Stability considerations and implementation of cantilevers allowing dynamic force microscopy with optimal resolution: the qPlus sensor

In frequency modulation atomic force microscopy, the stiffness, quality factor and oscillation amplitude of the cantilever are important parameters. While the first atomic resolution results were obtained with amplitudes of a few hundred (a) over circle ngstrom, it has subsequently been shown that smaller amplitudes should result in a better signal-to-noise ratio and an increased sensitivity to the short-range components of the tip-sample interaction. Stable oscillation at small amplitudes is possible if the product of stiffness and amplitude and the energy stored in the oscillating cantilever are large enough. For small amplitudes, stability can be achieved by using stiff cantilevers. Here, we discuss the physical requirements for small amplitude operation and present design criteria and technical details of the qPlus sensor, a self-sensing cantilever with large stiffness that allows small amplitude operation.