Surface potential measurement on organic ultrathin film by Kelvin probe force microscopy using a piezoelectric cantilever

We measured surface potential (SP) on a pi-conjugated thiophene oligomer monolayer film deposited on a metallic substrate by Kelvin probe force microscopy using a piezoelectric cantilever. Since the cantilever has a relatively large spring constant (calculated as about 150 N/m), the frequency modulation detection method was used for tip-sample distance regulation in order to achieve high-sensitivity SP measurement. A contact potential difference between monolayer regions and the metallic substrate was clearly observed in an SP image. Furthermore, an apparent change in a contrast of the SP image was observed while the sample was irradiated with ultraviolet light.