Versatility of Self-Oscillation Technique with Mechanical-Acoustic Excitations for Frequency Modulation Atomic Force Microscope in Liquids

Abstract

We demonstrated that a cantilever with a small spring constant could be self-oscillated in liquids using a commercial atomic force microscope (AFM) employing a mechanical-acoustic excitation and that the present AFM system can image biological samples such as protein and deoxyribonucleic acid (DNA) in an aqueous solution in regions of slight contact. The present study together with the previous one [T. Okajima et al., Appl. Surf. Sci. 210 (2003) 68.] indicate that a self-oscillation technique with mechanical-acoustic excitations is a versatile method for frequency modulation (FM)-AFM in liquids, although the vibration properties of the cantilever in liquids, which affect the sensitivity of FM detection, have to be more optimized. It was also demonstrated that a noncontact force such as an electrostatic force was detected by the present FM-AFM.