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: $<3μm$⁠) as well as for focusing a laser beam (laser spot size: $∼10μm$⁠). Even for a broad range of cantilevers with lengths from $35to125μm$⁠, the sensor provides deflection noise densities of less than $11fm∕Hz$ in air and $16fm∕Hz$ in water. In particular, a cantilever with a length of $50μm$ gives the minimum deflection noise density of $5.7fm∕Hz$ in air and $7.3fm∕Hz$ in water. True atomic resolution of the developed FM-AFM is demonstrated by imaging mica in water.