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Träfflista för sökning "WFRF:(Andersen J) srt2:(1990-1994)"

Sökning: WFRF:(Andersen J) > (1990-1994)

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1.
  • Wassdahl, N., et al. (författare)
  • Soft x-ray emission studies of adsorbates
  • 1992
  • Ingår i: Physical Review Letters. - 0031-9007. ; 69:5, s. 812-815
  • Tidskriftsartikel (refereegranskat)abstract
    • Soft x-ray emission spectroscopy is for the first time applied to surfaces and adsorbates. Surface sensitivity is achieved by employing synchrotron radiation in grazing incidence for the excitation. We present O K emission from adsorbed atomic oxygen on Ni(100) and Cu(100) and molecular CO on Ni(100). The observed spectral features correspond to the occupied 2p partial density of states of the adsorbates.
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2.
  • Andersen, J. N., et al. (författare)
  • Intermixing in the Na on Al(111) system
  • 1992
  • Ingår i: Physical Review Letters. - 0031-9007. ; 68:1, s. 94-97
  • Tidskriftsartikel (refereegranskat)abstract
    • Ordered structures formed by Na adsorption on the Al(111) surface are investigated by high-resolution core-level spectroscopy. It is shown that, contrary to the common picture of alkali adsorption, two of the structures formed at room temperature consist of intermixed Na-Al layers. The results for the (3 ×)-rotated-30°structure are also consistent with intermixing although they do not provide any definite proof. For Na layers deposited at 100 K no intermixing is found.
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3.
  • Elango, M., et al. (författare)
  • Autoionization phenomena involving the 2p53d configuration of argonlike ions in ionic solids
  • 1993
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:18, s. 11736-11748
  • Tidskriftsartikel (refereegranskat)abstract
    • The photon-induced Auger and photoelectron spectra of the argonlike ions Cl- (in NaCl), K+ (in KCl), Ca2+ (in CaCl2 and CaF2), and Sc3+ (in Sc2O3) have been measured in the vicinity of the L23 absorption edges of these ions. It is shown that at the 2p6→2p53d(4s) resonance a spectator structure appears in the L23M23M23 Auger spectra, which shifts to higher kinetic energies with increasing photon energy. This structure originates from the 3p-23d(4s) final configuration arising as a product of the Auger resonant-inelastic-scattering process of the incident photons. We demonstrate that the peculiarities of this process and the role of the collapsing 3d electron in it can be largely understood in terms of an atomic treatment. The solid-state effects, caused by the crystal field and the lattice polarization, may play an additional role.
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4.
  • Heskett, D., et al. (författare)
  • Alkali-alkali interactions on Al(111) : segregation and islanding in Na-Rb mixtures
  • 1994
  • Ingår i: Surface Science. - 0039-6028. ; 316:3, s. 303-308
  • Tidskriftsartikel (refereegranskat)abstract
    • The low temperature coadsorption of Na and Rb on an Al(111) surface is examined with a combination of LEED and core level photoemission spectroscopy. We observe LEED pattern sequences and alkali core level binding energies which are consistent with a net total alkali coverage and can be explained by Na-Rb repulsion, segregation, and islanding, though other models cannot be definitely excluded.
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5.
  • Nyholm, R., et al. (författare)
  • ADSORPTION-SITE DETERMINATION OF ORDERED YB ON SI(111) SURFACES
  • 1993
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 47:15, s. 9663-9668
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-energy-electron-diffraction (LEED), scanning-tunneling-microscopy (STM), and photoelectron-spectroscopy measurements have been performed on the ordered submonolayer surface reconstructions of Yb on Si(111). Two of these reconstructions, namely, 3 X 1 and 2 X 1, have been studied in detail. STM and LEED revealed that what was considered to be the 3 X 1 reconstruction is actually a 3 X 2 reconstruction. By combining STM and photoelectron-spectroscopy results from the 3 X 2 and 2 X 1 reconstructions, we conclude that the Yb atoms are adsorbed in bridge sites.
