Vibrational modes induced by a pair of impurities

Presence of a polarizable impurity atom in an ionic crystal induces a localized vibrational mode of the lattice. The frequency of the mode is distinct from the propagating modes of the pure crystal. It is shown in this paper that the frequency of the mode depends on the polarizability of the impurity atom and on the distance of separation between two adjacent impurities.     

Anomalous temperature dependence of the band gap in AgGaSe2 and AgInSe2

The lowest band gaps of AgGaSe₂ and AgInSe₂ single crystals in the temperature range from 90 to 300 K were determined from photoconductivity measurements. Below (above ≈ 120 K in AgInSe₂ and ≈ 125 K in AgGaSe₂ the temperature coefficient of the band gap is +5 × 10⁻⁴ eV/K (−1.5 × 10⁻⁴ eV/K) and +1.1 × 10⁻⁴ eV/K (−4.28 × 10⁻⁴ eV/K), respectively. The positive value is explained with the lattice dilation effect being the dominant mechanism for the band gap variation at the temperatures less than ≈ 120–125 K.     

Surface layer relaxation on Mo(111) measured by low energy alkali ion scattering

The surface of clean Mo(111) has been studied using Li⁺ ion scattering at 1000 eV. The dependence of single scattering intensity was measured as a function of incident polar angle in the [12̄1] and the [21̄1̄] azimuths for various total scattering angles. Very pronounced intensity cut-offs are observed and are readily assignable to shadowing and blocking effects in scattering from first, second or third layer atoms. After taking certain precautions to avoid interference from deeper layers, the measured positions of the features yield the first-second layer spacing which is found to be strongly contracted by (18 ± 2)% compared to the bulk spacing. The method also indicates that the second-third layer spacing is possibly expanded (4 ± 4)%, but this result is uncertain due to possible contributions from deeper layers which make this value an upper limit of the layer spacing. The physical implications of these results and the uncertainties in the technique are discussed.     

Darstellung und NMR-spektroskopische charakterisierung einiger di-n-alkyl- und n-alkylaryl-chlorphosphane

A series of di-n-alkyl and n-alkylaryl chlorophosphines has been prepared by the reaction of tetraorganodiphosphines with chlorodiphenyl or dichlorophenyl phosphine and characterized by ³¹P and ¹³C NMR spectra.     

Trihydridoruthenium(IV) complexes: preparation and photo-induced H/D exchange reaction

The trihydrides (η⁵-C₅Me₅RuH₃(PR₃ = PMe₃, FEt₃, Pipr₃, PCy₃, PPh₂Me, and PPh₃) (2) are formed in the reaction of paramagnetic (η⁵C₅Me₅)RuCl₂(PR₃) (1) with NaBH₄ in ethanol. The reaction of 1 with NaBH₄, in THF yields intermediary tetrahydroborate complexes (η⁵-C₅Me₅)Ru(PR₃)(BH₄) (3), which are converted to the trihydrides 2 by treatment with ethanol. Irradiation of 2c and 2f in C₆D₆ solution with UV light causes H/D exchange reaction among the solvent, hydride ligands, and the coordinated phosphine.     

5-germaspiro[4.4]nona-2,7-dienes

A novel series of bicyclic organogermanium derivatives: 5-germaspiro[4.4]nona-2,7-dienes have been prepared by reaction of 1,1-dihalogermacyclopent-3-enes with the appropriate conjugated diene and an alkali metal in a suitable organic solvent. The best results were obtained by using 1,1-dichlorogermacyclopentenes with isoprene or 2,3-dimethylbutadiene and lithium in 5/1 ether/tetrahydrofuran. Except for 2,3,7,8-tetramethyl-5-germaspiro[4.4]nona-2,7-diene, which is crystalline, the 5-germaspirononadienes are colourless liquids, which distil without decomposition under reduced pressure but which slowly polymerize on standing. In the mass spectra of all the spiradienes, the main peak corresponds to the loss of one ring, the less substituted in the case of unsymmetrical molecules. Attempts to obtain 5-germaspiro[4.4]nona-2,7-diene were unsuccessful.     

Theoretical discussion of the scanning tunneling microscope applied to a semiconductor surface

A free-electron model that we recently developed for a metal-metal microscope is extended to the case of a semiconducting sample. The probe, biased positive with respect to the sample, is taken to be a free-electron metal in the shape of a plane with a hemispherical projection. The sample, its surface being a parallel plane, is assumed to have spherical energy bands. The penetration probability is assumed to be the WKB result along the central axis using a potential energy which includes multiple image effects. We calculate current versus voltage curves at several electrode spacings for a tungsten/silicon combination.