Two-dimensional electron-hole system in a HgTe-based quantum well

A two-dimensional electron-hole system consisting of light high-mobility electrons with a density of N _s = (4–7) × 10¹⁰ cm^?2 and a mobility of μ _n = (4–6) × 10⁵ cm²/V s and heavier low-mobility holes with a density of P _s = (0.7–1.6) × 10¹¹ cm^?2 and a mobility of μ _p = (3–7) × 10⁴ cm²/V s has been discovered in a quantum well based on mercury telluride with the (013) surface orientation. The system exhibits a number of specific magnetotransport properties in both the classical magnetotransport (positive magnetoresistance and alternating Hall effect) and the quantum Hall effect regime. These properties are associated with the coexistence of two-dimensional electrons and holes.     

Features of changes in the surface structure of K-208 glass under electron—proton irradiation

Changes in the surface structure of K-208 glass after single-time irradiation of its samples with 20-keV electrons and protons are studied using atomic-force microscopy. Irradiation is performed in a vacuum chamber under a pressure of 10^–4 Pa; the densities of the electron (? _e ) and proton (? _р ) fluxes are varied in the range of 10¹⁰–2.5 × 10¹¹ cm^?2 s^?1. Analysis of the samples irradiated in the case where the parameters ? _e and ? _р increased in a stepwise manner makes it possible to study the appearance, growth, and evolution of microscopic structures on their surfaces. The radiation-stimulated processes of defect annealing and the release and field diffusion of alkali metal ions are accompanied by crystallization of the irradiated glass layer, which gives grounds for the use of dislocation mechanisms for mass transfer in explaining the formation of microprotrusions on its surface. It is shown that the character of changes in the structure is determined by the values of the parameters ? _e and ? _р and the ratio between them. In particular, it is established that, in the case of electron— proton irradiation of the glass, electrostatic discharges begin to noticeably affect the formation of microprotrusions for ? _е > 3? _р .     

Lithium diffusion in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based electrodes: a joint analysis of electrochemical impedance,cyclic voltammetry,pulse chronoamperometry,and chronopotentiometry data

In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li₃V₂(PO₄)₃), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10^?9 and 3 × 10^?10 cm² s^?1, respectively, for transfer in the bulk and 10^?12 cm² s^?1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10^?10 and 0.9–5 × 10^?10 cm² s^?1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10^?10 cm² s^?1 for lithiated (at a potential of 3.5 V) and 2.3 × 10^?9 cm² s^?1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10^?11 cm² s^?1 for anodic and 3.4 × 10^?11 cm² s^?1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li₃V₂(PO₄)₃ electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.     

Optical Properties of Nonstoichiometric Tantalum Oxide TaO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> &lt; 5/2) According to Spectral-Ellipsometry and Raman-Scattering Data

Optical properties of amorphous nonstoichiometric tantalum-oxide films of variable composition (TaO_x, x = 1.94–2.51) in the spectral range of 1.12–4.96 eV, obtained by ion-beam sputtering-deposition of metallic tantalum at different partial oxygen pressures (0.53–9.09 × 10^–3 Pa), have been investigated. It is shown by spectral ellipsometry that the character of dispersion of the absorption coefficient and refractive index in TaO_x of variable composition suggests that light-absorbing films with dispersion similar to that in metals are formed at oxygen pressures in the growth chamber below 2.21 × 10^–3 Pa, whereas transparent films with dielectric dispersion are formed at pressures above 2.81 × 10^–3 Pa. According to the data of quantumchemical simulation, the absorption peak at a photon energy of 4.6 eV in TaO_x observed in the absorptioncoefficient dispersion spectrum is due to oxygen vacancy. The peak in the Raman-scattering spectra of TaO_x films with metallic dispersion at frequencies of 200–230 cm^–1 is presumably related to tantalum nanoclusters.     

Ionization mechanisms of aluminum acceptor impurity in silicon

Processes of ionization of shallow acceptor centers (ACs) in silicon are studied. In crystalline silicon samples with phosphorus (1.6×10¹³, 2.7×10¹³, and 2.3×10¹⁵cm^?3) and boron (1.3×10¹⁵cm^?3) impurities, _μAl impurity atoms were produced by implantation of negative muons. It is found that thermal ionization is the main mechanism for ionizing the Al acceptor impurity in both p-type and n-type silicon with an impurity concentration of ?10¹⁵cm^?3 at T>45 K. The thermal ionization rate of Al ACs in Si varies from ～10⁵ to ～10⁶s^?1 in the temperature range 45–55 K.     

