B.B. Pate

The diamond (111) surface: A dilemma resolved

Abstract A dilemma due to the experimental observation of a “clean” unreconstructed elemental semiconductor surface without band gap states is resolved. Results from photon stimulated ion desorption, high resolution low energy electron loss spectroscopy and photoemission spectroscopy find that the conventionally polished (in olive oil) diamond (111) 1 × 1 surface is atomically terminated and electronically stabilized by hydrogen. Thermal desorption of hydrogen upon heating (∼1000°C) results in a reconstructed 2 × 2 2 × 1 surface with filled electronic surface states in and near the fundamental gap. Exposure of the reconstructed surface to atomic hydrogen (or dueterium) is found to again terminate the surface and remove the near band gap surface states. Apparent inconsistencies (with respect to the experimental literature) in the understanding of the diamond:hydrogen interaction are resolved in terms of our work.

The SSRL Insertion Device Beam Line 'Wunder'

Insertion devices as radiation sources on storage rings offer potential for substantial gains in beam brightness and flux delivered to a sample. Achieving these gains, however, requires several new aspects of beam line design. New aspects of beam line design arise from the high beam power, the complex spectral and geometrical characteristics, and the need for a wide spectral range. We discuss these aspects of insertion device soft X-ray synchrotron radiation beam lines with examples drawn from our project creating Beam Line Wunder at the Stanford Synchrotron Radiation Laboratory. The major research use envisioned for this beam line is for spectroscopic experiments which require the highest possible intensity and resolution for a tunable constant deviation source. We summarize the current status of each of the beam line major components: the Multi-undulator, the transport system, the Locust Monochromator, the computer control system, and the experimental area.

Valance-Band photoemission intensities in thorium dioxide

Abstract Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO2 are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d corelevel threshold energies (85 ⩽ hv ⩽ 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d.

Electron spectroscopy study of the heavy Fermion compound URu2Si2

Abstract We report x-ray photoemission, resonant photoemission and bremsstrahlung isochromat spectra of the 4f core levels, the valence band and the conduction band, respectively, of the heavy fermion compound URu 2 Si 2 . The resonant photoemission behavior of the uranium 5f weight resembles that of cerium 4f weight in that the portion away from the Fermi energy has a delayed resonance relative to that at the Fermi energy. We also assess current efforts to interpret uranium spectra.

Magnetic behaviour of ultra-thin iron overlayers on palladium (111)

Abstract A LEED, Auger photoemission study of ultra-thin overlayers of iron on palladium (111) is reported. At room temperature and below, the overlayer grows epitaxially in a simultaneous multi-layer mode. On annealing a sub-monolayer coverage to create flat two-dimensional platelets it was found that the density of the Fe 3d states at the Fermi level was reduced and the local iron magnetic moment could not be detected.

Valence-band densities of state in NiAs

Abstract Valence-band resonant photoemission data on NiAs are compared to corrected linear muffin-tin orbital (LMTO) density-of-state (DOS) calculations. The observed bandwidth is 6 eV with the main Ni 3d peak at 1.8 ev below the Fermi edge and shoulder ∼1 eV wide at E F , in agreement with the calculated Ni d-projected DOS.

Electron spectroscopy study of the heavy fermion compound U2Zn17

Abstract We report X-ray photoemission, resonant photoemission and Bremsstrahlung isochromat spectra of the 4f core levels, the valence band and the conduction band, respectively, of the heavy fermion compound U 2 Zn 17 and the reference compound Th 2 Zn 17 , and we assess current efforts to interpret such spectra.

Design process and modeling studies of SSRL beam line wunder

Abstract SSRL Beam Line Wunder will be the first soft X-ray energy range synchrotron radiation beam line specifically designed to exploit the unique aspects of periodic insertion devices in the wiggler-undulator (wunder) regime. Aspects of the development of this beam line are described in this paper and in particular, we discuss the design methodology adopted and emphasize the joint optical, thermal and mechanical optimization studies that were required.

Photoemission studies of a clean and oxidized niobium-aluminum alloy using synchrotron radiation

Abstract The alloy formation and oxidation of a Nb-rich Nb-Al alloy has been studied using core level photoemission in combination with synchroton radiation as a surface sensitive probe. Exactly the same chemical shifts were observed from both the Nb-Al alloy and an Al-evaporated Nb surface, indicating similar structural arrangements. It is found that the oxidation rate of Nb in these structures is drastically decreased in comparison to either pure Nb metal or Nb3Sn. Two stages in the oxidation of the Nb-Al alloy are clearly distinguished by chemical shifts of the Al2p, Nb4p and O2p levels.

Multi-Undulator Beam Line V at SSRL: A progress report

Abstract A progress report is given on the implementation of Multi-Undulator Beam Line V at SSRL, also known as Beam Line Wunder. The beam line has been designed to exploit insertion device technology in the spectral range from 10 to 1000 eV. Aspects of the multi-undulator, the Locust monochromator, and the experimental areas are described.