Weak antilocalization in thin films of the Bi<Subscript>2</Subscript>Te<Subscript>2.7</Subscript>Se<Subscript>0.3</Subscript> solid solution

A technology has been developed for the preparation of thin films of the Bi₂Te_2.7Se_0.3 solid solution through the thermal evaporation in a vacuum using the “hot-wall” method. The high quality of the thin films thus prepared has been confirmed by the X-ray diffraction and Raman scattering data. The electron transport has been investigated over wide ranges of temperatures (1.4–300 K) and magnetic fields (up to 8 T). It has been assumed that the observed weak antilocalization is associated with the dominant contribution from the surface states of a topological insulator. The dephasing length has been estimated.     

High-Temperature Exciton Photoconductivity of Ge1 – xNdxS Crystals

Crystallography Reports - The spectral dependences of photoconductivity in a wide temperature range (T = 80–300 K) of layered GeS single crystals, both intentionally undoped and Nd-doped,...     

Polymorphic transformation in TlSe and the electrical properties of phases

Alloys in the TlSe-Se system on the side of the TlSe compound in the phase diagram have been investigated using differential thermal, X-ray powder diffraction, and microstructural analyses. The phase diagram of the system has been constructed, and the temperature dependences of the electrical conductivity of the phases obtained have been examined. An analysis of the thermograms of alloys in the (TlSe)_0.96-Se_0.04 system has revealed a structural phase transition at a temperature of 470 ± 1 K. Investigations into the temperature dependences of the electrical conductivity in the range 120–450 K have demonstrated that the temperature dependence of the electrical conductivity for the (TlSe)_0.96-Se_0.04 alloy exhibits metallic behavior.     

Weakening of amide conjugation with a nitrogen atom included in a four-membered ring

The barriers to amide rotation about the N-N bond in 1-nitrosoazetidine, dimethylnitrosamine, 1-formylazetidine, 1,1-carbonylbisazetidine, 1-dimethylcarbamoylazetidine, and dimethylformamide were measured by dynamic NMR spectroscopy. 1,1-Carbonylbisazetidine and 1-dimethylcarbamoylazetidine, the structures of which were confirmed by data from the PMR and ¹³C NMR spectra, were obtained.Translated from Khimiya Geterotsiklicheskikh Soedenenii, No. 7, pp. 912–194, July, 1987.     

Features of the kinetics of electrical damage of polymers

The kinetics of electrical damage (breakdown) of polymer films 20–50 μm thick in a constant-sign field of 0.5–0.6 GV/m at 77–300 K has been studied. At elevated temperatures (250–300 K), the exponential temperature dependence of the durability and the above-barrier thermal-fluctuation mechanism of electron emission from traps, i.e., space charge accumulation leading to breakdown, take place. At low temperatures (77–200 K), there are separate local decreases in the durability (minima) at the athermal durability level. The identity of the temperatures of durability minima and measured thermoluminescence maxima of polymers was found. A conclusion is made about the mechanism of thermally stimulated tunneling (subbarrier emission) of electrons from traps.     

Effect of mechanical loading on the electrical durability of polymers

A decrease in the electrical durability, which is defined as an amount of time required for dielectric breakdown at a constant electric field strength, of polyethylene and Lavsan (polyethylene terephthalate) films under tensile loading is registered in a temperature range from 100 to 300 K. It is established that the pulling apart of the axes of neighbor chain molecules in consequence of tensile loading gives rise to a decrease in the energy level of the intermolecular electron traps. In the amorphous region of a polymer, this accelerates the release of electrons from the traps through over-barrier transitions at higher temperatures ranging from about 230 to 350 K and quantum tunneling transitions at lower temperatures in the range from about 80 to 200 K. As a result, the time required for the formation of a critical space charge, i.e., the waiting period of dielectric breakdown, decreases, which means a reduction in the electrical durability of polymers.

     

Synthesis of functional poly(amino acids) on cyclophosphazene templates

With the use of hexakis(p-aminophenoxy)cyclotriphosphazene and tetraphenyltetraaminocyclotetraphosphazene whose primary groups initiated the polymerization of L-α-alanine and γ-esters of L-α-glutamic acid n-carboxyanhydrides, poly(amino acids) containing an inorganic central ring have been prepared. Polypeptide chains of various lengths have been obtained by variation of the monomer-to-initiator molar ratio. The molecular masses of the synthesized samples are in good agreement with the calculated parameters, and the polymers show a narrow molecular-mass distribution (M _w /M _n < 1.3). The circular dichroism (CD) spectra and IR studies indicate a predominantly helical conformation of poly(amino acid) chains with the central triphosphazene ring and the disordered structure of poly(amino acid) chains bonded to cyclotetraphosphazene.     

Poly(amino acid) derivatives of cyclotriphosphazene with luminescent fragments

Poly(amino acid)s with a central triphosphazene cycle and a peripheral pyrene moiety were synthesized from hexakis(4-aminophenoxy)cyclotriphosphazene and 1-pyrenebutanoic acid and have been characterized. The introduction of the luminophore resulted in the formation of highly ordered structures containing fragments with three α helices in the trans position to the phosphazene cycle. The character of luminescence spectra suggests the presence of pyrene dimers; their appearance may be associated with the intermolecular aggregation of peptide chains with chromophore end groups. The DSC data revealed the glass transition due to the freezing out of the mobility of side chains, as well as an alteration in the helix type of the poly(amino acid) fragments.     

Chiroptical properties of the nonplanar amide chromophore in n-acylaziridines

The optically active 1-acyl-substituted (1R,2R)-2-methyl- and (1R,2S)-2-methoxycarbonylaziridines were synthesized. The nonplanarity of the amide chromophore in them and its high conformational mobility, which was caused by the rotation around the N-C(O) bond, were shown on the basis of the investigation of the CD spectra and the calculations of simple models by the MNDO method. The possible correlation of the sign of the Cotton effect of the long-wave p-* transition with the intrinsic chirality of the chromophore was studied.Communication 64 in the series Asymmetric Nitrogen, for Communication 63, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 41–47, January, 1989.