Higher-harmonic atomic force microscopy

To maximize the spatial resolution of atomic force microscopy (AFM), it is helpful to isolate the spurious short-range components from the plethora of force contributions acting between AFM tips and samples. It is shown theoretically and experimentally that higher-harmonic AFM, a technique that utilizes the anharmonic deflection contributions that arise when a cantilever oscillates in the highly nonlinear force field of a sample, is a suitable technique for maximizing spatial resolution. The qPlus sensor, a quartz cantilever that utilizes the piezoelectric effect for deflection detection, is particularly well suited for higher harmonic AFM because the physics of piezoelectric detection inherently magnifies the signal level of higher harmonics. Experimental results for W on graphite (0001), Si (111)-(7 × 7), NiO (100) and CaF2(111) are presented