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Atomic resolution microscopy of carbonates. Interpretation of contrast |
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| Authors: | A Meike H-R Wenk M A O'Keefe R Gronsky |
| Institution: | 1. Earth Sciences Division, Lawrence Berkeley Laboratory, 94720, Berkeley, CA, USA 2. Department of Geology and Geophysics, University of California, 94720, Berkeley, CA, USA 3. Lawrence Berkeley Laboratory, National Center for Electron Microscopy, 94720, Berkeley, CA, USA |
| Abstract: | The atomic resolution microscopy (ARM) at the National Center for Electron Microscopy, Lawrence Berkeley Laboratory, Berkeley, California has been used to image structural features in rhombohedral carbonates. The resolution of the microscope is better than 1.6 Å, but beam damage presently limits the resolution of some of our images to slightly better than 2.6 Å. More details can be extracted through image processing. We were able to interpret contrast in through focus series of “ideal” dolomite by comparing processed images with multibeam contrast calculations. Fair agreement was obtained for focus and thickness variations both of which display great changes. Even for ideal dolomite, the matching is not straight-forward, due to minor orientation variations, the presence of and amorphous overlayer, and surface roughness induced by ion beam thinning, etc. We also find good agreement for calcian δ-dolomite with a cation distribution model which assumes a periodic substitution of alternating Mg layers by Ca. Some atomic resolution examples are shown for coherent calcite-dolomite intergrowths and δ-dolomite domains in dolomite. |
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