Hi all,
I am going to use SEM to image Al2O3 thin film deposited on Si substrate. However, apparently since Al2O3 is not good a conductive we have to coat it with a conductive agent (e.g. carbon). Did anybody has the same experience? Would you say it is necessary to do that in order to be able to see the sample or it is only vital for having a good resolution and high quality image?
Thank you
Method of specimen preparation depends a lot on what you are going to look for and what a SEM do you have. If you have field emission SEM, especially with in-lens capability, do not coat. Otherwise you'd better coat (preferably Au-Pd or Pt, pure Au has too big islands).
If you want magnifications not higher than x50,000, then use coated with metal specimens - best contrast, nice pictures. If your need magnifications not higher than 10,000-20,000, carbon coating is OK (metal is still better). But if you want to use BSE or EDS, then carbon coating is preferable.
For a high resolution/magnification image, coat the surface with Gold conductive layer by a sputter coater.
No need for coatings at all, I would say. Coated samples always hide something or coatings can cause some artifacts.
Try to change the energy of primary beam to around 2.9 kV or 4.2 kV and you should be able to image the sample with no charging.
I also wouldn't use Au for coating in order to get high-resolution images since Au forms islands before a close layer is produced. Carbon is commonly even worse, There are better materials like Cr, Pt or Palladium which don't have this tendency. Using a PECS it also doesn't hide small topographic details since the object will be rotated during sputter coating so that even very complex surfaces can be observed.A good since easy going idea is that from Rostislav. Sometimes it works quite well. however the focus depth is not that big anymore and you have to go very close to the pole piece. Another option is a gas injection system. This locally decharges the sample surface. The loss in resolution is not that big as in a low vacuum SEM.
https://www.researchgate.net/post/Can_I_use_glass_as_substrate_to_observe_SEM_sample
Method of specimen preparation depends a lot on what you are going to look for and what a SEM do you have. If you have field emission SEM, especially with in-lens capability, do not coat. Otherwise you'd better coat (preferably Au-Pd or Pt, pure Au has too big islands).
If you want magnifications not higher than x50,000, then use coated with metal specimens - best contrast, nice pictures. If your need magnifications not higher than 10,000-20,000, carbon coating is OK (metal is still better). But if you want to use BSE or EDS, then carbon coating is preferable.
Dr. Dusevich said exhaustively. The sample preparation depends on the task. If your goal is the high resolution (few nanometers) and you equipment is very good (and an operator has the good skills :)), it is possible to examine the specimen without a coating for prevention the artifacts. If you task is just routine SEM examination of the surface morphology (less than x100.000) - just coat 5-10 nm gold. The carbon coating is not a good idea.
Good luck!
Thank you all for your valuable answers. Reading people's opinion, I decided to do the experiment with no coating initially using low voltage (1-2kV) for electron gun since the image resolution is not my primary concern. Based on that, I will decide whether to do the carbon coating or not (Gold sputtering if unsuccessful). I will update my post about the result.
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