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Short-pulse high-current-density photoemission in high electric fields

Description: We present the experimental results of photoemission studies on thin wires of gold-coated tungsten, held at surface fields in the range of 10/sup 6/ to 3 x 10/sup 8/ V/m, and illuminated by 10 ps long, 4.66 eV photon laser pulses. The wire cathodes arranged coaxially in an anode experienced a surface-field enhancement of 10/sup 2/ to 10/sup 3/ over the applied voltage. We obtained current densities exceeding 10 kA/cm/sup 2/ from a 50 ..mu..m diameter wire, from a (50 x 400) ..mu..m/sup 2/ area, under partially space-change-limited conditions. The quantum efficiency for emission-limited cases was in the range of 10/sup -5/. For these cases results using 50 ..mu..m and 4 ..mu..m diameter wires indicated linear dependence of charge density with optical energy density. The emission also scaled linearly with the emitting area. For surface fields above 3 x 10/sup 7/ V/m, a twofold enhancement of emission was observed for a tenfold increase in the field. 7 refs., 9 figs.
Date: January 1, 1987
Creator: Fischer, J. & Srinivasan-Rao, T.
Partner: UNT Libraries Government Documents Department

Report on the workshop on new directions in soft x-ray near-threshold phenomena

Description: The ''Workshop on New Directions in Soft X-Ray Near-Threshold Phenomena'' was held at the Asilomar Conference Center in Pacific Grove, CA on March 1--4, 1987. It was attended by 59 scientists from 8 countries, representing 27 institutions. Major funding for the meeting was donated by L-Division of the Lawrence Livermore National Laboratory, who hosted and organized two previous workshops on photoabsorption and scattering in the soft x-ray energy range. Additional funding was provided by the User's Group of the Advanced Light Source. The Workshop, as its name suggests, emphasized physical phenomena in atoms, molecules, and solids near inner-shell thresholds. Of particular interest were threshold ionization, post-collisional interaction, resonant photoemission and fluorescence, and multi-electron effects such as shake-up and shake-off. In these areas and others, special consideration was given to presenting recent discoveries and potential ''new directions'' for future work.
Date: July 1, 1988
Creator: Lindle, D.W. & Perera, R.C.C. (eds.)
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: January 1, 1993
Creator: Johnson, P.D.; Brookes, N.B.; Chang, Y. & Garrison, K.
Partner: UNT Libraries Government Documents Department

Understanding photoemission spectra in uranium based heavy fermion systems

Description: In 4f compounds, there is a two-peaked structure associated with 4f photoemission spectroscopy, while most 5f compounds yield a single broad triangular-shaped 5f intensity. Evidence is presented from measurements on ternary alloys that show that at least part of the extra-5f intensity is due to the hitherto missing main peak (or d-screened f-hole peak) just as in the 4f systems. The remaining intensity is consistent with a band structure DOS. (The compounds used were URh/sub 3/B/sub x/, UPd/sub x/Rh/sub 3-x/, ThBe/sub 13/, UIr/sub 3/, and UBe/sub 13/.) (DLC)
Date: December 1, 1986
Creator: Arko, A.J.; Yates, B.W.; Dunlap, B.D.; Koelling, D.D.; Mitchell, A.W.; Lam, D.J. et al.
Partner: UNT Libraries Government Documents Department

High-current, short-pulse, RF-synchronized electron gun for the Stanford Linear Accelerator

Description: For the generation of intense single and multiple bunches of electrons (> 8 nc per bunch) for accelerator studies at SLAC, a high peak current photoemission electron gun has been developed. A gallium arsenide photocathode is illuminated by the optical beam from a frequency doubled, actively mode-locked and Q-switched Nd:YAG laser. The mode-locked optical pulses are of variable, sub-nanosecond width and occur with a spacing of 8.4 nsec, synchronized with the 2856 MHz accelerator rf. The gun is designed to be space charge limited at 15 A and 200 kV, although emission of 60 A was obtained with a 57 kV test structure, corresponding to a current density of 180 A/cm/sup 2/. With the proper choice of laser wavelength, the electron beam may be 40% longitudinally polarized.
Date: February 1, 1981
Creator: Sinclair, C.K. & Miller, R.H.
Partner: UNT Libraries Government Documents Department

