Tuning Fork Scanning Probe Microscopes - Applications for the Nano-Analysis of the Material Surface and Local Physico-Mechanical Properties

Abstract

The atomic force microscopes (AFMs) or scanning force microscopes (SFMs) are a very high resolution type of scanning probe microscope (SPM), with demonstrated resolutions of a fraction of a nanometer. The AFMs are one of the foremost tools for imaging, measuring and manipulating matters at the nanoscale level. AFMs operate by measuring the atomic interaction (attractive or repulsive) forces between a tip and a sample [1]. Today, most AFMs employ an optical lever sensor an expensive system that can achieve pico-meter resolution. The optical lever (Fig.1 (a)) operates by reflecting a laser beam off the cantilever. The angular deflection of the cantilever causes a large twofold of the laser beam. The reflected laser beam strikes a position sensing photodetector consisting of two side-by-side photodiodes. The difference between the two photodiode signals indicates the position of the laser spot on the detector and thus the angular deflection of the cantilever. Because the cantilever-to-detector distance generally measures thousands of times the length of the cantilever, the optical lever greatly magnifies motions of the tip [2]. The advantages of optical lever are possibility to measure absolute force and commercial available but there are many disadvantages: external optical measuring system needed, very low stiffness, fragile and high cost of AFM.