Electric field induced exciton binding energy and its non-linear optical properties in a narrow InSb/InGaxSb1−x quantum dot

The effect of electric field on the binding energy, interband emission energy and the non-linear optical properties of exciton as a function of dot radius in an InSb/InGa_xSb_1?x quantum dot are investigated. Numerical calculations are carried out using single band effective mass approximation variationally to compute the exciton binding energy and optical properties are obtained using the compact density matrix approach. The dependence of the nonlinear optical processes on the dot sizes is investigated for various electric field strength. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of electric field induced exciton as a function of photon energy are obtained. It is found that electric field and the geometrical confinement have great influence on the optical properties of dots.     

Influence of Ni and N on generalized stacking-fault energies in Fe-Cr-Ni alloy: A first principle study

The alloying effects of Ni and N were examined in terms of the generalized stacking-fault (SF) energy (GSFE). GSFE is associated with the basal plane of Fe-Cr-Ni austenitic stainless steel. The GSFE profiles were obtained using first-principle calculations. The results show that Ni increases the intrinsic SF energy γ_isf and the unstable SF energy γ_us. N does the opposite. However, a γ_isf/γ_us ratio close to zero accompanies the addition of Ni or N. This ratio implies that deformation by partial dislocation is preferred. Overall, the effect of N on Fe-Cr-Ni alloys is more evident than that of Ni.     

Vibrational excitation of a molecule by a resonance current

Correct expressions are obtained for calculating a tunnel-resonance current through molecules. The participation of molecular vibrations in the resonance charge transfer through a molecule and vibrational excitation of the molecule are determined by the reorganization energy E _r of the vibrational system depending on the displacement of the equilibrium position of vibrational modes in passing from the neutral molecule to the resonance state of a molecular ion. The mean excitation energy of the molecule during the propagation of an elementary charge changes from E _r at the voltage across electrodes close to the threshold up to 2E _r at voltages considerably exceeding the threshold voltage. An expression is obtained for the stationary vibrational temperature of the molecule, which is proportional to the resonance current.     

Fundamental optical properties of Cd1-xMnxSe single crystals

The absorption near the fundamental edge of Cd_1-xMn_xSe was measured in the composition range 0<x<0.3 at room and liquid nitrogen temperature with the electric field of the radiation parallel and perpendicular to the hexagonal axis. An exponential dependence of the absorption coefficient versus photon energy was found, and a linear dependence of energy gap E₀ on composition was obtained. The room temperature reflectivity measurements in the energy range 2.5–5.2eV, for two polarization of light were performed, and a linear dependence of the interband transitions energies vs. alloy composition was found.     

The kinetic energy contribution U(ρ) to the potential energy in the Hougen-Bunker-Johns Hamiltonian

The pseudo potential energy term U(ρ) obtained from the kinetic energy term of the Hougen-Bunker-Johns (HBJ) rotation-vibration Hamiltonian has been obtained in general to order of magnitude κ²T_v. The expression obtained is relatively easy to evaluate and should be used in any semirigid bender or nonrigid bender Hamiltonian that is derived from the HBJ Hamiltonian.     

Dielectric modelling of the transmittance spectra of thin As20S80 films

As₂₀S₈₀ thin films with different thicknesses (49.4-763.1 nm) were deposited on glass substrates using a thermal evaporation technique. Spectrophotometric measurements of the films' transmittance were taken in the wavelength range of 190-2500 nm. The transmission spectra were simulated with a computer model based on dielectric modelling to determine the optical constants and thicknesses of the films. The O'Leary-Johnson-Lim (OJL) models implemented in the commercial software programme SCOUT were used. Thicknesses obtained by the simulated method were correlated to the results obtained from a surface profiler technique. Optical parameters, such as the refractive index n, the absorption coefficient k, the optical band gap E_g, the high-frequency dielectric constant ε_∞, the Urbach energy E_U, the single-oscillator energy and the dispersion energy, were determined. The results indicated that the thickness effect can be separated into two distinct groups for films of thicknesses either less than or greater than 312 nm.     

