Accurate Monitoring of Distance Between Two Probes Via Mechanical Interactions

 A method to monitor the distance between two tips of tuning fork-based AFM/NSOM systems is described. The distance monitoring is performed by recording the crosstalk signal which characterizes the interaction strength between the two oscillating tuning forks and tips.

( a) Two Probes Schematic setup. (b) and (c) are images of topographic and Crosstalk (respectively) interactions of the two probes with one scanning probe and a second stationary probe. (d) and (e) are line profiles represent topography and crosstalk signal along the dashed line (d). (e) is integrated signal values along the fast scanning axis.

 The measurements are based on aerodynamic and shear force interactions between the tips.  Both interactions increase with decreasing distance between the tips. The shear force interaction is a short-range effect and it is observed within a region of several tens of nanometers. This interaction leads to a sharp increase in the crosstalk signal once the scanning tip comes into the immediate vicinity of the stationary one. This effect is a reliable tool to detect the mechanical interactions between two tips and thus prevent them from colliding during scanning. (Klein et al)

Published: Appl. Phys. B. DOI 10.1007/s00340-012-5182-7 (2012)