Theory of ion reflection from amorphous surface at low glancing angles

A new theory of ion reflection from a smooth amorphous solid surface is developed. A continuous potential is introduced for describing the ion reflection from amorphous surfaces at low glancing angles. It is shown that the difference, between a true surface potential and a continuous one could be taken into account in terms of a correction factor, thus yielding a Fokker-Planck-type equation for a particle distribution in angle and transverse coordinate. Diffusion coefficients included in this equation are calculated with allowance for atom discrete positions and ion-electron collision effect. On the basis of the derived kinetic equation the angular and energy ion distributions in a reflected beam are analyzed. The presented theory, somewhat modified, can be used for describing ion reflection from a crystal surface as well.     

Deflection of an electron beam with a 1.8-MeV energy incident at glancing angles on a dielectric surface

The first results of investigations into the effect of self-deviation of an electron beam with intermediate energy by a dielectric surface, previously discovered by the authors for the interaction of electrons with a glass surface, are presented in the paper. It is shown that optimizing the deflection process and choosing a dielectric target, angles of beam deflection of the order of 5–8° can be obtained and stabilized during subsequent irradiation of the target, which is especially important for applications of this effect to electron-beam optics. Scientific Research Institute of Nuclear Physics at Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 12–17, September, 1999.     

Quantum reflection from a solid surface at normal incidence

We observed quantum reflection of ultracold atoms from the attractive potential of a solid surface. Extremely dilute Bose-Einstein condensates of 23Na, with peak density 10(11)-10(12) atoms/cm(3), confined in a weak gravitomagnetic trap were normally incident on a silicon surface. Reflection probabilities of up to 20% were observed for incident velocities of 1-8 mm/s. The velocity dependence agrees qualitatively with the prediction for quantum reflection from the attractive Casimir-Polder potential. Atoms confined in a harmonic trap divided in half by a solid surface exhibited extended lifetime due to quantum reflection from the surface, implying a reflection probability above 50%.     

Optical properties of solid benzene derived from electron energy losses

From energy loss measurements of fast electrons on polycrystalline benzene films the energy loss function Im(?1/?) and the dielectric constants ?=?₁+i?₂ are calculated up to 40 eV. The results are discussed in terms of ?₂ and are compared with the corresponding ?₂-spectrum of benzene vapour.     

Specular reflection of very slow metastable neon atoms from a solid surface

An ultracold narrow atomic beam of metastable neon in the 1s3[(2s)(5)3p:1P0] state is used to study specular reflection of atoms from a solid surface at extremely slow incident velocity. The reflectivity on a silicon (1,0,0) surface and a BK7 glass surface is measured at the normal incident velocity between 1 mm/s and 3 cm/s. The reflectivity above 30% is observed at about 1 mm/s. The observed velocity dependence is explained semiquantitatively by the quantum reflection that is caused by the attractive Casimir-van der Waals potential of the atom-surface interaction.     

Reflection of a slow cesium atomic beam from a naturally magnetized Nd-Fe-B surface

We have demonstrated the partly directed reflection of a slow cesium atomic beam by using the natural magnetic stray field above a Nd-Fe-B surface. From these experiments we determine the reflectivity and a minimum value for the magnetic stray field directly at the surface. Received: 5 July 1999 / Revised version: 6 October 1999 / Published online: 3 November 1999     

粗糙海面对高斯分布激光光束的反射模型推导

研究激光光束海面反射光强的方向分布特性对海上光电对抗等领域的工程实践具有重要意义.本文采用分形方法模拟粗糙海面,并在海面基准坐标系中建立起描述粗糙海面几何特征的数学方程,然后基于蒙特卡罗方法模拟高斯光束,依据几何光学原理在基准坐标系下推导了高斯光束的海面反射模型,采用该模型可以编程计算激光光束海面反射光强的方向分布.将模拟计算结果与实验结果进行了对比分析,结果表明该模型可以较好地反映激光光束海面反射光强的分布趋势,验证了模型的有效性.     

高通量中性原子氧束流的发生与控制

 采用微波同轴耦合氧气放电产生高密度氧等离子体, 经磁场约束后与一施加负偏压的金属板碰撞复合并反射, 得到通量在10¹³~10¹⁶atom/cm²×s范围可控, 动能约为6-10eV的中性氧原子束流。用双探针技术对生成的氧等离子体进行了诊断测量。根据聚酰亚胺在原子氧作用下的剥蚀率对原子氧束流进行了标定测量。     

Resonance minima and maxima in the diffraction intensities of atomic beams from solid surfaces

Resonance minima and maxima in the diffraction intensities of atomic beams from solid surfaces are explained by generalizing the Laue diffraction equation to include the effects of the atom-phonon interactions on the diffracted waves exactly.     

