Atomic force microscopy (AFM) is a branch of scanning probe microscopy that includes several dozen ways of scanning the surface of a tiny specimen to create an image. It can resolve images of objects mere nanometers long, over 1,000 times sharper than the best optical microscopes.
An atomic force microscope uses a cantilever with an incredibly fine silicon tip, or probe, that’s usually micrometers long and whose tip has a radius of under ten nanometers. The tip of the cantilever runs over the surface of the sample, making contact or maintaining a tiny distance depending on the settings dictated.
These microscopes can work in several modes that fall into two categories: static and dynamic. The cantilever is physically dragged over the sample’s surface in static mode and the contours of the specimen are directly measured.
In dynamic – or tapping – mode, on the other hand, the cantilever is oscillated and the varying forces that result from its interaction with the sample are recorded. The obvious advantage that dynamic mode has over static is that it can be used on ‘soft’ specimens, where contact might lead to degradation of both the sample and the tip.
Atomic Force Microscopy: Works
AFM: pros and cons
Scanning electron microscopy (SEM) is a different type of microscopy that deals with samples of a similar size to atomic force microscopy. AFM can boast certain advantages over SEM, but it also has some disadvantages.
AFM can create a 3D profile of the sample, unlike SEM’s 2D results and the samples don’t require any special coating either. This means specimens that might be changed or damaged by the SEM process (eg micro-organisms) can be studied. AFM can also be used in conjunction with other optical techniques and can yield higher resolutions even in liquid environments.
On the down side, AFM is limited with regard to the size of the sample scan image it can take – around 1,000 times smaller than the area SEM can capture in a single pass. Its scanning speed is slower too and an atomic force microscope can’t measure samples with particularly steep topography unless it’s specially modified.