Enhanced performance in contact mode atomic force microscopy

Abstract

Atomic force microscopy (AFM) had and continues to have a substantial impact on nanosciences and technologies. However, the low scanning speed continues to be one of the obstacles that impede the widespread adoption of AFM. This paper presents a solution to control system design issues for constant force contact AFM operation to enhance the performance of AFM systems with respect to scanning speed and image resolution. The purpose of the controller is to maintain a constant slope at the free end of the AFM cantilever through suitable displacement of the base end of the cantilever. Given that the sample surface profile is not known a priori, the difficulty in the controller design lies in attempting to track an unknown and time-varying reference signal, representing the unknown surface profile. To overcome this problem, it is proposed in this paper to use an adaptive regulator design approach. The regulator design approach is based on two steps. The first step involves using the Q-parameterization of stabilizing controllers to construct a set of parameterized stabilizing controllers for the system under consideration. The second step involves tuning the Q parameter in the expression of stabilizing controller so that the controller converges to the desired controllers needed to achieve regulation. The proposed control strategy makes it possible to use small contact forces and high scanning speeds, hence improving the performance of contact mode AFM systems.