Parallel atomic force microscopy using optical heterodyne detection

We report on an array of atomic force microscopes (AFM) based on a simple optical set-up using heterodyne detection. The deflection of AFM cantilevers is given by the path differences between the reference and the measuring wave in a Michelson interferometer. A matrix of micro-lenses is placed just above the cantilevers, in such a way that the deflected light from each cantilever is collected by one micro-lens. Both the micro-lenses and the cantilever chips are previously glued to increase the robustness of the system. The interference between the light from each micro-lenses and the reference light is selected by a diaphragm and subsequently detected by a photodetector. This procedure is repeated for each cantilever. In order to validate our instrument we measure the profile of a binary grating having a step height of 19.66 nm. By a piezoelectric platform a lateral range of 10 mu m was scanned with a speed of 1 mu m/s and an integration time of 10 mu m, which leads to a lateral resolution of 10 nm. The profiles measured by the cantilevers are in good agreement with the profile of the sample grating.