Small mass measurements for tuning fork-based atomic force microscope cantilever spring constant calibration

Cutting edge mass sensors are capable of discriminating mass changes as small as several dozens of atoms, however the smallest mass commercially available from NIST with a calibration traceable to the International System of Units (SI) is 0.5 mg. To bridge this gap, new metrological techniques are being developed. A mass change from the electrochemical dissolution of tungsten wire has been measured using a commercial microbalance, and applied to a dynamic calibration of the spring constant of a tuning fork oscillator designed for use in frequency modulated atomic force microscopy (FMAFM). The spring constant measured using the dynamic method agreed within experimental uncertainty with that determined using an instrumented indenter, however an improved model for the indenter’s contact mechanics will be necessary to validate the assumptions used in the dynamic method to less than 10 %.