Classical trajectory calculations of the energy distribution of ejected atoms from ion bombarded single crystals

The energy distribution of particles ejected from single crystal surfaces has been calculated using classical dynamics. The model utilizes a microcrystallite of 4 layers with ~60 atoms/layer which is bombarded by 600 eV Ar⁺ at normal incidence. Calculations have been performed for the clean (100) face of copper as well as for copper with oxygen placed in various coverages and site geometries. The energy distributions for Cu, O, Cu₂, CuO and Cu₃ are reported for this system. The distribution for clean Cu exhibits structure which is shown to arise from preferred ejection mechanisms in the crystal. For oxygen adsorbates, the effect of the oxygen binding energy on the peak in the energy distribution of the ejected oxygen atoms is examined by arbitrarily varying the well-depth of the Cu-O pair potential. In general, higher values of the binding energy produce a maximum in the curve at higher energies and also produce a broader energy distribution. The O₂ and Cu₂ dimer distributions are found to peak at approximately the same energy as the O and Cu curves when compared on a kinetic energy/particle basis, although their widths are considerably smaller. Finally, we predict that the CuO energy distribution should be wider than either the Cu₂ or O₂ distributions since it results from the convolution of the Cu and O distributions which are quite different.     

Double scattering of ions from polycrystalline materials

In this paper double scattering of ions from polycrystalline materials has been theoretically investigated. It is shown that double collision events contribute to the yield at low energy as well as to the high energy flanks of the peaks depending on whether or not the azimuthal angle ø₁ is greater than or less than a critical angle ø_1c at a given first scattering angle θ₁. There are various combinations of first scattering angle θ₁ and second scattering angle θ₂ which give the required retained energy in two successive collisions. Scattering cross sections derived from the Bohr potential and a double interpolation sub-routine are used to calculate the scattering yield at various angles. Two systems, Ne⁺ scattered from copper and Ar⁺ scattered from gold, each at 30 keV primary energy, have been compared with experimental results.     

Low energy electron spectroscopy of N2 in the 11.8–13.8 eV energy range

In the 11.8–13.8 eV energy range differential threshold and energy loss spectra of electrons scattered by N₂ molecules have been obtained at an incident energy of 14.3 eV and with a 30 meV experimental resolution. The study of the angular behaviour of the observed peaks permits us to distinguish between singlet-singlet and singlet-triplet transitions. The predicted F³Π_u and G³Π_u Rydberg states are observed. Also some levels of unknown triplet states are seen at 13.155, 13.395 and 13.635 eV.     

A method for determination of higher-order magnetic anisotropy constants — Importance of the cubic K3 and K4 for certain energy levels models

A method for determination of magnetocrystalline anisotropy constants of arbitrary order is proposed. The method is based on a least squares fitting of a phenomenological anisotropy energy for a given symmetry truncated at an arbitrary order term to a theoretical anisotropy energy computed exactly for a given energy level model. Several applications of the method to cubic systems are considered. The study reveals that the widely used expressions in the literature for the cubic constants K₁ and K₂ in terms of free energy for the three symmetry direction are of rather limitedvalidity only. The higher-order cubic constants K₃, K₄ and K₅ are determined besides the usual K₁ and K₂ in temperature range 0 to 300 K. The importance of the higher- order terms with respect to the first term in the cubic anisotropy energy is discussed. The results show that the cubic constants K₃ and K₄ cannot be neglected for most of the energy level models studied at certain temperatures.     

First-principles investigations on thermodynamic properties of the ordered and disordered Si0.5Ge0.5 alloys

The structure, formation energy, and thermodynamic properties of Si_0.5Ge_0.5 alloys are investigated through first-principles method. The ordered and disordered structures of Si_0.5Ge_0.5 compounds are considered. Our results show that thermodynamic instabilities of Si_0.5Ge_0.5 alloys at 0 K can be judged from the calculated formation energy. However, the alloy might be prepared at specified environment owing to the entropy effects considered. Moreover, the temperature dependence of the heat capacity, Debye temperature and thermal expansion coefficient of ordered and disordered structures are discussed.     

