Combined atomic force microscopy and voltage pulse technique to accurately measure electrostatic force

Abstract

We propose a new method of extracting electrostatic force. The technique is based on frequency modulation atomic force microscopy (FM-AFM) combined with a voltage pulse. In this method, the work that the electrostatic field does on the oscillating tip is measured through the cantilever energy dissipation. This allows us to directly extract capacitive forces including the longer range part, to which the conventional FM-AFM is insensitive. The distance-dependent contact potential difference, which is modulated by local charges distributed on the surfaces of the tip and/or sample, could also be correctly obtained. In the absence of local charges, our method can perfectly reproduce the electrostatic force as a function of the distance and the bias voltage. Furthermore, we demonstrate that the system serves as a sensitive sensor enabling us to check the existence of the local charges such as trapped charges and patch charges.

Analytical method for the measurement of the electrostatic force and the contact potential difference excluding the effect of the Casimir force with a conventional atomic force microscope

“…In a conventional FM-KPFM measurement, the measured CPD differs from V CPD (z ts ) due to local charges. 26) In this paper, -( ) F z A B ts could be the capacitive force [which is the first term of Eq. ( 2)] excluding ( ) F z lc ts caused by local charges, which is purely induced by V CPD (z ts ).…”

“…, 2 where C is the capacitance defined by the tip-sample surface geometry, ( ) V z CPD ts is the CPD when the tip-sample surface has the local charges, and ( ) F z lc ts is the additional electrostatic force caused by the local charges. 26) When the surfaces have no local charge, the CPD does not depend on the distance and the applied voltage that gives the minimum net force coincides with the CPD. However, the existence of the local charges makes the analyzing process more complicated.…”

“…However, the existence of the local charges makes the analyzing process more complicated. 25,26) In such a case, a ( ) V z CPD ts mapping image obtained by using conventional FM-AFM system does not reflect the valuation of the true CPDs. To overcome this problem, Inami and Sugimoto have proposed a novel method to evaluate the true CPDs based on the energy dissipation of the electrostatic force.…”

“…The electrostatic force that depends on bias voltage V applied between tip and sample is expressed by 25,26)…”

“…To overcome this problem, Inami and Sugimoto have proposed a novel method to evaluate the true CPDs based on the energy dissipation of the electrostatic force. 25,26) This method requires the additional experimental setups to the conventional FM-AFM system in order to measure the energy dissipation by applying bias pulses.…”