Kinks and Surface Potentials

9814055SpenceThis project addresses dislocation kink dynamics，and measurement of Coulomb potential normal to a surface by quantitative convergent-beam reflection high energy diffraction（Micro-probe RHEED）.位错扭结将通过原子分辨率TEM在诸如蓝宝石、SiC和MgO的材料中观察到，其中已经发现可以通过在氧气或真空中退火在中等（10-7托）真空条件下为薄TEM样品制备原子级平坦的阶梯表面。“禁止”布拉格反射，产生于部分位错之间的堆垛层错，将用于形成晶格图像，允许图像形成没有表面噪声。该方法是确定在给定的温度和应力条件下，哪个过程（扭结形成、扭结迁移或沿着位错线的障碍物）限制了扭结（并因此限制了位错）的速度。通过扩展以前的定量会聚束TEM测量晶体中的RHEED几何形状的结合，它计划细化从陶瓷表面延伸到真空中的静电势。这种电势对于表面的化学反应、吸附、催化、外延、扩散结合过程、氧化和半导体晶体生长至关重要。表面势垒在场致发射和二次电子发射等电子过程中也很重要。测量由单层或多层原子的沉积引起的对该电势的修改，可以提供对表面如何形成键以及原子电荷密度的修改的直接实验理解。该项目涉及材料科学专题领域的基础研究问题，具有很高的潜在技术相关性。该研究将为电子/光子器件的新方面提供基础材料科学知识。 现在已有实验工具，可以在原子水平上观察基本表面过程，如果能更好地了解这些过程，就可以在基础科学和技术方面取得进展。从研究中获得的基本知识和理解预计将有助于提高先进器件和电路的性能和稳定性，为设计和生产改进的材料和材料组合提供基本的理解和基础。 该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。9814055SpenceThis project addresses dislocation kink dynamics，and measurement of Coulomb potential normal to a surface by quantitative convergent-beam reflection high energy diffraction（Micro-probe RHEED）.位错扭结将通过原子分辨率TEM在诸如蓝宝石、SiC和MgO的材料中观察到，其中已经发现可以通过在氧气或真空中退火在中等（10-7托）真空条件下为薄TEM样品制备原子级平坦的阶梯表面。“禁止”布拉格反射，产生于部分位错之间的堆垛层错，将用于形成晶格图像，允许图像形成没有表面噪声。该方法是确定在给定的温度和应力条件下，哪个过程（扭结形成、扭结迁移或沿着位错线的障碍物）限制了扭结（并因此限制了位错）的速度。通过扩展以前的定量会聚束TEM测量晶体中的RHEED几何形状的结合，它计划细化从陶瓷表面延伸到真空中的静电势。这种电势对于表面的化学反应、吸附、催化、外延、扩散结合过程、氧化和半导体晶体生长至关重要。表面势垒在场致发射和二次电子发射等电子过程中也很重要。测量由单层或多层原子的沉积引起的对该电势的修改，可以提供对表面如何形成键以及原子电荷密度的修改的直接实验理解。该项目涉及材料科学专题领域的基础研究问题，具有很高的潜在技术相关性。该研究将为电子/光子器件的新方面提供基础材料科学知识。 现在已有实验工具，可以在原子水平上观察基本表面过程，如果能更好地了解这些过程，就可以在基础科学和技术方面取得进展。从研究中获得的基本知识和理解预计将有助于提高先进器件和电路的性能和稳定性，为设计和生产改进的材料和材料组合提供基本的理解和基础。 该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。

9814055SpenceThis project addresses dislocation kink dynamics, and measurement of the Coulomb potential normal to a surface by quantitative convergent-beam reflection high energy diffraction (Micro-probe RHEED). Dislocation kinks will be observed by atomic resolution TEM in materials such as sapphire, SiC and MgO, where it has been found possible to prepare atomically flat terraced surfaces for thin TEM samples under moderate (10-7 Torr) vacuum conditions by annealing in oxygen or vacuum. "Forbidden" Bragg reflections, arising from the stacking fault between partial dislocations, will be used to form lattice images, allowing images to be formed without surface noise. The approach is to determine which process (kink formation, kink migration or obstacles along the dislocation line) limits kink (and hence dislocation) velocity, for given conditions of temperature and stress. By extending prior quantitative convergent-beam TEM measurements of bonding in crystals to the RHEED geometry, it is planned to refine the electrostatic potential extending into the vacuum from ceramic surfaces. This potential is critical for chemical reactions at surfaces, for adsorption, catalysis, epitaxy, the diffusion bonding process, oxidation, and semiconductor crystal growth. The surface potential barrier is also critical in electronic processes, such as field emission and secondary electron emission. Measurements of the modification to this potential which result from the deposition of a monolayer or more, of atoms can provide a direct experimental understanding of how bonds are formed at surfaces, and of the modification of atomic charge densities.%%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic/photonic devices. Experimental tools are now available to allow atomic level observation of elementary surface processes which when better understood allow advances in fundamental science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance and stability of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.***9814055SpenceThis project addresses dislocation kink dynamics, and measurement of the Coulomb potential normal to a surface by quantitative convergent-beam reflection high energy diffraction (Micro-probe RHEED). Dislocation kinks will be observed by atomic resolution TEM in materials such as sapphire, SiC and MgO, where it has been found possible to prepare atomically flat terraced surfaces for thin TEM samples under moderate (10-7 Torr) vacuum conditions by annealing in oxygen or vacuum. "Forbidden" Bragg reflections, arising from the stacking fault between partial dislocations, will be used to form lattice images, allowing images to be formed without surface noise. The approach is to determine which process (kink formation, kink migration or obstacles along the dislocation line) limits kink (and hence dislocation) velocity, for given conditions of temperature and stress. By extending prior quantitative convergent-beam TEM measurements of bonding in crystals to the RHEED geometry, it is planned to refine the electrostatic potential extending into the vacuum from ceramic surfaces. This potential is critical for chemical reactions at surfaces, for adsorption, catalysis, epitaxy, the diffusion bonding process, oxidation, and semiconductor crystal growth. The surface potential barrier is also critical in electronic processes, such as field emission and secondary electron emission. Measurements of the modification to this potential which result from the deposition of a monolayer or more, of atoms can provide a direct experimental understanding of how bonds are formed at surfaces, and of the modification of atomic charge densities.%%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic/photonic devices. Experimental tools are now available to allow atomic level observation of elementary surface processes which when better understood allow advances in fundamental science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance and stability of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.***