mechanisms Of Protein Thermal Stability, Lucas Sawle Jan 2016

Molecular Mechanisms Of Protein Thermal Stability, Lucas Sawle

Electronic Theses and Dissertations

Organisms that thrive under extreme conditions, such as high salt concentration, low pH, or high temperature, provide an opportunity to investigate the molecular and cellular strategies these organisms have adapted to survive in their harsh environments. Thermophilic proteins, those extracted from organisms that live at high temperature, maintain their structure and function at much higher temperatures compared to their mesophilic counterparts, found in organisms that live near room temperature. Thermophilic and mesophilic homolog protein pairs have identical functionality, and show a high degree of structural and sequential similarity, but differ significantly in their response to high temperature. Addressing the principles ...


Relative Proper Motions In The Rho Ophiuchi Cluster, Bruce Wilking, Frederick Vrba, Timothy Sullivan Dec 2015

Relative Proper Motions In The Rho Ophiuchi Cluster, Bruce Wilking, Frederick Vrba, Timothy Sullivan

UMSL Faculty Works

Near-infrared images optimized for astrometry have been obtained for four fields in the high-density L 1688 cloud core over a 12 year period. The targeted regions include deeply embedded young stellar objects (YSOs) and very low luminosity objects too faint and/or heavily veiled for spectroscopy. Relative proper motions in R.A. and decl. were computed for 111 sources and again for a subset of 65 YSOs, resulting in a mean proper motion of (0,0) for each field. Assuming each field has the same mean proper motion, YSOs in the four fields were combined to yield estimates of the ...


Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov Jun 2015

Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov

Ames Laboratory Publications

We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (∼20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. These results set the stage for a comprehensive understanding of ...


Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield May 2015

Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield

Ames Laboratory Publications

Single crystals of Bi2Rh3S2 and Bi2Rh3.5S2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case ofBi2Rh3S2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi2Rh3S2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2Rh3.5S2; however, bulk superconductivity with a critical temperature, Tc≈1.7 K, was observed. The Sommerfeld coefficient γ and the ...


An Optical Spectroscopic Survey Of The Serpens Main Cluster: Evidence For Two Populations?, Kristen Erickson, Bruce Wilking, Michael Meyer, Jinyoung Kim, William Sherry, Matthew Freeman Feb 2015

An Optical Spectroscopic Survey Of The Serpens Main Cluster: Evidence For Two Populations?, Kristen Erickson, Bruce Wilking, Michael Meyer, Jinyoung Kim, William Sherry, Matthew Freeman

UMSL Faculty Works

We have completed an optical spectroscopic survey of a sample of candidate young stars in the Serpens Main star-forming region selected from deep B, V, and R band images. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys have been biased toward particular stages of pre-main sequence evolution. We have obtained over 700 moderate resolution optical spectra that, when combined with published data, have led to the identification of 63 association members based on the presence of Hα in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity ...


Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney Feb 2015

Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that ...


Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada Feb 2015

Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada

Chemical and Biological Engineering Publications

Magnetotactic bacteria that produce magnetic nanocrystals of uniform size and well-defined morphologies have inspired the use of biomineralization protein Mms6 to promote formation of uniform magnetic nanocrystals in vitro. Small angle X-ray scattering (SAXS) studies in physiological solutions reveal that Mms6 forms compact globular threedimensional (3D) micelles (approximately 10 nm in diameter) that are, to a large extent, independent of concentration. In the presence of iron ions in the solutions, the general micellar morphology is preserved, however, with associations among micelles that are induced by iron ions. Compared with Mms6, the m2Mms6 mutant (with the sequence of hydroxyl/carboxyl containing ...


Identification Of High Energy Cosmic Ray Electrons Using Advanced Techniques In Calet And Fermi Lat, Aaron James Worley Jan 2015

Identification Of High Energy Cosmic Ray Electrons Using Advanced Techniques In Calet And Fermi Lat, Aaron James Worley

Electronic Theses and Dissertations

Measurements of the cosmic ray electron spectrum have received much attention over the last decade as anomalies in both electron and positron observations have been detected independently by several experiments. The profound possible implications in the fields of high energy astrophysics and particle physics have allowed for many interpretations on the origin of these inconsistencies in the spectra. This research focuses on two space-borne cosmic radiation experiments at different stages in their mission lifetimes: the Calorimetric Electron Telescope (CALET) and the Fermi Large Area Telescope (LAT). We explore the proton-electron discriminating capabilities of the CALET instrument through Monte Carlo simulations ...


The Adsorption Of Polyatomic Molecules On Carbon Surfaces, Jared T. Burde Jan 2015

The Adsorption Of Polyatomic Molecules On Carbon Surfaces, Jared T. Burde

Electronic Theses and Dissertations

Carbon nanotubes exhibit the structure and chemical properties that make them apt substrates for many adsorption applications. Of particular interest are carbon nanotube bundles, whose unique geometry is conducive to the formation of pseudo-one-dimensional phases of matter, and graphite, whose simple planar structure allows ordered phases to form in the absence of surface effects. Although both of these structures have been the focus of many research studies, knowledge gaps still remain. Much of the work with carbon nanotubes has used simple adsorbates1-43, and there is little kinetic data available. On the other hand, there are many studies of complex ...


Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their ...


Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30◦ from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √ 3 times the surface lattice constant, a. Monte Carlo simulations are performed on ...


Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel Nov 2014

Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel

Chemistry Publications

We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.


Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld Oct 2014

Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld

Ames Laboratory Publications

A single crystal of isovalently substituted Ba(Fe1−xRux)2As2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×1019 e−/cm2. The electrical resistivity is measuredin situ at T=22  K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tccompared to other types of artificially introduced disorder, probably due to the strong short-range potential of the ...


Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman Oct 2014

Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman

Ames Laboratory Publications

Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At TN≈7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector (0 0 τ) with τ≈14 and the magnetic moment along the a axis of the orthorhombic unit cell. Below TLI≈5 K, the magnetic structure locks in to a commensurate structure with τ=14 and the magnetic moment remains along the a axis. Below T☆≈4 K, we find additional half-integer and integer ...


Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield Aug 2014

Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield

Ames Laboratory Publications

We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1−xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as ...


Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield Jul 2014

Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

We present a detailed characterization of the recently discovered i-R-Cd (R=Y,Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R ...