Tl overlayers on Si(1 0 0) and their self-assembly induced by STM tip

Formation of the thallium (Tl) overlayers on the Si(1 0 0) 2 1 surface has been studied using scanning tunneling microscopy (STM). It has been found that adsorption of Tl atom involves a charge transfer leading to the development of a static dipole which is responsible for the field-assisted migration of the Tl adsorbate on the surface. When the STM tip bias voltage is positive, Tl atoms are repelled out from the region underneath the tip apex. In the case of the negative bias voltage, Tl is accumulated underneath the tip. Thus, the observed structure of the surface is controlled not only by Tl coverage, but also by the STM bias voltage and tunneling current.