Why some materials cannot be measured by AFM

Is there a reason why some materials cannot be measured by AFM?

Atomic Force Microscopy (AFM) is a powerful technique for investigating surface properties and obtaining high-resolution images at the nanoscale. However, not all samples are suitable for AFM measurements. In this Nanosurf Insights post, we will explore one such example: rough samples. We will discuss the limitations of AFM systems regarding z-scanning range and the importance of sample attachment for successful imaging.

The Challenge of Rough Samples

AFM systems have a limited scanning range in the z direction, typically ≤20 µm. This means that the height variations within the area of interest should not exceed the z scanner range. When dealing with very rough samples that exhibit significant height variations, imaging the sample without causing damage becomes challenging. The AFM tip might come into uncontrolled contact or lose contact with the surface, causing artifacts in the acquired data (clipping). In case, the sample features are too high and the tip comes into uncontrolled contact with the sample damage to the tip or the sample are possible.

To overcome this limitation, certain solutions can be employed. Nanosurf recommends a z-actuator sample holder that can move up to 150 µm. This extended range allows for imaging rougher samples. However, it is important to note that the height of the AFM tip itself is limited. Therefore, careful consideration must be given to the sample's topography to ensure accurate and artifact-free measurements.

Reliable Imaging Requires Secure Attachment

Another critical aspect when considering samples for AFM measurements is their attachment to a surface. Samples must be securely attached and should not move during imaging. Loose attachment or samples floating in liquid are not suitable for AFM investigations.

The scanning process in AFM involves raster scanning a probe across the sample surface. Any movement or instability in the sample can result in distorted images or incomplete data acquisition. Therefore, it is necessary to prepare every sample in a way that ensures stability during imaging.

For solid samples, proper fixation techniques should be employed to securely hold them in place. This can include mounting the sample on a suitable substrate using adhesives or clamps. It is crucial to ensure that the chosen method of attachment does not interfere with the measurement or introduce artifacts that may impact the accuracy of the results.

In the case of samples that must be investigated in a liquid environment, such as biological specimens, it becomes even more challenging to ensure stability during imaging. Specialized sample preparation techniques, such as immobilization on functionalized substrates or using supporting matrices, may be required to overcome this challenge. These techniques provide a stable platform for imaging while preserving the integrity of the sample.

While AFM is a versatile and powerful tool for surface analysis and imaging, it is important to consider the suitability of samples for measurements. Rough samples that exceed the z-scanning range of AFM systems pose challenges in obtaining accurate and artifact-free results. Additionally, samples must be securely attached to a surface to ensure stability during imaging.

Understanding these limitations and considerations can help researchers and scientists choose appropriate samples and preparation protocols for AFM measurements. By selecting suitable samples, optimizing scanning parameters, and employing proper sample preparation techniques, the full potential of AFM can be harnessed to gain valuable insights into the nanoscale properties of various materials.

Conclusion

Remember, successful AFM measurements start with careful sample selection and preparation, paving the way for accurate and reliable data acquisition.

What is recommended for fixing nanoparticles to the substrate for contact mode? Or for sample deposition - can drop casting or spin coating be used? Find the answers to these and other questions in our frequently asked questions document here: