  Atomic force microscopy (AFM) has been constantly supporting nanosciences and
nanotechnologies for over 30 years, being present in many fields from condensed
matter physics to biology. It enables measuring very weak forces at the
nanoscale, thus elucidating interactions at play in fundamental processes. Here
we leverage the combined benefits of micro/nanoelectromechanical systems and
cavity optomechanics to fabricate a sensor for dynamic mode AFM at a frequency
above 100 MHz. This is two decades above the fastest commercial AFM probes,
suggesting opportunity for measuring forces at timescales unexplored so far.
The fabrication is achieved using very-large scale integration technologies
inherited from photonic silicon circuits. The probe's ring optomechanical
cavity is coupled to a 1.55 um laser light and features a 130 MHz mechanical
resonance mode with a quality factor of 900 in air. A limit of detection in
displacement of 3.10-16 m/sqrt(Hz) is obtained, enabling the detection of the
Brownian motion of the probe and paving the way for force sensing experiments
in the dynamic mode with a working vibration amplitude in the picometer range.
Inserted in a custom AFM instrument embodiment, this optomechanical sensor
demonstrates the capacity to perform force-distance measurements and to
maintain a constant interaction strength between tip and sample, an essential
requirement for AFM applications. Experiments show indeed a stable closed-loop
operation with a setpoint of 4 nN/nm for an unprecedented sub-picometer
vibration amplitude, where the tip-sample interaction is mediated by a
stretched water meniscus.
