Relaxation of the edge atoms of a stepped Cu(410) surface

The edge atom position of the stepped Cu(410) surface has been investigated with low energy ion scattering (LEIS) using 10–20 keV H⁺. It is possible to determine the atomic position by utilizing atomic shadowing effects. The scattered particles are analysed with a time-of-flight spectrometer. This means that we can detect scattered hydrogen leaving the copper surface in the neutral state as well as in the charged state, so the influence of neutralization of the scattered particles along different outgoing trajectories is eliminated. We find an inward relaxation of the edge atoms; assuming that this relaxation takes place in the (100) plane it amounts to about 8% of the interlayer spacing.     

Long time relaxation effect of liquid castor oil under high pressure conditions

Abstract

The relaxation times of Liquid castor oil have been investigated by observing the scattered light of a He-Ne gas laser during the slow or rapid application of pressure up to 0.7 GPa at 293 K. For the application of pressure above 0.36 GPa the strong increase of the scattered light intensity approximately by a factor of 10² has been observed 12 hours after an application of pressure. This pressure effect is also observed for subsequent pressure cycles, i.e., the pressure effect is reversible. Experimental results are interpreted according to a model of a liquid of long rod molecules.     

Kinetics of light scattering in an epoxy resin suspension of carbon microparticles

The relaxation kinetics of laser-induced scattering and absorption was investigated in a liquid epoxy resin suspension of carbon microparticles. The scattered light intensity and the optical transmittance at temperatures below +10°C demonstrate anomalous kinetics with a distinct build-up stage. The observed behavior is interpreted as a manifestation of processes of mechanical stress relaxation in epoxy layers around microbubbles. The microbubbles induced by laser irradiation of the suspension can be a tool for the investigation of mechanical stress relaxation in polymers.     

Magnetic susceptibility and short-range order in iron pnictides: Anisotropic J1-J2 Heisenberg model

The electron spin relaxation times by piezoelectric and polar optical phonon scattering in GaAs are calculated using the formula derived from the projection-reduction method. The temperature, magnetic field, and electron density dependences of the relaxation time are investigated. The electrons are found to be scattered mostly by piezoelectric phonons at low temperatures and polar optical phonons at high temperatures. The electron density affects the magnetic field dependence of the relaxation time at low temperatures but have only slight affects at high temperatures.     

Time-resolved spectrum for resonant light scattering in an exciton-phonon system

A formula is given for the time-resolved spectrum of the resonantly- scattered radiation from an exciton-phonon system, and it is applied to the calculation of two-LO-phonon assisted spectrum. Both the Raman component associated with virtual intermediate states and the luminescence with real intermediate states are obtained. A Raman-like component with an oscillatory behavior can be seen, when the exciton relaxation time is shorter than the excitation pulse duration. It is proposed that the energy dependence of exciton relaxation rate can be directly measured from the time decay of a hot luminescence spectrum.     

Influence of dephasing relaxation on the transient properties of parametric four-wave mixing

Transient parametric scattering is investigated theoretically using density matrix perturbation theory. Emphasis is placed on the effects of population and transverse or dephasing relaxation on the scattered parametric pulse durations. Pulse duration measurement provides important insight into the actual transient temporal behavior of four-wave mixing processes and is shown to be a potentially useful technique for the characterization of material time constants and incident pulse shape.     

Extremely asymmetrical scattering of slab modes in periodic Bragg arrays

The steady-state extremely asymmetrical scattering of electromagnetic modes in a slab with a periodically corrugated boundary is analyzed theoretically. A new approach, based on allowance for the diffractional divergence of a scattered wave, is used with the approximation of slowly varying amplitudes and a Fourier analysis. The structure of the incident and scattered waves inside and outside the array is determined. The amplitudes of the scattered waves are found to be much larger than the amplitude of the incident wave. The typical time of relaxation to steady-state scattering is found to depend on the distance from the array boundary through which the incident wave enters the array. Conditions of applicability of the results obtained are also presented.     

