Kinks and Surface Potentials

9814055Spence本项目研究位错扭结动力学，以及通过定量会聚光束反射高能衍射(Micro-Probe RHEED)测量垂直于表面的库仑电势。在蓝宝石、碳化硅和氧化镁等材料中，可以用原子分辨电子显微镜观察到位错扭结。在这些材料中，人们已经发现，在中等真空(10-7Torr)条件下，通过氧气或真空退火，可以为薄的透射电子显微镜样品制备原子平坦的梯形表面。由部分位错之间的堆积断层引起的“被禁止的”布拉格反射将被用来形成晶格图像，允许形成没有表面噪声的图像。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、扭结移动或位错线上的障碍物)限制了扭结(从而位错)的速度。通过将先前晶体中键合的定量会聚束电子显微镜测量扩展到RHEED几何结构，计划改进从陶瓷表面延伸到真空中的静电势。该电势对表面化学反应、吸附、催化、外延、扩散连接过程、氧化和半导体晶体生长至关重要。表面势垒在电子过程中也是至关重要的，例如场发射和二次电子发射。测量由单分子层或更多原子沉积引起的这种势的改变，可以提供对表面如何形成键的直接实验理解，以及原子电荷密度的改变。%该项目解决了具有高潜在技术相关性的材料科学的主题领域的基础研究问题。这项研究将在基础水平上为电子/光子器件的新方面贡献基本的材料科学知识。现在可以使用实验工具对基本的表面过程进行原子水平的观察，如果更好地了解这些过程，就可以推动基础科学和技术的进步。从研究中获得的基本知识和理解有望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，从而有助于提高先进器件和电路的性能和稳定性。该计划的一个重要特点是通过培训学生在基础和技术上具有重要意义的领域将研究和教育整合在一起。*9814055Spence本项目研究位错扭结动力学，并通过定量会聚光束反射高能衍射(Micro-Probe RHEED)测量垂直于表面的库仑电势。在蓝宝石、碳化硅和氧化镁等材料中，可以用原子分辨电子显微镜观察到位错扭结。在这些材料中，人们已经发现，在中等真空(10-7Torr)条件下，通过氧气或真空退火，可以为薄的透射电子显微镜样品制备原子平坦的梯形表面。由部分位错之间的堆积断层引起的“被禁止的”布拉格反射将被用来形成晶格图像，允许形成没有表面噪声的图像。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、扭结移动或位错线上的障碍物)限制了扭结(从而位错)的速度。通过将先前晶体中键合的定量会聚束电子显微镜测量扩展到RHEED几何结构，计划改进从陶瓷表面延伸到真空中的静电势。该电势对表面化学反应、吸附、催化、外延、扩散连接过程、氧化和半导体晶体生长至关重要。表面势垒在电子过程中也是至关重要的，例如场发射和二次电子发射。测量由单分子层或更多原子沉积引起的这种势的改变，可以提供对表面如何形成键的直接实验理解，以及原子电荷密度的改变。%该项目解决了具有高潜在技术相关性的材料科学的主题领域的基础研究问题。这项研究将在基础水平上为电子/光子器件的新方面贡献基本的材料科学知识。现在可以使用实验工具对基本的表面过程进行原子水平的观察，如果更好地了解这些过程，就可以推动基础科学和技术的进步。从研究中获得的基本知识和理解有望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，从而有助于提高先进器件和电路的性能和稳定性。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。

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.***