We did Scanning Electron Microscopy and found that our result is not satisfactory. We used two types of coating. Initially, it was chromium coating. However, the focus of the SEM to our samples caused the burning of the sample. Then, we applied gold coating and the result was better even with some burnt. The burnt was not appear when we reduced the voltage to as low as 1.5 KV.
Just wonder, whether the burnt was influenced by the melting temperature of the coating, Aurum (gold) 1064 deg C, and Chromium 1907 deg C. Or, it was due to the proton that available to the ion, as Au2+ and CR3+.
Hope for further explanation. Thank you!
I suspected this. Polymers and biological/organic materials will always be more difficult than inorganic materials. The problem will be exacerbated by (attempted) higher magnifications where the material can degrade or even boil (if this is a possibility for the material) under the intense electron beam. Metal coatings typically adhere poorly to such materials too. General rules are to keep the eV and magnification as low as possible. Different metals may adhere better and this may be the case here. You could also try a carbon coating for better compatibility.
Yes, I was thinking of it too. The sample is a biofilm that is rich of positive ions. Thus, suspected it is one of the factor Prof.
It may be explained by a major reactivity on the Chromium surface. Some pollution will be always deposited when you transfer your samples to atmosphere, but gold is quite a really "clean" material.
I've worked as a SEM technician and I've observed the same thing. Anyway, how are you preparing your samples? Are you on a HV SEM or an ambiental one? What kind of sample do you have? All of this can contribute to the "burning" of your sample and also with the charging problem.
I suspected this. Polymers and biological/organic materials will always be more difficult than inorganic materials. The problem will be exacerbated by (attempted) higher magnifications where the material can degrade or even boil (if this is a possibility for the material) under the intense electron beam. Metal coatings typically adhere poorly to such materials too. General rules are to keep the eV and magnification as low as possible. Different metals may adhere better and this may be the case here. You could also try a carbon coating for better compatibility.
Thank you very much Prof Alan! Carbon coating seems interesting to be tested as the biofilm is formed by carbon atoms as well.
Sir David, I really appreciate your input. I will check further regarding HV SEM or an ambiental. Thank you!
I think you deposited films on the same samples with different technique, what is the sample (substrate) material? The SEM analysis of two samples coated by two different techniques will be different because the deposition parameters are different so the SEM will give different results, moreover, it is well known that selection of samples, suitable technique and deposition parameters play an important role. So the results will differ 100 %.
Most probably what you see is "burning" of your specimen under a layer of coating with subsequent deformation and cracking of it.
I would not recommend Cr coating for routine SEM work. A lot of artefacts.
Some specimens are prone to beam damage ("burning") and some delicate specimens could be ruined by any coating. Depending on SEM you have you may want to try ESEM and/or low kV modes.
Thank you everyone! We will evaluate further the water content of the sample by drying it with silica gel etc. and the voltage that will be used. The coating; gold, chromium, and carbon, will also be counted. Thank you again!
It is a biopolymer that is organic based Prof. Vladimir Dusevich. We are going to run it this Thursday. Currently, we have conditioned the sample for nearly a week to reduce the presence of water. We plan to use lower voltage and have to check the availability of the coating as well.
Try to use dehydration with ethanol solutions (well-known technique in histology), then coat a clean stub with gold (about 20 nm), deposit the biofilm and coat with 5 nm gold. I used this way for microbial biofilms, it worked well.
Melting temperature of the coating metal doesn't play any role in this case (there is a connection with grain size and parameters of coating, but it is another story). The main parameters of any coating in SEM: thickness, adhesion, homogeneity, heat conduction and chemical stability (oxidation, etc.). In real practice, just 5 nm gold coating is enough almost for all conventional tasks.
Residual water is the most common cause of "bad behavior" under the beam for soft biological samples. Dehydration is an important part of preparation.
Good luck!
It all depend on your sample and the conductivity of the coating with respect to your sample. Try to reduce the voltage to get the right feedback
I would recommend Pt-Pd coating. If works very well for UHR HV imaging of cellulose based materials and other types of polymers. And yes the sample preparation is playing the most important role. Highly outgassing samples will give you severe instabilities in SEM and moreover will contaminate the HV system. Good luck 🤞
Pt-Pd is a noble coating materials. Yet it is expensive. I think it will works
@ Gabi Nehme
Pt-Pd is the most common material for coating SEM specimens. 5 nm of coating is not really expensive.
Some information about Target material selection
https://www.microtonano.com/TIN-Target-material-selection-for-coating-SEM-samples-using-an-SEM-sputter-coater.php
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