Variation of potential energy surface height and bound state depth induced by laser phase along the reaction path in atom-molecule reactions: Application to Li + CH<Subscript>4</Subscript> → LiH + CH<Subscript>3</Subscript>

Laser atom-molecule reaction interaction through polarizability and dipole moment contribution leads to potential energy surface barrier reshaping and bound states along the reaction path. The polarizability is maximum in the transition state. We will show here by using gauge representation (electric field gauge) for wave length λ = 20.6 μm, intensity I = 1 × 10¹² W/cm², I = 5 × 10¹² W/cm², I = 1 × 10¹³ W/cm², I = 3 × 10¹³ W/cm², that we can create laser induced potential energy surface barrier reshaping in the transition state region (–1–0.5 a. u.). We illustrate such effects for the LiH + CH₃ ? Li + CH₄ reaction with a barrier using ab-initio methods for calculating the reaction path, polarizability and dipole moment contribution of the atom-molecule reaction.     

Plasma-volume generation of H<Superscript>−</Superscript> ions in a low-voltage xenon-hydrogen discharge. II

A low-voltage xenon-hydrogen discharge is considered theoretically at an interelectrode distance of L = 1 cm and cathode emission current densities of j _s = 2–20 A/cm². Basic parameters of the discharge plasma, in particular, the total hydrogen and xenon densities, are optimized to attain the maximum possible density of negative hydrogen ions \(N_{H^ - } (L)\) at the plasma-anode boundary. The distributions of the plasma parameters over the discharge gap are calculated for optimized regimes. According to calculations, at intermediate cathode emission current densities (j _s ≈ 5–10 A/cm²) in optimized discharge regimes, the density of negative hydrogen ions in the anode region of the plasma is \(N_{H^ - } (L)\) ≈ (1.5–2.5) × 10¹² cm^?3 and the total plasma pressure is p ₀ = 0.5–0.6 Torr.     

Single-electron charge transfer and excitations at collisions between Bi<Superscript>4+</Superscript> ions in the kiloelectronvolt energy range

Pioneering theoretical data for single-electron charge transfer and excitations due to collisions between Bi⁴⁺ ions in the ground (6s) and metastable (6p) states are gained in the collision energy interval 5–75 keV in the center-of-mass frame. The cross sections of the processes are calculated in terms of the close-coupling method in the basis of two-electron quasi-molecular states for the Coulomb trajectory of nuclei. It is found that single-electron capture into the singlet 6s ² states of Bi³⁺ ions makes a major contribution to the charge transfer total cross section for Bi⁴⁺(6s) + Bi⁴⁺(6s) collisions (reaction 1), whereas single-electron capture into the singlet 6s6p states is the basic contributor to the total cross section in Bi⁴⁺(6s) + Bi⁴⁺(6p) collisions (reaction 2). In the collision energy interval mentioned above, the collision cross sections vary between 1.2 × 10^?17 and 1.9 × 10^?17 cm² for reaction 1 and between 3.8 × 10^?17 and 5.3 × 10^?17 cm² for reaction 2. In reaction 1, the 6s → 6p excitation cross sections vary from 0.6 × 10^?16 to 0.8 × 10^?16 cm² for the singlet channel and from 2.2 × 10^?16 to 2.8 × 10^?16 cm² for the triplet channel. The calculation results are compared with the data obtained in experiments with crossed ion beams of kiloelectronvolt energy. The fraction of metastable ions in the beams is estimated by comparing the experimental data with the weighted average theoretical results for the cross sections of reactions 1 and 2. From the data for the charge transfer cross sections, one can estimate particle losses in relativistic beams due to a change in the charge state of the ions colliding with each other in the beam because of betatron oscillations.     

Study of the Influence of Implanted Atoms on the Coefficients of the Sputtering of Silicon and Silicon with a Thin Oxide Film

The results of theoretical and experimental studies of the influence of Ba-atom implantation and the presence of an oxide film on the Si-surface sputtering coefficient under ion bombardment are presented. It is shown that, in the dose range of D = 10¹⁴–5 × 10¹⁵ cm^—2, the Si sputtering coefficient increases linearly, then this increase decelerates, and is almost constant, starting from 10¹⁶ cm^–2. In the range of D = 5 × 10¹⁵–5 × 10¹⁶ cm^—2, the Ba sputtering coefficient increases sharply, which is explained by an increase in the Ba concentration in the surface layer during the ion bombardment process.     

Static and high-frequency hole transport in <Emphasis Type="Italic">p</Emphasis>-Si/SiGe heterostructures in the extreme quantum limit

Complex high-frequency (HF), σ^AC = σ₁ ? iσ₂, and static, σ^DC, conductivities, as well as current-voltage characteristics, have been measured in p-Si/SiGe heterostructures with a low hole density (p = 8.2 × 10¹⁰ cm^?2) at temperatures T = 0.3–4.2 K in the ultraquantum limit, when the filling factor is v < 1. In order to determine the components of the HF conductivity, the acoustic contactless method in the “hybrid configuration” is used, when the surface acoustic wave propagates on the surface of the LiNbO₃ piezoelectric and the heterostructure is pressed to the surface by a spring. The conductivities σ₁ and σ₂ are determined from the damping and velocity of the surface acoustic waves that are measured simultaneously with varying the magnetic field. The revealed HF conductivity features—σ₁ ? |σ₂|, the negative sign of σ₂, the threshold behavior of the current-voltage characteristic, and the dependence I ∝ exp(-A/V ^0.3) in the subthreshold region—indicate the formation of a pinned Wigner crystal (glass) in the ultraquantum limit (T = 0.3–0.8 K, B > 14 T).     

