Nonadiabatic effects in the phonon spectrum of metal compounds

It is shown that nonadiabatic corrections to the dispersion law of optical phonons in the region of small wave vectors in the case of branches, for which the vibration with a zero wave vector is not accompanied by the appearance of a dipole moment in the ionic lattice, are significant for all possible directions of the wave vector. If a dipole moment arises, nonadiabatic corrections reach a noticeable value only for the wave-vector directions that are almost perpendicular to the direction of the dipole moment.     

Vacancies in transition metals: Formation energy and formation volume

This work describes a calculation of the formation energy and volume for a vacancy in transition metals. One uses a tight-binding scheme for the d band and a Born-Mayer type potential to account for the repulsive part of the energy at small distances. The results show that the relaxation energy is small in all cases, less than 0.1 eV. This seems to be coherent with the good agreement obtained for the theoretical and experimental values of the formation energy E_f^v of the vacancy, without including relaxation. The center of the transitional series is found to give a contraction (formation volume of order ?0.4 at. vol.) whereas the edges are found to produce dilatations.     

介观金属双环系统中的持续电流和量子能谱

基于电荷的不连续性,对处于外磁场中的介观双环系统进行量子化.假设系统在电荷表象中具有变换的对称性,通过求解电流和Hamilton算符的本征值方程,给出介观金属环互感系统中的量子电流和能谱关系;分析和研究了介观金属环中量子电流和能谱的性质.结果表明,持续电流和量子能谱不仅与外磁场、介观双环参数有关,而且还明显地依赖于电荷的量子化性质.     

The energy spectrum of a nonsimple metal with negative U centers

For a nonsimple metal superconductor with negative U centers, the energy gap functions of conduction electrons and localized electrons have been discussed. It has been shown that the attractive interaction of the negative U centers can make the peak of the density of states slightly shift to higher energy and the instability of the Cooper pairs occurs.     

Vacancies in binary alloys: III. The energy of vacancy formation

A general expression for the energy of formation of a single vacancyE _F in substitutional binary alloys having two types of lattice sites is derived, which takes into account the interaction of neighbouring atoms. It is shown, that near the Curie temperature Θ the formation energy exhibits an anomaly.     

A theoretical study of disorder in transition metal aluminides: Vacancies and antistructure atoms

Korringa-Kohn-Rostoker-Coherent-Potential-Approximation (KKR-CPA) calculations were performed on FeAl and NiAl in the CsCl structure with various concentrations of vacancies on the transition metal sublattice and antistructure atoms on both sublattices. It is found that transition metal vacancies only bring about minor changes in the density of states, whereas Fe atoms on the Al sublattice give rise to additional states near the Fermi energy. X-ray photoelectron spectra were calculated and-in the case of NiAl-compared with experiment.     

The phonon spectrum of high energy heat pulses generated in thin metal films

The phonon spectrum of high energy heat pulses (10⁴W/cm²) generated by current pulses in thin evaporated metal films was studied in ruby by time resolved optical spectroscopy. The experiments show that the population temperature of the phonon states rises with rising phonon energies in accordance with theoretical predictions of Perrin and Budd [1, 2]. The thermalization of the phonon spectrum needs a time of approximately 900 µs in ruby flushed with cold helium gas.This work was supported by the Deutsche Forschungsgemeinschaft, SFB65     

X-ray emission spectra and chemical bonding in TiC,TiN and TiO

The experimental X-ray emission spectra of titanium carbide, nitride and oxide have been obtained. Quantum-chemical calculations of the electronic structure of clusters in TiC, TiN and TiO have been carried out by the semiempirical Mulliken-Wolfsberg-Helmholtz method with self-consistency on charges and configurations. The results of these calculations are in good agreement with the X-ray spectroscopy data and offer a reasonable explanation of the experimental spectra. Chemical bonding and electronic structure of the compounds are discussed. Ionicity is shown to increase from TiC to TiO according to the electronegativity principle, the calculated charges on the metal ions being close to experimental estimates. The role of metal-metal and metal-nonmetal interactions in the chemical bonding is analysed. Vacancy models for TiO and their effect on the X-ray emission spectra are investigated. By the CNDO method with configurational interactions the optical spectrum of titanium carbide has been calculated. It is shown that this spectrum may be interpreted from the results for the [TiC₆] cluster, without introducing the Lye-Logothetis band scheme with negative charge on the metal ion.     

The fractal energy measurement and the singularity energy spectrum analysis

The singularity exponent (SE) is the characteristic parameter of fractal and multifractal signals. Based on SE, the fractal dimension reflecting the global self-similar character, the instantaneous SE reflecting the local self-similar character, the multifractal spectrum (MFS) reflecting the distribution of SE, and the time-varying MFS reflecting pointwise multifractal spectrum were proposed. However, all the studies were based on the depiction of spatial or differentiability characters of fractal signals. Taking the SE as the independent dimension, this paper investigates the fractal energy measurement (FEM) and the singularity energy spectrum (SES) theory. Firstly, we study the energy measurement and the energy spectrum of a fractal signal in the singularity domain, propose the conception of FEM and SES of multifractal signals, and investigate the Hausdorff measure and the local direction angle of the fractal energy element. Then, we prove the compatibility between FEM and traditional energy, and point out that SES can be measured in the fractal space. Finally, we study the algorithm of SES under the condition of a continuous signal and a discrete signal, and give the approximation algorithm of the latter, and the estimations of FEM and SES of the Gaussian white noise, Fractal Brownian motion and the multifractal Brownian motion show the theoretical significance and application value of FEM and SES.     