Measurements of analyzing powers Ay, Axx, Ayy and Axz in dp elastic scattering at Ed = 56 MeV

The differential cross section and all components of the analyzing powers A_y, A_xx, A_yy and A_xz have been measured in dp elastic scattering at 56 MeV. This is the first measurement of A_xz in the cyclotron energy region. A_xz has been measured with the beam polarized in the horizontal plane using the polarization tagging method. Faddeev calculations have been performed for four cases of the NN interaction. The Coulomb correction gave smaller effects at the present energy than at lower energies. Three of them reproduce the experimental data well. The agreement between the calculations and data for A_xz was better than that reported at lower energy. The deuteron asymptotic D- to S-state ratio has been obtained and is consistent within the limits of uncertainty with previously obtained values.     

Determination of the cross section of the pion and nucleon interaction with iron nuclei in the energy range 0.5–5.0 TeV

Direct measurements of the total cross sections of the cosmic ray pion, proton and neutron inelastic interaction with iron nuclei in the energy range 0.5–5.0 TeV are performed. The σ_πⁱⁿ, σ_pⁱⁿ and σ_nⁱⁿ dependences on energy are determined. The results are compared with the data obtained from accelerators as well as with multiple scattering theory conclusions.     

Total reaction cross section from the interaction of 4He ions with 28Si at 10–30 MeV

New results have been obtained for the energy dependence of the total reaction cross section σ _R of ⁴He on ²⁸Si in the energy range E _α ≤ 30 meV.     

Secondary ion emission from Si under nitrogen ion bombardment

The yield and energy distribution of positive secondary ions emitted from Si under N₂⁺ ion bombardment were measured. The obtained mass peaks correspond to three types of secondary ion species, that is, physically sputtered ions (Si⁺, Si₂⁺), chemically sputtered ions (SiN⁺ Si₂N⁺) and doubly charged ions (Si²⁺). The dependence of secondary ion emission on the primary ion energy was studied in a range of 2.0–20.0 keV. The yields of physically and chemically sputtered ions were almost independent of the primary ion energy. The yield of the doubly charged ion strongly depended on the primary ion energy. The energy distribution of secondary ions of the three types showed the same dependence on the primary ion energy. The most probable energy of the distribution increased with the primary ion energy. On the other hand, for the energy distribution curves of sputtered ions, the tail factors N in E^?N were constant and showed a m/e dependence.     

Unified calculations of the optical and electron paramagnetic resonance spectral data for Ce ion in Y3Ga5O12 crystal

Seven crystal field energy levels (obtained from the optical spectra) and three g factors g_x, g_y and g_z (obtained from electron paramagnetic resonance (EPR) spectra) for Ce³⁺ ion in Y₃Ga₅O₁₂ crystal are calculated together by diagonalizing a complete energy matrix. The Hamiltonian of this energy matrix includes all the interactions for 4f¹ ion Ce³⁺ in rhombic crystal field and under an external magnetic field, and so the optical and EPR data can be studied in a unified way. The calculated crystal field energy levels are in better agreement with the experimental values than the calculated values in the previous paper, and the g factors (which have not been calculated previously) are explained reasonably. The results are discussed.     

Terahertz spectroscopy of quantum-well narrow-bandgap HgTe/CdTe-based heterostructures

The energy spectra of quantum-well narrow-bandgap Hg_{1 ? y} Cd _y Te/Cd _x Hg_{1 ? x} Te heterostructures have been studied. The dependences of the effective cyclotron mass on the density (in classical magnetic fields) and the transition energy (in quantizing fields) have been obtained from the cyclotron resonance measurements. These dependences confirm the near-linear dispersion law for the electrons with small mass at the band bottom (the minimum cyclotron mass measured is 0.003 m ₀). The interband photoconductivity of the CdHgTe-based structures with the long-wavelength photoresponse edge lower than 6 meV has been demonstrated.     

Computer simulation of the effect of an ultra soft phase on the magnetic properties of nanocrystalline permanent magnets

Micromagnetic models of assemblies of randomly oriented, exchange coupled, nanocrystals consisting of a magnetically hard uniaxial phase (typified by Nd₂Fe₁₄B) together with an ultra-soft phase (typified by α-iron) have been studied numerically. The hard crystallites were located on a three dimensional cubic lattice, and cubic crystallites of the soft phase were inserted at the junctions of every group of eight hard crystallites. Demagnetizing curves were obtained as a sequence of static equilibrium states in an incrementally changing applied field. Values of the coercivity, remanence and energy product are reported as functions of Δ_GH, the grain size of the hard phase, and of ϕ_S, the fractional volume of the soft phase. The dependence on Δ_GH falls quite rapidly with increasing ϕ_S. The low anisotropy and high saturation magnetization of the α-iron make approximately equal contributions to remanence enhancement in the model. Its remanence values are in quite good agreement with experimental values for Nd₂Fe₁₄B containing α-iron. However, its values for the coercivity and energy product, though decidedly lower than those obtained computationally by some other authors, significantly exceed those obtained experimentally, but show a similar variation with Δ_GH and ϕ_S.     