Optical and photoelectric properties of pure and cadmium-and lead-doped neodymium sesquisulfide thin films

A technique for preparing γ-Nd₂S₃ crystalline thin films through discrete vacuum thermal evaporation of a presynthesized bulk material is developed. The films deposited are doped with cadmium and lead. The reflectance and transmittance spectra of the films are measured in the photon energy range 0.2–3.0 eV at a temperature of 300 K. The frequency analysis of the absorption coefficient demonstrates that the γ-Nd₂S₃ films are characterized by an exponential absorption edge. The photoconductivity spectra and temperature dependences of the photoconductivity for the γ-Nd₂S₃ films doped with cadmium and lead are measured in the photon energy range 0.2–3.3 eV at temperatures varying from 115 to 380 K. The experimental data obtained are interpreted under the assumption that the acceptor levels formed by vacancies in the cation sublattice and compensated for by cadmium and lead donor dopants play a crucial role in the photoconduction. The ionization energy at the lead donor level is determined.     

用赝势微扰法计算某些半导体的能带结构(用于GaAs,GaP和Ga[As1-xPx]合金)

用赝势微扰法计算了GaAs,GaP和Ga[As_1-xP_x]合金的能带。赝势选择的原则是使计算所得直接能隙和间接能隙与实验值相符合。计算结果表明,不但能带次序准确,而且与室温下的实验值符合得很好。基于由GaAs到GaP晶格常数和赝势是线性变化的假设,计算了GaP含量为20％,50％和80％时Ga[As_1-xP_x]合金的能带。当GaP含量为41％时,直接能隙和间接能隙相等,这一数值刚好是Spitzer和Fenner的实验值的平均值。此时,由于很好满足光激射器p-n结所要求的条件,因此可望在光激射器中得到应用,它们的能带也就有一定的参考价值。     

Production and Laser Characteristics of Fe<Superscript>2+</Superscript>:ZnS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Polycrystals

A method is developed for producing active laser elements (spectrum range 4 to 5 μm) based on polycrystalline solid solutions ZnS_xSe_x-1 doped with iron ions. Bilateral diffusion doping of the elements by Fe²⁺ ions is performed during hot isostatic pressing. Spectral and energy characteristics of the laser are investigated with the Fe²⁺:ZnS_0.1Se_0.9 active element kept at room temperature. It is found that the absorption band of the Fe²⁺:ZnS_0.1Se_0.9 crystal is blueshifted with respect to the Fe²⁺:ZnSe absorption band, while the lasing spectra of the Fe²⁺:ZnSe and Fe²⁺:ZnS_0.1Se_0.9 lasers and their energy parameters are almost identical. The lasing energy of 580 mJ is obtained at the slope efficiency with respect to the absorbed energy of 46%. Further increase in the lasing energy is limited by development of transversal parasitic oscillation at a large size of the pump beam spot.     

Measurement of radiation energy by spectrometric systems based on uncooled silicon detectors

The results of measurements of radiation energy for single-channel detection systems based on uncooled silicon planar detectors and spectrometric readout electronics, developed at the Kharkiv Institute of Physics and Technology National Scientific Center, are presented. Radiation sources of ⁵⁵Fe, ²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, and ^99MTc and characteristic X-ray radiation (CXR) are used in the experiments. The radiation energy in the range of E _γ = 3–140 keV is measured by a spectrometer based on a Si PIN detector. The energy resolution (full width at half maximum, FWHM) in this energy range changes with increasing photon energy from 0.97 to 1.3 keV. The CXR of calcium (K _α = 3.69 keV) is measured by a Si planar detector with an input aluminum foil. Emission lines in the energy range of E _γ = 0.04–0.662 MeV are measured by a CsI(Tl) scintillator-silicon PIN-photodiode detection system. The energy resolution of the spectrometer changes with quantum energy increasing from 22 to 70 keV. The CXR from cesium and iodine with K _α 31 and 28.6 keV, respectively, is recorded.     