Electron energy loss spectroscopy of TiC,ZrC and HfC

The dielectric properties of commercial TiC, ZrC and HfC powders were determined by analyzing the low loss region of the EELS spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) were obtained by Kramers–Kronig analysis. As maxima observed in the OJDS spectra are assigned to interband transitions across the energy gap, these spectra can be interpreted on the basis of existing energy-band calculations. Comparison between experimental results and theory shows good agreement.     

Electron energy loss study of TiC [111]

The electron energy loss (EEL) spectra of TiC (111) were measured over a wide range of electron primary energies. The electron energy losses below 16 eV were analyzed using the theoretical band calculations of Price and Cooper [11]. The volume and surface plasma excitations were identified from their electron primary energy dependence. Energy losses due to core electrons autoinization effects were identified above 35 eV. We observed a difference in the electronic structure of the surface vs the bulk of TiC. The temperature dependence of the EEL spectra was studied between 300 to 1250 K. The reaction of the TiC surface with ethylene and oxygen was also investigated. The ethylene bonding to the TiC surface was found to be very weak. There is evidence of the formation of surface defects on the TiC (111) surface at high temperatures.     

On the energy spectrum of helium II

It is shown that the spectrum of the bulk excitations in helium II, which ends at the Pitaevskii point, should be recovered at a certain critical point with the coordinates of about several roton energies and momenta in the form of the spectrum of vortex rings. As the momentum increases, the spectrum of surface capillary waves should be transformed to the spectrum of surface vortex half-rings.     

On the energy spectrum of cosmogenic neutrons

The processes of the generation of cosmogenic neutrons (cg-neutrons) underground are considered. The neutrons produced by cosmic-ray muons in their interactions with matter are called cosmogenic. Deep-inelastic πA-collisions of pions in muon-induced hadronic showers are mainly their source at energies above 30 MeV. The characteristics of the energy spectrum for the generation of cg-neutrons have been determined by invoking the additive quark model of deep-inelastic soft processes and the mechanism for the interactions of high-energy nucleons in a nucleus. The three-component shape of the spectrum is explained, and the energy of the “knee” in the spectrum has been found to depend on the mass number A. The peculiarities of deep-inelastic πA-scattering lead to the conclusion that the spectrum of cg-neutrons steepens sharply at energies above 1 GeV. The calculated quantitative characteristics of the spectrum are compared with those obtained in measurements.     

Singularity in the LEIS spectrum of metal nanoclusters

The asymmetry of lines has been observed in the spectra of the inelastic scattering of low-energy ions interacting with nanoclusters of d metals. It is attributed to the mechanism of exciting e-h pairs with low energies and high momenta (infrared catastrophe). Analysis of the asymmetry of x-ray photoelectron spectra and spectra of low-energy scattered ions shows that the Anderson singularity indices α associated with the electron states on the surface and in bulk have different behaviors as functions of the nanocluster size. The results cannot be explained in the framework of the available concepts of the redistribution of these contributions with decreasing of the nanocluster size.     

Electron energy loss spectra near structural defects in TiN and TiC

In this study, we use first principles multiple scattering calculations on atomic clusters to show how the carbon and nitrogen K-edge fine structures are modified in the vicinity of structural defects in TiN and TiC. Changes in the electron energy loss spectra are due to changes in the atomic structure of the first atomic shells around the absorbing atom. Two different kinds of defects, which both modify the structure of these atomic shells, are investigated here. In a first part, we describe a method which correctly takes into account the statistical spatial distribution of nitrogen vacancies in a TiN cluster. We study the influence of vacancy concentration on the shape of the nitrogen K-edge spectra and we find that vacancies mainly affect the height of the second peak of the spectra. This peak decreases when the number of vacancies in the second nitrogen shell increases. In a second part, we study the carbon K-edge spectrum modification near stacking faults in TiC. Two different stacking faults are studied. These two-dimensional defects are responsible for changes in the position of the carbon as well as titanium atoms of the atomic shells centered on the absorbing carbon atom. The shape of the spectra is strongly modified near the stacking faults and several peaks are affected by these modifications. We show that these fine structure modifications only concern the very first carbon atomic layers near the two-dimensional defects.     

Excitation spectrum and superconductivity in diamond-type compounds

The occurrence of superconductivity in a diamond-type lattice is investigated. For each integer interval of electron concentration n _p , narrow concentration regions are discovered in which the superconducting transition temperature has the highest possible value. Analysis is carried out under the assumption that the energy of strong electron-electron correlations is the largest energy parameter. The results are in qualitative agreement with experimental data.     

Dynamical localization and nondispersion of energy spectrum

Within a finite band model, we present a proof of the theorem that dynamical localization happens if and only if the energy spectrum is dispersionless for an electron in a semiconductor superlattice under the influence of time-periodic electric fields. The electron may display several localization patterns.     

Transition metal and rare-earth metal atoms on single-layer graphene: Estimations of the charge transfer and adsorption energy

A Hamiltonian accounting for s- and d(f)-states of adatoms has been proposed to describe adsorption of atoms of d- and f-metals on single-sheet graphene. It has been shown that s-electrons mainly contribute to the charge transfer Δn _a between the adatom and graphene substrate. Analytical formulas proposed previously within the M-model of the graphene density of states are used for Δn _a calculations. To estimate the adsorption energy, a simple analytical expression is proposed. Calculations are performed for 3d-, 4d-, 5d-, and 4f-adatoms. The results of calculations are compared with the data obtained by other authors.