Practical Electron Microscopy and Database

For rigorous requirements, e.g. to have a uniform 5-nm silicon (Si) thickness for STEM, we should not use ion milling technique due to the unavoidable damage from implantation that could cause a mistaken for dopant clusters in Si. The samples can be thinned using double-wedge mechanical polishing or tripod polishing techniques with diamond-coated lapping film and colloidal silica. Note that the amorphized surface layer produced by chemical-mechanical polishing is quickly oxidized. The oxide can be stripped away with a 30-second etch in 100:1 hydrofluoric acid solution immediately before the sample is placed in the STEM. This method can give very good STEM output. For example, using this method in combination with a good STEM, the Sb atoms doped in Si was observed and the result was published in a high impact journal [1].

Some materials, e.g. ceramic crystals, can be prepared by crushing in liquid nitrogen. The obtained “nano-”particles can represent the structure of the original materials, are dispersed in acetone and then are put on carbon-film Cu (copper) TEM grids.

[1] Atomic-scale imaging of individual dopant atoms and clusters in highly n-type bulk Si, P. M. Voyles, D. A. Muller, J. L. Grazul, P. H. Citrin, and H.-J. L. Gossmann, Nature, 416 (2002) 826.