Electron energy loss study of titanium dioxide,barium titanate and silica in the range between 0.02 and 2eV

This work discusses the energy loss spectra of TiO₂, BaTiO₃, silica, and graphite in the range between 0.02 and 2eV. The observed energy losses of crystalline TiO₂ and BaTiO₃ are located energetically between the excitation energies of the transversal and longitudinal optical phonons. This means that the energy losses are due to three (TiO₂) or two (BaTiO₃) different types of surface phonons. The energy loss spectra of the amorphous TiO₂, BaTiO₃, and silica are broadened and show certain similarities to the one-phonon density of states like Raman and infra-red absorption spectra. Rather sharp energy losses in the spectrum of the amorphous TiO₂ are partially interpreted as vibrational excitation of TiO or TiO₂ molecular states.In the energy loss range between 0.2 and 2eV the spectra of the amorphous and crystalline polar material are due to the coupling of the beam electrons to the electromagnetic field of the transition radiation. In the spectrum of graphite, however, which is referred to as comparison, the excitation of the almost free conduction electrons predominates.Part of this work has been presented at the Third International Conference on Thin Films Basic Problems, Applications and Trends, Budapest, Hungary, 1975 [1] and at the International Conference on Lattice Dynamics, Paris 1977 [2]     

Intermolecular potential energy extrapolation method for weakly bound systems: Ar2, Ar–H2 and Ar–HF dimers

Two methods are presented and compared for modifying the intermolecular potential energy extrapolation routine SIMPER, to overcome the problems occurring at small intermolecular separation associated with the use of a Coulomb approximation. The first modification uses a charge density overlap pseudopotential added to the effective Hamiltonian of each interacting fragment. The second treats the problem perturbatively, truncating the polarization expansion series at third order. The methods are used to produce potential energy curves for Ar₂ dimer and several one-dimensional cuts through the Ar–H₂ and Ar–HF potential energy surfaces. Both approaches are competitive with supermolecule dimer calculations at high levels of theory, and significantly reduce the computational cost.     

Fermi level pinning at CdS/Cu(In,Ga)(Se,S)2 interfaces: effect of chalcopyrite alloy composition

We introduce a quantitative model for the band diagram of ZnO/CdS/Cu(In,Ga)(Se,S)₂ heterostructures and for carrier recombination at the CdS/chalcopyrite interface. We derive analytical expressions for the open circuit voltage and the Fermi energy position at the active interface. The open circuit voltage under interface recombination is almost independent from the band gap energy of the chalcopyrite when the valence band edge of the absorber remains at the same energy position. The analytical calculations are in relatively good agreement with numerical simulations. Experimental current–voltage analysis indicates that devices prepared from Cu-poor Cu(In,Ga)(Se,S)₂ chalcopyrites are dominated by recombination in the bulk of the absorber while interface recombination prevails if the absorbers are prepared under Cu-excess. In the latter case, the experimentally determined interface barriers reveal that the interface Fermi energy position shifts upward on the energy scale upon increasing the Ga content into the absorber and remains at a relatively low energy value under S/Se alloying.     

B$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;$lt;/sub$gt;($lt;i$gt;n$lt;/i$gt;=2—15)团簇的几何结构和电子性质

应用密度泛函理论中的B3LYP方法计算并分析了不同生长模式下B_n（n=2—15）团簇的几何结构及电子性质. 同时,比较和讨论了不同生长模式下硼团簇的原子束缚能、能级间隙和第一电离势. 研究表明：直线构型稳定性最低,金属性较强,尤其在n=8时能隙仅有0.061 eV,说明该团簇已具有金属特征. 平面或准平面构型稳定性最高,非金属性强. 立体构型的稳定性与金属性介于直线和平面构型之间. 另外,还讨论了基态团簇的束缚能、能量二阶差分、能级间隙和第一电离势随团簇尺寸的变化,结果表明B₁₂与B₁₄是幻数团簇. 关键词： n团簇')" href="#">B_n团簇 密度泛函理论 几何结构 电子性质     

Rotational statistics and thermodynamic functions of hydrogen peroxide

Partition functions for both the rotational modes (hindered internal rotation and overall rotation) of the hydrogen peroxide (H₂O₂) molecule in the ground electronic state are studied using quantum and classical Gibbsian statistical mechanics. The partition functions are used to calculate rotational thermodynamic functions (internal energy, enthalpy, Helmholtz free energy, Gibbs free energy and entropy) of a hydrogen peroxide gas of weakly interacting molecules at temperatures above 300 K.     

