Lateral force calibration for atomic force microscope cantilevers using a suspended nanowire

Friction measurement via atomic force microscope (AFM) relies on accurate calibration for the torsional spring constant of the AFM cantilever and its lateral deflection sensitivity. Here we describe a method that employs a suspended nanowire (SNW) as a reference beam to quantify the torsional spring constant of AFM cantilevers. Based on the fact that a uniform SNW with cylindrical symmetry has an identical spring constant when bent in any direction perpendicular to its axis, the spring constant of the SNW in a normal direction is determined by an AFM cantilever with a known normal spring constant, and is subsequently used as a force transfer standard to calibrate the torsional spring constant of the AFM cantilever. The lateral deflection sensitivity can be accurately measured by pushing the AFM tip laterally on the groove edge. The calibration result is compared to the well-known diamagnetic lateral force calibrator method and shows an uncertainty of 15% or better. The presented method is applicable for the lateral force calibration of AFM cantilevers in a wide range of instruments including inverted configurations and in an ultrahigh vacuum.