AFM

From one AFM user to another...

Last month we asked AFM users what caused them frustration when they first started using AFM and what advice they’d give to new starters.

 
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Here is what they came up with:

Robert Friedfeld at the Stephen F. Austin State University found it difficult to find interesting AFM research.

Many journal publishers will now allow you to set up email alerts or subscribe to their RSS feed based on your topic of choice, which will allow you to keep up to date with the latest publications related to AFM. You can also save a search related to AFM as an email alert in Google Scholar. Social media can also be a useful resource for discovering the latest AFM-related research. At NuNano, we like to keep up to date with the latest developments in AFM. We post links to the latest AFM-related journal articles on our Twitter and LinkedIn accounts most Fridays. In January 2019, we’ll be sending out a run-down of all the AFM-related articles published in 2018 via our e-newsletter. Subscribe to our mailing list if you’re interested in receiving this list.

James Bowen at the Open university wished he had known about the importance of sample preparation, in particular when you should use double-sided tape, glue, or magnets for sample immobilisation. He generally follows these rules:

  • Double-sided tape: when a small amount of vertical or lateral drift is not a problem OR when you need the sample back without any adhesive attached (e.g. if it needs to be used again in a different instrument).

  • Glue: when vertical or lateral drift could be a problem (e.g. long duration scans).

  • Magnets: when working under liquid, and for whatever reason adhesives are not suitable (e.g. sample will be immersed in an organic solvent).

 
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When Maxim Ivanov at the University of Coimbra first started out on the AFM, he was overwhelmed with all the potential modes, approaches, and probe types to choose from for each sample he was imaging.

Can you simultaneously perform for example conductive and standard AFM to produce a conductivity and topography map of the surface in the same scan. It should be noted that this is possible with a conductive tip.

After this, it was which type of probe is appropriate for which mode or type of AFM and for which sample. It is useful to know that a metal-coated tip is most commonly used for conductivity-related imaging and coating the backside of the cantilever in metal simply increases the signal of the laser reaching the photodetector. Furthermore, cantilevers are most commonly made of silicon or silicon nitride, which are suitable for imaging hard samples such as metals and soft samples such as cells, respectively.

 
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Iddo Amit of Durham University and Jeffrey Wolinski of Grove City College have stressed that the AFM is not “a plug-and-play instrument” such as the scanning electron microscope (SEM) or optical microscope. It is important to keep an eye on the signals that you are not recording such as the tapping amplitude, to know when your lock-in amplifier loses the lock on the frequency and when the tip has collided with something and is no longer scanning over the surface. To this end, you should never leave the instrument while it is scanning or try to do other work in parallel. Furthermore, you should recognise that image artifacts are common and that the image produced is not always a true representation of your sample surface.

 
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Héctor Corte-León of the National Physical Laboratory advises not to take high resolution images of your sample in the beginning. You should firstly identify what you are trying to image by conducting some low-resolution scans of your sample. High resolution images should only be sought when you have identified the key element you want to image.

We hope that these pieces of advice from experienced AFM users will make it easier for new starters to get to grips with the AFM. If you have any other advice that you’d like to share, please feel free to leave it in the comments below.

If you liked this blog post, you may also like 5 top tips for effective AFM imaging: a beginners guide and (Nearly) Everything you ever wanted to know about AFM but were afraid to ask.