Atom scattering as a probe of the surface electron-phonon interaction at conducting surfaces

IF 8.2 1区 化学 Q1 CHEMISTRY, PHYSICAL
J.R. Manson , G. Benedek , Salvador Miret-Artés
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引用次数: 5

Abstract

An atomic projectile colliding with a surface at kinetic energies in the thermal or hyperthermal range interacts with and is reflected by the electronic density well in front of the first layer of target atoms, and it is generally accepted that the repulsive interaction potential is proportional to the density of electrons extending outside the surface. This review develops a complete treatment of the elastic and inelastic scattering of atoms from a conducting surface in which the interaction with the electron density and its vibrations is treated using electron-phonon coupling theory. Starting from the basic principles of formal scattering theory, the elastic and inelastic scattering intensities are developed in a manner that identifies the small overlap region in the surface electron density where the projectile atom is repelled. The effective vibrational displacements of the electron gas, which lead to energy transfer through excitation of phonons, are directly related to the vibrational displacements of the atomic cores in the target crystal via electron-phonon coupling. The effective Debye-Waller factor for atom-surface scattering is developed and related to the mean square displacements of the atomic cores. The complex dependence of the Debye-Waller factor on momentum and energy of the projectile, including the effects of the attractive adsorption well in the interaction potential, are clearly defined. Applying the standard approximations of electron-phonon coupling theory for metals to the distorted wave Born approximation leads to expressions which relate the elastic and inelastic scattering intensities, as well as the Debye-Waller factor, to the well known electron-phonon coupling constant λ. This treatment reproduces the previously obtained result that the intensities for single phonon inelastic peaks in the scattered spectra are proportional to the mode specific mass correction components λQ,ν defined by the relationship λ = 〈λQ,ν〉. The intensities of elastic diffraction peaks are shown to be a weighted sum over the λQ,ν, and the Debye-Waller factor can also be expressed in terms of a similar weighted summation. In the simplest case the Debye-Waller exponent is shown to be proportional to λ and for simple metals, metal overlayers, and other kinds of conducting surfaces values of λ are extracted from available experimental data. This dependence of the elastic and inelastic scattering, and that of the Debye-Waller factor, on the electron-phonon coupling constant λ shows that measurements of elastic and inelastic spectra of atomic scattering are capable of revealing detailed information about the electron-phonon coupling mechanism in the surface electron density.

原子散射作为导电表面电子-声子相互作用的探针
在热或超热动能范围内与表面碰撞的原子抛射体与目标原子第一层前的电子密度相互作用并被反射,一般认为排斥相互作用势与延伸到表面外的电子密度成正比。本文用电子-声子耦合理论对原子在导电表面的弹性和非弹性散射进行了完整的处理,其中电子密度及其振动与原子的相互作用进行了处理。从形式散射理论的基本原理出发,以确定抛射原子被排斥的表面电子密度中的小重叠区域的方式开发了弹性和非弹性散射强度。电子气体的有效振动位移通过激发声子导致能量传递,与目标晶体中原子核的电子-声子耦合振动位移直接相关。建立了原子表面散射的有效德拜-沃勒因子,并将其与原子核的均方位移联系起来。明确地定义了德拜-沃勒因子对弹丸动量和能量的复杂依赖关系,包括相互作用势中吸引吸附阱的影响。将金属电子-声子耦合理论的标准近似应用于畸变波玻恩近似,可以得到弹性和非弹性散射强度以及Debye-Waller因子与众所周知的电子-声子耦合常数λ相关的表达式。这种处理再现了先前得到的结果,即散射光谱中单声子非弹性峰的强度与模式比质量修正分量λ q,ν成正比,由关系λ = < λ q,ν >定义。弹性衍射峰的强度是λQ,ν的加权和,Debye-Waller因子也可以用类似的加权和来表示。在最简单的情况下,Debye-Waller指数被证明与λ成正比,对于简单金属,金属覆盖层和其他类型的导电表面,λ的值是从可用的实验数据中提取的。弹性和非弹性散射以及德拜-沃勒因子对电子-声子耦合常数λ的依赖表明,原子散射的弹性和非弹性光谱的测量能够揭示表面电子密度中电子-声子耦合机制的详细信息。
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来源期刊
Surface Science Reports
Surface Science Reports 化学-物理:凝聚态物理
CiteScore
15.90
自引率
2.00%
发文量
9
审稿时长
178 days
期刊介绍: Surface Science Reports is a journal that specializes in invited review papers on experimental and theoretical studies in the physics, chemistry, and pioneering applications of surfaces, interfaces, and nanostructures. The topics covered in the journal aim to contribute to a better understanding of the fundamental phenomena that occur on surfaces and interfaces, as well as the application of this knowledge to the development of materials, processes, and devices. In this journal, the term "surfaces" encompasses all interfaces between solids, liquids, polymers, biomaterials, nanostructures, soft matter, gases, and vacuum. Additionally, the journal includes reviews of experimental techniques and methods used to characterize surfaces and surface processes, such as those based on the interactions of photons, electrons, and ions with surfaces.
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