Difference: FibTest (2 vs. 3)
Revision 302 Oct 2009 - Main.RubenDiaz
Assessment of FIB instrumentsVisit to NIHOverallThe instrument at the NIH is a FEI Quanta SEM with a focused ion beam. The focused ion beam is the usual Gallium source, and the images are captured after a beam of electrons coming from a FEG are directed towards the sample. I was greeted at 9AM in room 403 of Building 50 at NIH by Gavin Murphy, who is a postdoc in Sriram Subramaniam's lab. Gavin has a background on TEM tomography, as he got his degree in the laboratory of Grant Jensen at Caltech.Sample preparationThe sample was prepared in the usual way. It was a resin embedded sample, with Osmium and lead citrate. He says that similar results are obtained from HP frozen samples which are freeze substituted. The specimens are trimmed to be ~1mm^3 on each side, glued to the SEM stubb with gold paint and sputter coated with gold. Then the SEM stubb is placed in the chamber (at least another 3 specimens can be placed in the same stubb) and this is evacuated. Venting the chamber took a long time (~10 minutes), but this was likely an unusual glitch. After the specimens were mounted in their holder and the chamber was under vacuum (which took just a few minutes), the e-beam was used to collect a low magnification image of the specimen. This low mag image was correlated with an image of the specimen from the light microscope, in order to find the area of interest where to start digging the trench. | ||||||||
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| > > | Once an area of interest is found, platinum is evaporated on the area where the data is expected and the trench made, as well as two canyons on the side of the area of interest. The trench is usually 100um wide, and 30um long and ~3um deep, according to the settings, but usually the trench goes deeper, as the instrument assumes that the material is silicon, which is harder than resin. The thickness of the platinum coat is between 0.5 and 1um. Overall, it takes about 6 hours of preparation, from the mounting of the samples in the stub, to the start of data collection. The particle beams in this instrument are not controlled by a system of condenser lenses, but instead they are simply collimated by restricting apertures. The 4th aperture in the electron column was used, with a potential of 3kV for data collection. The ion beam was used with an aperture setting of 0.5nA and an accelerating voltage of 30kV. | |||||||
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