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High accuracy electron-impact photoemission cross section measurements for the EUV radiometric standard. Final report

Description: This project was concerned with high-accuracy measurements of electron-impact photoemission cross sections for transitions of atoms and molecules in the EUV spectral region (30 nm to 200 nm). The spectrometer-detector system that was employed in the measurements was calibrated using well-parameterized synchrotron radiation. The 58.4 resonance line of He was chosen to establish the overall accuracy of the apparatus and data collection procedures. The measurement of this line can be compared to accurate theoretical calculations and to one other experimental cross section measurement in which a different excitation channel was observed.
Date: December 31, 1989
Creator: Risley, J. S.
Partner: UNT Libraries Government Documents Department

Spin polarized photoemission studies of interfacial and thin film magnetism

Description: Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe(001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fct Co(001) substrate. Tight-binding modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.
Date: June 1, 1993
Creator: Johnson, P. D.; Brookes, N. B.; Chang, Y. & Garrison, K.
Partner: UNT Libraries Government Documents Department

A photoemission study of Au, Ge, and O{sub 2} deposition on NH{sub 4}F etched Si(111)

Description: We have studied the interaction of a metal, Au, a semiconductor, Ge, and a non-metal, O{sub 2}, with the NH{sub 4}F etched Si(111) surface with photoemission spectroscopy. Two components were present in Si 2p core level spectra from the H-terminated surface. We observed the flat band condition from the as-etched, n-type, Si(111) surface. We performed stepwise depositions of Au and measured the band bending with photoemission spectroscopy. The Fermi level pinned near mid-gap as Au was deposited onto the as-etched surface. After the deposition of 1 ML of Au, a Au-silicide layer formed. This interfacial component indicated that the passivating H layer was compromised. As the Au coverage was increased, layers of pure Au formed between the bulk silicon and the Au-silicide layer. The observed behavior was nearly identical to that of Au deposition on the Si(111) 7 {times} 7 surface. Next, we tested the ability of the monohydride layer to sustain surfactant assisted growth of Ge. Ge islanding was observed at 400{degree}C indicating that good surfactant growth was not obtained. Although the monohydride layer was not a good surfactant for the Si(111) surface at this temperature, further study at different temperatures is needed to determine the ability of the ideal monohydride layer to act as a surfactant. Finally, we observed no oxidation of the as-etched surface at room temperature upon exposure to molecular oxygen.
Date: March 1, 1994
Creator: Terry, J.; Cao, R.; Wigren, C. & Pianetta, P.
Partner: UNT Libraries Government Documents Department

Wake-field and space charge effects on high brightness beams calculations and measured results for the laser driven photoelectrons at BNL-ATF

Description: We discuss the formalism used to study the effects of the interactions between the highly charged particles and the fields in the accelerating structure, including space charge and wake fields. Some of our calculations and numerical simulation results obtained for the Brookhaven National Laboratory (BNL) high-brightness photoelectron beam at the Accelerator Test Facility (ATF) and the measured data at ATF are also included.
Date: May 1, 1993
Creator: Parsa, Zoreh
Partner: UNT Libraries Government Documents Department

A structural determination using magnetic x-ray circular dichroism in spin-polarized photoelectron diffraction

Description: The first structural determination with spin-polarized, energy-dependent photoelectron diffraction using circularly-polarized x-rays is reported for Fe films on Cu(001). Circularly-polarized x-rays produce spin-polarized photoelectrons from the Fe 2p doublet, and intensity asymmetries in the 2p{sup 3/2} level are observed. . Fully spin-specific multiple scattering calculations reproduce the experimentally determined energy and angular dependences. A new analytical procedure which focuses upon intensity variations due to spin-dependent diffraction is introduced.
Date: May 26, 1994
Creator: Waddill, G. D.; Tobin, J. G.; Guo, X. & Tong, S. Y.
Partner: UNT Libraries Government Documents Department

