Controllable modification of fractured Nb-doped SrTiO$_{3}$ surfaces

Nano-scale surface modification of a fractured Nb-doped SrTiO$_{3}$(Nb:STO) surface is demonstrated in a controlled way using scanning tunneling microscopy. It is revealed with high-resolution images that by fracturing Nb:STO at low temperature, about 50 \% of SrO adatoms are randomly distributed on large ($>$500 nm) TiO$_{2}$ terminated terraces. By applying positive voltage pulses with appropriate bias and pulse duration, holes can be created with desired width and depth. By applying negative bias, the hole can be partially refilled from the transfer of adsorbates on the tip. The change of dI/dV contrast when creating/refilling the hole is consistent with the model of exposure/covering of the underlying TiO$_{2}$ layer by removal/deposition of SrO. This entire modification process can be explained by a surface atom manipulation mechanism.