The high-resolution imaging technique used in liquid environments involving dynamic mode atomic force microscopy (AFM) with a frequency modulation (FM) detection technique has been newly developed on the basis of a commercial atomic force microscopy (AFM) apparatus, which is, generally, extremely difficult because of the large decrease in Q-factor caused by hydrodynamic damping in liquids. Through various improvements and optimization, the noise density of the improved deflection sensor was 29 fm/\sqrt{Hz} (f0 = 141 kHz) in liquid. In addition, the noise level and bandwidth of the FM detector were improved to 6 mHz/\sqrt{Hz} and 6 kHz, respectively. Thermal drift was successfully regulated at less than 1 nm/min in air for a sufficiently long time without any special air conditioning treatments. As a result, we succeeded in obtaining high-resolution images of polypropylene sheet, Au thin film, and DNA structures in a buffer solution. Therefore, liquid environments are proved to be suitable for high-resolution imaging by FM-AFM under ultrahigh vacuum (UHV) condition.

doi:10.1143/JJAP.49.08LB12