Supun Meegahakumbura To optimize SEM images, it's crucial to balance the amount of gold coating on non-conductive materials like zeolite. Too little can cause distortion, while too much can obscure the delicate surface features of zeolite particles, making accurate analysis difficult. Excessive gold coating can blur the edges of particles and reduce the depth and three-dimensionality of the image.

Sputter coating, Carbon/gold co-sputtering, and cryo-SEM are recommended coating techniques for thin gold layers, enhancing conductivity while preserving a thinner gold layer, and avoiding conductive coating in cold samples.

An overview (from a manufacturer):

https://www.leica-microsystems.com/science-lab/life-science/brief-introduction-to-coating-technology-for-electron-microscopy/

Using too much gold coating on non-conductive materials, such as fine zeolite particles, in SEM imaging can lead to several issues. While the gold coating is applied to enhance conductivity and minimise charging effects, an excessive amount may result in image quality and interpretation challenges. Here are some potential consequences of using too much gold coating:

• Loss of Surface Detail: Thick gold coatings can cover the fine protruding features of zeolite particles, leading to a loss of surface detail. This can affect the ability to study the morphology of the particles accurately.
• Blurring and Smoothing: Excessive coating may result in blurring and smoothing of surface features, reducing the sharpness of the images.
• Shadowing and edge effects: Thick coatings can cause shadowing effects and edge enhancements, impacting the contrast and interpretation of SEM images.
• Increased Background Signal: Too much gold coating may contribute to increased background signal, making it challenging to distinguish between coated and uncoated areas.
• Distorted Analysis: If the gold coating is too thick, it may interfere with analytical techniques such as energy-dispersive X-ray spectroscopy (EDS), potentially distorting the elemental analysis.

Recommended Coating for Non-Conductive Powder Samples:

Given the specific requirements of studying fine zeolite particles, using a coating that provides sufficient conductivity without compromising surface morphology is essential. Some alternative coating options include:

• Platinum or palladium coating: Platinum or palladium coatings are often used as alternatives to gold for SEM imaging. These coatings can provide good conductivity and may be suitable for preserving surface morphology.
• Carbon Coating: Carbon coating is another option for non-conductive samples. It is often thinner than metal coatings, allowing for better preservation of surface details.
• Low-Voltage SEM: Conductive coatings may be less critical when using low-voltage SEM, as lower accelerating voltages can reduce charging effects. However, not all SEM systems are equipped for low-voltage imaging.
• Variable Pressure SEM (VP-SEM): VP-SEM, which operates at higher chamber pressures, is another option for imaging non-conductive samples without requiring extensive coating.

It is recommended to perform optimisation experiments with different coating thicknesses and materials to find the best balance for preserving surface morphology while achieving sufficient conductivity. Additionally, adjusting SEM parameters, such as accelerating voltage and working distance, can also help mitigate charging effects.

Alvena Shahid Thank you for your valuable insights.

Pipasa Layak Thank you for your valuable insights. I performed SEM analysis with different coating times and was able to distinguish how image quality and distortions vary with the coating. Hope to do further trials to identify the exact amount of coating which is ideal for my material. Further, I hope to try this with lower EHT voltage values. Thank you for sharing your knowledge on this.

Stefan Baunack, the link you shared contains detailed information about the coating required for SEM. Thank you for sharing.

Blurring occurs in images Supun Meegahakumbura

The excessive gold layer can also attenuate the secondary electrons emitted from the sample, which are crucial for generating the SEM image. This can lead to a loss of information and contrast, making it harder to interpret the image and draw accurate conclusions

I will agree that some experimentation will be necessary to determine optimum. I also heartily endorse the Leica overview.

I will note that it may be good to invest in better techniques (e.g., iridium coating) rather than trying to get by with gold as the usual method. We chose to invest in such a coater after we purchased an FE-SEM. It was one of our better decisions. Gold contributed textures (grains) to the sample that were not present before. Iridium provided smoother, continuous layers using less metal (typically 2-5 nm). We also purchased the option to rotate the sample under the source to get more complete coverage.

I disagree with Harshitha's point that too much gold will lead to fewer secondary electrons. It will definitely lead to more. Metal is helpful in this regard for carbon nanotubes or other conductive samples. While they are conductive enough, they have a low SE yield. Metal will proved a better signal-to-noise ratio.

There are several concerns already mentioned of blurriness or obscuring features. That will be true for EDS as well. The metal will become progressively more of the signal in the spectrum and it is definitely possible to go too far.

Harshitha Mahesh,

Thank you for your valuable insights. I recently experienced the same incident.