Photoemission measurements for low energy x-ray detector applications

Description: Photoemission has been studied for nearly 100 years as both a means of investigating quantum physics, and as a practical technique for transducing optical/x-ray photons into electrical currents. Numerous x-ray detection schemes, such as streak cameras and x-ray sensitive diodes, exploit this process because of its simplicity, adaptability, and speed. Recent emphasis on diagnostics for low temperature, high density, and short-lived, plasmas for inertial confinement fusion has stimulated interest in x-ray photoemission in the sub-kilovolt regime. In this paper, a review of x-ray photoemission measurements in the 50 eV to 10 keV x-ray region is given and the experimental techniques are reviewed. A semiempirical model of x-ray photoemission is discussed and compared to experimental measurements. Finally, examples of absolutely calibrated instruments are shown.
Date: January 1, 1981
Creator: Day, R.H.
Partner: UNT Libraries Government Documents Department

Interaction of radiation with matter

Description: During 1978, these conclusions were reached and are reported: Innershell Coulomb ionization cross sections show significant relativistic effects even for the lighter atoms, because ionization occurs near the nucleus in our range of low particle energies. Atomic excitation and ionization in deep atom--atom collisions can be described in terms of a model with random walk in energy space to the continuum. This model may be best suited for the analysis of heavy ion--atom encounters. Energy straggling of charged particles in matter are affected by inhomogeneities in and surface conditions of the medium. Using molecular ions as incident projectiles it is concluded that moving protons do not have bound states in solids. Projectiles in close proximity to each other exhibit larger energy losses than isolated projectiles indicating interactions of the electron density fluctuations established behind moving projectiles in solids. Heterogeneous oxidation of SO/sub 2/ by holes has been found at an organic (PAH) aqueous interface. The process has a reasonably high quantum efficiency (approx. >0.1) for anthracene. Various experiments are being carried out to determine whether SO/sub 3//sup =/ or HSO/sub 3/- is involved. Photoemission from PAH organic aerosols has been investigated. The rate of emission from tetracene is found to go as the maximum electron kinetic energy cubed. It is found that the particle may be used as an electron spectrometer for determining the electron kinetic energy distribution. A new way of characterizing small aerosols by mass has been found. The method utilizes the detection of a single electron imbalance in a Millikan chamber. Aerosol masses as small as 1 pgm can be measured to better than 1%. The potent carcinogen benzo (a) pyrene (BP) when metabolized in vivo is found to have a physical structure in which the BP7,8-dihydrodial 9,10-oxide adduct (BPDE) is bound on the outside of the ...
Date: May 1, 1978
Partner: UNT Libraries Government Documents Department

5f-band narrowing in UX/sub 3/B compounds: evidence from resonant photoemission. [X = Ru or Rh]

Description: Resonant photoemission at the uranium 5d disorption edge has been used to determine the 5f emission in URu/sub 3/, URh/sub 3/, URu/sub 3/B, and URh/sub 3/B polycrystalline samples. The observed 5f band narrowing (from 2.0 to 1.5 eV as one goes from URu/sub 3/ to URu/sub 3/B, and from 2.8 to 1.1 eV for URh/sub 3/ and URh/sub 3/B respectively) is explained as due to a decrease in the f-d hybridization between uranium and rhodium (ruthenium) atoms.
Date: October 1, 1985
Creator: Zolnierek, Z.; Arko, A.J. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band structure of UO/sub 2/: an angle resolved and resonant photoemission study

Description: A detailed study of angle resolved photoemission of UO/sub 2/ <100> in the normal emission configuration is presented. The results are compared to a semirelativistic LAPW band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands. f-p hybridization is found at the leading edge of the valence band and not at the bottom of the valence band. p-d hybridization is found throughout the valence bands.
Date: October 1, 1985
Creator: Arko, A.J.; Koelling, D.D.; Boring, A.M.; Ellis, W.P. & Cox, L.E.
Partner: UNT Libraries Government Documents Department

