Ab Initio Calculations of New α-L5-7a and β-L5-7a Graphyne Polymorphic Varieties

Calculations of the structural and energy parameters, band structure and density of electronic states of new structural varieties of graphyne have been performed by the density functional theory method. The initial structure of the nine polymorphs was theoretically constructed on the basis of the 5-7a graphene layer. As a result of the calculations, the structure of only five graphyne layers was found to be stable: α-L5-7a, β1-L5-7a, β2-L5-7a, β3-L5-7a and β4-L5-7a. The structure of layers γ1-L5-7a, γ2-L5-7a, and γ3-L5-7a is transformed into the structure of graphene layers by geometric optimization, and the graphyne layer γ4-L5-7a is transformed sp+sp2 layer L3-6-13. The sublimation energy of the stable graphyne polymorphs varies from 6.66 to 6.78 eV/atom. The density of electronic states at the Fermi energy level for all α-L5-7a and β-L5-7a layers of graphyne is different from zero, so the new graphyne polymorphs should have metallic properties.

Holey Graphene: Topological Control of Electronic Properties and Electric Conductivity

This paper studies holey graphene with various neck widths (the smallest distance between two neighbor holes). For the considered structures, the energy gap, the Fermi level, the density of electronic states, and the distribution of the local density of electronic states (LDOS) were found. The electroconductive properties of holey graphene with round holes were calculated depending on the neck width. It was found that, depending on the neck width, holey graphene demonstrated a semiconductor type of conductivity with an energy gap varying in the range of 0.01–0.37 eV. It was also shown that by changing the neck width, it is possible to control the electrical conductivity of holey graphene. The anisotropy of holey graphene electrical conductivity was observed depending on the direction of the current transfer.

Электронные и теплофизические свойства газовых гидратов: результаты моделирования из первых принципов

The results of an ab-initio molecular dynamics study of the electronic and thermophysical properties of methane hydrate with a cubic sI structure are presented. Good agreement of the simulation results for heat capacity at constant volume and density with experimental data is found. Based on the analysis of the density of electronic states, the temperature dependences of the electronic properties of methane hydrate, including the Fermi energy level, width and boundaries of the band gap are determined. For the empty framework of the hydrate (water clathrate framework), the electron energy spectra E(k) were calculated along the directions M-X, X-G, G-M, and G-R. It was found that the presence of CH4 molecules in an aqueous clathrate leads to an increase in the Fermi energy of the hydrate from 2.4 to 3.0 eV.

Электронная структура и оптические спектры соединений GdFeAl и GdFeSi

Results of investigations of electronic structure and optical properties of GdFeAl and GdFeSi compounds are presented. Spin-plarized density of states and interband optical conductivity spectra were calculated in frame of DFT+U technique with a correction for strong correlation effects in 4f shell of Gd. Optical properties were measured by ellipsometric technique in wavelength interval of 0.22 – 16 μm. Nature of quantum light absorption is discussed on the base of comparative analysis of experimental and calculated spectra. It is shown that main features of frequency dependencies of the optical conductivity are interpret qualitatively by the calculated density of electronic states.

Anomalous Properties of the Dislocation-Free Interface between Si(111) Substrate and 3C-SiC(111) Epitaxial Layer

Thin films of single-crystal silicon carbide of cubic polytype with a thickness of 40–100 nm, which were grown from the silicon substrate material by the method of coordinated substitution of atoms by a chemical reaction of silicon with carbon monoxide CO gas, have been studied by spectral ellipsometry in the photon energy range of 0.5–9.3 eV. It has been found that a thin intermediate layer with the dielectric constant corresponding to a semimetal is formed at the 3C-SiC(111)/Si(111) interface. The properties of this interface corresponding to the minimum energy have been calculated using quantum chemistry methods. It has turned out that silicon atoms from the substrate are attracted to the interface located on the side of the silicon carbide (SiC) film. The symmetry group of the entire system corresponds to P3m1. The calculations have shown that Si atoms in silicon carbide at the interface, which are the most distant from the Si atoms of the substrate and do not form a chemical bond with them (there are only 12% of them), provide a sharp peak in the density of electronic states near the Fermi energy. As a result, the interface acquires semimetal properties that fully correspond to the ellipsometry data.

Электронная структура и оптические свойства соединения FeAl-=SUB=-2-=/SUB=-

Electronic structure and optical properties of the FeAl2 intermetallic compound are investigated. Spin-polarized calculations of the electronic structure were carried out, magnetic moments of the atoms were determined. Optical properties of the compound were measured by ellipsometric technique in spectral interval 0.22 – 15 μm. It is shown that the experimental optical conductivity is satisfactory interpreted on the base of the calculated density of electronic states.

INFLUENCE OF ULTRASONIC ACTION ON THE RATE OF CHARGE FORMATION OF THE INVERSION LAYER IN METAL-GLASS-SEMICONDUCTOR STRUCTURES

Исследовано влияние ультразвукового воздействия на плотность электронных состояний, локализованных на межфазной границе раздела Si-стекло. Предложена методика определения величин скорости поверхностной и объемной генерации носителей заряда, на основе расчета временной зависимости ширины области пространственного заряда (ОПЗ) и сравнении её с экспериментальной зависимостью. Ультразвуковая обработка структур Al-n-Si стекло Al, частотой 2.5 мГц мощностью 0.5 Вт, в течение 40 минут приводит к уменьшению скорости формирования заряда инверсионного слоя. Это обусловлено уменьшением интегральной плотности электронных состояний, локализованных на межфазной границе раздела полупроводник-стекло, при этом энергетический спектр объемных электронных состояний в полупроводнике не меняется. The effect of ultrasonic action on the density of electronic states localized at the Si-glass interface is studied. A method is proposed for determining the surface and volume generation rates of charge carriers using the calculated time dependence of the space charge region width (SCR) when comparing it with the experimental dependence. Ultrasonic treatment of Al-n-Si glass Al structures with a frequency of 2.5 MHz and a power of 0.5 W for 40 minutes leads to a decrease in the rate of charge formation of the inversion layer. This is due to a decrease in the integral density of electronic states localized at the semiconductorglass interface and does not affect the energy spectrum of bulk electronic states in asemiconductor.

Investigation of Electronic Structure of Zr1-xVxNiSn Semiconductive Solid Solution

The peculiarities of electronic and crystal structures of Zr1-xVxNiSn (x = 0 - 0.10) semiconductive solid solution were investigated. To predict Fermi level εF behavior, band gap εg and electrokinetic characteristics of Zr1-xVxNiSn, the distribution of density of electronic states (DOS) was calculated. The mechanism of simultaneous generation of structural defects of donor and acceptor nature was determined based on the results of calculations of electronic structure and measurement of electrical properties of Zr1-xVxNiSn semiconductive solid solution. It was established that in the band gap of Zr1-xVxNiSn the energy states of the impurity donor εD2 and acceptor εA1 levels (donor-acceptor pairs) appear, which determine the mechanisms of conduction of semiconductor.