NANOMETER-SCALE MODIFICATIONS OF GOLD SURFACES BY SCANNING TUNNELING MICROSCOPE

The modification of gold surfaces with scanning tunneling microscopy in ultrahigh vacuum was investigated. At a tunneling resistance higher than 1 GΩ, a hole was created by applying a negative voltage pulse to a gold tip, and a mound by a positive one. The existence of a critical field together with the purity dependence suggests that a mechanism of the modification would be the field evaporation of positive Au ions. On the other hand, at a low resistance, a mound adjacent to a hole was often created by the negative pulse and the current kept flowing even after the voltage pulse. These results indicate that the formation of a mound in the case of negative pulses is a result of necking after the massive transfer of gold from the surface to the tip apex. The size of the hole created by applying the negative pulse with the threshold voltage decreased as the initial tunneling resistance decreased.