Photoemission from single-crystal EuBa/sub 2/Cu/sub 3/O/sub 6+x/ cleaved below 20K: Metallic-to-insulating surface transformation

Description: Valence band ultraviolet photoemission spectra (UPS) of single-crystal EuBa/sub 2/Cu/sub 3/O/sub 6+x/ (x > 0.6) samples cleaved in vacuum at 20 K demonstrate that the metallic superconducting phase undergoes an irreversible transformation via near-surface oxygen loss to an insulating state upon annealing above 50 K. Freshly cleaved surfaces at 20 K exhibit a density of states at the Fermi level comparable to that of copper, and have both O(2p) and Cu(3d) character at E/sub F/ based on the photon energy dependence of the intensity. Reasonably good agreement between band structure calculations and the present data would suggest theoretical models using the band state as a starting point. 18 refs., 2 figs.
Date: January 1, 1988
Creator: List, R.S.; Arko, A.J.; Fisk, Z.; Cheong, S.W.; Conradson, S.D.; Thompson, J.D. et al.
Partner: UNT Libraries Government Documents Department

Excited states in electronic structure calculations

Description: A first-principles quasiparticle approach to the electronic excitation energies in crystals and at surfaces is described. The quasiparticle energies are calculated within the GW approximation for comparison with photoemission and other spectroscopic experiments. Applications of the method to bulk semiconductors and the Si(111)2[times]l, Ge(111)2[times]l. and H/Si(III) surfaces are presented. In both cases, significant self-energy corrections arising from many-electron effects to the excitation energies are found. Using atomic positions from total energy minimization, the calculated excitation energies explain quantitatively the experimental spectra. This approach thus provides an ab initio means for analyzing and predicting results from spectroscopic probes.
Date: July 1, 1992
Creator: Louie, S.G.
Partner: UNT Libraries Government Documents Department

Electron spectroscopy studies of high temperature superconductors: Y/sub 1/minus/x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7/minus/delta/

Description: We itemize our previous work on high T/sub c/ superconductors, and describe more fully the results of an electron spectroscopy study and impurity Anderson Hamiltonian analysis of the Pr 4f spectrum of Y/sub 1/minus/x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7/minus/delta/, a system in which superconductivity is quenched as x increases. It has been speculated that Pr has valence 4+, resulting in extra charge in the Cu-O planes, and causing T/sub c/-suppression. We find that the Pr valence is close to 3+ for all x but that there is extensive Pr 4f hybridization with other valence band states. The Cu valence is essentially unchanged with x. From these findings, we speculate that Pr 4f hybridization with other valence band states has enabled Pr spin fluctuations to cause the T/sub c/-suppression. 41 refs., 4 figs.
Date: January 1, 1989
Creator: Kang, J.S.; Allen, J.W.; Lee, B.W.; Maple, M.B.; Shen, Z.X.; Yeh, J.J. et al.
Partner: UNT Libraries Government Documents Department

The use of light emission in failure analysis of CMOS ICs

Description: The use of photon emission for analyzing failure mechanisms and defects in CMOS ICs is presented. Techniques are given for accurate identification and spatial localization of failure mechanisms and physical defects, including defects such as short and open circuits which do not themselves emit photons.
Date: January 1, 1990
Creator: Hawkins, C.F. (New Mexico Univ., Albuquerque, NM (USA). Dept. of Electrical and Computer Engineering); Soden, J.M.; Cole, E.I. Jr. & Snyder, E.S. (Sandia National Labs., Albuquerque, NM (USA))
Partner: UNT Libraries Government Documents Department