Electronic energy band calculation in β-PbO2 comparison with SnO2 and GeO2 energy band structures

The energy band structure of β-PbO₂ is determined semi-empirically by the Kohn-Korringa-Rostoker method. It is believed to be the first PbO₂ calculated band structure that appears in literature. The direct band gap value that is obtained directly from this method is 2.7eV. It is lowered to the value of 1.6 eV which seems to be the most likely value of β-PbO₂ energy gaps that were already obtained. This energy band structure is compared with those of other oxides whose lattices belong to the same space group (D¹⁴_4h).     

Level-density parameters in the back-shifted Fermi gas model

The parameters a and δ_eff appearing in the back-shifted Fermi gas model are determined for about 3000 nuclei on the basis of modern estimated experimental data and the proposed systematics. For 272 of these nuclei, the parameters are deduced from experimental data on the cumulative numbers of low-lying levels and on mean spacings between S-wave neutron resonances at the neutron binding energy in the nuclei. For 952 nuclei, the parameter δ_eff is calculated by using the cumulative numbers of low-lying levels and values of the parameter a that were obtained via an interpolation from the points corresponding to the aforementioned 272 nuclei. For the remaining nuclei, the parameters a and δ_eff are obtained on the basis of the proposed systematics. An expression is constructed for taking into account the damping of shell effects with increasing excitation energy of nuclei. The results are compared with those from other studies.     

Resonant excitation of nitrogen bound excitons in Ga As1−xPx alloys

The luminescence spectra at 18 K of nitrogen-bound exciton in Ga As_1−xP_x; x = 0.59 excited with the energy 2.540 eV show bands that lay in an energy range of about 136 meV. Luminescence spectra obtained with resonant excitation energies show sharp lines that appear on the band's energy range. They are attributed to TA^X, LA^X, 2TA^X, LO^loc, TO^Γ_p and LO^Γ_p modes. These lines have different relative-intensities. In this paper, we identify phonon peaks and we give a possible interpretation of different recombination processes.     

The stationarity of the free energy in the Ising model of spin glasses

The stationarity of the high-temperature free energy in the Ising model for spin glasses has been proved by use of the generalized Legendre transformation between the functionals U_c(h_α) and U'_c(S_α). If we retain only the first two diagrams of the free energy then the well-known result of Thouless et al. is obtained.     

Electronic states and the resonant optical non-linearity of exciton in a narrow band InSb quantum dot

Binding energy, interband emission energy and the non-linear optical properties of exciton in an InSb/InGa_xSb_1−x quantum dot are computed as functions of dot radius and the Ga content. Optical properties are obtained using the compact density matrix approach. The dependence of non-linear optical processes on the dot sizes is investigated for different Ga concentrations. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of the exciton are calculated for different concentrations of gallium content. It is found that gallium concentration has great influence on the optical properties of InSb/InGa_xSb_1−x dots.     

On the problem of a linear complex H4

The energy minimum of a linear chain of four hydrogen atomsH₄ was investigated in dependence on the inner atomic distancea and the ?surface” distanceb. An energy minimum was obtained for somea ≠b. Some comments of methodological character are added.     

Radiation widths of resonances in the <Superscript>40</Superscript>Ar(pγ)<Superscript>41</Superscript>K reaction

The excitation function for the ⁴⁰Ar(pγ)⁴¹K reaction at the accelerated proton energy E _p= 450–2700 keV is studied. Positions of 168 resonances identified as levels of the ⁴¹K nucleus are observed in this energy range. The data for the proton energy E _p < 1 MeV and E _p > 2 MeV are obtained for the first time. Relative yields of γ rays observed in the decay of the resonances are calculated from a comparison with the yield of the calibrating resonance at E _p= 1102 keV. Total radiation widths of the resonances are calculated on the basis of the data obtained.