Pseudo-non-contact mode: why it can give true atomic resolution

Pseudo-non-contact (PNC) mode of scanning in atomic force microscopy (AFM) is a modification of the contact mode while the AFM tip and sample are immersed in a rather diluted aqueous surfactant solution. An additional repulsion due to the presence of surfactant leads to a decrease of the tip-sample interaction, mostly friction, during scanning. Experiments have shown considerable improvement in the resolution over a regular contact scanning. In this paper, further theoretical evidence is suggested that the PNC mode is capable of reaching the true atomic resolution, i.e., imaging of atomic defects. Forces acting between the AFM tip and sample under surfactant solution were measured. These data were used to simulate behavior of the AFM tip while scanning in the vicinity of an atomic defect, vacancy. It is shown that the scan force needed to remove the topmost atom is considerably higher in the presence of surfactant. Consequently, a regular force of a few nano-Newtons can be used in imaging with true atomic resolution