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6.
  • Nyholm, R., et al. (författare)
  • Surface core-level shifts of the Al(100) and Al(111) surfaces
  • 1991
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 44:19, s. 10987-10990
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface core-level shifts of the Al(100) and Al(111) surfaces have been measured by high-resolution photoelectron spectroscopy. For the Al(100) surface we obtain a value of (-965) meV. This value is in excellent agreement with a recent ab initio calculation by Feibelman. The surface core-level shift of the Al(111) surface is found to be close to zero, and an upper limit of 15 meV is obtained.
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7.
  • Qvarford, M., et al. (författare)
  • Polarisation-dependent X-ray absorption in high- and low-Tc Bi2Sr2Can-1CunO4+2n superconductors
  • 1993
  • Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 214:1-2, s. 119-126
  • Tidskriftsartikel (refereegranskat)abstract
    • Taking advantage of the linear polarisation of synchrotron radiation, the polarisation dependence of the O K and Cu L3 X-ray absorption edges has been compared for in situ cleaved Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 single crystals. The X-ray absorption spectra were measured by means of total electron yield detection. The spectra show for both crystals that the lowest unoccupied Cu 3d and O 2p orbitals are dominantly oriented parallel to the a-b plane, but also the presence of a small amount of unoccupied orbitals oriented perpendicular to the a-b plane can be deduced from both the O K and Cu L3 absorption spectra. A shift of the order of 0.5 eV between absorption into the in-plane and the out-of-plane Cu 3d orbitals was measured for the Bi2Sr2CaCu2O8 crystal, but no such shift was found for the Bi2Sr2CuO6 crystal.
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8.
  • Ruus, R., et al. (författare)
  • M4,5N4,5N4,5 Auger decay spectra of the resonantly excited 3d94f configuration of xenonlike ions in solids
  • 1994
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 49:21, s. 14836-14844
  • Tidskriftsartikel (refereegranskat)abstract
    • The synchrotron-radiation-induced Auger and photoelectron spectra of the xenonlike ions I- (in CsI), Cs+ (in CsI), Ba2+ (in BaF2), and La3+ (in LaF3) have been measured in the vicinity of the M4,5 absorption edges of these ions. It is shown that the spectra of La and Ba measured at 3d10→3d94f resonances exhibit a very intense 4f-spectator structure which changes its energy and intensity with the energy of the exciting photons. Calculation of the Auger decay of the 3d-14f configuration shows that this structure is due to transitions to the 4d-24f+4p-1 final ionic configuration, the high-energy part of which overlaps the 4d-2 continuum. In the case of Ba this structure coexists with the normal Auger structure which appears as a result of the M4M5N6,7 Coster-Kronig transitions. The spectra of I- contain only the normal M4,5N4,5N4,5 Auger structure related to the 3d-1→4d-2 transitions. The spectra of Cs+ are similar to those of I- with a small admixture of the 4f-spectator-like structure.
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9.
  • Andersen, J. N., et al. (författare)
  • Alkali metal adsorption on Al(111)
  • 1993
  • Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 289:3, s. 307-334
  • Tidskriftsartikel (refereegranskat)abstract
    • The submonolayer adsorption of Na, K, Rb, and Cs on the Al(111) surface at 100 K and at room temperature is investigated by high resolution core level spectroscopy and low energy electron diffraction. It is found that the first alkali atoms on the surface adsorb at surface defects. At higher coverages, up to approximately one third of the maximum submonolayer coverage, alkali atoms adsorbed at defects coexist with a dispersed phase. At higher coverages island formation is found to occur for the majority of the systems. It is argued that all of the ordered structures formed at room temperature involve a disruption of the Al(111) surface in contrast to the situation at 100 K where the alkali atoms adsorb as adatoms.
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10.
