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

w：\awards\awards96\*.doc 9801830 Plummer 这个实验研究项目集中了广泛的表面物理技术来探测金属表面的电子密度波。 一个中心议题是表面过渡从弗里德尔 振荡 到 电荷 密度 波 弗里德尔振荡的表面将被成像与一个可变的温度STM和测量的能带（高分辨率ARPES）和响应函数在费米能量与动量分辨电子散射确定。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的转变。 表面声子色散将通过高分辨率非弹性电子散射测量，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。 特别感兴趣的主题是：a）从弗里德尔振荡到CDW的转变，B）非自由电子能带结构的弗里德尔振荡的波长，c）多体作用 影响 在 弗赖代尔 振荡 和 表面转变，d）通过表面声子色散的温度依赖性，由于长程Friedel振荡引起的表面屏蔽的差异，以及e）由温度依赖性表面响应函数驱动的温度依赖性表面结构。这项研究计划是跨学科的性质，涉及几个前和研究生的学生，谁收到 为职业生涯做准备的优秀培训 在工业界、政府实验室或学术界。 这个实验研究项目致力于研究 晶体金属表面的原子与晶体体中的原子相比。 这些差异是微妙的，难以衡量，但它们具有实际意义。金属的表面性质很重要，例如在化学催化中，所涉及的化学试剂仅与表面原子接触。 在现代实验室中，可以利用先进的技术来具体揭示表面原子的性质。 几种技术是扫描隧道显微镜，低能电子衍射，角分辨光电子能谱和高分辨率非弹性电子散射。所有这些技术都被应用在这个基础研究项目中。 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， 涉及改进的催化剂。该研究计划是跨学科的性质，涉及几个预科和研究生，谁接受在工业，政府实验室或学术界的职业生涯准备优秀的培训。 ***

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. ***