Using synchrotron radiation, Auger electron, and H+/D+-ion yields have been studied at and above the O 1s excitation energies for condensed H2O/D2O layers of varying thickness, and for two reproducible adsorbate layers (so-called bilayers and monolayers) on Ru(001). Decay electron spectra as well as polarization dependences, angular distributions, and energy distributions of desorbing ions have been investigated. For polarizations with sufficient E component perpendicular to the surface, a sharp peak in the H+ NEXAFS spectrum is seen for all layers which has no direct counterpart in the Auger NEXAFS spectra, and whose intensity maximizes for E oriented in the detection direction. This observation is interpreted as due to the 1a1→4a1 core-to-bound transition of the surface molecules whose final state decays electronically and dissociates on comparable time scales. This appears to have the consequence that the symmetry of the coupled excitation is different from that expected for the primary photoabsorption process. There appears also to be an influence of hydrogen bonding on these effects. Similarities and differences between the various layers investigated are also analyzed.

The friction of a clean diamond tip on diamond (111) and (100) surfaces is studied using an ultrahigh vacuum force microscope that simultaneously measures forces parallel and perpendicular to the surface. The 30 nm radius diamond tip is fabricated by chemical vapor deposition. The attractive normal force curve between the tip and surface agrees well with calculated dispersion interactions. The frictional force exhibits periodic features, which on the (100) surface are tentatively associated with a 2×1 reconstructed surface convoluted over an asymmetric tip shape. The (111) surface shows features that cannot be simply related to the surface structure. As the tip is scanned back and forth along a line, the same features are observed in each direction, but offset, suggesting the presence of a conservative force independent of the direction of motion as well as a nonconservative force. The friction is approximately ≂3×10−9 N independent of loads up to 1×10−7 N.

For condensed benzene ice layers, core photoabsorption near edge structure (x-ray absorption; recorded by Auger electron yield measurements), decay electron spectra for resonant and nonresonant excitation, and fragmentation as evident in yields of hydrogen and other ions, have been measured in the C1s region. The absorption spectrum is better resolved than most previously published spectra, exhibits some new features, and shows a high degree of parallelity to the spectrum of isolated molecules. Interestingly, the hydrogen ion yield indicates a particular dissociativeness of a certain core excitation resonance, X, which in the molecule has previously been assigned to a Rydberg state. This selective dissociation suggests that the responsible excitation is strongly antibonding for the carbon–hydrogen bond, while the degenerate Rydberg states broaden into a conduction band in the solid; and that the bond breaking probably occurs or at least starts in the core-excited state, thus proceeding on an extremely short time scale, similarly to observations for other hydrogen-containing molecules. The decay spectra are analyzed in terms of autoionization vs normal Auger decay and indicate that, apart from the first strong π resonance (which leads to pure autoionization) and the X resonance, the core resonances partly or fully ionize before core decay takes place. For the X resonance, the decay spectrum contains a contribution which cannot be assigned to intact benzene; this is taken as additional evidence for ultrafast dissociation, i.e., competitive with core decay. We use these results for a discussion of the influence of condensation on excitation, decay, and fragmentation.

Titanium disilicide formation on heavily doped silicon substrates was investigated with sheet resistance measurements, elemental depth profiling, and transmission electron microscopy. As found in a previous study [H.K. Park, J. Sachitano, M. McPherson, T. Yamaguchi, and G. Lehman, J. Vac. Sci. Technol. A 2, 264 (1984)], the TiSi2 growth rate depended on the dopant concentration. The growth rate was highest on undoped substrates, intermediate on heavily phosphorus-doped substrates, and lowest on heavily arsenic-doped substrates. However, the critical dopant concentration effect reported by Park et al. was not observed. The uniformity of the titanium-silicon reaction was not seriously affected by heavy substrate doping. For heavily arsenic-doped substrates (3.0×1021 As/cm3), TiAs precipitates formed at C49 TiSi2 grain boundaries, and the C49-to-C54 transformation temperature increased to 850 °C. For heavily phosphorus-doped substrates (1.0×1021 P/cm3), no phosphides were unambiguously detected, and the C49-to-C54 transformation temperature remained below 800 °C. Discrete blocking layers at the silicide-silicon interface, such as the native silicon oxide or a dopant-rich phase, did not cause the reduction in silicide growth. Thus, it is concluded that dopant and knock-on oxygen atoms in solid solution in both the silicide and the silicon retard TiSi2 growth.