RUI: Halogen-Etched and Chemically-Sputtered Germanium Surfaces

该项目是一个多方面的研究单晶锗表面改性反应卤素蚀刻剂和高能离子轰击。使用扫描探针显微镜（SPM），反射高能电子衍射（RHEED），和光电子能谱（PES）的蚀刻锗衬底上的一系列实验计划。初始阶段将研究Ge（100）-（2x1）和Ge（111）-c（2x8）表面被双原子卤素分子（Cl 2，Br 2，I2）蚀刻的形态。通过理论分析（相关函数、粒度分布等），的SPM图像从蚀刻表面，比较表面粗糙化的理论模型，以评估竞争的平滑和粗糙化机制。这些数据也将比较从蚀刻硅表面收集的数据具有相同的取向。锗和硅的化学相似性，预计产生相同的卤化表面物种后，暴露于卤素蚀刻剂，这将被验证的PES测量进行合作者在威斯康星州同步辐射中心。结构差异，特别是在（111）取向的表面上，预计会产生不同的表面结构，从而深入了解表面演化的结构机制。化学溅射（同时将表面暴露于高能离子和中性卤素分子）将在Ge（100）-（2x1）表面上进行。SPM结果从这些实验中结合那些从简单的蚀刻系统和那些从简单的溅射系统将识别表面结构的相似性和差异。化学溅射法的独特之处是由于在高能离子和反应性化学蚀刻剂的存在下可以发生的蚀刻的协同增强。在蚀刻过程中原位进行的动态RHEED测量将能够监测表面结晶度。可以调整蚀刻参数，使得获得RHEED振荡，指示逐层去除。PES测量将用于评估化学溅射后高度卤化物质的浓度。独特的表面形态来自材料去除。蚀刻坑、表面缺陷、再生长二聚体链和再生长岛是可以通过蚀刻剂通量、蚀刻剂注量和衬底温度控制的纳米结构种类的示例。这些表面特征的大域可以被创建并用作薄膜生长的模板。研究的目的是探索这些纳米结构对薄膜成核和生长的影响。SPM数据的统计分析将允许监测表面形态的演变。问题包括这些表面结构是否提高成核密度，岛聚结是如何影响的，以及如何影响界面的不规则性。在进行薄膜生长实验之前，必须从表面去除残留的卤素原子，优选地不干扰蚀刻表面的结构。原子氢提取卤素原子已被证明是有效的使用光谱技术，然而，这一过程的影响还没有从形态学的角度进行探讨。将收集SPM和PES数据，以验证该技术在表面改性方面的有效性。%该项目涉及材料科学专题领域的基础研究问题，具有技术相关性。本科生将在该项目中发挥主要作用，研究机会直接融入他们的学术课程，并在夏季继续全职。该研究计划将使前沿研究和获得最先进的表面科学设备的本科生。该项目的一个重要特点是高度重视教育，并将研究与教育相结合。***

This RUI project is a multifaceted study of single crystal germanium surfaces modified by reactive halo-gen etchants and energetic ion bombardment. Using scanning probe microscopy (SPM), reflection high-energy electron diffraction (RHEED), and photoemission spectroscopy (PES) a sequence of experiments on etched germanium substrates are planned. Initial stages will investigate the morphology of Ge(100)-(2x1) and Ge(111)-c(2x8) surfaces etched by diatomic halogen molecules (Cl2 , Br2 , I2 ). Through statis-tical analyses (correlation functions, size distributions, etc.) of SPM images from the etched surfaces, comparisons with theoretical models of surface roughening will be made to assess competing smoothing and roughening mechanisms. These data will also be compared to data collected from etched silicon sur-faces with the same orientations. The chemical similarity of germanium and silicon is predicted to yield the same halogenated surface species upon exposure to the halogen etchant-this will be verified by PES measurements to be carried out with collaborators at the University of Wisconsin Synchrotron Radiation Center. Structural differences, particularly on the (111)-oriented surfaces are expected to yield different surface structures, thereby yielding insight into structural mechanisms of surface evolution. Chemical sputtering (the simultaneous exposure of a surface to energetic ions and neutral halogen molecules) will be carried out on Ge(100)-(2x1) surfaces. SPM results from these experiments in conjunction with those from simple etch systems and those from simple sputter systems will identify similarities and differences in surface structure. Features unique to the chemical sputtering method are expected due to the synergis-tic enhancements in etching that can occur in the presence of both energetic ions and reactive chemical etchants. Dynamic RHEED measurements taken in situ during etching will enable monitoring of surface crystallinity. Etching parameters can be tuned so that RHEED oscillations are obtained, indicative of layer-by- layer removal. PES measurements will be used to assess concentrations of highly halogenated species after chemical sputtering. Unique surface morphologies result from material removal. Etch pits, surface defects, regrowth dimer chains, and regrowth islands are examples of the kinds of nanostructures that can be controlled via etchant flux, etchant fluence, and substrate temperature. Large domains of these surface features can be created and used as templates for thin-film growth. The goal of the research is to explore the influence of these nanostructures on the nucleation and growth of thin films. Statistical analysis of SPM data will allow monitoring evolution of surface morphology. Questions being addressed include whether or not these surface structures enhance nucleation density, how island coalescence is af-fected, and how interface abruptness is affected. Before the thin-film growth experiments take place, re-sidual halogen atoms must be removed from the surfaces, preferably without disturbing the structure of the etched surface. Extraction of halogen atoms by atomic hydrogen has been shown to be effective using spectroscopic techniques; however, the effect of this procedure has not been explored from a morpho-logical perspective. SPM and PES data will be collected in order to verify the effectiveness of this tech-nique with respect to surface modification.%%% The project addresses fundamental research issues in a topical area of materials science having techno-logical relevance. Undergraduate students will play a primary role in the project, with opportunities for research integrated directly into their academic program, and continued full time in the summer. The re-search program will enable forefront research and access to state-of-the-art surface science equipment to undergraduate students. An important feature of the project is the strong emphasis on education, and the integration of research and education. ***