Clean and oxidized (104–1015 L of O2) surfaces of α-GeTe have been investigated with x-ray photoelectron spectroscopy by using the synchrotron radiation facility BESSY II as well as an Al Kα source. To understand the first steps of oxidation, complementary quantum chemical calculations were performed. The cleaved surfaces of α-GeTe were found to be rumpled with (111) domains that can be related to the domain (twin) structure of the bulk. Both the Ge 3d and the Te 4d spectra of freshly cleaved surfaces exhibit at least three components, which are explained by a Ge or Te termination of the surface domains with possible contributions of a surface reconstruction. The surface oxidation starts at exposures of 104 L and proceeds via several steps. At low exposures, only changes in the Ge spectra are observed. Consequently, the first step of the reaction is associated with the formation of intermediate peroxidelike structures, wherein both oxygen atoms are bonded to germanium atoms. In the range of exposures between 1010 and 1015 L, a layer of a relatively stable oxidation product with the approximate stoichiometry Ge1+δ+4Te1−δ0O2(1+δ)2− is formed, which shows growth kinetics that obey a time-logarithmic law. At this stage, the peroxidelike structures are still present at the oxide/crystal interface. Once the oxidized layer exceeds a thickness of ≈2.5 nm at ∼1013 L, a transformation of the Te0 state into the Te+4 state is observed at the surface of the oxide layer. The final oxidation product can be described as mGeO2×nTeO2.

High-resolution S 2p −1 photoelectron spectra and S 2p −1 → X 1 A 1 ͑2b 1 −2 ͒ normal Auger electron spectra ͑AES͒ of H 2 S were measured for various photon energies in the range from 180 to 240 eV. The equilibrium geometry, vibrational energies ប, and anharmonicities x ប , for the S 2p −1 intermediate and X 1 A 1 ͑2b 1 −2 ͒ final states were derived from the energy splittings and the intensity distributions of the vibrational substates. The relative intensities of the various S 2p −1 → X 1 A 1 ͑2b 1 −2 ͒ normal Auger transitions as well as the lifetimes of the various S 2p −1 core-ionized states were also derived. In addition to the S 2p −1 → X 1 A 1 ͑2b 1 −2 ͒ transitions, some weak structures were observed in the AES, with intensities that exhibit pronounced photon-energy dependences.

The interaction of the semiconductor compounds PbS, PbSe, and PbTe with H2S was studied using X-ray photoemission spectroscopy performed at the synchrotron radiation facility BESSY II. For all surfaces sulfidation subsequent to dissociation of H2S was observed. For PbS, the sulfur atoms occupy the surface anion vacancies. In the case of PbSe, either a similar interaction or an anion substitution at the surface takes place; besides, H2S adsorption leads to the agglomeration of additional sulfur atoms forming S n 2-. For the reaction of H2S with PbTe surfaces we suggest a mechanism which includes at least three steps. The first step leads to a formation of Pb−S−Te bonds, which is also supported by the results of quantum chemical calculations performed in the framework of cluster approach. The subsequent steps include further gradual oxidation of the tellurium atoms and result finally in the formation of quite stable thiotellurite species.

Partial photoionization cross sections (PCSs), σ n , leading to final states of singly ionized helium, He + (n), were measured in the region of doubly excited helium below the ionization thresholds I 8 and I 9. The experiments were performed at BESSY II at high photon resolution, E ∼ = 6 meV, using a time-of-flight electron spectrometer. A comparison with recent eigenchannel R-matrix calculations reveals good agreement. The results of these measurements underline previous studies on quantum chaos in helium, which were mainly based on theoretical results. They also allow a critical assessment of the theoretical methods that produce the data used for a statistical analysis of double-excitation states with respect to quantum chaos, which is expected to occur very close to the double-ionization threshold. PCSs provide additional information to that derivable from total cross sections (TCSs). In the present PCS spectra, the resonance 8, 4 10 of the secondary series, which could not be resolved in the TCS, is clearly observed.

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