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Structure and ad-atom thermal vibrational amplitude for the Ga/Si(001) 2x1 surface

Description: Fundamental and higher-order harmonic x-ray standing wave measurements were combined to directly measure the lattice positions and thermal vibrational amplitudes of Ga adatoms on the Si(001) surface. In this room temperature study, surface structural parameters such as ad-dimer bond lengths were also determined with much higher accuracy than previous studies.
Date: October 1, 1994
Creator: Qian, Yonglin & Bedzyk, Michael J.
Partner: UNT Libraries Government Documents Department
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Local vibrational modes of Se-H complexes in AlSb

Description: Using infrared spectroscopy the authors have observed local vibrational modes (LVMs) arising from Se-H complexes in AlSb. At liquid-helium temperatures, hydrogenated AlSb:Se samples have three stretch mode peaks at 1,606.3, 1,608.6, and 1,615.7 cm{sup {minus}1}, whereas deuterated samples have only one peak at 1,173.4 cm{sup {minus}1}. The anomalous splitting of the se-H stretch mode may be explained by a resonance between the stretch mode and two multi-phonon modes. As the temperature or press… more
Date: September 1, 1996
Creator: McCluskey, M. D.; Hsu, L.; Haller, E. E.; Walukiewicz, W. & Becla, P.
Partner: UNT Libraries Government Documents Department
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Non-Equilibrium Creation of Intrinsically Localized Vibrations in Uranium Using X-Ray and Neutron Scattering

Description: In an anharmonic crystal, large-amplitude vibrational fluctuations on the scale of the lattice spacing can develop frequencies that do not resonate with the normal modes, causing energy to become trapped in intrinsically localized modes (ILMs)--also called 'discrete breathers' or 'lattice solitons'. This mechanism has been observed in analogous systems on a larger scale, but unambiguous sightings in atomic lattice vibrations, where quantum mechanics may play a role, have proved difficult. Two c… more
Date: July 2, 2007
Creator: Manley, M.; Alatas, A.; Trouw, F.; Leu, B. M.; Lynn, J. W.; Chen, Y. et al.
Partner: UNT Libraries Government Documents Department
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Shear horizontal vibrations at the (001) surface of beryllium

Description: The authors report the results of a high-resolution Electron-Energy Loss Spectroscopy (EELS) investigation of Be(0001) surface. Two dispersive surface vibrational modes are observed in the {bar {Gamma}} to {bar M} direction: a sagittal-plane mode (the Rayleigh wave) and a shear horizontal mode. They have compared their experimental results to a 300-layer slab calculation and to a semi-infinite Green`s function calculation of Sameth and Mele. Compared with the experimental results, both calculat… more
Date: June 1, 1993
Creator: Hannon, J. B. & Plummer, E. W.
Partner: UNT Libraries Government Documents Department
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Thermodynamic Modeling and First-Principles Calculations

Description: The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of a… more
Date: December 15, 2005
Creator: Turchi, P.; Abrikosov, I.; Burton, B.; Fries, S.; Grimvall, G.; Kaufman, L. et al.
Partner: UNT Libraries Government Documents Department
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An inelastic nuclear resonant scattering study of partial entropies of ordered and disordered Fe{sub 3}Al

Description: Inelastic nuclear resonant scattering spectra were measured on alloys of Fe{sub 3}Al that were chemically disordered, partially-ordered, and DO{sub 3}-ordered. The phonon partial DOS for {sup 57}Fe atoms were extracted from these data, and the change upon disordering in the partial vibrational entropy of Fe atoms was obtained. By comparison to previous calorimetry measurements, it is shown that the contribution of the Fe atoms to the vibrational entropy is a factor of 10 smaller than that of th… more
Date: November 29, 1999
Creator: Fultz, B.; Sturhahn, W.; Toellner, T. S. & Alp, E. E.
Partner: UNT Libraries Government Documents Department
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Time-resolved Studies of Phase Transition Dynamics in Strongly Correlated Manganites

Description: Ultrafast light pulses can be used to control electronic, magnetic and structural phases of complex solids. Here, we investigate the dynamics of insulator-metal phase transitions in colossal magnetoresistive (CMR) manganites by a combination of femtosecond visible-to-midinfrared pump-probe techniques and transport measurements. We show that an insulator-metal transition can be stimulated in CMR manganites by both above bandgap excitation and selective excitation of individual vibrational degree… more
Date: December 5, 2008
Creator: Rini, M.; Tobey, R.; Dean, N.; Wall, S.; Ehrke, H.; Zhu, Y. et al.
Partner: UNT Libraries Government Documents Department
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Inelastic scattering of synchrotron radiation from electrons and nuclei for lattice dynamics studies.

