Inelastic scattering of slow electrons in solids

A theory of the inelastic scattering of slow electrons in solids due to excitation of interband transitions is developed. It is shown that both nondirect and direct transitions occur which can be described by a generalization of the formalism used in solid state optics. Experiments with 30–200 eV electrons scattered from Si (111) surfaces with well defined surface structures as determined by low energy electron diffraction confirm the theoretical predictions. They indicate that the inelastic scattering of slow electrons can be understood in terms of the three-dimensional band structure of solids and suggest the use of inelastic low energy electron scattering as a tool for band structure analysis.     

Characteristics of potential-resonance elastic scattering of slow electrons by calcium atoms

The characteristics of elastic scattering of electrons by atomic systems are described by the potential resonance method in terms of the energy dependence of integral-type cross section S taken using a hypocycloidal electron spectrometer. The effect of ² D shape resonance on the run of the curve S(E) is demonstrated with scattering of slow (of energy no higher than 2 eV) electrons by calcium atoms. The energy and width of the resonance are derived from the extrema (minimum and maximum) of the experimental curve S(E). This dependence also serves to find the electron scattering differential cross sections. Two slightly differing scattering angles are taken into account. The differential cross sections derived from the experimental data qualitatively agree with theoretical results, albeit being somewhat lower.     

Influence of exchange and polarization on the elastic scattering of slow electrons from rare gases and mercury

The elastic scattering of slow electrons from A, Kr and Hg is calculated by means of phase shift analysis. In addition to the Hartree potentials radial symmetric potentials are used simulating electron exchange and polarization of the shell electrons. It is found that spin polarization and differential cross-section are in relatively good agreement with the experimental results.     

Inelastic scattering of slow electrons from adsorbed molecules

The inelastic scattering of slow electrons from molecules adsorbed on a metal surface is studied. Previous calculations are improved by including the Coulomb interaction between the incident electrons and the induced charge density that they give rise to in the surface region of the metal.     

Inelastic scattering of slow electrons from adsorbed CO

We have investigated how the cross section for vibrational excitation of adsorbed CO by slow electrons varies with the angle of incidence. Experimental results for the NiCO and CO stretching vibrational modes are presented and compared with a recently developed dipole scattering theory. Good agreement between theory and experiment is obtained.     

Inelastic scattering of slow electrons by lanthanum oxide

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 6, pp. 988–993, December, 1991.     

On the theory of elastic scattering of slow particles

A theory describing scattering of particles with low energy E from an arbitrary 3D potential is proposed. An exact expression is derived for the s scattering amplitude in the limit E → 0. Phenomenological constant κ appearing in the expression for the resonance scattering amplitude is expressed in terms of the parameters typical of the given potential.     

Elastic scattering of slow electrons and level shifts in Ar

The differential and total cross sections for elastic scattering of slow electrons and the energy shifts of hole levels in Ar have been obtained using the self-energy part of the single-particle Green function found in the random phase approximation with exchange.     

Resonant elastic X-ray scattering in chemistry and materials science

The applications of anomalous scattering for locating metal atoms and discriminating between different elements has increased when optimised with synchrotron X-radiation.The on-resonance effect enhances the targeted elemental signal and allows small occupancies to be determined, including in situations of a mixed metal population at a single atomic site. Thus the applications of resonant elastic X-ray scattering in biological, inorganic and materials chemistry is being widely applied to single crystals, which is our emphasis, but also powders, fibres, solutions, amorphous and thin film states of matter. Recent developments have included the use of high photon energies (upto 100 keV) as well as softer X-rays (2 keV). The various instrument and technical capabilities have improved in the last 15 years. This ease of measurement of the resonant scattering signals along with absorption edge shifts indicates an expansion to the measurement of multiple data sets, to allow monitoring of redox changes. Whilst crystal structure determination in biological crystallography has been revolutionised by the MAD method, it is not a requirement for chemical or materials crystallography, as other phasing techniques are routine. Synchrotron source upgrades will allow nano-sized X-ray beams to be more widely available. The new X-ray lasers suggest new capabilities too.     

Resonant states for the scattering of slow particles by screened potentials

Partial resonant situations for the scattering of slow particles with nonzero angular momenta by short-range screened Yukawa and Buckingham potentials are considered. The problem of electron scattering by a hydrogen atom placed in a plasma medium is discussed. A general scheme of resonances has been constructed in the Pais approximation.     

Multiple scattering of slow electrons in a gas. Part II

The formulas derived in part I are used in measurements for elastic scattering cross section for He, Ne, and Ar.     

Improving the Born approximation for the scattering of ultrasound in elastic solids

It has recently been demonstrated that the Born approximation for predicting the scattering response of flaws can be improved through the use of simple modifications called the "doubly distorted Born approximation". In this paper the doubly distorted Born approximation itself is modified with phase and amplitude corrections that further improve the Born scattering results for isotropic elastic media. The reliability of this new modification of the Born approximation has been evaluated by comparison with the exact solution for spherical inclusions obtained with the method of separation of variables. Unlike the ordinary Born approximation which works well only for very weak scattering inclusions, our modification of the doubly distorted Born approximation gives improved scattering results for both weak and strong scattering inclusions.     

固体中多孔媒质球的声共振散射特性

利用Flax等提出的声共振散射模型,以铁中多孔石墨为例数值上研究了平面声纵波入射时固体中多孔媒质球体背向散射纵波和散射横波的频谱以及不同阶分波的共振散射谱,并由此研究了铁中多孔球形石墨不同模式的共振频率随石墨孔隙率的变化。结果表明,球形石墨的背向散射谱及各阶分波中的共振频率均随孔隙率的增加向低频移动,其形态也发生变化。因此,如果用实验测定球墨铸铁样品的超声背向散射谱或各阶分波中共振频率,有可能确定多孔石墨的孔隙率。     

The elastic scattering of low energy electrons from Xenon

Calculations are presented of angular distributions for electrons elastically scattered from xenon in the energy range 5.5 to 10 eV. The potential describing the xenon atom is determined by the X_α-approximation. The relative dependence with energy of the differential cross section at 30° scattering angle has been calculated in the range 30 to 200 eV. The theoretical results are in very good agreement with experimental data.     

On the test ofT-invariance in elastic scattering of electrons from polarized deuterons

An additional (magnetic) form factor G₂ which violatesT-invariance is introduced in the electromagnetic vertex of the deuteron. This additional interaction yields a right-left asymmetry in the scattering of electrons from polarized deuterons. For our numerical evaluations we used values of G₂ which are consistent with the deviations from the impulse approximation found in measurements of the unpolarized cross section. A maximum asymmetry of approximately 40 percent was obtained at q=3.5 f^?1. However, care must be taken in the preparation of the polarized target, as a suitable tensor polarization may also produce asymmetry.