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Small Amplitude Frequency Modulation Atomic Force Microscopy of Lead Phthalocyanine Molecules Using Cantilever with Very High Spring Constant

In frequency modulation atomic force microscopy (FM-AFM), the average interaction force is detected as the frequency shift of the oscillating cantilever. Therefore, it is desirable to oscillate a cantilever with a small amplitude in order to achieve a high resolution. However, the oscillation may become unstable or the tip may jump into a static contact unless a cantilever with a high spring constant is used. In this study, we used a silicon cantilever with a spring constant as high as 700 N/m, which is far larger than those for conventional FM-AFM. We demonstrated molecular-resolution FM-AFM on lead phthalocyanine thin films with an oscillation amplitude of 2 nm.