A plasma resonance study of valley transfer in (001) Si inversion layers

We observed the two-dimensional plasmons of the two-component electron plasma in the (001) Si-inversion layer resulting from simultaneous population of the [001] valley, E₀, and the [010] valley, E₀′, subbands under a compressional uniaxial stress along [010]. Our data show an onset of electron transfer from E₀ to E₀′ at X = (1.4 ± 0.1) kbar for n = 1.67 × 10¹² cm^?2 and X = (1.2 ± 0.2) kbar for n = 2.60 × 10¹² cm^?2, consistent with the theory of Takada and Ando that includes the electron-electron correlation effects.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

Parameters of the cathode spot upon field emission

This work is devoted to studying the parameters of the cathode spot of a vacuum arc. According to calculations under conditions of autoelectronic emission, the temperature of the cathode spot is T _n = (1–2.5) × 10³ K, the electric-field strength is E = (1–6) × 10⁷ V cm^?1, and the current density in the spot is j _n = (0.15–3) × 10⁷ A cm^?2. The values of the cathode-spot parameters for cathodes of different materials are obtained and the type of electron emission is determined.     

The average structure of 5.10-Dihydro-5.10-Diethylphenazinium-Iodide (E2P·I1.6): A new linear chain Polyiodide compound

Upon oxidation of 5.10-dihydro-5.10-diethylphenazine (E₂P) with iodine golden-green lustrous crystals of a compound with stoichiometry E₂P.I_1.6 were isolated. The compound crystallizes in the tetragonal space group D₄² with $\text{a = 12.321(2)}\text{A}\text{?}$ and $\text{c = 5.330(2)}\text{A}\text{?}$. The E₂P and I form interpenetrating incommensurate sublattices along c, with an iodine repeat distance of 9.7 Å. Static susceptibility measurements at room temperature give χ_g = + 0.994 × 10^?6g^?1 × cm³. This corresponds to one unpaired electron spin per two formular units. Single-crystal EPR indicates that the paramagnetism is associated with weakly interacting E₂P⁺ cation radicals. The 300K-d.c. conductivity of 3×10^?2Ω^?1cm^?1 and activation energy of 0.17±0.02eV for single crystals is consequently associated with the polyiodide chains, and not with the E₂P⁺ cation radicals.     

EPR and Optical Absorption Study of Cr3+-Doped Dipotassium Tetrachloropalladate

X-band electron paramagnetic resonance (EPR) study of Cr³⁺-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr³⁺ ion-doped DTP for site I are: g _x  = 2.096 ± 0.002, g _y  = 2.167 ± 0.002, g _z  = 2.220 ± 0.002, D = (89 ± 2) × 10^?4 cm^?1, E = (16 ± 2) × 10^?4 cm^?1. EPR study indicates that Cr³⁺ ion enters the host lattice substitutionally replacing K⁺ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm^?1, C = 2,861 cm^?1), cubic crystal field splitting parameter (Dq = 1,851 cm^?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.     

Diffusion of hydrogen and deuterium on the (111) plane of tungsten

The diffusion of ¹H and ²H on the (111) plane of a W field emitter has been studied by the fluctuation method at various coverages. Both activated and unactivated diffusion is observed; the latter shows very little isotope effect, suggesting that coupling to the substrate is so strong that mass renormalization makes the effective masses of ¹H and ²H nearly identical. Values of D in the tunneling, i.e. temperature independent, regime are 10^?13?5 × 10^?14 cm²/s depending on coverage. For activated diffusion at high coverages, corresponding to population of the β₁ state E = 2.4?3.2 kcal/mol and D₀ = 2 × 10^?8 ?5 × 10^?7 cm²/s, depending on coverage. For lower coverages, corresponding to β₂ population, E = 7–9 kcal/mol, D₀ = 9 × 10^?6 ?2 × 10^?3 cm²/s, again depending on coverage. Similar values are obtained for ²H, with E and D₀ values slightly reduced. An exponentially decaying correlation signal for clean W was also seen and interpreted in terms of flip-flop of W atoms.     

