Hi,
I am doing TEM routinely in my daily research work. Most of my TEM samples are the inorganic oxide-metal nanocomposite films deposited on single crystal oxide substrate (such as STO, MgO). After exposed in air for sometime, the TEM samples need to be plasma cleaned (with Ar80%/O220% mixture gas) to remove the moist, dust and other contaminants on their surface before being put into the microscope.
However, recently I ran into a tough problem. Even after being plasma cleaned, the fresh TEM samples still show very strong carbon contamination under the e-beam illumination in one 300kev Cs-corrected TEM. The attached pic shows the low-mag STEM image for one sample with the e-beam focusing on its substrate for only 10 seconds. I tried to prolong to plasma cleaning time, but nothing obviously changed and the carbon contamination was still there. The same issue happens to all of my samples.
More strangely, this issue never happens in the other 200kev TEM. After only 30s cleaning, the same TEM sample never exhibit the contamination issue in that 200kev TEM.
I am suspecting the main column of the 300kev TEM is dirty which cause this issue. But the technician indeed is doing cryo-cycle for that microscope routinely.
So I really have no idea why this contamination happens and how to resolve this problem. I am hoping some microscope experts here could give me some advice or suggestions. Thank you very much in advance!
Hello,
I think it is not an issue of plasma cleaning, it is rather a question of TEM specimen preparation. How did you prepare your TEM specimens? TEM image shown above is cross-sectional image. The contamination on the substrate surface might be due to inorganic oxide, which can be re-deposited during high-energy ion milling. So, try to clean the surface by low-energy ion milling (900-500 eV) rather than to clean it by plasma cleaning since you can remove inorganic part as well. I also suggest to use H2/O2 plasma instead of Ar/O plasma if possible.
To judge whether the column of 300keV TEM is contaminated or not, I would use a standard TEM specimen (e.g. cross-grating). If the column is clean, the contaminations will not be formed even after extensive e- beam exposure in STEM mode. The only requirements are a low pressure in TEM column (lowest possible, which can be reached after TEM holder insertion, ask for that a technician and how long you should wait for that) and LN2 cooling (of cause).
Regards,
Andriy
100% cleaning not possible, though u can control using standard cleaning methods used in IC fabrication or blowing away ultra pure nitrogen.
I am attaching some standard methods for cleaning/contamination removal procedures adopted by semiconductor industry
Sample contamination and sometime static charges raised the problems and reduce the quality of images. Attached study may help you.
Hello,
I think it is not an issue of plasma cleaning, it is rather a question of TEM specimen preparation. How did you prepare your TEM specimens? TEM image shown above is cross-sectional image. The contamination on the substrate surface might be due to inorganic oxide, which can be re-deposited during high-energy ion milling. So, try to clean the surface by low-energy ion milling (900-500 eV) rather than to clean it by plasma cleaning since you can remove inorganic part as well. I also suggest to use H2/O2 plasma instead of Ar/O plasma if possible.
To judge whether the column of 300keV TEM is contaminated or not, I would use a standard TEM specimen (e.g. cross-grating). If the column is clean, the contaminations will not be formed even after extensive e- beam exposure in STEM mode. The only requirements are a low pressure in TEM column (lowest possible, which can be reached after TEM holder insertion, ask for that a technician and how long you should wait for that) and LN2 cooling (of cause).
Regards,
Andriy
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