Direct observation of one-dimensional Ga-atom migration on a Si(100)-(2 x 1)-H surface: A local probe of adsorption energy variation

Atomic-scale surface migration of a Ga atom on a hydrogen-terminated Si(100 )-(2 x 1)-H surface is studied using low-temperature scanning tunneling mic roscopy and first-principles calculations. The Ga atom migrates in a linear potential well confined by adjacent dimer rows and local dihydride defects , and is observed as a continuous linear protrusion (Ca-bar structure) at a narrow range of temperatures near 100 K. We point out that the height of t he Ga-bar structure maps out the local variation in potential energy at ind ividual adsorption sites.