Phase detection of electrostatic force by AFM with a conductive tip

Electrostatic force measurements were performed by the Kelvin probe force microscopy, which consists of the atomic force microscopy and a conductive tip. Sample surface potential was evaluated through the electrostatic force, which works between the sample and the tip when we apply an AC bias at a frequency fs with a DC offset. If the DC offset voltage is equal to the surface potential difference between the sample and the tip, the amplitude of the fs component in the electrostatic force becomes zero, and the phase of the fs component jumps 180° there. We found that the complementary use of the amplitude and phase signals improved the accuracy of the determination of the surface potential. We measured both the work functions of some metals and the surface Fermi levels of an InAs layers on (1 0 0) and (1 1 0) GaAs substrates based on the phase detection method of the electrostatic force.