Frequency and damping noise of atomic force microscopy cantilevers with optomechanically modified quality factor at low temperature

Noise in the frequency and damping signals are key parameters in determining microscope performance in frequency modulation atomic force microscopy (FM-AFM). We present a study of noise in the frequency and damping signals of AFM cantilevers used in a low temperature FM-AFM system with fiber-optic interferometric sensing of the cantilever deflection [1]. Due to a strong optomechanical coupling between cantilever oscillation and the optical field, the quality (Q) factor and resonant frequency are both dependent on the optical cavity length (formed by the fiber-cantilever distance). A systematic experimental study was undertaken to determine cavity lengths with the best signal to noise ratio, as well as the influence of optomechanically enhanced Q factor on frequency shift and damping noise. An automated protocol was developed to scan the fiber cantilever distance and measure the Q factor, resonant frequency, and frequency noise at each position. A digital phase-locked loop based self-excitation system was used to drive the cantilever oscillation and measure the frequency and Q. Actuation of the cantilever oscillation was achieved via optical force [1]. The fiber position was scanned using a computer-controlled piezoelectric stick-slip motor. A python script was used to unify control of the system.

[1] Y. Miyahara et al., “Optical excitation of atomic force microscopy cantilever for accurate spectroscopic measurements”, EPJ tech. Instrum. 7:2 (2020).