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 x 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 x 7 domain boundaries) already at coverages as low as 4 x 10(12) cm(-2). These islands may be responsible for the previously reported work function lowering and enhanced chemical reactivity upon K deposition.