Surface potential imaging with atomic resolution by frequency-modulation Kelvin probe force microscopy without bias voltage feedback

We investigated the capability of obtaining atomic resolution surface potential images by frequency-modulation Kelvin probe force microscopy (FM-KPFM) without bias voltage feedback. We theoretically derived equations representing the relationship between the contact potential difference and the frequency shift (Δf) of an oscillating cantilever. For the first time, we obtained atomic resolution images and site-dependent spectroscopic curves for Δf and VLCPD on a Si (111)-7 × 7 surface. FM-KPFM without bias voltage feedback does not involve the influence of the FM-KPFM controller because it has no deviation from a parabolic dependence of Δf on the dc-bias voltage. It is particularly suitable for investigation on molecular electronics and organic photovoltaics, because electron or ion movement induced by dc bias is avoided and the electrochemical reactions are inhibited.