Nucleation of Ge clusters at high temperatures on Ge/Si(001) wetting layer

Difference in nucleation of Ge quantum dots during Ge deposition at low (< 600C) and high (> 600C) temperatures on the Si(001) surface is studied by high resolution scanning tunneling microscopy. Two process resulting in appearance of {105}-faceted clusters on the Ge wetting layer have been observed at high temperatures: Pyramids have been observed to nucleate via the previously described formation of strictly determined structures, resembling blossoms, composed by 16 dimers grouped in pairs and chains of 4 dimes on tops of the wetting layer M x N patches, each on top of a separate single patch, just like it goes on at low temperatures; an alternative process consists in faceting of shapeless heaps of excess Ge atoms which arise in the vicinity of strong sinks of adatoms, such as pits or steps. The latter process has never been observed at low temperatures; it is typical only for the high-temperature deposition mode.Comment: 13 pages, 4 figures; a revised versio

Synthesis and structure of methyltriphenylphosphonium dicyanodibromoaurate [Ph3PCH3] [Au(CN)2Br2]

Methyltriphenylphosphonium dicyanodibromoaurate (1) [Ph3PMe]+[Au(CN)2Br2]- was synthesized by the reaction of potassium dicyanodibromoaurate with methyltriphenylphosphonium bromide in an aqueous solution and was structurally characterized. The complex is a yellow-col-ored, air-resistant crystalline substance with a clear melting point. The structure of the compound was established by IR spectroscopy, NMR spectroscopy and X-ray diffraction analysis. An intense absorption band was observed in the IR spectrum of compound at 2220 cm-1, corresponding to the stretching vibrations of cyano groups. The absorption band of the deformation vibrations of the P-SPh bonds in the IR spectrum is at 1438 cm-1. In the recorded 1N, 13S, and 31R NMR spectra, signals are observed for the number, value of chemical shifts and integral intensity that do not contradict the proposed complex structure. The X-ray diffraction analysis of crystal 1 was carried out on a Bruker D8 QUEST diffractometer (MoKα radiation, λ = 0.71073 A, graphite monochrom-ator). [C21H18AuBr2N2P, M = 686.13, crystal system triclinic, space group P-1, a = 8.802(5), b = 8.989(5), c = 15.233(11) A, V = 1143.8(13) A3, Z = 2, μ = 10.002 mm-1, F(000) = 644, crystal size 0.41x0.30x0.22 mm]. According to the X-ray diffraction analysis (XRDA) data there are two types of centrosymmetric crystallographically independent monomeric dicyanodibromoaurate anions and methyltriphenylphosphonium cations in the crystal of compound MFDDA. The cations have a distorted tetrahedral configuration: the CPC angles equal 108.8(2)°-110.0(2)°, the P-S distances are 1.791(5)-1.800(5) A. All SAuC and BrAuBr trans-angles are 180.0° in the [Au(CN)2Br2]-an-ions. The Au-C distances in anions differ from each other and equal 2.040(7), 2.024(1), 1.991(2) A. These values are close to the sum of the covalent radii of atoms (2.03 A). The Au-Br bond lengths are equal to 2.4162(14), 2.4591, 2.474(5) A in dicyanodibromoaurate anions. Formation of the crystal structure occurs due to formation of weak N···N-S hydrogen bonds between cations and anions (2.68, 2.59, 2.38 A) and Br···N-S (3.03, 3.02 A). Complete tables of coordinates of atoms, bond lengths and valence angles are deposited at the Cambridge Crystallographic Data Centre. © 2020, Ivanovo State University of Chemistry and Technology.Ministry of Education and Science of the Russian Federation, Minobrnauka: 4.6151.2017/8.9South Ural State University is grateful for the financial support of the Ministry of Education and Science of the Russian Federation (grant No. 4.6151.2017/8.9)

Structure and peculiarities of the (8 x n)-type Si(001) surface prepared in a molecular-beam epitaxy chamber: a scanning tunneling microscopy study

A clean Si(001) surface thermally purified in an ultrahigh vacuum molecular-beam epitaxy chamber has been investigated by means of scanning tunneling microscopy. The morphological peculiarities of the Si(001) surface have been explored in detail. The classification of the surface structure elements has been carried out, the dimensions of the elements have been measured, and the relative heights of the surface relief have been determined. A reconstruction of the Si(001) surface prepared in the molecular-beam epitaxy chamber has been found to be (8 x n). A model of the Si(001)-(8 x n) surface structure is proposed.Comment: 4 pages, 8 figures. Complete versio