Patent ID: 8695108

Claim:
An in-liquid potential measurement device that measures a surface potential of a sample in a liquid, the in-liquid potential measurement device comprising: a cantilever having a cantilever structure including a free end with a sharp probe that is an electrode; an electrostatic force measurement unit configured to measure a voltage corresponding to electrostatic force between the probe and the sample; an AC source that applies an AC voltage between the probe and the sample; and a signal detection unit configured to detect signals of certain frequency components from the voltage measured by the electrostatic force measurement unit, and output values corresponding to the detected signals, wherein a frequency of the AC voltage applied by the AC source is 10 kHz or higher, and wherein the signal detection unit is configured to detect, from the voltage measured by the electrostatic force measurement unit, (1) an amplitude of a signal having a frequency component that is a same frequency as a frequency of the AC voltage applied by the AC source, (2) an amplitude of a signal having a frequency component that is a frequency that is twice as high as the frequency of the AC voltage, and (3) a frequency component having a same phase as a phase of the frequency that is the same as the frequency of the AC voltage.