Enhancement of the ICISS method by simultaneous detection of ions and neutrals

ICISS (detection of scattered ions only) and NICISS (detection of scattered ions and neutrals) are compared in situ by Ne scattering at a Pt(111) surface. The ICISS data suffer from the high neutralization during ion scattering which obscures important features in the ψ_in patterns limiting the method to first-layer information. The determination of surface structure (e.g. reconstruction or relaxation), however, requires the knowledge of atom positions within the first few atomic layers. As NICISS supplies a real-space image of the geometrical structure of the first 2–3 surface layers averaged over a macroscopic area, the method is ideally suited for the determination of surface reconstruction and relaxation.     

Influence of the Miniband Width on the Relaxation Time of Superlattice Electrons Scattered by Impurity Ions

Based on the Boltzmann equation, the influence of the miniband width on the relaxation time of nondegenerate electrons scattered by impurity ions in the GaAs/Al _x Ga_1–x As superlattice with doped quantum wells is numerically analyzed. The wave function being the eigenfunction of the ground state of the lower miniband of the superlattice is used to calculate the scattering probability. The dispersion of the longitudinal and transverse relaxation times versus the longitudinal wave vector is investigated.     

Specific features of the electrooptical effect and light scattering of water dispersed system of carbon nanotubes

Results of an electrooptical study of a water solution of carbon nanotubes obtained using the catalytic method are presented. It is shown that nanotubes, which anisotropically absorb light, are oriented in an electric field and create a pronounced linear electric dichroism due to light absorption, rather than light scattering (as in the case of colloids with particles with sizes close to that of nanotubes). An analysis of the relaxation dependences of the electric dichroism shows that nanotubes deform, which are oriented in the electric field; in this case, the deformation sublinearly depends on the field amplitude and reaches a limiting value. The relaxation dependence of the field-induced dichroism agrees with the autocorrelation function of depolarized light scattered perpendicular to the incident light flux.     

Polar optic phonon scattering of two dimensional electron gas in a rectangular potential well

The mobility of a two-dimensional electron gas (2DEG) in a rectangular potential well formed in a AlGaAs/GaAs/AlGaAs structure scattered by polar-optic phonon is calculated by an iterative solution of Boltzmann equation. The values are significantly different from those calculated by using a relaxation time. The polar-optic mobility is found to dominate over acoustic mobility over a temperature range of 100–300 K when the well thickness is about 10 nm. The mobility values for 2DEG are, however, found to be lower than the bulk values.     

Elastic scattering of acoustic phonons on point mass defects

The relaxation of homogeneous states of long-wave acoustic phonon gas scattered by point mass defects in transversely—isotropic media is studied. The spectrum of the suitable collision operator of the Boltzmann-Peierls equation is investigated. It consists of a continuous part and several discrete eigenvalues. Both continuous and discrete part of the spectrum depend on the values of components of the elastic constant tensor. For some values of elastic constants the continuous part splits up into two separate intervals and some of the discrete eigenvalues appear in the gap. The number of discrete eigenvalues and their arrangement are also affected by elastic properties of medium.     

亚表面异质缺陷对功能梯度材料表面温度场的影响

基于双曲型热传导方程,采用镜像法和波函数展开法,求解了含亚表面异质圆柱缺陷的半无限功能梯度材料的表面温度场,给出了功能梯度材料中热波散射的一般解.分析了亚表面异质圆柱缺陷的几何参数(如埋藏深度)和热物理参数(如导热系数、热扩散长度、热扩散率及热弛豫时间等)对功能梯度材料表面温度场的影响.温度波由调制的超短脉冲激光在功能梯度材料表面激发,异质圆柱缺陷表面的边界条件为导热边界.研究结果可望为功能梯度材料的红外热波无损检测、导热反问题提供计算方法和参考数据.     

Effect of the spatial distribution of probe beam on the results of measurements of the disperse composition of nanoparticles by dynamic light scattering method

The model of dynamic scattering on a finite ensemble of Brownian particles in liquid is considered. It is shown that an artifact characteristic relaxation time appears in the autocorrelation function of the scattered light intensity, which is much longer than the correlation time controlled by particle diffusion in the scattering volume.     