Description: The inelastic scattering of x-rays, one of the first applications of x-rays to the field of condensed matter physics, has been rejuvenated in the last decade. The availability of synchrotrons radiation from wiggler and undulator sources combined with advances in monochromatization of the incident beam and analysis of the scattered beam with meV resolution led to the measurement of phonon dispersion relations. In addition, the use of Moessbauer nuclei as scatterer and analyzers has led to the di… more
Date: December 3, 1999
Creator: Alp, E. E.; Sturhahn, W.; Sinn, H.; Toellner, T.; Hu, M.; Sutter, J. et al.
Partner: UNT Libraries Government Documents Department
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LO phonons in La{sub 1.85}Sr{sub .15}CuO{sub 4}

Description: Dispersion of the highest energy LO phonons in La{sup 1.85}Sr{sub .15}CuO{sub 4} was studied by neutron inelastic scattering. At T = 10 K the dispersion along (h, 0, 0) is anomalous forming dispersion branches with a discontinuity at h = 1/4. A possible relation of this anomaly to the spin-charge stripes with be discussed.
Date: November 1, 1997
Creator: Egami, T.; Petrov, Y.; McQueeney, R.J.; Petrov, Y.; Yethiraj, M.; Shirane, G. et al.
Partner: UNT Libraries Government Documents Department
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Effects of dynamic Jahn-Teller distortions by Raman spectroscopy in the layered CMR manganite La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}, x = 0.36

Description: The close interplay among charge, spin, and lattice degrees of freedom in the colossal magnetoresistive (CMR) manganite oxides is believed to play an important role in the transport mechanism in these itinerant ferromagnets. While the work on CMR materials has concentrated on the 3D perovskite manganites, the discovery of the layered compounds La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} as another class of CMR oxides provides a rich opportunity to explore the relationship between structure … more
Date: December 1, 1998
Creator: Bordallo, H. N.; Argyriou, D. N.; Mitchell, J. F. & Strouse, G. F.
Partner: UNT Libraries Government Documents Department
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Experimental investigation of 4-dimensional superspace crystals

Description: The symmetry of incommensurate crystals can be described by higher dimensional space groups in the so called superspace approach. The basic ideas are explained and used for showing that superspace groups provide an adequate frame for analyzing experimental results on incommensurate crystals.
Date: September 1, 1983
Creator: Rasing, Th. & Janner, A.
Partner: UNT Libraries Government Documents Department
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High resolution electron energy loss studies of surface vibrations. Final report, August 1, 1984--October 31, 1995

Description: This document summarizes technical progress made on `High Resolution Electron Energy Loss Studies of Surface Vibrations` (DE-FG02-84ER45147). The project was concerned with the measurement of surface vibrational waves (phonons) on a variety of materials, in particular the dispersion of these waves at short wavelengths. The principal experimental method employed was high-resolution electron energy loss spectroscopy (EELS) at an energy resolution of {approximately} 5 MeV (40 cm{sup {minus}1}) and… more
Date: January 1, 1996
Creator: Kesmodel, L.L.
Partner: UNT Libraries Government Documents Department
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Constant Q measurements of collective modes in Mg{sub 70}Zn{sub 30} glass

Description: In this study the Neutron Brillouin Scattering technique has been used to measure longitudinal excitations in a magnesium-zinc glass at momentum transfers within the first pseudo-Brillouin zone. The measurements were performed at room temperature and constant momentum transfer, which enables the data to be readily and reliably compared with theory. The experimental results taken down to Q = 6.2 nm{sup {minus}1} and E = 27 meV show a 5 meV downward shift in the dispersion energy of the longitudi… more
Date: November 1, 1997
Creator: Benmore, C.J.; Sweeney, S.; Robinson, R.A.; Egelstaff, P.A. & Suck, J.B.
Partner: UNT Libraries Government Documents Department
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Kinetic and Prediction of Hydrogen Outgassing from Lithium Hydride

Description: In most industrial or device applications, LiH is placed in either an initially dry or a vacuum environment with other materials that may release moisture slowly over many months, years, or even decades. In such instances, the rate of hydrogen outgassing from the reaction of LiH with H{sub 2}O can be reasonably approximated by the rate at which H{sub 2}O is released from the moisture containing materials. In a vacuum or dry environment, LiOH decomposes slowly with time into Li{sub 2}O even at r… more
Date: August 31, 2006
Creator: Dinh, L. N.; Schildbach, M. A.; Smith, R. A.; Balazs, B. & McLean, W., II
Partner: UNT Libraries Government Documents Department
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The Dynamics of Adsorption on Clean and Adsorbate-Modified Transition Metal and Metal Oxide Surfaces

Description: Research directed toward understanding the dynamical factors governing the adsorption of molecules typically involved in heterogeneous catalytic processes has been continued. Adsorption is the first step in any catalytic process, and predictions of rates of adsorption are fundamental to calculations of rates of catalytic reactions. Dissociative adsorption can occur either directly upon impact with the surface or as the result of the migration of a temporarily trapped species across the surface.… more
Date: March 31, 2006
Creator: Madix, Robert J.
Partner: UNT Libraries Government Documents Department
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Phonon density of states in epitaxial Fe/Cr(001) superlattices

