Manipulation of Atoms and Molecules by Electronic Excitation

该优先领域项目于1998- 2001财年开展，旨在通过8个研究小组的合作，分享共同的材料系统和思想，阐明半导体中电子激发诱导原子运动机制的全图，从而开发出在固体材料中具有高可控性（选择性）和高效率的操纵原子和分子的新技术，这些技术有望用于实现下一代设备。实际研究的材料包括典型的半导体，如Si， C和GaAs，电子激发方法基于光子照明（激光和x射线），粒子束（电子和离子），电流注入和电荷状态控制。今年的活动致力于总结三年的项目，包括两次小组领导委员会会议，一次公开研讨会和出版新闻信函。通过这些活动，我们提出了提高电子激发原子和分子操纵的效率和选择性的一般指导方针：有效可控的材料体系应该是由于轨道简并激发态而具有固有结构不稳定性的半导体缺陷中心、激发态中具有高迁移率的氢等轻元素、具有结构柔性的缺陷或表面以及具有柔性轨道杂化的碳固体。利用高密度激励、协同激励和并行过程产生的长寿命双孔态也将提高一次激励的效率。此外，为了达到局域激发所期望的位置选择性，有必要抑制扩展能带状态下激发电子（空穴）的空间扩散。

This priority area project carried out in 1998- 2001 FY aimed to elucidate, with cooperation of 8 research groups sharing common material systems and thoughts, the whole picture of the mechanisms of electronic excitation induced atomic movements in semiconductors thereby developing novel techniques for manipulating atoms and molecules with high controllability (selectivity) and efficiency in solid materials that are expected to be useful for realization of next generation devices. The materials actually studied have included typical semiconductors such as Si, C and GaAs, and the electronic excitation methods have been based on photon illumination (laser and X-ray), particle beams (electron and ion), current injection, and charge state control. The activities this year, devoted to summarizing the 3 years project, have included two committee meetings of group leaders, an open workshop, and publication of a News Letter. Through these activities, we have proposed a general guide line for enhancing the efficiency and : the selectivity of atomic and molecular manipulation by electronic excitations : The material systems efficiently controllable should be defect centers in semiconductors possessing inherent structural instability due to orbitally-degenerate excited states, light elements such as hydrogens with high mobility in the excited states, defects or surfaces with structural flexibility, and carbon solids with flexible orbital hybridization. The use of long lifetime two-hole states generated by high density excitations, cooperative excitations and parallel processes will also promote the efficiency of the primary excitations. Further, to attain the site-selectivity expected in localized excitations, it is necessary to suppress the spatial spread of the excited electrons (holes) in the extended band states.