Canted magnetic moments at the Gd(0001) surface

Description: With spin polarized electron spectroscopies, the authors have investigated ordered Gd(0001) films deposited on W(110). The photoemission features of the gadolinium 5d surface state, the 4f levels, and the background exhibit considerable spin polarization along the same direction in the plane of the film, indicative of ferromagnetic coupling between the surface and the bulk. The 4f spin polarized photoemission data provides strong evidence that the surface 4f polarization differs from the bulk 4f polarization for Gd(0001). The temperature dependent measurements with spin polarized secondary electron spectroscopy conclusively establishes that the surface of clean Gd(0001) possesses a perpendicular polarization component which persists to an enhanced surface Curie temperature. Small amounts of contamination at the surface result in the disappearance of the perpendicular component and, therefore, a more perfect ferromagnetic coupling between the surface and the bulk.
Date: June 1, 1993
Creator: Donggi, Li; Jiandi, Zhang; Dowben, P. A.; Garrison, K.; Johnson, P. D.; Tang, H. et al.
Partner: UNT Libraries Government Documents Department

Photoemission studies of Zn, Co, and Gd substituted YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}

Description: Zn and Co substitute for Cu in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} at the plane and chain sites, respectively. We report a high resolution angle-resolved photoemission study on Zn and Co substituted YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystals to determine the effects on electronic structure. The valence states near E{sub F} along {Gamma}-S are virtually unaffected by the substitutions for samples that are superconducting. However, the spectral weight near E{sub F} disappears for a higher Co-doped, nonsuperconducting crystal. Results are compared with earlier studies on pure YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} with controlled oxygen stoichiometry. Measurement on Gd-123 crystals with reduced oxygen stoichiometries show gradual reduction of spectral weight for a band along {Gamma}-Y(X), in contrast to the results for the bands along {Gamma}-S. The differences are probably due to a different admix of Cu-O chain and plane characters in these bands. We also measured Gd 4f resonance spectra which exhibit complex structure, indicating the presence of Gd atoms in chemically inequivalent (probably bulk and near surface) sites.
Date: June 1, 1993
Creator: Gu, Chun; Veal, B. W. & Liu, R.
Partner: UNT Libraries Government Documents Department

Vacuum ultraviolet electronic properties of liquids. Final performance report, 1 February 1988--31 July 1989

Description: The principal aim of this program has been to study the electronic structure of insulating liquids of biological interest over a broad energy range from 0 to 30 eV. The studies basically consist of measuring the reflectance, transmittance, photoemission and photoionization of dielectric liquids in the vacuum ultraviolet spectral region as a function of angle of incidence and energy. these in turn may be interpreted in terms of the electronic structure of each liquid as it is excited by the passage of a charged particle. Optical data provides indirect evidence that collective effects occur in liquids. Direct observation of their existence is substantiated in studies of the energy distribution of electrons specularly scattered from the liquid surface.
Date: December 31, 1989
Creator: Painter, L. R.
Partner: UNT Libraries Government Documents Department

Photoemission study of diamond (100) surface

Description: The electronic structure of the diamond C(100)-(2 {times} 1)/(2 {times} 2) has been investigated by means of angle-resolved photoelectron spectroscopy for the first time. A surface-related shift has been observed in the C 1s core level spectrum. The surface-state band dispersion was measured along the symmetry axis {Gamma}-J{prime} in the surface Brillouin zone. For k{sub {parallel}} = 0, there is a very pronounced surface state 1.5 eV below Fermi level E{sub F}, and it disperses downwards with increasing k{sub {parallel}}. Near the boundary of the surface Brillouin zone J{prime}, we find two states with binding energies of 1.9 and 2.4 eV with respect to E{sub F}.
Date: March 1, 1993
Creator: Wu, J.; Cao, R.; Yang, X.; Pianetta, P. & Lindau, I.
Partner: UNT Libraries Government Documents Department

Synchrotron studies of narrow band materials. Progress report, July 1, 1993--June 30, 1994

Description: This progress report is divided into: activity (beamtime, data analysis, lab studies); model Fermi liquids and non-Fermi liquids (TiTe{sub 2}-further ARPES and lineshape analysis, TiS{sub 2} ARPES, K{sub 0.3}MoO{sub 3} and Li{sub 0.9}Mo{sub 6}O{sub 17} ARPES); insulator to metal transitions (early transition metal oxides, Fe{sub 3}O{sub 4}, La{sub 2-x}Sr{sub x}CuO{sub 4} ARPES); rare earth and actinide materials (U(Cu{sub 1-x}Pd{sub x}){sub 5}, U(Pt{sub 1-x}Pd{sub x}){sub 3}, CeAl{sub 3} and CeSi{sub 2} resonant photoemission, CeFe{sub 2}/CeRh{sub 3}B{sub 2}/CeCo{sub 2}/CeCo{sub 5} x-ray magnetic circular dichroism); and technique oriented resonant photoemission studies (resonant ARPES in TiTe{sub 2}, resonant photoemission at 2p edge in TiTe{sub 2}).
Date: June 1, 1994
Partner: UNT Libraries Government Documents Department