Hot luminescence in polyacetylene

We propose that the unusual frequency dependent lineshapes observed in Raman scattering experiments on polyacetylene are due to hot luminescence in very long polyene chains. Employing a generalized equation of motion technique we find that a photoexcited polyene is unstable with respect to a variety of symmetry lowering distortions which vary as a function of the frequency of the exciting radiation. Radiative decay during this relaxation is observably strong in the inelastically scattered photon spectrum and would explain the dominant observed lineshape variations.     

A characterization of the scattered acoustic intensity field in the resonance region for simple spheres

The properties of the scattered acoustic vector fields generated by simple spheres illuminated by monotonic continuous wave (CW) plane waves are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. Of particular interest is the understanding of the characteristics of the scattered acoustic vector field in the near-to-far-field transition region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions for a rigid sphere. A method of mapping nulls in the scattered intensity field components is described. The analysis is then extended to include a simple fluid-filled boundary and finally the evacuated thin-walled shell. Near field acoustic intensity field structures are compared against mechanical material properties of vacuous shells. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field from rigid spheres.     

Similarity effects in multiple scattering of coherent radiation: Phenomenology and experiments

Based on phenomenological concepts of statistics of effective optical paths for multiple scattering of coherent radiation, an analysis is carried out of similarity effects observed for the dependences of statistical moments of the scattered field on the relaxation parameters with a dimension of reciprocal length. Within the framework of the diffusion approximation, expressions are obtained that describe the autocorrelation function of fluctuations of the scattered-field amplitude, the degree of polarization, and the normalized intensity of scattered light for media with a finite absorption length in the case of forward scattering of coherent radiation in a plane layer of an isotropic scattering medium. The results of the analysis show the similarity of the dependences of these quantities on the corresponding spatial scales. Experiments with model scattering media (aqueous suspensions of polystyrene spherical particles) supported the existence of similarity effects in multiple scattering. An experimental study was made of the relation between the characteristic depolarization length and the transport length for multiple scattering of coherent radiation in a plane layer. The effective value of the radiation diffusion coefficient providing the best agreement between the experimental and the calculated values of parameters of the scattered field is shown to be independent of the absorption coefficient of a medium.     

On the theory of irreversible processes in molecular liquids and liquid crystals, nonequilibrium phenomena associated with the second and fourth rank alignment tensors

A theory for nonequilibrium phenomena primarily associated with the molecular orientation in liquids and liquid crystals is developed within the framework of irreversible thermodynamics. The alignment tensors of rank 2 and 4 are taken into consideration as additional macroscopic variables. With appropriate assumptions concerning the dependence of the internal energy, specific volume and the entropy on the alignment, a dynamic Landau theory is obtained. Nonlinear relaxation equations are derived for the alignment tensors. They possess zero and nonzero stable stationary solutions corresponding to the isotropic and nematic phases of a liquid crystal when the temperature is above or below the transition temperature. Some further applications of the relaxation equations are discussed, in particular fluctuations of the intensity of the depolarized component of scattered light.     

Relaxation effects in resonance Raman spectra

A density-matrix theory of resonance scattering spectroscopy is presented to characterize the relaxation processes which may be studied in these spectra. The distinction between Resonance Raman and Fluorescence emerges clearly from this treatment. It is shown that novel properties of the rotational and vibrational relaxation may be obtained from the lineshape of the scattered light. A new effect is discovered in the Resonance Raman excitation profile which, in principle, could be used to study the relaxation rate between specific vibronic levels of an excited electronic state.     

Physical optics theory for the scattering of waves by an impedance strip

The physical optics integral of the scattered waves by an impedance strip is derived by using the modified theory of physical optics. The surface currents of the physical optics integral, which was introduced for the scattered waves by an impedance half-plane, are taken into account. The uniform diffracted fields of the impedance strip are evaluated asymptotically. The second order diffraction terms are also obtained. The total scattered field and its subcomponents are plotted and the effect of the second order diffraction and strip width to the scattering is investigated numerically.