Line strengths,spin-splittings,and forbidden transitions in the (101) band of 14N16O2

Measurements of line strengths in the (101) and (111)-(010) bands of ¹⁴N¹⁶O₂ have been made at a resolution of 0.02 cm^?1 in the region 2863 to 2934 cm^?1. The strength data in the (101) band were analyzed to determine a vibrational band strength and coefficients of the F factor. Each subband for K_?1 ≤ 9 was analyzed separately and all the F-factor coefficients in terms of the rotational quantum number, N, were found to be too small to be of significance. However, F was found to be dependent on K_?1 and the experimentally determined subband strengths were least-squares fitted to the expression S_v⁰·F, where S_v⁰ = 68.3 cm^?2 atm^?1 at 296 K and F = 1 + (2.899 × 10^?3)K_?1 + (4.08 × 10^?3)K_?1² ? (2.34 × 10^?4)K_?1³. The integrated strengths for the (101) and (111)-(010) bands were found to be 70.9 ± 2.3 and 2.7 ± 0.3 cm^?2 atm^?1 at 296 K, respectively. Also included in this study are measurements of line center positions in the two bands and spin-splittings in the (101) band. Recent frequency measurements of lines with K_?1 ≤ 8 in the (101) band have been made at a resolution of 0.0033 cm^?1 by V. Dana and J. P. Maillard (J. Mol. Spectrosc.71, 1–4) (1978)) for the region above 2889 cm^?1 and our values are in excellent agreement with theirs. Separations of the split lines measured in this work (K_?1 ≤ 10) agree well with calculated values using expressions which include the η_aaaaK_?1⁴ term with η′_aaaa = ?1.70 ± 0.15 × 10^?4 cm^?1 as derived for the (101) state. Three forbidden (ΔN ≠ ΔJ, ΔK_?1 = 0) transitions in the (101) band were observed with their identifications based on the agreement between measured and calculated line positions and strengths.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

Absolute coverage and isostemc heat of adsorption of deuterium on Pt(111) studied by nuclear microanalysis

The absolute coverage (θ) of deuterium adsorbed on Pt(111) in the ranges 180< T<440 K and 5 × 10^?6 < P < 5 × 10^?2 Pa D₂ has been determined by nuclear microanalysis using the D(³He, p)⁴He reaction. From these data, the isosteric heat of adsorption (E_a) has been determined to be 67 ± 7 kJ mol^?1 at θ ? 0.3. This heat of adsorption yields values of the pre-exponential for desorption (10^?5 to 10^?2 cm² atom^?1 s^?1) that lie much closer to the normal range for a second order process than those determined from previous isosteric heat measurements. The E_a versus θ relationship indicates that the adsorbed D atoms are mobile and that there is a repulsive interaction of 6–8 kJ mol^?1 at nearest neighbour distances. At 300 K the coverage decreases to ? 0.05 monolayer (? 8 × 10¹³ D atoms cm^?2) as P→ 0, apparently invalidating a recent model of site exchange in the adsorbed layer.     

Deep levels in gallium arsenide by capacitance methods

The three capacitance methods, i.e., TSCAP, PHCAP, and transient capacitance measurements, are applied to determine electronic properties of deep levels inn-GaAs. In the boat-grown wafer detected are the 0.30 eV electron trap withN _T =3.6×10¹⁶ cm^?3 andS _n =2.4×10^?15 cm², and the 0.75 eV electron trap withN _T =2.0×10¹⁶ cm^?3 andS _n =1.2×10^?14 cm². In the epitaxial wafer, the 0.45 eV hole trap is detected withN _T >1.5×10¹³ cm^?3 andS _p =1.4×10^?14 cm² as well as the 0.75 eV electron trap withN _T =2.4×10¹³ cm^?3.     

