Tuning-fork-based fast highly sensitive surface-contact sensor for atomic force microscopy/near-field scanning optical microscopy

We have developed a surface-contact sensor on the basis of a tuning fork which differs from the previously described ones in that it has a high operating speed (up to 100 times as fast as the so-called Q limit), requires no external piezoelectric drive, has a sufficiently high sensitivity, and features a “soft” probe attachment which makes the lifetime of the probe equal to that of the standard atomic force microscopy. When using a “soft” probe with a rigidity of 0.5 N/m, one can reliably detect probe tip-to-sample distance variations as small as 0.1 nm. The resonance frequency resolution attained amounted to 2×10−3 Hz. The rate of transient rise is τ=1.5 ms (this refers to the response time of the sensor proper with the Z-coordinate feedback loop open and not to the response time of the microscope as a whole). We have theoretically substantiated the fact that the Q limit, where Q∼10 000 is the Q factor of the tuning fork proper, is not a fundamental restriction on the operating speed of the sensor. This ...