Understanding the structure, function and stimulus response of individual molecules and other nanoscale structures is becoming increasingly important in research in all branches of hard sciences, in engineering and in materials development. The atomic force microscope (AFM) is a metrology tool that combines the requisite resolution with the ability to work with unmodified samples in various environments, including liquids. But AFM goes well beyond metrology to include nanometer-scale functional testing and mapping of surfaces, and even surface modification and manipulation.

AFM operation is conceptually straightforward. A hyper-fine tip on the end of a microfabricated cantilever is brought into contact or near contact with the test sample surface. (Common materials for the tip include single-crystal silicon and silicon nitride.) The tip is affected by forces interacting with the sample surface, which are initially attractive and then become repulsive as the tip contacts the surface. This contact may be perpetual (contact mode) or intermittent (TappingMode AFM). The tip-sample interactions are detected by bouncing a laser beam off the cantilever and measuring its movement with a position-sensing photodetector. Centimeters-long optical leverage and stringent vibration isolation enable routine measurement of subangstrom cantilever deflections...