  • Andersen, J. N., et al. (författare)
  • Changes in the local surface geometry with conserved adsorbate coverage and long-range order caused by annealing
  • 1992
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 46:19, s. 12784-12787
  • Tidskriftsartikel (refereegranskat)abstract
    • The ordered c(2×2) Na on Al(100) and (3 × 3) R30°K on Al(111) structures formed at either 100 K or at room temperature are studied by high-resolution core-level spectroscopy. For both systems equal alkali coverages are found at these two temperatures. The core-level spectra, however, show strong changes with temperature. This behavior leads to the surprising conclusion that annealing at room temperature causes an irreversible change in the local geometry, i.e., of the adsorption site, of the overlayer even though neither the long-range order nor the adsorbate coverage changes.
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11.
  • Andersen, J. N., et al. (författare)
  • Differences in the Cs 4d and 5p surface and interface core-level shifts
  • 1994
  • Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 226:1-2, s. 106-110
  • Tidskriftsartikel (refereegranskat)abstract
    • Core-level binding energy shifts of Cs induced by changes in the surroundings of the Cs atoms are measured for two different Cs core levels, 5p and 4d, and are found to be different for these two levels. The surface core-level shift of Cs is found to differ by 25 meV between the two levels. In the case of the Cs core-level shifts between bulk Cs atoms and Cs atoms at an interface between Cs and an Al(111) surface the difference between the two levels is found to be as large as 60 meV. The implications of these results for the precision of the Z+1 approximation are discussed.
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12.
  • Andersen, Jesper N, et al. (författare)
  • Photoemission Spectroscopy At Max-Lab
  • 1991
  • Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 4:4, s. 15-19
  • Tidskriftsartikel (refereegranskat)
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13.
  • Andersen, J. N., et al. (författare)
  • Surface core-level shifts as a probe of the local overlayer structure : CO on Pd(100)
  • 1991
  • Ingår i: Physical Review Letters. - 0031-9007. ; 67:20, s. 2822-2825
  • Tidskriftsartikel (refereegranskat)abstract
    • The bonding energies of the Pd 3d and the C 1s core levels have been studied for the p(2 S 2 × 2) R45°, p(3 s2 × S2) R45°, and p(4 S 2 × S 2) R45°structures of CO on Pd(100). Adsorption of CO shifts the Pd 3d surface emission to higher binding energies with the magnitude of the shift depending almost linearly on the number of Pd to CO bonds; the measured shift per bond is close to 0.5 eV. A direct relation is established between the detailed geometry of the CO overlayer and the changes in the Pd 3d spectra.
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14.
  • Andersen, J. N., et al. (författare)
  • Surface core-level shifts of some 4d-metal single-crystal surfaces : Experiments and ab initio calculations
  • 1994
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 50:23, s. 17525-17533
  • Tidskriftsartikel (refereegranskat)abstract
    • High resolution measurements are reported of the surface core-level shift of the 3d level for the Rh(111), Rh(110), Pd(111), Pd(110), and Ag(111) single-crystal surfaces. These measurements and earlier ones for the Mo(110), Rh(100), and Pd(100) surfaces are analyzed by ab initio calculations of the surface core-level shift. The calculations are found to reproduce well the trends of the experimental shifts with the 4d metal and with the crystal plane. The comparison between these experimental and theoretical results demonstrates the importance of proper inclusion of final-state effects for accurate calculations of surface core-level shifts. A core hole in a surface atom is found to be better screened than one in a bulk atom for the 4d metals to the left of Pd in the Periodic Table. The use of the Z+1 approximation to describe the core hole is investigated both by explicit use of this approximation and by performing calculations for 1s and 3d core holes, respectively. The Z+1 approximation is found to be well obeyed in the case of Ag whereas for the rest of the 4d transition metals it is less precise, introducing errors of typically 0.1 eV.
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15.
