Feedback Control in an Atomic Force Microscope Used as a Nano-Manipulator

Abstract

This paper offers a concise survey of the most commonly used feedback loops for atomic force microscopes. In addition it proposes feedback control loops in order to minimize the effect of thermal noise on measurements of weak forces, and to improve the manipulability of the AFM. Growing requirements to study and fabricate systems of ever-shrinking size mean that ever-increasing performance of instruments like atomic force microscopes (AFM) is needed. A typical AFM consists of a micro-cantilever with a sharp tip, a sample positioning system, a detection system and a control system. Present day commercial AFMs use a standard PI controller to position the micro-cantilever tip at a desired distance from the sample. There is still a need for studies showing the optimal way to tune these controllers in order to achieve high closed-loop positioning performance. The choice of other controller structures, more suitable for dealing with the robustness/performance compromise can also be a solution.