High force sensitivity in Q-controlled phase-modulation atomic force microscopy

We investigate the dependence of effective Q-factor on force sensitivity in Q-controlled phase-modulation atomic force microscopy. With Q-control, the phase noise density spectrum shows a characteristic dependence on modulation frequency (f(m)). The phase noise density spectrum is nearly constant in the low-f(m) region, whereas it decreases inverse-proportionally to f(m) in the high-f(m) region. Such a decrease enhances the force sensitivity. We demonstrate that force sensitivity can be markedly increased with Q-control to exceed the limit of force sensitivity without Q-control. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457431]