Photo-induced bond breaking and new phase formation on Si(001) surface

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1.We studied laser-induced bond breaking and new phase formation on Si(001)-(2x1) surfaces, and obtained the results as follows :(1)Repeated irradiation induces progressive growth of vacancies as well as newly formation of monovacancies. Vacancy clusters elongated along dimer rows are predominantly formed on the surface, indicating a strong site-dependent rate of bond breaking(2)Excitation above 100mJ/cm2 induces formation of ad-dimers on the terrace, and then ad-dimer islands are produced under repeated excitation Laser-induced ad-dimer formation disturbs the formation of defect-free atomic-leveled flat surface.(3)Scanning tunneling microscopic(STM) study revealed that laser-induced removal of surface dimers forms a new phase, which has never been obtained by thermal processes. We succeeded in removing 95 % of surface dimers by repeated irradiation.2.We studied structural instability of the Si(111)-(7x7) surface induced by low energy electron excitation, and obtained the following result.(1)Low energy electron induces removal of adatoms from the Si(111)-(7x7) surface, rate of which is linear with respect to excitation flux and is strongly dependent on the primary energy of electron beam. We proposed plasmon-related bond breaking mechanism for explaining the electron-induced structural instability.