Perturbation of atomic energy levels by a metal surface

The energy level shifts of one-electron atomic particles H, He⁺, Li⁺⁺, etc. which interact with a metal surface have been investigated. In the approximation of image charges, an operator describing perturbations of atomic levels has been obtained. By numerically solving the Schro dinger equation, we have calculated energy levels of H(1s), H*(n=2), and C⁵⁺(n) as functions of the distance between an atom and surface. Asymptotic behavior of atomic levels at large distances from the surface has been studied. The linear Stark effect for excited states, which was earlier mentioned by A. V. Chaplik, has been found and investigated in detail. Zh. éksp. Teor. Fiz. 116, 236–256 (July 1999)     

Droplet model of an atomic cluster at a solid surface

A method for calculating the characteristics of the stability, energy, and geometry of an atomic cluster at a solid surface is proposed, which is based on a droplet model that takes into account the cluster-solid interaction. As an example, the interaction of a neutral argon cluster with a (001) surface of graphite is considered. The results of calculations performed within the framework of the droplet model show good agreement with the results of numerical simulation based on a dynamic search for the most stable isomers in the course of cluster growth. It is shown that the droplet model can be used for simple evaluation of the geometry, stability, and energy characteristics of clusters at solid surfaces.     

非晶氧化钛薄膜形成过程中钛离子能量对表面结构影响的机理

研究了非晶氧化钛薄膜沉积过程中入射钛离子能量对表面结构形成机理以及薄膜特性的影响.模拟结果表明,通过提高入射钛离子能量,可以有效降低成膜表面粗糙度,从而减小薄膜表面的光学散射损耗.研究发现,当入射离子能量提高后,薄膜生长模式从"岛"状生长过渡到了"层"状生长,且离子入射点附近的平均扩散系数也有显著增加,这有利于形成更加平整的高质量薄膜表面.     

Angular pattern of electron diffraction by reflection in the plasmon channel of energy losses

We have constructed a theory for the excitation of plasmons by a fast charged particle that undergoes diffraction in a single crystal and then is scattered elastically and incoherently through a large angle. The theory allows the 30-year-old experimental results that have seemed strange to be explained. An increase in the diffraction contrast in the channel of inelastic electron scattering related to the excitation of a bulk plasmon compared to the diffraction contrast of elastically and incoherently reflected electrons was observed in these experiments. Based on this theory, we show that the excitation of a surface plasmon affects only slightly the angular diffraction pattern, leaving it almost the same as that for elastically reflected electrons. These peculiarities of elastic and inelastic diffraction can be used to identify the type of energy plasma loss.     

有限入射声束在液固界面声反射的数值研究

采用将有限声束分解为一系列平面波的方法，对液固界面声束的声反射问题进行了数值研究，结果表明，当声束入射角为瑞利疲激角时，反射声速有明显位移；当声束在液固界面“掠射”时，反射声速显著变宽，文中还讨论了束宽对反射声速横截面上声场分布的影响。     

Selective reflection of a laser beam from a dilute rubidium vapor

We study the selective reflection of the laser beam from rubidium atomic vapor at the D₂ line (wavelength λ = 780 nm) at different atomic densities. We use a tunable free-running diode laser. We observed a measurable signal at a low atomic density N when the mean distance between resonance atoms reached two wavelengths. In our experiment, the dimensionless parameter N ^1/3 λ varied from 0.5 to 2.8. The reflectivity increased with density monotonically. It is interesting to perform experiments when the parameter N ^1/3 λ ≪ 1.     

Generation of terahertz radiation during reflection of femtosecond laser pulses from a metal surface

The features of terahertz radiation generated upon oblique incidence of a femtosecond laser pulse on a metal surface are investigated theoretically. We propose a Cherenkov-type generation mechanism associated with excitation of low-frequency surface currents by a p-polarized optical field. The nonlinear surface currents and corresponding electrodynamic characteristics of low-frequency radiation are calculated analytically and by numerical simulation using the hydrodynamic model. The features of Cherenkov generation of terahertz radiation are analyzed, and techniques are proposed for increasing efficiency.     

Imitative modeling of the evolution of surface structures during crystal growth from a molecular beam

An imitation model of layered crystal growth from a molecular beam is presented which takes account of the random character of the formation of nuclei and the dependence of their growth rate on their mutual positions. The dependence of the form of the oscillations in the intensity of specular reflection of a fast electron beam on the nucleation rate has been studied within the framework of the model presented. The possible causes of oscillation damping have been analyzed in connection with the time evolution of the surface structure. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 103–109, August, 1997.