Spectroscopic diagnostics and electric field measurements in the near-cathode region of an atmospheric pressure microplasma jet

Linear Stark splitting of the H\(_{\beta}\) Balmer line components and spatially resolved optical emission spectroscopy (OES) measurements were used to estimate the electric field gradient in the cathode sheath region (~70 μm long) of an atmospheric pressure direct current argonflow-stabilized microplasma jet. Also, plasma parameters in the negative glow region were investigated by both OES and electrical diagnostics. The microplasma jet was operated for current ranging from 10 to 110 mA. OH (A² \({\rm\Sigma}^+\), v = 0 \(\to\) X ² \({\rm\Pi}\), v’ = 0) rotational bands at 306.357 nm and also the Ar 603.213 nm line were used to determine the gas temperature, which ranges from 600 to 1000 K. Electron number density, ranging from4.1 × 10¹⁴ to 8.5 × 10¹⁴ cm^-3, was determined through analysis of the H\(_{\beta}\) line.Electron excitation temperature was also measured from the ratio of two Mo lines (8500–18?000 K) and from Boltzmann-plot of Ar 4p–4s and 5p–4s transitions (11?000–13?500 K).     

Intercalation of graphene on iridium with samarium atoms

Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 10¹⁴ atoms cm^–2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 10¹⁴ atoms cm^–2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional “gas” and samarium islands and are desorbed in the range of temperatures of 1000–1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200–2150 K. Model conceptions for the samarium–graphene–iridium system in a wide temperature range are developed.     

Low-temperature thermal conductivity of tellurium-doped bismuth

Phonon thermal conductivities κ₂₂ (?T ‖ C1) and κ₃₃ (? T ‖ C₃) of tellurium-doped bismuth with an electron concentration in the range 1.8 × 10¹⁹ ≤ n_L ≤ 1.4 × 10²⁰ cm^?3 were studied in the temperature interval 2 < T < 300 K. The temperature dependence of the phonon thermal conductivity obtained on doped bismuth samples of both orientations exhibits two maxima, one at a low temperature and the other at a high temperature. The effect of various phonon relaxation mechanisms on the dependence of both phonon thermal conductivity maxima on temperature, impurity concentration, and electron density is studied.     

Crystal structure and magnetic susceptibility of (CuInSe<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(2MnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The crystal structure of samples in the (CuInSe₂)_{1 ? x} (2MnSe) _x system at room temperature and their magnetic susceptibility in the temperature range 77–1000 K are investigated. It is established that compositions with concentrations 0≤ x ≤ 0.2 form solid solutions with a tetragonal structure, space group I \(\bar 4\)2d (122). The specific magnetic susceptibility χ of samples with 0.1 ≤ x ≤ 0.4 at 77 K lies in the range 9 × 10^?4?1.6 × 10^t-3cm³/g. The temperature dependence of the inverse magnetic susceptibility of the sample with x = 0.4 suggests the presence of a component with antiferromagnetic ordering and a reliably measured Néel temperature that is characteristic of MnSe. The dependences χ = f(T) of the compositions with x = 0.1, 0.2, 0.3, and 0.4 indicate the occurrence of magnetic phase transitions with a change in the spin state.     

Lichtausbeute von α-Teilchen in kristallinem und dampfförmigem Anthrazen

The light output,S _v by α-particles stopped in anthracene vapour has been measured as a function of vapour pressure (10–700 mm Hg) and temperature (250°C–385°C). The comparison of the results for an idealised vapour neglecting collisions with the light output,S _c, from anthracene crystals by α-particles impinging parallel to thec′-axis yields the unexpected results: S_v(8.78 MeV)/S_c(8.78 MeV)=0.46±0.05 andS _v(6.05 MeV)/S _c(6.05 MeV)=0.57±0.08. A simple model assuming quenching by collisions of the vapour molecules could explain the observed dependence of the light output on the vapour pressure at fixed temperature. The path lengthsR _v of α-particles in anthracene vapour were determined to be R_v(8.78 MeV)=(9.0±0.6) mg/cm²,R _v(6.05 MeV)=(4.9±0.6) mg/cm² and the ratio of the light output by the two different α-energiesS _v(8.78 MeV)/S _v(6.05 MeV)=1.42±0.2.     

