Grooves a few nanometers wide can be formed on a Si(111) surface with a scanning tunneling microscope when the tip is above a critical voltage. This may provide a promising approach to nanodevice fabrication. The dependence of the critical voltage on tunneling current, tip polarity, and tip material was studied with silver, gold, platinum, and tungsten tips. The results are consistent with field emission of positive and negative silicon ions. The variation of critical voltage with current is explained quantitatively by a simple tunneling equation that includes the effect of the contact potential between tip and sample.

Zinc(ii)-quinoxaline complexes, [Zn(hqxc)(2)(py)(2)] and [Zn(hqxc)(2)(DMSO)(2)] (hqxc = 3-hydroxy-2-quinoxalinecarboxylate, py = pyridine, DMSO = dimethyl sulfoxide), were prepared and characterized by X-ray crystallography and fluorescence spectroscopy. In both complexes, the zinc ion is six-coordinated by two equatorial bidentate hqxc ligands with an intramolecular hydrogen bond and two axial monodentate ligands such as pyridine or DMSO. In spite of similar coordination geometries, there is a remarkable difference between their solid-state fluorescent properties. The pyridine complex is strongly fluorescent (fluorescence quantum yield Phi = 0.22), giving rise to a significantly Stokes-shifted spectrum. From its thin film photopumped by a nitrogen gas laser, amplified spontaneous emission was observed. These results suggest that the fluorescence occurs by way of excited-state intramolecular proton-transfer (ESIPT) in the hydrogen bond of hqxc. On the other hand, the DMSO complex shows fluorescent intensity (Phi = 0.08) lower than that of the pyridine complex, and shows normal emission in addition to ESIPT emission. From IR measurements for these complexes, it is concluded that axial ligands influence the hydrogen bond strength of the equatorial hqxc ligand via zinc and thus the ESIPT efficiency.

Electron impact multiple ionization relative cross sections of rare gas atoms (Ne, Ar, Kr and Xe) have been measured using a pulsed electron beam and a pulsed ion extraction combined with a time-of-flight analysis of the charge. The measurements cover a larger range of energies and charges than in earlier experiments, from threshold to 1 keV and from charge n = 1 to 4 (Ne), 5 (Ar), 7 (Kr) and 6 (Xe). The average number (γ) of electrons ejected from the atom per ionization event is calculated and used to evaluate the contributions of the inner-shell processes. The results are also compared with those in the case of photon impact. As regards the major ions produced, relative uncertainty as low as 1.3% for the ionization cross section ratios is achieved for all the sample gases, except near threshold. As for the γ-values, relative uncertainty is estimated to be as low as 1.2%.

In a scanning tunneling microscope (STM) operated in ultra-high vacuum, if we place a well-prepared W tip above the Si(111)-7×7 surface at a separation of ∼1 nm and apply an appropriate voltage pulse to it, we can extract a single Si atom from a predetermined position routinely at room temperature. The extracted Si atoms are redeposited onto the surface with a certain probability, their positions always being at a fixed crystallographic site. The redeposited Si atoms can be displaced intentionally to other crystallographically equivalent sites. In case of the Si(001)-2×1 surface, usually two Si atoms forming a dimer are extracted together. For both surfaces, Si atoms at crystallographically different sites including step edges are extracted with different probabilities. The microscopic mechanisms of these processes are discussed.

Using synchrotron radiation as a continuum light source, dissociative photoionization of CF 4 has been studied in the photon-energy region of 23-120 eV. Ion branching ratios were obtained by analyzing time-of-flight mass spectra and were converted to the absolute partial cross sections for the production of singly charged CF 3 ϩ , CF 2 ϩ , CF ϩ , F ϩ , and C ϩ ions, as well as doubly charged CF 3 2ϩ and CF 2 2ϩ ions by using the reported total absorption cross sections of CF 4 . Ion branching ratios were differentiated with respect to the incident photon energy. The results obtained by this analytical photoion spectroscopy clearly show dissociation pathways of the CF 4 ϩ and CF 4 2ϩ ions, many of which are observed for the first time in the present study. These pathways are discussed by comparing with the reported electronic states of the ions.