  • Ausmees, A., et al. (författare)
  • Secondary photoelectron spectra of ionic solids as a function of the incident photon energy
  • 1991
  • Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 308:1-2, s. 219-222
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy distributions of slow electrons (0-10 eV) emitted by thin layers of NaCl, KBr, CsBr, and CsI irradiated by monochromatic XUV photons with various energies in the interval of 50-300 eV are measured. The contributions of slow secondaries, hot secondaries and primary photoelectrons are obtained. It is shown that the higher the absorption coefficient for incident photons, the stronger the contribution of hot secondaries. The relationship between their contribution and the electron-phonon scattering process is discussed.
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16.
  • Ausmees, A., et al. (författare)
  • Secondary photoelectron spectra of NaCl and KBr excited by XUV radiation : Experiments and computer simulations
  • 1990
  • Ingår i: Solid State Communications. - 0038-1098. ; 76:12, s. 1383-1386
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy distributions of slow electrons (0 to 10eV) emitted by thin layers of NaCl and KBr irradiated by monochromatic XUV photons with various energies in the interval of 50 to 300 eV are measured. For all cases the photoelectron spectrum starts with an intense peak of slow secondaries and has a hot-secondary structure at the energies 1 to 5 eV. The smaller the photon absorption depth, the stronger is this structure. An attempt is made to reproduce such a behaviour of spectra by a Monte Carlo simulation of electron-electron and electron-phonon scattering sequences induced in solids by XUV photon absorption. It appears that for high-energy ( > 2 to 3 eV) conduction electrons the electron-phonon scattering is mainly due to acoustic phonons.
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17.
  • Berg, C., et al. (författare)
  • Observation of a low-binding-energy peak in the 2p core-level photoemission from oxidized Al(111)
  • 1993
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:19, s. 13063-13066
  • Tidskriftsartikel (refereegranskat)abstract
    • High-resolution photoemission studies of oxidation of the Al(111) surface have been performed. The appearance of a component at lower binding energy than the metallic bulk Al emission in the Al 2p spectrum at oxygen exposures above ∼50 langmuir (1 L = 10-6 Torr s) is argued to be due to Al atoms which do not bond directly to oxygen atoms at the oxide-metal interface. Low-energy electron diffraction initially shows a 1×1 structure, which subsequently fades away at higher oxygen exposures, 400 L.
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18.
  • Björneholm, O., et al. (författare)
  • Resonant photoemission at core-level shake-up thresholds : Valence-band satellites in nickel
  • 1990
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 41:15, s. 10408-10412
  • Tidskriftsartikel (refereegranskat)abstract
    • Three-hole satellites (3d7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p53d9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M2,3M4,5M4,5 Auger spectrum.
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19.
  • Johansson, H. I P, et al. (författare)
  • Core-level shifts on Be(101̄0)
  • 1994
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 49:24, s. 17460-17463
  • Tidskriftsartikel (refereegranskat)abstract
    • A high-resolution photoemission study of the Be (101̄0) surface, at a sample temperature of 100 K, is reported. Three surface-shifted Be 1s components are revealed having shifts of -700, -500, and -220 meV. These are interpreted as originating from the first, second, and third plus fourth atomic layers while the bulk signal originates from the fifth and deeper layers. The surface layer shift for this more open Be(101̄0) surface is found to be smaller than for the close-packed Be(0001) surface. Reasons for this unusual behavior are suggested.
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20.
  • Johansson, L. I., et al. (författare)
  • Surface core level shift on Be( 112̄0)
  • 1994
  • Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 321:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A photoemission study of the Be(112̄0) surface carried out at a sample temperature of 100 K is reported. A surface shifted Be 1s component, having a shift of - 410 meV, is resolved on this surface. The extracted surface to bulk intensity ratio indicate that this component originates from atoms in the surface layer only. This is opposite to previous observations on both the close-packed Be(0001) surface and the Be(101̄0) surface where sub-surface shifted Be 1s levels were unambiguously identified. Among these three surfaces a surface layer atom is expected to have the lowest coordination on the (112̄0) surface but the surface layer shift is found to be smallest on this surface. Compared to findings on other metals this is unusual and reasons contributing to this behaviour are suggested and discussed.
