Nanoscale reversible molecular extraction from a self-assembled monolayer on gold(111) by a scanning tunneling microscope

Alkanethiol self-assembled monolayers (SAMs) on Au(lll) deposited in a vacuum were studied on the nanometer scale using a scanning tunneling microscope (STM). After about 17 h from the gas dose of 4200-6000 langmuirs nonanethiol, two-dimensional crystallized domains were observed. The areas covered with the molecules and the bare gold surface were identified by topography, current-voltage characteristics, and the threshold voltage required to modify the surface. By applying 2.6-3.0 V to the sample, we could extract molecules and create holes with diameters of 2-5 nm in the SAM film. Applying 14 voltage pulses of 2.6 V to a 10 nm diameter circle on the sample locally removed the SAM film. We could then observe the dynamic formation process of the SAM film with molecular resolution using the STM, and within 5 min, the removed area was seen to be almost recovered with the molecular lattice except for a small number of incurable defects. Since the recovered area looked identical to the pristine film, we concluded that the molecules can be locally extracted without causing damage to the gold substrate under this condition.