High harmonic exploring on different materials in dynamic atomic force microscopy

In atomic force microscopy (AFM), high-frequency components consisted in dynamic tip-sample interaction have been recently demonstrated as a promising technique for exploring more extensive material properties. Here we present an exploratory study of high harmonic atomic force microscopy by force-spectroscopy and high harmonic imaging. Since these components are very weak compared to the fundamental response, we firstly designed a high harmonic cantilever by tuning the second order flexural resonance frequency to an integer 6 times of its fundamental mode (i.e. (omega 2)=6 (omega 1)). Moreover, it is verified that high harmonic can discern extra features than topographies on different samples with amplitude/frequency modulation (AM/FM) dynamic AFM mode. In AM mode, the first resonance amplitude and 6th harmonic amplitude were discussed. The 6th harmonic is more sensitive than the first order response. In FM mode, it is noted that the decaying rate of the 6th harmonic frequency is approximately 6 multiples to the slope of the fundamental frequency shift when the tip approaches to the surface of sample. This non-destructive method was also adopted to investigate the local interlayer coupling and intercalation in the two-dimensional graphene films tentatively.