Improvement of Tapping Mode AFM Imaging Stability by Operation Far Below Resonance Frequency of a Cantilever

摘要

In tapping mode AFM, a cantilever is driven near its resonance frequency and intermittently strikes the sample while raster scanned across a surface. The oscillation amplitude is monitored via a feedback loop to extract topographical information of surfaces at the nanoscale. This paper deals with major factors limiting scanning speed: 1) the slow transient response of the cantilever, and 2) instabilities associated with systems with high quality factors (Q). Due to the slow transient response, the AFM has difficulty in instantly responding to steps along the surface, resulting in the need for slower scan rates. By driving the cantilever well below its resonance frequency, stability of the system is greatly improved, resulting in better feature tracking and the ability to scan at faster speeds.