Experimental study on energy dissipation induced by displacement current in non-contact aomic force microscopy imaging of molecular thin films

The electrical dissipation in non-contact atomic force microscopy (NC-AFM) was investigated in connection with the displacement current flowing between a tip and a sample, both of which were in the bias circuit loop. Oligothiophene sub-monolayer films deposited on a Pt substrate were used for studying dissipation images. The resistance (R-bias) in the bias circuit was changed in order to observe variations in the dissipation images. The electrical dissipation showed strong dependence on R-bias, revealing that the displacement current in the bias line plays an important role in the electrical dissipation process. However, the dependence cannot be explained by the simple Joule dissipation at R-bias We also used Kelvin probe force microscopy to cancel out the dissipation variation. Although the contrast was clearly suppressed by KFM bias feedback, it did not completely disappear probably due to the remaining ac bias modulation voltage.