Accurate force measurement in the atomic force microscope: a microfabricated array of reference springs for easy cantilever calibration

Abstract

Calibration of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules. We have developed a compact and easy-to-use reference artefact for this calibration. This consists of an array of dual spiral-cantilever springs, each supporting a polycrystalline silicon disc of 170 µm in diameter. These were fabricated by a two-layer polysilicon surface micromachining method. Doppler interferometry is used to measure the fundamental resonant frequency of each device accurately. We call such an array a microfabricated array of reference springs (MARS).