Simple laser-driven, metal photocathodes as cold, high-current electron sources

Description: Recent developments in excimer laser design have made near ultraviolet light intensities of several MW/cm/sup 2/ possible in unfocused beams. These advances and recent experiments indicate that high-current, simple-metal photoemissive electron guns are now feasible. Producing more than 50 A/cm/sup 2/ of illuminated cathode surface, the guns could operate at vacuums of 10/sup -6/ torr with no complicated system components inside the vacuum enclosure. The electron beam produced by such photoemission guns would have very low emittance and high brightness. This beam would also closely follow the temporal characteristics of the laser pulse, making fast risetime, ultrashort electron beam pulses possible.
Date: January 1, 1987
Creator: Saunders, J.D.; Ringler, T.J.; Builta, L.A.; Kauppila, T.J.; Moir, D.C. & Downey, S.W.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation photoemission study of metal overlayers on hydrogenated amorphous silicon at room temperature

Description: In this dissertation, metals deposited on a hydrogenated amorphous silicon (a-Si:H) film at room temperature are studied. The purpose of this work is mainly understanding the electronic properties of the interface, using high-resolution synchrotron radiation photoemission techniques as a probe. Atomic hydrogen plays an important role in passivating dangling bonds of a-Si:H films, thus reducing the gap-state distribution. In addition, singly bonded hydrogen also reduces states at the top of the valence band which are now replaced by deeper Si-H bonding states. The interface is formed by evaporating metal on an a-Si:H film in successive accumulations at room temperature. Au, Ag, and Cr were chosen as the deposited metals. Undoped films were used as substrates. Since some unique features can be found in a-Si:H, such as surface enrichment of hydrogen diffused from the bulk and instability of the free surface, we do not expect the metals/a-Si:H interface to behave exactly as its crystalline counterpart. Metal deposits, at low coverages, are found to gather preferentially around regions deficient in hydrogen. As the thickness is increased, some Si atoms in those regions are likely to leave their sites to intermix with metal overlayers like Au and Cr. 129 refs., 30 figs.
Date: September 21, 1990
Creator: Pi, J.
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: January 1, 1993
Creator: Li, Dongqi; Zhang, Jiandi; Dowben, P.A. (Syracuse Univ., NY (United States)); Garrison, K.; Johnson, P.D. (Brookhaven National Lab., NY (United States)); Tang, H. et al.
Partner: UNT Libraries Government Documents Department

Optical techniques for actinide research

Description: In recent years, substantial gains have been made in the development of spectroscopic techniques for electronic properties studies. These techniques have seen relatively small, but growing, application in the field of actinide research. Photoemission spectroscopies, reflectivity and absorption studies, and x-ray techniques will be discussed and illustrative examples of studies on actinide materials will be presented.
Date: January 1, 1978
Creator: Veal, B.W.
Partner: UNT Libraries Government Documents Department

UV photoemission studies of metal photocathodes for particle accelerators

Description: Photoemission from several metals was studied with 10 ps laser pulses at 266 nm. The yield was linear with energy and with area. Quantum efficiencies (/eta/) were determined (up to 10/sup /minus/3/ e/photons for samarium), and found to vary as (h..nu..-/phi/)/sup 2/. /eta/ also increased with the field. The field assisted efficiencies were calculated for some metals and confirmed by experiment for gold, up to surface fields of /approximately/3/times/10/sup 8/ V/m. High charge and current densities, close to 10/sup 5/ A/cm/sup 2/ from macroscopic areas, were measured or indicated. Results are then related to applications in accelerators. 18 refs., 15 figs., 4 tabs.
Date: September 1, 1988
Creator: Fischer, J. & Srinivasan-Rao, T.
Partner: UNT Libraries Government Documents Department

