Development of liquid-environment frequency modulation atomic force microscope with low noise deflection sensor for cantilevers of various dimensions

We have developed a liquid-environment frequency modulation atomic force microscope (FM-AFM) with a low noise deflection sensor for a wide range of cantilevers with different dimensions. A simple yet accurate equation describing the theoretical limit of the optical beam deflection method in air and liquid is presented. Based on the equation, we have designed a low noise deflection sensor. Replaceable microscope objective lenses are utilized for providing a high magnification optical view (resolution: < 3 mu m) as well as for focusing a laser beam (laser spot size: similar to 10 mu m). Even for a broad range of cantilevers with lengths from 35 to 125 mu m, the sensor provides deflection noise densities of less than 11 fm/root Hz in air and 16 fm/root Hz in water. In particular, a cantilever with a length of 50 mu m gives the minimum deflection noise density of 5.7 fm/root Hz in air and 7.3 fm/root Hz in water. True atomic resolution of the developed FM-AFM is demonstrated by imaging mica in water. (c) 2006 American Institute of Physics.