Atomic force microscopy (AFM) is a powerful tool for nanoscale to atomic level characterisation of a wide range of samples from cells to metals. You may be already familiar with the technique scanning electron microscopy (SEM) for imaging at the nanoscale. In this article, the benefits of AFM are discussed by comparing it to SEM.
Scanning Electron Microscopy VS Atomic Force Microscopy
While SEM makes use of the reaction of electrons in relation to a sample, in order to image its nanoscale surface structures, AFM harnesses the powers between the nanoscale apex of a tip and the sample. This tip is placed at the end of a cantilever and together, they can be described as an AFM probe. NuNano currently produce two silicon AFM probes: the Scout 350 and Scout 70.
The probe is positioned over the sample with the tip apex facing the surface of the sample. As can be seen in Figure 1, a basic diagram of an AFM system, a laser is reflected from the tip-less side of the cantilever onto a photodetector.
The tip is scanned over the surface of the sample, causing the cantilever to deflect as a result of the force between the tip and the surface. As the tip comes across surface features of varying heights, there will be variation in the level of deflection, leading to change in the position of the laser beam on the photodetector.
This variation in position creates an image of the sample surface topography at the nano- to atomic scale. As shown in Figure 1, with the color bar indicating the height of the features, this can then be output to a PC.
Benefits of Atomic Force Microscopy
As an instrument for nanoscale imaging, AFM has many benefits over SEM. While SEM must be carried out in a vacuum, AFM can be undertaken in a number of different environments, encompassing ambient, liquid, and vacuum. It is ideally suited to the analysis of biological samples due to its ability to image in a liquid environment.
Figure 1. Schematic of AFM setup
In addition to this, SEM can only be carried out with samples that are conductive. As a result, a non-conductive sample must be covered in metal to allow imaging to take place. This additional work to prepare the sample is not necessary with AFM.
When conducting SEM, the size of the electron beam spot on the sample, itself dependent on the wavelength of the electrons and the system creating the beam, restricts the resolution of the images. Conversely, AFM imaging depends on the sharpness of the tip. NuNano rigorously inspect every probe before it gets packaged to guarantee tip sharpness. The tip of an AFM probe can be produced to be of a much smaller size than the electron beam spot. Consequently, images of a far higher resolution can be produced with AFM over SEM.
Furthermore, AFM is significantly more adaptable than SEM. AFM can produce a three-dimensional image of a sample surface with quantification of the surface roughness, while only two dimensions of imaging are possible with SEM.
Lastly, adaptations can allow an atomic force microscope to determine the chemical make-up, conductivity, electric field, magnetic structure, elasticity, and work function of a sample surface, while SEM can ascertain chemical make-up alone. Despite this, it is worthwhile to note that SEM and AFM can complement one another as instruments for materials characterization.
Many STEM (Science, Technology, Engineering, and Maths) disciplines have made use of AFM, including its application for imaging of DNA, two-dimensional materials such as graphene, and the chemical bonds of single molecules. AFM may just be the tool needed to enhance your work.
This information has been sourced, reviewed and adapted from materials provided by Nu Nano Ltd.
For more information on this source, please visit Nu Nano Ltd.