Preliminary soft x-ray studies of beta-SiC

Description: We have looked at beta-SiC with soft x-ray emission and photoemission spectroscopy. From the Si L{sub 23} and C K emissions, the Si s+d-like and C p partial density of states in the bulk valence band are identified, and compared with valence band photoemission. In addition to bulk electronic structural features, photoemission from a (3 {times} 2) Si-rich surface shows two surface-derived valence features at {approximately}{minus}2.6 and {approximately}{minus}1.6 eV relative to the Fermi level. The intensities of these valence features vary as those of surface Si 2p core level components shifted by {minus}0.5 eV and {minus}1.4 eV from the bulk-like SiC Si 2p core level. We have also used the Si L{sub 23} absorption edge as a probe of the unfilled states near the conduction, band minimum.
Date: June 1, 1994
Creator: Shek, M. L.; Miyano, K. E.; Ederer, D. L.; Dong, Q. Y. & Callcott, T. A.
Partner: UNT Libraries Government Documents Department

Desorption measurements of copper and copper alloys for PEP-II

Description: PEP-II will be a meson factory circulating asymmetric beams of 9 GeV and 3.1 GeV having maximum currents of 3.0A. Copper beam chambers and absorbers will intercept resulting synchrotron radiation and it is critical that the dynamic gas load from photo stimulated desorption (PSD) and thermal outgassing is below 2 {times} 10{sup {minus}1} molecules per photon. An experiment was set up to measure PSD from 1m long bar samples and a chamber sample, fabricated from selected copper and copper alloys then exposed to white light with a critical energy of 500 eV, on beamline U10B at the VUV ring of the National Synchrotron Light Source (NSLS). Based on U10B results a prototype chamber was built and will be exposed to white light with higher critical energies of up to 5 KeV, on beamline X-28A at the X-ray Ring of the NSLS. This paper presents the measurements of H{sub 2}, CO, CO{sub 2} and CH{sub 4} desorption yields as function of accumulated photon flux, angle of incidence, sample material, and surface condition. The results are compared with that of previous work on similar materials and with that of others for copper.
Date: December 31, 1992
Creator: Foerster, C. L.; Halama, H.; Korn, G.; Calderon, M. & Barletta, W.
Partner: UNT Libraries Government Documents Department

Briefing paper for the proposed ultraviolet free-electron laser (UV- FEL) facility at Brookhaven National Laboratory

Description: The proposed Brookhaven National Laboratory ultraviolet free-electron laser (UV-FEL) user facility will provide picosecond and sub-picosecond pulses of coherent ultraviolet radiation for wavelengths from 300 to 75 nm. Pulse width will be variable from about 7 ps to {approx} 200 fs, with repetition rates as high as l0{sup 4}Hz, single pulse energies > 1 NJ and hence peak pulse power > 200 MW and average beam power > 10 W. The facility will be capable of ``pump-probe`` experiments utilizing the FEL radiation with: (1) synchronized auxiliary lasers, (2) a second, independently tunable FEL beam, or (3) broad-spectrum, high-intensity x-rays from an insertion device in the x-ray ring of the adjacent National Synchrotron Light Source. The UV-FEL consists of a high repetition rate recirculating superconducting linear accelerator which feeds pulses of electrons to two magnetic wigglers. Within these two devices, photons from tunable ``conventional`` lasers are frequency multiplied and amplified. By synchronously tuning the seed laser and modulating the energy of the electron beam, tuning of as much as 60% in wavelength is possible between alternating pulses supplied to different experimental stations, with Fourier transform limited resolution. Thus, up to four independent experiments may operate at one time, each with independent control of the wavelength and pulse duration. A total of eight experimental stations are planned, with two currently assigned to general users, two each for solid state and chemical physics, and one each for atomic physics and biology. This document provides a few representative examples of experiments in these fields, as well as an introduction to the facility, its limitations, and its potential for future growth.
Date: July 15, 1992
Creator: Johnson, E. D.
Partner: UNT Libraries Government Documents Department