Resonance and threshold effects in photoemission up to 3500 eV

Description: Beam lines at the Stanford Synchrotron Radiation Laboratory (SSRL) now provide photon beams throughout the entire energy range 5 to 5000 eV, with a pulse structure very well-suited to time-of-flight (TOF) photoelectron spectroscopy. We have used this facility, together with a TOF spectrometer, to measure photoemission cross sections sigma(epsilon) and asymmetry parameters ..beta..(epsilon) for several interesting systems. A summary of early results is given. Metal vapors (Ba, Cd, Mn, Hg) were studied using a high-temperature oven. Resonant photoemission was observed in several cases. Both sigma(epsilon) and ..beta..(epsilon) showed resonant behavior at 21.1 eV for several lines in Cd. The 4d, 5s, and 5p sigma(epsilon) line profiles differed dramatically, illustrating the detailed information about continuum states that is available from photoemission. Correlation satellites in photoemission from rare gases have been observed over a very wide energy range, including those seen in the K-shells of He, Ne and Ar and in the L-shell of Ne. The structure and preliminary intensity variations of these satellites will be discussed. Molecular shape resonances in C(1s), N(1s), and O(1s) photoemission were observed for the first time, in the molecules CO, CO/sub 2/, OCS, CF/sub 4/, N/sub 2/ and NO. Both the ..pi.. and sigma resonances were observed in KVV Auger emission, and the sigma resonances were studied by photoemission. The asymmetry parameters were measured in all cases. The results are in fair agreement with theory, but show systematic deviations and trends. 31 references.
Date: August 1, 1982
Creator: Shirley, D.A.; Kobrin, P.H.; Lindle, D.W.; Truesdale, C.M.; Southworth, S.H.; Becker, U. et al.
Partner: UNT Libraries Government Documents Department

Physical adsorption: rare gas atoms on solid surfaces. Progress report, June 1, 1980-May 31, 1981

Description: This project has entailed investigation of three areas during the current term: physical adsorption, photostimulated field emission (PSE), and phonon reflection at interfaces. The principal effort has been directed toward understanding interactions associated with physical adsorption and the associated properties of a film. The specific topics pursued include the detailed form of the long range interaction, the configuration space wave function, and the interaction between adatoms. Experimental confirmation of the last two come from neutron scattering and thermodynamic measurements, respectively. The research in PSE has yielded results which improve upon previous calculations. There is, however, a remaining disagreement with experiment; suggestions for the origin are discussed. The phonon reflection work is directed toward understanding the role of surface roughness, an important factor in increasing the energy transmission across interfaces. A formalism has been developed which will be evaluated in the future.
Date: February 1, 1981
Creator: Cole, M.W.
Partner: UNT Libraries Government Documents Department

Surface studies: a proposal for a participating research team at NSLS. Technical progress report

Description: The Stony Brook/Brookhaven National Laboratory Participating Research Team (PRT) are planning to be ready to exploit the National Synchrotron Light Source as soon as it becomes operations. This is scheduled to be in July 1981. The experimental equipment for angle-resolved photoemisson studies which comprises a beam line with a monochromator and an experimental chamber has been designed by the PRT and is well along in construction. An approximate two-year lead time has been required to complete the beam line and prepare it for installation and commissioning. In 1979 all the effort went into the detailed optical and mechanical design of the beam line, a layout drawing of which is attached. The present report details progress made on the individual items in 1980.
Date: unknown
Partner: UNT Libraries Government Documents Department

Mechanisms of interaction of radiation with matter

Description: This progress report is a summary and update of the research performed under DOE grant FG-02086-ER60405 from September 1, 1989 to August 31, 1990. Part I deals with mechanisms of photoemission from organic particulates, theoretical studied of the photoemission of electrons into atmospheres containing scavenger molecules, and theoretical studies of the possible existence of excitonic ions. Part II deals with the mechanisms of electrolytic reactions which occur at solid anthracene/aqueous electrolyte interfaces. Part III describes our most recent results on the physico-chemical interactions of mutagenic and carcinogenic polycyclic aromatic hydrocarbon (PAH) derivatives with nucleic acids. 3 refs., 14 figs., 2 tabs.
Date: January 1, 1990
Partner: UNT Libraries Government Documents Department

Status of Switched-Power Linac studies at BNL (Brookhaven National Laboratory) and CERN (European Organization for Nuclear Research)

Description: The switched-power linac (SPL) concepts are reviewed briefly, and recent work on computer-modelling of the photoemission process at the photocathode and the experimental study of the process are discussed. Work on rf-modelling of the properties of the radial transmission line is outlined. (LEW)
Date: October 31, 1986
Creator: Aronson, S.
Partner: UNT Libraries Government Documents Department