Description: Incoherent nuclear resonant absorption of synchrotron radiation at the 14.413 keV nuclear resonance of {sup 57}Fe was employed to measure directly the Fe-projected (partial) photon density of states (DOS) in epitaxial [Fe(8.7ML)/Cr(8ML)]{sub 200} superlattices and alloy films MBE-grown on MgO(001). Isotopically depleted {sup 56}Fe was used which gives no resonance signal. 0.7 monolayers (ML) thick {sup 57}Fe-probe layer (1{angstrom}) of 95.5% enrichment were placed either at the {sup 56}Fe-on-C… more
Date: October 21, 1999
Creator: Ruckert, T.; Keune, W.; Sturhahn, W.; Hu, M. Y.; Sutter, J. P.; Toellner, T. S. et al.
Partner: UNT Libraries Government Documents Department
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Localized excitations in UPdSn

Description: The authors have measured the inelastic neutron-scattering response of UPdSn at various temperatures using the HET and PHAROS spectrometers at the ISIS and MLNSC facilities, respectively. UPdSn shows some quasielastic scattering, which may be attributed to the hybridization of the 5f electrons with the conduction electrons. Furthermore, they find a clear excitation around 40meV above 40K in addition to the phonon contribution. While this excitation may be indicative of crystal fields in UPdSn, … more
Date: November 1, 1997
Creator: Nakotte, H.; Robinson, R. A.; Swan, T.; Kelley, T.; Bull, M.; McEwen, K. A. et al.
Partner: UNT Libraries Government Documents Department
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Stark effects on band gap and surface phonons of semiconductor quantum dots in dielectric hosts

Description: The authors have investigated quantum-confined Stark effect (QCSE) on GaAs and CdSe nanocrystals and the electric field effect on surface phonons of GaAs nanocrystals isolated in sapphire substrates. For a strongly quantum-confined system, GaAs quantum dots illustrated no exciton energy shift. When the excitons are weakly confined in CdSe, a {approximately} 2 meV red-shift was observed. On the other hand, the results of the electric field effect on surface phonon are dramatic both phonon oscill… more
Date: January 1, 1996
Creator: Mu, R.; Ueda, A.; Tung, Y. S.; Henderson, D. O.; Zhu, J. G.; Budai, J. D. et al.
Partner: UNT Libraries Government Documents Department
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Coherent orbital waves during an Ultrafast Photo-induced Isulator-metal Transition in a magnetoresistive manganite

Description: Photo-excitation can drive strongly correlated electron insulators into competing conducting phases1,2, resulting in giant and ultrafast changes of their electronic and magnetic properties. The underlying non-equilibrium dynamics involve many degrees of freedom at once, whereby sufficiently short optical pulses can trigger the corresponding collective modes of the solid along temporally coherent pathways. The characteristic frequencies of these modes range between the few GHz of acoustic vibrat… more
Date: June 1, 2007
Creator: ULTRAS-INFM-CNR Dipartimento di Fisica, Politecnico di Milano, Italy
Partner: UNT Libraries Government Documents Department
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The unusual properties of beryllium surfaces

Description: Be is a ``marginal metal.`` The stable phase, hcp-Be, has a low Fermi-level density of states and very anisotropic structural and elastic properties, similar to a semiconductor`s. At the Be(0001) surface, surface states drastically increase the Fermi-level density of states. The different nature of bonding in bulk-Be and at the Be(0001) surface explains the large outward relaxation. The presence of surface states causes large surface core-level shifts by inducing a higher electrostatic potentia… more
Date: December 31, 1994
Creator: Stumpf, R.; Hannon, J. B. & Plummer, E. W.
Partner: UNT Libraries Government Documents Department
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Hydrogen local vibrational modes in semiconductors

Description: Following, a review of experimental techniques, theory, and previous work, the results of local vibrational mode (LVM) spectroscopy on hydrogen-related complexes in several different semiconductors are discussed. Hydrogen is introduced either by annealing in a hydrogen ambient. exposure to a hydrogen plasma, or during growth. The hydrogen passivates donors and acceptors in semiconductors, forming neutral complexes. When deuterium is substituted for hydrogen. the frequency of the LVM decreases b… more
Date: June 1, 1997
Creator: McCluskey, M. D.
Partner: UNT Libraries Government Documents Department
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{beta}-Decay probing the electron bulk correlations

Description: The theoretical approach based on the Boltzman-Langevin model is applied to study the thermal properties of the excitation phenomena in condensed matter. This approach making use of the advantages of the thermodynamic Green`s function method provides a tool for the self-consistent description of the many-body correlations. It is demonstrated that such a correlation modifies significantly the excitation strength properties of the electron gas. The resonant thermal effects in electron bulk excita… more
Date: December 31, 1994
Creator: Kondratyev, V.N. & Ayik, S.
Partner: UNT Libraries Government Documents Department
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Neutron scattering studies of the RENi{sub 2}B{sub 2}C (RE = Lu, Y, Ho, Er): Lattice dynamics

Description: The first chapter gives a brief overview of the system discussed in this dissertation. Chapters 2--5 and Appendix B of this dissertation consist of papers that are published, or have been submitted, which show experimental data regarding the phonon softening of LuNi{sub 2}B{sub 2}C. These papers have been removed and processed separately. Chapter 6 will contain a summary of the conclusions up to date. Appendix A will consist of a brief derivation of {chi}(q) which is talked about in the introdu… more
Date: February 23, 1998
Creator: Bullock, M.
Partner: UNT Libraries Government Documents Department
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