High-order harmonic generation with short-pulse lasers

Description: Recent progress in the understanding of high-order harmonic conversion from atoms and ions exposed to high-intensity, short-pulse optical lasers is reviewed. We find that ions can produce harmonics comparable in strength to those obtained from neutral atoms, and that the emission extends to much higher order. Simple scaling laws for the strength of the harmonic emission and the maximium observable harmonic are suggested. These results imply that the photoemission observed in recent experiments in helium and neon contains contributions from ions as well as neutrals.
Date: December 1992
Creator: Schafer, K. J.; Krause, J. L. & Kulander, K. C.
Partner: UNT Libraries Government Documents Department

4f bands in Ce heavy fermions and mixed valent compounds at T {much_gt} T{sub K}

Description: We report evidence of 4f band character in Ce 4f states at {Tau}{much_gt}{Tau}{sub K} using the technique of high-resolution angle-resolved resonant photoemission. The Ce intermetallic compound CePt{sub +x} was grown and studied in situ by the method of MBE and was characterized by LEED, XPS and XAS. These new findings would suggest a need for a reexamination of 4f photoemission in Ce compounds.
Date: August 1, 1994
Creator: Andrews, A. B.; Joyce, J. J.; Arko, A. J.; Thompson, J. D.; Tang, J.; Fisk, Z. et al.
Partner: UNT Libraries Government Documents Department

Image potential states at metal-dielectric interfaces

Description: Angle-resolved two-photon laser photoemission was used to observe the image potential electronic states on the (111) face of a silver single crystal. The transient image potential states were excited from the occupied bulk bands with photons whose energy was tunable around 4 eV. Photoemission of the image potential states was accomplished with photons of energy tunable around 2 eV. Image potential states were found to persist in the presence of physisorbed adlayers of xenon and cyclohexane. On clean Ag(111), the effective mass of the n=1 image potential state was found to be 1.4{plus_minus}0.1 times the mass of a free electron (m{sub e}). A binding energy of 0.77 eV, measured by earlier workers, was assumed in analysis of the data for the clean surface. On Ag(111), at 75 K covered by one monolayer of xenon, the binding energy of the n=1 image potential state was unchanged relative to its value on the clean surface. An effective mass of (1.00{plus_minus}0.05) {center_dot} m{sub e} was obtained. On Ag(111) at 167 K, covered by one monolayer of cyclohexane, the binding energy of the n=2 member of the image potential series was 0.30{plus_minus}0.05 eV. The energy of the n=1 state was again unchanged by deposition of the adsorbate. The effective masses of both states were (0.90{plus_minus}0.1) {center_dot} m{sub e}.
Date: April 1, 1992
Creator: Merry, W. R. Jr.
Partner: UNT Libraries Government Documents Department

Spin polarized photoemission studies of surfaces and thin-films

Description: Spin polarized photoemission is used to study the magnetic states associated with the clean iron (001) surface. These studies reveal evidence for a minority spin surface state in agreement with first principles calculation. Studies of the same surface with silver and chromium epitaxial overlayers reveal evidence for interface states derived from the states found on the clean surface. In the case of the silver overlayer the binding energy of this state is found to be dependent on the layer thickness of the overlayer. With chromium overlayers the binding energy for the same interface state does not show the same thickness dependence. However, a second interface state is observed immediately below the Fermi level.
Date: December 31, 1991
Creator: Johnson, P. D.; Brookes, N. & Chang, Y.
Partner: UNT Libraries Government Documents Department

Putting synchrotron radiation to work for technology: Analytic methods

Description: This report contains viewgraphs on: Advanced Light Source; Ultra-ESCA: Advanced Capabilities of XPS with High-Brightness Synchrotron Radiation; High-Resolution (20 nm) XPS and XANES with the ALS; Photoelectron Spectroscopy in Industry: Current Capabilities, Needs, and Possible Roles for the ALS; Materials Analysis by Photoemission: Is This Practical at ALS?; Applications of Long-Wavelength X-Ray Fluorescence Spectrometry and X-Ray Powder Diffractometry.
Date: February 1, 1992
Partner: UNT Libraries Government Documents Department

