In order
to fabricate highly functional nanostructure devices for future
technology, it is essential to establish strategies to control
structure and composition of hetero-structures at the atomic level.
We aim to establish the fundamentals for controlling chemical
bonding in epitaxial processes by means of laser-induced atomic
reactions. We have shown that dramatic structural changes are induced by the excitation of the electronic system when the excitation energy is localized at certain lattice points. These are featured by the conversion of bonding modes typically between sp2 and sp3 like and between ionic and covalent; important factors governing atomic bonding can be controlled by electronic excitation during epitaxial processes.
It is now well known that laser is the most sophisticated source of excitation of atoms and solids; the mode of excitation can be controlled temporally, spatially, spectroscopically, and in magnitude. Therefore, lasers of several different types are used in this project of "excited-state epitaxy". Two different, but closely related, topics are studied. One is controlling structures of substrate surfaces at the atomic level to generate, for example, completely defect-free surfaces. The other is controlling chemical bonding during deposition of excited-state atoms on well-characterized surfaces to generate new crystalline phases which cannot be achieved by conventional methods. By combining these two topics, our goal is to construct highly functional hetero-structures of new types.
