Tools of the trade
An atomic force microscope (AFM) comprises a sharp tip about 1010 m in diameter mounted at the end of a soft cantilever spring, which can be brought in direct mechanical contact with the sample. The deflection of the spring is measured via a laser beam reflecting from the cantilever and onto a position-sensitive photodiode. The sample can be moved in all three dimensions by a piezoelectric scanner, which allows the contours of its surface to be mapped out. The AFM can also be used to apply or measure forces at very specific points on the sample.