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21.
  • Johansson, L. I., et al. (författare)
  • Three surface-shifted core levels on Be(0001)
  • 1993
  • Ingår i: Physical Review Letters. - 0031-9007. ; 71:15, s. 2453-2456
  • Tidskriftsartikel (refereegranskat)abstract
    • The results of a high resolution photoemission study of the Be(0001) surface carried out at temperatures between 100 and 450 K are reported. At 100 K, three distinctly shifted Be 1s levels, exhibiting shifts of -825, -570, and -265 meV, are revealed and interpreted to originate from the three outermost atomic layers. Identification of two subsurface core level shifts and a first layer surface shift of -825 meV is unique among close-packed metal surfaces. Temperature dependent broadening effects observed in the bulk and surface BE 1s peaks are also reported.
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22.
  • Kikas, A., et al. (författare)
  • Auger Spectra of K+ L23 Excitations in Potassium Halides
  • 1991
  • Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 15:6, s. 683-686
  • Tidskriftsartikel (refereegranskat)abstract
    • The L23M23M23 Auger spectra of K+ L23 excitation in potassium halides are measured using photon excitation with different energies in the region of the K+ L23 absorption edge (around 300 eV). It is shown that the screening of the two 3p holes caused by the collapsed 3d electron of the K+ L23 exciton leads to a considerable shift (by about (6÷7) eV) of the K+ L23M23M23 Auger bands to higher energies. Only the low-energy component of the crystal-field-split K+ 3d orbital forms a genuine bound state with 2p holes, whereas its high-energy component lies in the conduction band continuum and behaves like a shape resonance.
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23.
  • Lundgren, E., et al. (författare)
  • Alkali core-level binding-energy shifts in alkali/4d-metal interface systems
  • 1994
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 50:7, s. 4711-4717
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoemission from different alkali core levels (Na 2p, K 3p, Rb 4p, and Cs 4d) has been studied for thin alkali films deposited on four different 4d metal surfaces: Mo(110), Rh(111), Rh(110), and Pd(100). Alkali atoms at the interface, the bulk, and at the surface of the adsorbed alkali film are found to have different core-level binding energies. It is found that the core-level binding-energy shifts of the alkali metals induced by the 4d-metal substrate increase with increasing atomic number of the alkali metal and with increasing atomic number of the 4d metal. Thermodynamical quantities such as interface segregation energies and adhesion energies are deduced from the layer-resolved shifts. Estimates of the experimental binding-energy shifts are given using semiempirical calculations, and certain complications in doing that are discussed.
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24.
  • Lundgren, E., et al. (författare)
  • Layer dependent core level binding energy shifts : Na, K, Rb and Cs on Al(111)
  • 1993
  • Ingår i: Surface Science. - 0039-6028. ; 281:1-2, s. 83-90
  • Tidskriftsartikel (refereegranskat)abstract
    • Layer resolved core level spectra are presented for Na, K, Rb and Cs films on Al(111). From the development of the spectra, it is possible to distinguish emission from alkali atoms at the interface, in the bulk, and at the surface of the adsorbed layers. The core level binding energy shifts are discussed in terms of adhesion and interface segregation energies. It is found experimentally that the Al induced core level binding energy shifts of the alkalis are increasing with increasing atomic number of the alkali metal. This trend is qualitatively reproduced by semi-empirical calculations.
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25.
  • Lundgren, E., et al. (författare)
  • Surface core-level shift of the Mo(110) surface
  • 1993
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 48:8, s. 5525-5529
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface core-level shift of the Mo(110) surface is determined from high-resolution photoemission measurements of the Mo 3d level. The 3d core-level binding energy of the surface atoms is found to be lowered by 333±10 meV relative to that of the bulk atoms. This result agrees well with semiempirical estimates and with the results of recent ab initio calculations. Decompositions of the spectra indicate that the 3d core-hole lifetime is shorter for a surface than for a bulk atom.
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26.
  • Nilsson, A., et al. (författare)
  • Photoabsorption and the unoccupied partial density of states of chemisorbed molecules
  • 1992
  • Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 197:1-2, s. 12-16
  • Tidskriftsartikel (refereegranskat)abstract
    • The 1s to 2π* resonances have been studied for CO strongly chemisorbed on Ni(100) and weakly chemisorbed on Cu(100) using high resolution X-ray absorption spectroscopy. We show that the spectra can be consistently described in terms of the local density of unoccupied 2π* electron states with the Fermi level obtained from corresponding X-ray photoelectron spectra. The core hole is demonstrated to induce large shifts in the unoccupied 2π* density of states.
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27.
  • Nyholm, R., et al. (författare)
  • ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE
  • 1991
  • Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 180:1-4, s. 120-123
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.
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28.
  • Nyholm, R., et al. (författare)
  • EPITAXIAL SILICIDE FORMATION IN THE MG/SI(111) SYSTEM
  • 1993
  • Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 289:3, s. 290-296
  • Tidskriftsartikel (refereegranskat)abstract
    • The silicide formation has been studied in the Mg/Si(111) system by IOW energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg2Si silicide is responsible for the (2/3 square-root e x 2/3 square-root 3)R30-degrees reconstruction in this system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 +/- 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 +/- 0.1 eV below the Fermi level.
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29.
  • Nyholm, R., et al. (författare)
  • FORMATION OF SM SILICIDES ON SI(111) - COMPOSITION AND EPITAXY
  • 1993
  • Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 293:3, s. 254-259
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi2-x, the other being tentatively ascribed to SmSi.
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30.
  • Nyholm, R., et al. (författare)
  • SYNCHROTRON-RADIATION SOFT-X-RAY PHOTOEMISSION-STUDY OF LEAD ON BI2CASR2CU2O8
  • 1992
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:10, s. 6488-6494
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present a study of the interaction of Pb with a clean single-crystal Bi2CaSr2Cu2O8 superconductor surface based on photoemission and low-energy electron diffraction (LEED). Deposition of Pb on a Bi2CaSr2Cu2O8 Crystal kept at room temperature gives rise to the formation of metallic Bi and oxidized Pb at the interface. This behavior could not be observed when the crystal was kept at 100 K during Pb deposition. For all investigated Pb overlayers on a cold crystal (100 K), surface-sensitive photoelectron spectroscopy revealed the growth of a covering metallic Pb overlayer film. The growth at 100 K, contrary to the growth at room temperature, preserved the original LEED 5 X 1 pattern even for Pb depositions corresponding to a 24-angstrom thick overlayer indicating epitaxial growth. Furthermore, a rigid 0.4-eV shift of the valence band and the Bi 5d core levels is observed upon initial Pb deposition and is tentatively attributed to electron doping.
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31.
  • Nyholm, R., et al. (författare)
  • The surface core-level shift of the Pd(100) single-crystal surface
  • 1992
  • Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 4:1, s. 277-283
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface core-level shift of the Pd(100) single-crystal surface has been measured from high-resolution Pd 3d core-level spectra. The surface atoms are found to have 0.44+or-0.03 eV lower binding energy than the bulk atoms. The result is compared with theoretical estimates.
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32.
