Highly sensitive AFM using self-excited weakly coupled cantilevers

Abstract

In this article, we propose a method, using weakly coupled cantilevers, to enhance the sensitivity of atomic force microscopy (AFM) by several orders of magnitudes. There are two major dynamics AFM methods, i.e., amplitude modulation AFM and frequency modulation AFM (FM-AFM). In FM-AFM, which is based on the eigenfrequency shift of a single cantilever, the enhancement in sensitivity is restricted because of the limitations of miniaturization in the manufacturing process. By contrast, we used coupled cantilevers based on the eigenmode shift, which corresponds to the amplitude ratio between the cantilevers. This enabled us to increase the sensitivity by reducing the coupling stiffness between cantilevers without relying on further miniaturization. In addition, to detect the eigenmode shift, even in high-viscosity environments, we produced self-excitation in the weakly coupled cantilevers by feedback control. Using this prototype system of coupled macroscale cantilevers subjected to the magnetic force, which simulates the atomic force, we confirmed the high sensitivity of the proposed method.