5 things to consider when choosing an AFM

Atomic force microscopy (AFM) is based on a simple measuring principle. In order to measure reliably on a nanometer scale, however, a sophisticated instrument design is required. In practice, this usually also implies a complex user interface. Users are often expected to deal with complicated settings; they should have prior knowledge of AFM technology and need a substantial amount of time for their measurements. But does a sophisticated instrument necessarily have to imply complex usability? Find out which aspects you should consider when choosing an AFM!

Fast and easy cantilever handling

Before being able to perform a measurement with an AFM, a (micro)cantilever needs to be mounted. The cantilevers in an optical lever AFM are very small – commonly between 50 and 300 µm long, about 20 to 60 µm wide, and 2 to 8 µm thick. Cantilever handling normally requires experience: not only can cantilever mounting be quite fidgety in practice (and costly in case you use up several cantilevers for mounting), it can also be frustrating if the laser alignment does not work because the cantilever was not mounted properly. In this case, the user has to go back to the cantilever exchange step, re-mount the cantilever (or mount a new one), and re-start the laser alignment procedure. This is why cantilever handling should ideally be fast, easy, and reliable.

Look for a modern AFM instrument with a user-friendly interface that offers innovative solutions to this problem, so that cantilever mounting is fast and reliable, rather than tricky and time-consuming.

Automatic laser alignment

After placing the probe in the instrument, the alignment of the optical lever is carried out. In order to perform AFM measurements correctly and reliably, proper laser alignment is crucial. Poor alignment can reduce the sensitivity of the optical lever, introduce imaging artifacts, or even prevent imaging[1]. However, manual laser alignment can be time-consuming and difficult to perform.

Fig.1. Automatic laser alignment

Look for an AFM that provides a fully automatic laser alignment function. Modern AFM instruments carry out the laser alignment automatically after just two clicks in the control software.

Coarse approach with side-view camera

One of the major challenges in AFM design is building a motion control system that permits the approach of the probe to the surface before scanning. This must be done in such a way that the probe does not crash into the surface and break[1]. However, once the motion control system is successfully designed and integrated into the AFM, the user has to control how the probe approaches the surface of the sample. This is particularly challenging for transparent samples, dark samples, and samples with complex geometry, as it is difficult to estimate the distance between the probe and the sample. This process carries a substantial risk of crashing the probe into the sample.

Fig. 2: Coarse approach with side-view camera

New generations of AFMs are equipped with a side-view camera, so that the user can see the exact position of the cantilever in relation to the surface, and safely move the cantilever close to the surface. The automatic engagement procedure can then be started in the software – and within seconds the cantilever is ready for scanning.

Short time-to-measure

Time is important to everyone. When working with an AFM, the time-to-measure – the time it actually takes to start a measurement – is essential. The user needs to perform five steps:

  1. Load the cantilever
  2. Load the sample
  3. Align the laser
  4. Navigate to the feature
  5. Approach and start the measurement

For those AFM instruments with tricky cantilever exchange, manual laser alignment, no side-view camera, and lack of automation these five steps can take quite a while to say the least. In addition, if users are not AFM veterans (which they should not have to be!) or the samples are not always of the same type, it can take even longer to carry out these steps.

Look for an AFM with a high level of automation. This reduces the time-to-measure, so you can focus on more important tasks.

Decoupled xy and z scanners

Piezoelectric ceramics must be configured in such a way that they can move the probe (or sample) in the direction of the x, y, and z axes. One of the most commonly used three-dimensional scanner configurations is the tube scanner – mainly because it is easily fabricated. However, it has some disadvantages: due to their geometry, tube scanners are subject to a lot of non-linearity, particularly bow, when using the full range of the scanner. Scanner bow comes from the fact that the trajectory of the tube scanner is curved, so the result is an apparent curvature or “bow” in the height of measured samples.

Look for an AFM with decoupled xy and z scanners. In this scanner design, the xy scanner is placed under the sample while the z scanner is placed in the head in order to reduce the cross talk between the scanners (Fig. 3).

Fig. 3: Decoupled xy and z scanners

Do you need an atomic force microscope that fulfills all of the above mentioned aspects? Try the new generation AFM: Tosca™ 400.  As automation is an integral element on every level of operation of Tosca™ 400, you will benefit from increased efficiency and simplified handling of your AFM measurements.

1. Eaton, P. and West, P. (2010): Atomic Force Microscopy. New York: Oxford University Press.

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