Fundamental absorption edge and normal dispersion of β-LiNaSO4 single crystal

Lithium sodium sulfate (LiNaSO₄)single crystal is synthesized and grown by the slow evaporation of supersaturated aqueous solution at constant temperature (303 K). Powder X-ray diffraction is measured at room temperature in order to identify the grown crystal. Transmittance and reflectance measurements are used to study the optical properties of this crystal at room temperature phase (β-LiNaSO₄). The type of transition is determined. The values of optical energy gap, phonon energy and phonon equivalent temperature are calculated. Refractive index and extinction coefficient are calculated as functions of photon energy. The obtained optical data of β-LiNaSO₄ crystal are used to check the validity of both Wemple-DiDomenico and Cauchy-Sellimaier dispersion relations. Normal dispersion parameters of this crystal are calculated for the first time.     

Negative pion production by 800 MeV/A C,Ne, and Ar beams

Energy and angular distributions of π's produced in relativistic heavy-ion collisions have been measured at 800 MeV/A incident energy. Cross sections for low-energy pions (E_cm ≈ 100–200 MeV) are forward and backward peaked in the nucleon-nucleon c.m. frame. Such anisotropy becomes weaker for higher energy pions. The shape of the energy spectra at θ_cm = 90° is approximately exponential. Their slopes are steeper than those observed for protons. The data are discussed in terms of several models.     

Low energy electron attachment to C<Subscript>60</Subscript>

Low energy electron attachment to the fullerene molecule (C₆₀) and its temperature dependence are studied in a crossed electron beam–molecular beam experiment. We observe the strongest relative signal of C₆₀ anion near 0 eV electron energy with respect to higher energy resonant peaks confirming the contribution of s-wave capture to the electron attachment process and hence the absence of threshold behavior or activation barrier near zero electron energy. While we find no temperature dependence for the cross-section near zero energy, we observe a reduction in the cross-sections at higher electron energies as the temperature is increased, indicating a decrease in lifetime of the resonances at higher energies with increase in temperature.     

Theoretical investigation of V2xFe2(1-x)Zr and ScxY1-xFe2 (0

《Physics letters. A》2020,384(26):126658

Broadband spectral conversion due to cooperative and phonon-assistant energy transfer from ZnO to Yb3+

The broadband spectral conversion from near-UV absorption into near-infrared emission around 1???m is reported in the ZnO?CLiYbO₂ hybrid phosphor, which is the benefit from the efficient energy transfer from ZnO to the Yb³⁺ ions that are specifically located at the interfacial diffusion regions between ZnO and LiYbO₂, rather than those in LiYbO₂ crystals. The Li⁺-related and Yb³⁺-related defect energy levels are formed inside the ZnO band gap in the ZnO?CLiYbO₂ hybrid phosphor; the former act as the quenching centers for the excitons in ZnO and meanwhile the efficient energy donors for Yb³⁺ ions, and the latter are responsible for the red shift of ZnO visible emission when the excitation energy is lower than E _g. The excitation power dependence of Yb³⁺ emission intensities is measured to investigate the number of photons that are involved in the energy transfer process, which reveals that there are two channels for the sensitizing of Yb³⁺: One is due to the energy transfer by the recombination of electrons and holes, which is a cooperative energy transfer process, and the other is via the energy feeding from the Li⁺-related energy levels, which is a phonon-assistant energy transfer process.     

Progress towards determining the density dependence of the nuclear symmetry energy using heavy-ion reactions

The latest development in determining the density dependence of the nuclear symmetry energy using heavy-ion collisions is reviewed. Within the IBUU04 version of an isospin- and momentum-dependent transport model using a modified Gogny effective interaction, recent experimental data from NSCL/MSU on isospin diffusion are found to be consistent with a nuclear symmetry energy of E _sym(ρ)≈31.6(ρ/ρ₀)^1.05 at subnormal densities. Predictions on several observables sensitive to the density dependence of the symmetry energy at supranormal densities accessible at GSI and the planned Rare Isotope Accelerator (RIA) are also made.