Atomic force microscopy (AFM) is an incredibly versatile and high resolution technique for imaging at the nano to atomic scale. To ensure that AFM is performed as effectively as possible, there are some key points to consider around the sample you are imaging, operating the AFM instrument, and your probe of choice.
When preparing your sample, expertise is imperative, as the same steps must be repeated during each imaging run. If any deviation in the preparation occurs, it is likely that an adverse interaction will occur during imaging and will subsequently affect the final image seen with the AFM.
Prior to imaging, it is important that the researcher is knowledgeable on the probable dimensions, shape of the sample features and structure. Some useful questions to ask prior to imaging include:
- What width and height are my features?
- Are the features evenly distributed across the sample or sporadically clustered?
Once these properties of the sample are well established, the researcher can set the parameters on the AFM accordingly. If the wrong settings are used, the researcher will lose a significant amount of time during the imaging process without achieving a good final image.
The probe for AFM imaging will vary depending upon the sample. Once the sample material is established, a probe that can both maximize the image resolution and stability without damaging the sample should be chosen. For materials exposed to air, standard AC mode silicon probes for tapping/non-contact imaging are often suitable, such as the Scout 350 and Scout 70 probes that NuNano offer. However, further considerations must be taken when the sample is softer or when imaging is performed in liquid..
Surface topography also plays an important role in choosing the correct probe for AFM. Whether the surface of the sample exhibits salt flats or alpine peaks, and even if the bottom of a trench requires imaging, NuNano is available to offer advice on ensuring that researchers select the most accurate probe for their given sample requirements.
When choosing a probe, it is also important to consider whether the probe was used before, as this may play a role in contamination during the imaging process. It is always recommended that a new probe is used, especially when the aquired images will be used for future publications.
Prior to imaging, the laser spot should be aligned above the tip at the end of the cantilever. While this may appear to be a simple task, new users who are not familiar with the construction of an AFM probe may believe they have successfully realised strong laser reflection from the cantilever without actually doing so. The size and shape of the different components of the probe therefore play a crucial role in ensuring that alignment is accurate, as proper alignment of the laser at the end of the cantilever will provide the researcher with the highest sensitivity for AFM imaging.
When someone first learns how to drive, it is not expected that the first time they get behind the wheel of a car that they will drive perfectly and effortlessly arrive at their destination on time. Likewise, when a researcher begins working with AFM, it is not expected that they will produce perfect images on their first attempt.
In fact, many scientific insights arise from this learning and problem solving aspect, in which the researcher is able to fully understand what they are and are not visualizing, and how to change their imaging process accordingly. With some patience and practice, the researcher will continue to become more attuned to how the AFM and the sample of interest are interacting.
This information has been sourced, reviewed and adapted from materials provided by NuNano Ltd.
For more information on this source, please visit NuNano.