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.
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. However, manual laser alignment can be time-consuming and difficult to perform.
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. 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.
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:
- Load the cantilever
- Load the sample
- Align the laser
- Navigate to the feature
- 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.
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.
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.