Frequency Noise in Frequency Modulation Atomic Force Microscopy

Atomic force microscopy (AFM) using the frequency modulation (FM) detection method has been widely used for atomic/molecular-scale investigations of various materials. Recently, it has been shown that high-resolution imaging in liquids by the FM-AFM is also possible by reducing the noise-equivalent displacement in the cantilever displacement sensor and by oscillating the cantilever at a small amplitude even with the extremely reduced Q-factor due to the hydrodynamic interaction between the cantilever and the liquid. However, it has not been clarified how the noise reduction of the displacement sensor contributes to the reduction in the frequency noise in the FM-AFM in low-Q environments. In this article, the contribution of the displacement sensor noise to the frequency noise in the FM-AFM is described in detail to show how it is important to reduce the noise-equivalent displacement in the displacement sensor especially in low-Q environments.