AFM- Atomic Force Microscopy
The atomic force microscopy is a powerful technique for imaging on the atomic level and it is not restricted to conductive samples. The scanning tip is at the end of an oscillating cantilever. A laser beam is directed towards the end of the cantilever and the position of the reflected beam is detected with a position sensitive detector. This allows to monitor the oscillation frequency. Each cantilever has its own resonance frequency. Close to the surface the "van der Waals" forces of the surface atoms change the resonance frequency of the cantilever. Selecting a frequency close to the resonance determines a certain height obove the surface. During a lateral scan the frequency is controlled and the height of the tip is matched to the selected frequency. Therefore this correction is a measure for the surface topography and can be used to generate images. This is the description of a "non-contact" measurement several other probes are in application this ranges from mechanically touching the surface ("contact-mode") to modification of the tip for making it sensitive to other properties e.g. for magnetic response.