Thursday, June 16, 2011

Resolution Test

Every SEM and TEM has a resolution benchmark. This is a recipe that combines a specific resolution standard sample with a standard instrumentation configuration. In electron microscopy a common resolution standard sample is Au clusters on HOPG. Such a sample is produced by evaporating Au on HOPG at such a temperature that mobility is limited and Au nucleates into clusters. Au/HOPG is an ideal resolution standard because gold has very good secondary electron emission efficiency while carbon very poorly emits secondaries.

In the case of the JEOL 5900 the test configuration is a 30 kV beam energy with a 10 mm working distance. We use a sample that has Au clusters with gaps of ~ 10 nm between them. It should be noted that Au/HOPG samples with different cluster gap distances can be obtained. After aligning the column and objective aperture, clearing the lenses and optimizing focus and stigmation one should be able to easily observe gaps of ~ 10 nm between these gold clusters.

It should be noted that there are some horizontal lines on the image. This is periodic in time and will manifest differently with different acquisition times. It is due to vibration in the building. It can also be mitigated using frame averaging.

Generally speaking, for work requiring resolution below a few 10's nm I would recommend a field emission SEM (FE-SEM). BSIR, The Biological Science Imaging Resource, has a FEI Nova 400 nanoSEM that is available to the research community. It provides 1.0 nm resolution at 15 kV and 1.8 nm resolution at 1 kV.

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