  • QVARFORD, M, et al. (författare)
  • X-RAY-ABSORPTION AND RESONANT-PHOTOEMISSION STUDY OF CA IN THE HIGH-TEMPERATURE SUPERCONDUCTOR BI2SR2CACU2O8
  • 1992
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:21, s. 14126-14133
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of Ca in the high-temperature superconductor Bi2Sr2CaCu2O8 has been studied by x-ray-absorption spectroscopy and resonant-photoemission at the Ca L2,3 absorption edge. In the x-ray-absorption spectrum no edge structure is seen at the energy corresponding to the Ca 2p3/2 core-level binding energy, in agreement with the very low Ca density of states at the Fermi level predicted by band-structure calculations. Furthermore, the crystal-field splitting of the Ca 3d level, which is characteristic of ionic Ca compounds, is clearly observed in the x-ray-absorption spectrum. The photoemission spectra display strong resonant enhancements of the Ca 3s and 3p core levels as well as strong changes in the intensity and the line shape of the Ca L2,3M2,3M2,3 Auger structure at the Ca L2,3 threshold, showing the localized nature of the 3d states in core ionized Ca. The 3d induced spectator shift of the Ca L2,3M2,3M2,3 complex is fairly small as compared to what has been reported for CaF2, indicating that the screening of the normal Auger final state by the charge carriers in the surrounding Cu-O2 layers is quite efficient. From the Ca L2,3M2,3M2,3 data it is also suggested that, at the Ca L2 threshold, the excited 3d electron participates in a Coster-Kronig-type decay resulting in a 2p3/2 core hole followed by a normal L3M2,3M2,3 Auger decay.
  •  
33.
  • Sandell, A., et al. (författare)
  • THE INNER VALENCE REGION OF CO ADSORBED ON PD(100)
  • 1994
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:19, s. 10659-10668
  • Tidskriftsartikel (refereegranskat)abstract
    • The inner valence region of CO/Pd(100) p(2square-root2 x square-root2)R45-degrees has been studied by angular resolved photoemission at the Pd 4d Cooper minimum, and with resonant Auger spectroscopy at photon energies corresponding to the C 1s and O 1s x-ray absorption (XA) maxima of the unoccupied parts of the 2pi*-Pd 4d hybrid (2pi(un)). Previously unobserved inner valence states are revealed in the direct photoemission and are compared with resonant Auger results. The interpretation and assignment of the different spectral features to different main final state configurations are based on energy, symmetry and intensity arguments, as well as comparisons with previous results.
  •  
34.
  • Wigren, C., et al. (författare)
  • Sm- and Yb-induced reconstructions of the Si(111) surface
  • 1993
  • Ingår i: Physical Review B. - 0163-1829. ; 48:15, s. 11014-11019
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy results from the submonolayer Sm- and Yb-induced surface structures are presented. Several similar metal-induced surface reconstructions are found to exist for Yb and Sm on Si(111) for low submonolayer coverages: 3×2, 5×1, and 7×1. At higher submonolayer coverage, Yb induces a 2×1 reconstruction while Sm induces a (3 × 3) R30°-like reconstruction. Yb is found to be divalent in all structures, whereas the Sm valence increases with increasing coverage. In the 3×2 structure only divalent Sm is present, in the 5×1 and 7×1 structures a small amount of trivalent Sm appears, and, finally, in the (3 × 3) R30°structure approximately half of the Sm atoms are trivalent. The surface Fermi-level position in the band gap for the different Sm and Yb reconstructions has been measured. The difference in valence stability between Sm and Yb is suggested to be the cause of the difference in the high-coverage structures found and the differences in pinning level for the two elements observed for the 5×1 and 7×1 structures. © 1993 The American Physical Society.
  •  
35.
  • Zdansky, E. O F, et al. (författare)
  • Electronic structure of atomic adsorbates from x-ray-absorption spectroscopy : Threshold effects and higher excited states
  • 1993
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 48:4, s. 2632-2641
  • Tidskriftsartikel (refereegranskat)abstract
    • Atomic C, N, and O chemisorbed on Ni(100) have been studied by x-ray-absorption spectroscopy. The atomic 2p orbitals are shown to form hybrid orbitals with the Ni 3d and 4sp bands. The spectral contributions from these hybrids are identified at the absorption threshold and in a region 6-12 eV above this. Between those regions, states derived from atomic 3p and higher np orbitals are observed. The threshold region shows vibrational and dynamical effects, which are discussed in connection with the corresponding photoemission spectra. The substrate Ni 2p3/2 x-ray-absorption spectrum is also presented. Its large similarity to the Ni 2p3/2 x-ray photoemission spectrum is discussed.
  •  
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