A compact torsional reference device for easy, accurate and traceable AFM piconewton calibration

The invention of the atomic force microscope led directly to the possibility of carrying out nanomechanical tests with forces below the nanonewton and the ability to test nanomaterials and single molecules. As a result there is a pressing need for accurate and traceable force calibration of AFM measurements that is not satisfactorily met by existing calibration methods. Here we present a force reference device that makes it possible to calibrate the normal stiffness of typical AFM microcantilevers down to 90 pN nm(-1) with very high accuracy and repeatability and describe how it can be calibrated traceably to the International System of Units via the ampere and the metre, avoiding in that way the difficulties associated with traceability to the SI kilogram. We estimate the total uncertainty associated with cantilever calibration including traceability to be better than 3.5%, thus still offering room for future improvement.