M. Domke

Performance of the high-resolution SX700/II monochromator

This article reports on the high‐resolution performance of the grazing‐incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universitat Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5‐μm exit slit. We report on high‐resolution gas‐phase studies in the double‐excitation region of He, as well as at core‐excitation thresholds of Ne, Ar, Kr, and Xe in the photon‐energy range from ≂45 eV to ≂900 eV. In addition, high‐resolution core‐excitation spectra at the K thresholds of C, N, and O are presented for gas‐phase CO, N2, and O2. In all cases, high‐n Rydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further imp...

Carbon and oxygen K-edge photoionization of the CO molecule

Abstract High-resolution, high-intensity photoionization studies were performed near the carbon and oxygen K-edges of gas-phase CO. At least 37 absorption lines were resolved at the carbon K-edge, and new information was obtained about the π*, Rydberg, and double-excitation resonances, including Rydberg states up to n=7 and vibrational transitions up to v′ = 3. Vibrational structure in oxygen is 1s−1π* and Rydberg states was resolved for the first time. The derived molecular structure parameters are consistent with the Z+1 approximation. High-resolution, high-intensity core-level photoabsorption promises new opportunities in vibrational state-to-state chemistry and surface science.

Bandlike character of 4f electrons in CeRh3

The electronic structure of CeRh 3 was studied by photoemission and bremsstrahlung isochromate spectroscopy (BIS). An analysis of the spectra, taken at different temperatures, on the basis of the Anderson single-impurity model leads to considerable inconsistencies that mark the limits ofapplicability of the model. On the other hand, the BIS spectrum of CeRh 3 can be well described by the results of a local-density-approximation band-structure calculation. These findings confirm a bandlike character of the 4f states in strongly hybridized Ce systems

Photoemission study of alkali/GaAs(110) interfaces

A detailed core-level photoemission study of interfaces between thin alkali films andn-orp-type GaAs (110) formed at different substrate temperatures 85 K and 300 K) is reported. All the interfaces grown at 85 K (with Na, K, Rb, and Cs) were found to be non-reactive, while at 300 K, the interface with Na is reactive and that with Cs remains non-reactive. In case of the non-reactive interfaces, a strong band bending of ≊1.0 eV is observed forp-GaAs at alkali coverages as low as θ≊0.01 monolayers, but practically none forn-GaAs. This striking asymmetry in band bending is interpreted as a consequence of the donor character of the alkali atoms. On the other hand, an approximately symmetric band bending at low coverages is observed for the reactive interfaces of Na withn- andp-GaAs and assigned to defect states. For high alkali coverages (θ>2 monolayers), the final band bending is characterizeds by the same Fermilevel position forn- andp-GaAs, independent of the reactivity of the interface, and assigned to metal-induced gap states. Furthermore, systematic trends along the alkali series in Fermi-level position ionization energy, plasmon-loss features, and layer-dependent binding-energy shifts of alkali core levels are discussed.

Resonance parameters of photo doubly excited helium

Using theoretical results from complex rotation calculations and data from experimental photoionization cross sections, the quantum defects, the widths, the oscillator strengths and the shape parameter of Rydberg series of autoionizing resonances in helium, excited with synchrotron radiation from the ground state, are reviewed and analysed systematically. The relation of these resonance properties to the propensity rules for radiative and non-radiative transitions in two-electron atoms is established.

Core-level binding energies and Auger electron energies in epitaxial rare-gas layers on graphite (001)

Abstract Layer-dependent shifts of core-level binding energies and Auger electron kinetic energies are reported for epitaxial multilayers for Xe, Kr, and Ar adsorbed on graphite (001). Despite negligible changes of the substrate work function, clearly resolved shifts are observed, which are described by layer-dependent hole screening effects. As with metallic substrates, the Auger electron energies shift three times more than the core-level binding energies, but the magnitudes of the shifts are reduced due to the small electron density in graphite.

Resonant Photoemission vs. Coster-Kronig Auger Decay At the LIII Thresholds of Ni Metal and CuO

We report on a resonant photoemission study of Ni metal and CuO at the LIII soft-X-ray absorption thresholds. The valence band spectra exhibit a strong enhancement of electron emission at resonance, which is shown to be mostly due to an incoherent superposition of a photoemission signal with a more intense signal from L3M4,5M4,5 Coster-Kronig decay of the core-ionized state. The resonant enhancement of the valence band photoemission satellite amounts to a factor of 12, far short of the recent claim of a giant resonance. Implications of these results with respect to the nature of the 3d states in these materials are briefly discussed.

Distinction of Band Bending Mechanisms at the Na/GaAs(110) Interface

Detailed As-3d and Ga-3d photoemission studies of the Na/GaAs(110) interface reveal substantial differences in band bending behaviour for n- and p-type substrates and for different substrate temperatures. For nonreactive interfaces grown at 85 K, a strong initial band bending of 1.0 eV is observed for p-GaAs at very low Na coverages ( 0.01 ML) due to electron transfer from Na to p-GaAs holes, while for n-GaAs the opposite mechanism is inhibited. For reactive interfaces formed at 300 K, on the other hand, defect states contribute strongly to band bending at low coverages. At higher coverages, band bending is dominated in both cases by virtual gap states.

Layer resolved photoemission study of the Cs/Si(111)2×1 interface

For Cs multilayers grown on Si(111)2×1 at 130 K, Cs 5p and Cs 4d core levels exhibit shifts to higher binding energies for second-layer Cs atoms as compared to first-layer atoms by 1.0 and 1.1 eV, respectively. For thick Cs layers, Cs 5p emission from bulk and surface atoms is resolved, resulting in a surface core level shift of 0.23 eV. These results are quantitatively described on the basis of the (Z+1) approximation using a Born-Haber cycle. In addition, layer dependent differences of the photoemission line widths and the Cs 5p spin-orbit splitting are reported as well as an anomalous energy dependence of the electron mean free path.

S 2p photoexcitation spectra of SO2 at high resolution

The S 2p photoabsorption spectrum of gas-phase SO2 was studied at high resolution (ΔE≅30 meV) using synchrotron radiation. The spectrum contains excitations to both valence orbitals and Rydberg states. The lowest core-to-valence excitation, S 2p−13b1, was found to be fivefold split, and vibrational subbands originating from the symmetric-stretching mode could be resolved. A Franck–Condon analysis of these five states reveals different geometries depending on the symmetry of the total electronic wave function in the final state. In the Rydberg region, both the spin–orbit splitting (≅1.20 eV) and the ligand-field splitting (≅95 meV) were resolved.