We describe a method to calibrate the spring constants of cantilevers used in atomic force microscopy (AFM) by means of a piezoresistive cantilever. Before use, the piezoresistive cantilever was calibrated with an absolute force standard, the NIST electrostatic force balance (EFB). In this way, the piezoresistive cantilever acts as a force transfer standard that is traceable to the International System of Units (SI). Seven single-crystal silicon cantilevers with rectangular geometries and nominal spring constants from 0.2 N/m to 40 N/m were measured with the piezoresistive cantilever method. The values obtained for the spring constant were compared to measurements by four other techniques: the thermal noise method, the Sader method, force loading by a calibrated nanoindentation load cell, and direct calibration by force loading with the EFB. Results from different methods for the same cantilever were generally in agreement, but differed by up to 300 % from nominal values. When used properly, the piezoresistive cantilever approach provides spring-constant values that are accurate to + or - 5 %. Methods such as this will improve the ability to extract quantitative information from AFM methods.
Citation: Review of Scientific Instruments
Pub Type: Journals
AFM cantilever calibration, atomic force microscopy, force calibration, spring constant