Hopping conductivity of carbynes modified under high pressures and temperatures: Galvanomagnetic and thermoelectric properties

The conductivity, thermopower, and magnetoresistance of carbynes structurally modified by heating under a high pressure are investigated in the temperature range 1.8–300 K in a magnetic field up to 70 kOe. It is shown that an increase in the synthesis temperature under pressure leads to a transition from 1D hopping conductivity to 2D and then to 3D hopping conductivity. An analysis of transport data at T ≤ 40 K makes it possible to determine the localization radius a ～ (56?140) Å of the wave function and to estimate the density of localized states _g(E _F) for various dimensions d of space: _g(E _F) ≈ 5.8 × 10⁷ eV^?1 cm^?1 (d=1), _g(E _F) ≈5×10¹⁴ eV^?1 cm ^?2 (d=2), and _g(E _F)≈1.1×10²¹ eV^?1 cm_?3 (d=3). A model for hopping conductivity and structure of carbynes is proposed on the basis of clusterization of sp ² bonds in the carbyne matrix on the nanometer scale.     

Small-angle neutron scattering study of radiation defects in synthetic quartz

The superatomic structure of synthetic quartz single crystals with dislocation densities ρ = 54 and 570 cm^?2 was studied in the initial state and after irradiation with fast neutrons with energies E _n > 0.1 MeV in a WWRM reactor (St. Petersburg Nuclear Physics Institute) in the fluence range F = 0.2 × 10¹⁷?5.0 × 10¹⁸ neutrons/cm². Weak irradiation with F = 0.2 × 10¹⁷ neutrons/cm² causes only slight structural changes, whereas appreciable generation of defects with radii of gyration r _g ～ 1–2 nm and R _G ～ 40–50 nm occurs at F = 7.7 × 10¹⁷?5.0 × 10¹⁸ neutrons/cm². As the fluence increases further, the number and volume fraction of point defects, as well as extended (channels ～2 nm in radius) and globular (amorphous phase nuclei) defects, increase.     

Inverse Raman spectrum of the ν1-fundamental of CF4

We have obtained fully resolved spectra of the ν₁ (Q-branch) band of CF₄ at a pressure of 4 Torr using a variation of stimulated Raman spectroscopy. With an experimental resolution of ≤0.004 cm^?1, no detectable tensor splitting of the rotational levels exists up to J = 55. The spectrum is readily fit with a band origin α = 909.0720 cm^?1 and a single rotational term β ? β₀ = ?3.417 × 10^?1cm^?1. We have also observed an underlying hot band, which we tentatively assign as the ν₁ + ν₂ ← ν₂ transition, with α′ = 909.1997 cm^?1 and (β ? β₀)′ = ?3.405 × 10^?4cm^?1.     

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.     

Ionic conductivity of Zr1−xIn2xO2−x

As x in Zr(In)O_2?x is increased from 0.08 to 0.16 (9–19 mole per cent In₂O₃) the activation energy E(x) for ionic conduction increases from 1.05 to 1.51 eV; the concuctivity decreases from 2 × 10^?5 to 3 × 10^?6Ω^?1cm^?1at 400°C, is composition-independent at about 580°C, and increases from 1 × 10^?2 to 4 × 10^?2Ω^?1cm^?1 at 800°C. The pre-exponential term of the Boltzmann-type conductivity equation depends exponentially on E(x), a much stronger dependence on x than theoretically expected with a model for ionic conductivity that includes nearest-neighbor defect interactions. Analysis of reported conductivity data for Zr(M)O_2?x (M = Sc, Y, Ca and rare earth metals) and other doped oxide electrolytes with fluorite-type structure reveals that the same relationship is observed with these materials when x γ0.08. It is shown that ionic conduction in these oxides is consistent with nearest neighbor vacancy-cation defect interaction forx < 0.08 but that an additional complex interaction with composition-dependent free energy ΔG(x) occurs when xγ 0.08.The lattice constant of Zr(In)O_2?x with the cubic fluorite-type structure is independent of composition, 5.114 ± 0.002 Å, in agreement with ionic size considerations.     