Absorption spectra of some radiation-doped A<Subscript>3</Subscript>B<Subscript>5</Subscript> compounds

Temperature dependences of the absorption coefficient in A₃B₅ crystals before and after irradiation by electrons with an energy of 6 MeV and a dose of Ф = 2 × 10¹⁷ electron/cm² are studied. A low-lying E_v + 0.4 eV center of a nonimpurity origin is found in both undoped GaAs crystals and those doped with various impurities (Te, Zn, Sn, Ga_1–xIn_xAs, InP, and InP〈Fe〉).     

Type III - Type I transition and strain-effect in Hg1−xCdxTeCdTe and Hg1−xZnxTeCdTe superlattices

In this paper, the results of Hg_1−xZn_xTeCdTe strained layer superlattices grown by MBE are reported, and compared to Hg_1−xCd_xTeCdTe superlattices. Both Type III and Type I Hg_1−xZn_xTeCdTe superlattices with different strain have been grown on CdTe(111)B/GaAs(100) and CdTe(100)/GaAs(100) substrates and characterized by electron, X-ray diffraction, infrared transmission and Hall measurements. The values of hole mobility between 5×10³ up to 2×10⁴cm²v⁻¹s⁻¹ at T = 23K along (111)B growth orientation and up to 4.9×10⁴cm²v⁻¹s⁻¹ at T = 5K along (100) growth orientation are obtained for Type III superlattices whereas in Type I superlattices, the hole mobility is between 200–300cm²v⁻¹s⁻¹. This drastic change in the hole mobility between Type III and Type I superlattices along with the role of the strain are discussed in this paper.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Reconstruction of the 2D hole gas spectrum for selectively doped <Emphasis Type="Italic">p</Emphasis>-Ge/Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>ix</Subscript> heterostructures

The magnetic field (0≤B≤32 T) and temperature (0.1≤T≤15 K) dependences of longitudinal and Hall resistivities have been investigated for p-Ge_0.93Si_0.07/Ge multilayers with different Ge layer widths 12≤d _w ≤20 nm and hole densities p _s =(1–5)×10¹⁵ m^?2. An extremely high sensitivity of the experimental data (the structure of magnetoresistance traces, relative values of the inter-Landau-level gaps deduced from the activation magnetotransport, etc.) to the quantum well profile is revealed in the cases where the Fermi level reaches the second confinement subband. An unusually high density of localized states between the Landau levels is deduced from the data. Two models for the long-range random impurity potential (the model with randomly distributed charged centers located outside the conducting layer and the model of the system with a spacer) are used to evaluate the impurity potential fluctuation characteristics: the random potential amplitude, the nonlinear screening length in the vicinity of integer filling factors v=1 and v=2, and the background density of states (DOS). The described models are suitable for explanation of the observed DOS values, while the short-range impurity potential models fail. For half-integer filling factors, a linear temperature dependence of the effective quantum Hall effect plateau-plateau (PP) transition widths v₀(T) is observed, contrary to the expected scaling behavior of the systems with short-range disorder. The finite T→0 width of the PP transitions may be due to an effective low-temperature screening of a smooth random potential due to the Coulomb repulsion of electrons.     

Studies on structural and electrical properties of Mg<Subscript>0. 5+y</Subscript> (Zr<Subscript>2-y</Subscript>Fe<Subscript>y</Subscript>) <Subscript>2</Subscript> (PO<Subscript>4</Subscript>) <Subscript>3</Subscript> ceramic electrolytes

The sample of Mg_{0. 5+y} (Zr_1-y Fe_y) ₂ (PO₄) ₃ (0.0 ≤y ≤0.5) was synthesized using the sol-gel method. The structures of the samples were investigated using X-ray diffraction and Fourier transform infrared spectroscopy measurement. XRD studies showed that samples had a monoclinic structure which was iso-structured with the parent compound, Mg_0.5Zr (PO₄) ₃. The complex impedance spectroscopy was carried out in the frequency range 1–6 MHz and temperature range 303 to 773 K to study the electrical properties of the electrolytes. The substitutions of Fe³⁺ with Zr⁴⁺ in the Mg_0.5Zr (PO₄) ₃ structure was introduced as an extrainterstitial Mg²⁺ ion in the modified structured. The compound of Mg_0.5+y (Zr_1-y Fe_y)₂(PO₄)₃ with y?=?0.4 gives a maximum conductivity value of 1.25?×?10^?5 S cm^?1 at room temperature and 7.18?×?10^?5 S cm^?1 at 773 K. Charge carrier concentration, mobile ion concentration, and ion hopping rate are calculated by fitting the conductance spectra to power law variation, σ _ac (ω)?=?σ _o ? +?Aω ^α . The charge carrier concentration and mobile ion concentration increases with increase of Fe³⁺ inclusion. This implies the increase in conductivity of the compounds was due to extra interstitial Mg²⁺ ions.