Atomic force microscopy (AFM) is part of the family of techniques known as scanning probe microscopy, and has proved itself extremely valuable and versatile as an investigative tool. The AFM invented by Gert Binnig and others in the mid 1980s differed in many ways from today’s instruments, but its basic principles remain the same. Binnig had already received the Nobel Prize in Physics for his creation of the scanning tunnelling microscope (STM), and the first AFMs in fact relied on an integrated STM tip. But the AFM had a major advantage over STM; it could be used for insulating as well as conducting samples.
Over the years, AFM has already had a significant impact in many disciplines, from surface science to biological and medical research. Because of its ability to image samples on an atomic scale, it has been vital to the advance of nanotechnology.
This AFM image shows the surface of a thin film of GaN. The surface morphology is dominated by terraces and steps. The step heights are approximately 0.25 nm, corresponding to one layer of gallium and nitrogen atoms. This illustrates the ability of AFM to measure very small height changes on surfaces.
The figure above is a topographic AFM image of a collagen fibril. The fibril is the striped structure running diagonally across the middle of the image. The periodicity of the narrow stripes or bands seen in the image is 64 nm. AFM can be used to image biological samples such as collagen without requiring a conductive coating to be added. It is even possible to take images of live cells in a fluid environment
In simple terms, the atomic force microscope works by scanning a sharp probe over the surface of a sample in a raster pattern. By monitoring the movement of the probe, a 3-D image of the surface can be constructed. Below is a schematic diagram of an AFM.
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