  We report on progress in developing compact sensors for atomic force
microscopy (AFM), in which the mechanical transducer is integrated with
near-field optical readout on a single chip. The motion of a nanoscale,
doubly-clamped cantilever was transduced by an adjacent high quality factor
silicon microdisk cavity. In particular, we show that displacement sensitivity
on the order of 1 fm/(Hz)^(1/2) can be achieved while the cantilever stiffness
is varied over four orders of magnitude (\approx 0.01 N/m to \approx 290 N/m).
The ability to transduce both very soft and very stiff cantilevers extends the
domain of applicability of this technique, potentially ranging from
interrogation of microbiological samples (soft cantilevers) to imaging with
high resolution (stiff cantilevers). Along with mechanical frequencies (> 250
kHz) that are much higher than those used in conventional AFM probes of similar
stiffness, these results suggest that our cavity optomechanical sensors may
have application in a wide variety of high-bandwidth AFM measurements.
