MINIMUM DETECTABLE DISPLACEMENT IN NEAR-FIELD SCANNING OPTICAL MICROSCOPY

The probe-to-sample separation in near-field scanning optical microscopes can be regulated by a noncontact atomic shear force sensing scheme that allows simultaneous acquisition of optical and shear force images. We have measured the minimum detectable displacement that can be achieved with a scheme based on diffracting a focused laser beam from the vibrating probe. The minimum detectable displacement determines the smallest resolvable change in force acting on the probe. The measured shot-noise-limited value is 2.8x10(-3) Angstrom(rms)/root Hz, and the practical sensitivity is limited by thermal vibration noise to 7x10(-3) Angstrom rms/root Hz. These values compare well with those calculated theoretically. (c) 1994 American Institute of Physics.