Two-photon photoemission and the dynamics of electrons at interfaces

Description: A new instrument for angle-resolved two-photon photoemission with exceptional sensitivity and energy resolution has allowed a detailed examination of the interaction of image-state electrons with adsorbates. In addition to measuring the electrostatic properties of molecular-thickness films, the technique serves as a probe of adsorbate growth modes, and provides new opportunities to explore the dynamics of electrons in well-controlled two-dimensional systems.
Date: January 1, 1994
Creator: Padowitz, D. F.; Harris, C. B.; Jordan, R. E.; Lingle, R. L. Jr.; McNeill, J. D. & Merry, W. R.
Partner: UNT Libraries Government Documents Department

Applications of circularly polarized photons at the ALS with a bend magnet source

Description: The purpose of this workshop is to focus attention on, and to stimulate the scientific exploitation of, the natural polarization properties of bend-magnet synchrotron radiation at the ALS -- for research in biology, materials science, physics, and chemistry. The topics include: The Advanced Light Source; Magnetic Circular Dichroism and Differential Scattering on Biomolecules; Tests of Fundamental Symmetries; High {Tc} Superconductivity; Photoemission from Magnetic and Non-magnetic Solids; Studies of Highly Correlated Systems; and Instrumentation for Photon Transport and Polarization Measurements.
Date: February 1, 1992
Partner: UNT Libraries Government Documents Department

Highly anisotropic but nodeless gap from a valence-fluctuation pairing mechanism

Description: We have refined and quantitatively explored a valence-fluctuation pairing mechanism, the finite-U mechanism introduced by Newns. This can provide an s-like (nodeless) gap. We use an Anderson-lattice Hamiltonian, with realistic parameter values derived from photoemission and BIS data. The Landau-Luttinger quasiparticle spectrum and the pairing interaction are obtained from a many-body variational formalism. Adequate pairing attraction is obtained, together with band narrowing (mass enhancement) and an extremely short coherence length, in reasonable agreement with experiment. These fully self-consistent results were obtained with an isotropic approximation to the band structure of a single CuO{sub 2} plane. Now, using a simplified treatment for a more realistic band structure, we find that the gap has strong in-plane anisotropy, although it should probably still remain nodeless. This conclusion is consistent with a variety of data.
Date: April 1, 1993
Creator: Brandow, B. H.
Partner: UNT Libraries Government Documents Department

Observation of electron polarization above 80% in photoemission from strained III-V compounds

Description: Spin-polarized electron photoemission has been investigated for strained III--V compounds; (1) strained In{sub x}Ga{sub 1-x}As epitaxially grown on a GaAs substrate, and (2) strained GaAs grown on a GaAs{sub 1-x}P{sub x} buffer layer. The lattice mismatched heterostructure results in a highly strained epitaxial layer, and electron spin polarization as high as 90% has been observed.
Date: February 1, 1992
Creator: Garwin, E. L.; Maruyama, T.; Prepost, R. & Zapalac, G. H.
Partner: UNT Libraries Government Documents Department

Positron studies of defected metals, metallic surfaces. Final report, July 1, 1985--December 1, 1991

Description: Specific problems proposed under this project included the treatment of electronic structure and momentum density in various disordered and defected systems. Since 1987, when the new high-temperature superconductors were discovered, the project focused extensively on questions concerning the electronic structure and Fermiology of high-{Tc} superconductors, in particular, (i) momentum density and positron experiments, (ii) angle-resolved photoemission intensities, (iii) effects of disorder and substitutions in the high-{Tc}`s.
Date: December 31, 1991
Creator: Bansil, A.
Partner: UNT Libraries Government Documents Department

A method of producing high quality oxide and related films on surfaces

Description: Aluminum oxide or aluminum nitride films were deposited on MBE grown GaAs(100) using a novel cryogenic-based reactive thin film deposition technique. The process involves the condensation of molecular oxygen, ammonia or other gases normally used for reactive thin film deposition on the substrate before the metal is deposited. The metal vapor is deposited into this layer and reacts with the molecular solid form the desired compound or a precursor than can be thermally decomposed to generate the desired compound. The films produced by this method are free of impurities and the low temperatures can be used to control the film and interfacial structure. The process can be easily integrated with existing MBE-systems and on going research using the same apparatus suggests than photon or electron irradiation could also be used to promote the reactions needed to give the intended material.
Date: December 31, 1991
Creator: Ruckman, M. W.; Strongin, M. & Gao, Yongli
Partner: UNT Libraries Government Documents Department