Patent ID: 8763160

Claim:
A method for measuring a surface potential of a portion of material, wherein an electrically conductive detection tip is placed above a surface of said portion of material, with a first piezoelectric actuator arranged to control a mean distance of the detection tip above said surface of the portion of material, and a second piezoelectric actuator arranged to control a mechanical oscillation of said detection tip above said surface of the portion of material as a function of a voltage existing between two control electrodes of said second piezoelectric actuator, said method comprising the following steps: applying a measurement voltage between the detection tip and the portion of material, said measurement voltage comprising a direct component and an alternating component having a selected angular frequency of excitation; detecting variations in an instant height of the detection tip while applying the measurement voltage; measuring an amplitude of a component of said variations in the instant height of the detection tip, for said angular frequency of excitation; adjusting a value of the direct component of the measurement voltage in a manner that reduces or cancels the amplitude of the component of the variations in the instant height of the detection tip for the angular frequency of excitation, the adjusted value of said direct component of the measurement voltage constituting a result of the measurement of the surface potential of the portion of material; while the variations in the instant height of the detection tip are being detected: the two control electrodes of the second piezoelectric actuator are electrically connected to two respective reference terminals; and a control voltage is applied between the two control electrodes of the second piezoelectric actuator using the two reference terminals, said control voltage having a zero amplitude alternating component for the angular frequency of excitation; compensating for a contribution to an electrical detection signal for the component of the variations in the instant height of the detection tip for the angular frequency of excitation while said variations in the instant height of the detection tip are being detected, said contribution resulting from a direct coupling between the measurement voltage applied between the detection tip and the portion of material, and a detector used to detect the variations in the instant height of the detection tip; and prior measurements of the contribution of the direct coupling to an electrical signal for detecting the variations in the instant height of the detection tip, for angular frequencies different from the angular frequency of excitation, wherein said contribution of the direct coupling to the component of the variations in the instant height of the detection tip for the angular frequency of excitation is compensated for by an extrapolation, at said angular frequency of excitation, of results from the prior measurements for angular frequencies different from the angular frequency of excitation.