The role of adsorbed alkali metal atoms in the enhancement of surface reactivity: A scanning tunneling microscopy study of low coverage K/Si(111)7×7 surfaces

Atomically resolved surface photovoltage imaging and tunneling barrier imaging were performed with a scanning tunneling microscope to elucidate the nature of the initial adsorption state of potassium on room temperature Si(111)7×7 surface, which appears as a missing center Si-adatom. No evidence was found to support the fact that this adsorption mode is charged. K islands start to grow (and accumulate at 7×7 domain boundaries) already at coverages as low as 4×1012 cm−2. These islands may be responsible for the previously reported work function lowering and enhanced chemical reactivity upon K deposition.