Electron Density Waves at Metal Surfaces: From Friedel Oscillations to Charge Density Waves

这个实验研究项目集中于广泛的表面物理技术来探测金属表面的电子密度波。一个中心主题是从弗里德尔振荡到电荷密度波的表面跃迁。表面的弗里德尔振荡将用变温STM成像，并与能带测量值（高分辨率ARPES）和动量分辨电子散射确定的费米能量响应函数进行比较。表面的原子结构作为温度的函数将通过结合表面x射线散射（简单分析）和LEED（表面灵敏度）来确定。在非弹性电子散射中可以观察到金属到非金属跃迁的存在。表面声子色散将通过高分辨率非弹性电子散射来测量，并与Hulpke（德国）合作，使用非弹性氦散射。所有工作都将与世界各地的理论家密切合作完成。特别感兴趣的主题有：a)从弗里德尔振荡到CDW的转变，b)非自由电子带结构中弗里德尔振荡的波长，c)多体效应在弗里德尔振荡和表面转变中的作用，d)通过表面声子色散的温度依赖，由于远距离弗里德尔振荡而导致的表面筛选差异，e)由温度相关表面响应函数驱动的温度相关表面结构。这个研究项目本质上是跨学科的，涉及几名预科和研究生，他们接受了优秀的培训，为在工业、政府实验室或学术界的职业生涯做准备。这个实验研究项目致力于研究金属晶体表面的原子与晶体内部原子的不同行为。这些差异是微妙的，难以衡量的，但它们具有实际的重要性。金属的表面性质很重要，例如在化学催化中，所涉及的化学试剂只与表面原子接触。在现代实验室中，可以使用先进的技术来具体地揭示表面原子的性质。其中包括扫描隧道显微镜、低能电子衍射、角分辨光发射光谱和高分辨非弹性电子散射等技术。所有这些技术都应用于本基础研究项目。这项基础研究将增加对表面原子性质的理解，并可能间接导致，例如，改进催化剂。这个研究项目本质上是跨学科的，涉及几名预科和研究生，他们接受了优秀的培训，为在工业、政府实验室或学术界的职业生涯做准备。＊＊＊

w:\awards\awards96\*.doc 9801830 Plummer This experimental research project focuses a wide range of surface physics techniques to probe electron density waves at metal surfaces. A central topic is the surface transition from Friedel oscillations to Charge Density Waves. Friedel oscillations at the surface will be imaged with a variable temperature STM and compared to measurements of the energy bands (high-resolution ARPES) and to the response function at the Fermi energy determined with momentum-resolved electron scattering. The atomic structure of the surface as a function of temperature will be determined by combining surface x-ray scattering (simple analysis) with LEED (for surface sensitivity). The presence of a metal-to-nonmetal transition is observable in inelastic electron scattering. Surface phonon dispersion will be measured by high resolution inelastic electron scattering, and, in collaborations with Hulpke (Germany), using inelastic helium scattering. All work will be done in close collaboration with theorists around the world. Topics of specific interest are: a) the transition from Friedel oscillations to a CDW, b) wavelengths of Friedel oscillations for a non-free-electron band structure, c) role of many-body effects in Freidel oscillations and surface transitions, d) difference of surface screening due to long range Friedel oscillations, via the temperature dependence of the surface phonon dispersion, and e) the temperature dependent surface structure driven by the temperature dependent surface response function. This research program is interdisciplinary in nature and involves several pre- and post-graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project is devoted to the distinct behavior of the atoms at the surface of a crystalline metal compared to atoms located in the bulk of the crystal. These differences are subtle and difficult to measure, but they have practical importance. Surface properties of metals are important for example in chemical catalysis, where the chemical reagents involved come into contact only with surface atoms. In modern laboratories advanced techniques are available which reveal specifically the properties of atoms at the surface. Several of the techniques are the Scanning Tunneling Microscope, Low Energy Electron Diffraction, Angle Resolved Photoemission Spectroscopy and high resolution inelastic electron scattering. All of these techniques are employed in this basic research project. This basic research will add to the understanding of atomic properties at surfaces, and could indirectly lead, e.g., to improved catalysts. This research program is interdisciplinary in nature and involves several pre- and post-graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***