Atomic Force Microscopy

AFM is an imaging technique, sometimes referred to as a type of scanning probe microscopy, that offers nanometre-scale resolution. However AFM can also by used as a spectroscopic method that is used to measure atomic forces directly. It is used widely in nanotechnology to visualise and measure materials of interest.

More generally, AFM is used in surface chemistry to understand material properties and it is also widely used in biological science to understand cell-wall behaviour and the mechanical properties of proteins.

Imaging

AFM employs a cantilevered tip which is rastered across the surface of the sample.

As the tip moves over the sample it is deflected up and down according to Hooke’s law by atomic forces such as electrostatic and van der Waals forces.

The deflection of the tip reflects the topography of the sample and is measured either directly, using a laser to monitor the position of the tip, or indirectly, for example by measuring the force required to keep the tip in a constant position.

Spectroscopy

By forcing the tip towards and away from the sample in a controlled manner and observing the response of the tip via the piezoelectric effect an understanding of the atomic forces, both attractive and repulsive, at work can be gained thus furthering understanding of the surface and material properties at the nano-scale.

AFM can be used to look at the topography and surface properties of biological and inorganic samples at the nanoscale.

The surface properties of nanoparticles can be deduced which can inform downstream applications such as drug delivery.

In biology, AFM can be used to measure the mechanical and morphological properties of cell walls and other biomolecules.

For analysis of bulk solids, samples are typically cut to the desired size and then attached to a substrate to prevent the sample from moving/ vibrating during measurement.

Powders are typically suspended in a liquid and then placed on a suitable medium, such as mica, and allowed to dry to form a deposited layer for analysis.