Spectroscopy of the electron subbands on (1 1 1)-Si

We present measurements of infrared inter-subband absorption for electron subbands on (1 1 1)-Si for densities N_s up to ～ 10¹³ cm^?2 at 4.2 K for both parallel- and perpendicular-excitation geometries. Contrary to previously published work the depolarization shift is identified as a sizeable splitting of the resonance energies E^⊥₀₁ and E^z.dfnc;₀₁. The comparison with a recent calculations is given.     

Energy levels of n-channel accumulation layer on InP surface

Electronic structure of the low lying quantized subbands is calculated for the electron accumulation layer on InP (100) system in a metal-insulator-semiconductor (MIS) structure. Hartree self-consistent technique at an arbitrary temperature has been used, neglecting many-body effects. In contrast to Si MIS system, a second subband is found to be populated even at low temperatures and moderate densities. Excitation energy, E₁₀, is found to be about 30–40 meV in the temperature range 0–300 K at an electron density of 10¹² cm^?2.     

Vibrational spectra and force constants of symmetric tops: High-resolution spectra of H374Ge35Cl in the ν1ν4 region near 2100 cm−1

The gas-phase infrared spectrum of monoisotopic H₃⁷⁴Ge³⁵Cl has been studied in the ν₁, ν₄ region near 2100 cm^?1 with a resolution of 0.008 cm^?1. Rotational fine structure for ΔJ = ±1 branches has been resolved for both fundamentals. ν₁ (a₁), 2119.977 03(19) cm^?1; and ν₄ (e), 2128.484 65(8) cm^?1 are weakly coupled by Coriolis x,y resonance, Bξ_1,4^y 2.6 × 10^?3 cm^?1, and l-type resonance within ν₄, q₄⁽⁺⁾ ?8.4 × 10^?6 cm^?1, has been observed. An extended Fermi resonance with ν₅^±1 + 2ν₆^±2, which mainly affects the kl = ?14 and ?15 levels of ν₄, has been detected and analyzed. In addition, several weak and local resonances perturb essentially every K subband of ν₄ and some of ν₁, and a qualitative model is proposed to account for the features observed in the spectrum. Disregarding the transitions involved in local perturbations, the rms deviation of the fit to the remaining 2021 lines is σ = 1.34 × 10^?3 cm^?1.     

Estimate of the fraction of primary photons in the cosmic-ray flux at energies ∼1017 eV from the EAS-MSU experiment data

We reanalyze archival EAS-MSU data in order to search for events with an anomalously low content of muons with energies E _μ > 10 GeV in extensive air showers with the number of particles N _e ? 2 × 10⁷. We confirm the first evidence for a nonzero flux of primary cosmic gamma rays at energies E ～ 10¹⁷ eV. The estimated fraction of primary gamma rays in the flux of cosmic particles with energies E ? 5.4 × 10¹⁶ eV is ε_γ = (0.43 _?0.11 ^+0.12 )%, which corresponds to the intensity I _γ = (1.2 _?0.3 ^+0.4 ) × 10^?16 cm^?2 s^?1 sr^?1. The study of arrival directions does not favor any particular mechanism of the origin of the photon-like events.     

Influence of the defect state of samples on the luminescence spectra of CdS single crystals irradiated by electrons

The photoluminescence spectra of CdS single crystals irradiated by electrons (E = 1.2 MeV, Φ = 2×10¹⁷ cm^?2) are investigated in the visible and near-infrared regions of electromagnetic radiation. Some samples of the CdS single crystals are preliminarily irradiated by neutrons (E = 2 MeV, Φ = 2 × 10¹⁸ cm^?2) with the aim of increasing the concentration of initial structural defects. From analyzing the peak intensities of photoluminescence in the irradiated single crystals at the wavelengths λ_m = 0.720, 1.030, and 0.605 μm, it is concluded that the CdS samples with a low concentration of structural defects in the initial state possess the highest resistance to electron radiation. It is assumed that the observed transformation of the photoluminescence spectra of the imperfect CdS single crystals subjected to electron irradiation is determined by either the mechanisms of subthreshold defect formation or the transformation of the defect complexes in elastic and electric fields near the large structural damages of the crystal lattice.