Magnetic force microscopy with frequency-modulated capacitive tip-sample distance control

Abstract

In a step towards routinely achieving 10 nmspatial resolution with magnetic force microscopy, we have developed a robust method for active tipsample distance control based on frequency modulation of the cantilever oscillation. It allows us to keep a well-defined tipsample distance of the order of 10 nmwithin better than ±0.4 nmprecision throughout themeasurement even in the presence of energy dissipative processes, and is adequate for single-passage non-contact operation in vacuum. The cantilever is excited mechanically in a phase-locked loop to oscillate at constant amplitude on its first flexural resonance mode. This frequency is modulated by an electrostatic force gradient generated by tipsample bias oscillating from a few hundred Hz up to a few kHz. The sum of the side bands amplitudes is a proxy for the tipsample distance and can be used for tipsample distance control. This method can also be extended to other scanning probe microscopy techniques.