AFM - Atomic Force Microscope

Imaging principle of an AFM in contact mode: (A) With the optical-lever technique the bending of the cantilever is detected by measuring the movement of a laserspot, which is being reflected from the back-side of the cantilever, on a position sensitive detector (PSD). The change in position can be related to a bending in nm. (B) By means of the optical lever technique the bending of the cantilever (which generates a force on the sample) is set. The feedback electronics keeps this bending constant by adjusting the z-piezo accordingly. (C) A topographical feature results consequently in an extension/ retraction of the zpiezo. Thus the movement of the z-piezo can directly be interpreted as a topography.

The AFM is a very high-resolution type of scanning probe microscope. The AFM is not a classical microscopy were the topography is captured by imaging with light, quite in contrast the AFM analyzes the surface by ”feeling” the surface with a mechanical probe. Since its development in 1986 the AFM was succesfully applied in many research fields as one of the most important routine tools for imaging, measuring and manipulating matter at the nanoscale under athmospheric and UHV conditions. Capillary forces, tip-sample geometry as well as thermal noise of gas/ liquid molecules (i.e. Brownian motion) are limiting the lateral resolution under ambient conditions to about a nanometer. The height resolution under ambient conditions is about 1-2 Angstrom. Moreover, besides imaging the AFM can also be used for sensing surface forces with pN accuracy by means of force "distance" spectroscopy. Yet, it has to be pointed out that an AFM can actually not measure a distance, which makes force distance spectroscopy in contrast to SFA (see other eqipment) somewhat ambiquous!

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