Nano-scale patterning on sulfur terminated GaAs (001) surface by scanning tunneling microscope

We perform nano-scale patterning on a sulfur (S) terminated GaAs (001) surface by a scanning tunneling microscope (STM) in ultra-high vacuum (UHV). A multi-layer of S deposited by using (NH4)2Sx solution is changed to a mono-layer after annealing at 560°C for 15h, which terminates the GaAs (001) surface. Groove structures with about 0.23nm in depth and about 5nm in width are patterned successfully on the S-terminated surface. We investigate dependences of both depth and width of the patterned groove on the tunneling current and the scanning speed of tip. It is observed that topmost S atoms are extracted together with first-layer Ga atoms, because of the larger binding energy of SGa bond.