Dear all,
I used carbon coated copper grid 200 mesh for my sample (gold nanoclusters dispersed in ethanol) to get images. Sometimes I got different types of ring-shaped damage after few seconds (10 s - 30 s) exposure at high magnification (the image was attached, please find it). But low magnification would not give any damage. My doubt is, why this occurred and how to avoid this issue.
Thanks in advance.
Dear Mustapha Jouiad
Thank you very much sir.
The problem occurred even I prepared the sample with a heating lamp.
Anyway, I will follow all those ways in next time.
Thank you once again.
You are concentrating your electron beam into too small an area. Decrease the magnification.
Dear @Alan F Rawle , I need to analyze small area. so I can not decrease the magnification.
Dear Gopi,
I agree with Mustapha Jouiad and in addition to his comment I have another item. In line with my experience, if sample is held in gonio-stage vacuum too long before entering into column, the small amount of oil vapour from rotary pumps may cause contamination of sample. For extra quality high-resolution imaging I insert holder inside as quick as possible to avoid this problem.
You don't specify the TEM acceleration voltage you used, nor the electron source (is it a FEG, maybe aberration corrected ?). I wonder whether you get radiation damage, e.g. thinning of carbon. In this case you don't add but remove materials in the illuminated area. You can find an interesting article on these problems in Microscopy and Microanalysis (2006) issue 12 pp.65-71 (Egerton, Wang & Crozier)
Dear A. Armigliato,
The Acceleration voltage for tungsten filament is 200 kV.
Thanks.
This looks like a concentric C-contamination... LN2 in anti-contamination device (ACD) can make some difference ...
Contamination: hydrocarbons deposited on a specimen surface condense at an electron-beam irradiation area by the electrostatic force of the electron beam and are polymerized by the electron beam. This phenomenon is called "(specimen) contamination." Contamination is particularly severe when a small specimen area is irradiated with a focused, high-density electron beam, for example CBED or STEM.
Anti-contamination device: A device that is used for suppressing the deposition of hydrocarbons on a specimen in a TEM. By the condensation action of the cooled fin with liquid nitrogen which is set to surround the specimen holder, contamination on the specimen due to hydrocarbons is largely decreased. In this device, two small aperture holes are placed at the top and bottom to allow the electron beam to pass through the holes. The tip of the specimen holder (specimen part) is inserted into the fin through the opening at its lateral side.
Wow, It's very interesting answer and new for me.
Thank you so much Janez
- Badges
- Science method