International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C. ch. 3.5, p. 176
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Long-chain compounds, paraffins, phospholipids, etc., can be prepared epitaxically from solution in molten naphthalene or benzoic acid (Fryer, McConnell, Dorset, Zemlin & Zeitler, 1997; Wittmann & Lotz, 1990). For example, a dilute solution of a compound in naphthalene is alternatively solidified and liquified within a few degrees of the melting point to order the long-chain material relative to the naphthalene. When finally solidified, the compound is ordered along the (110) plane of the naphthalene. In practice, the final solidification is carried out on a carbon film and the naphthalene is removed under vacuum. The crystals are lath shaped and are aligned with the long-chain major axis on the carbon film across the lath and hence normal to the electron beam. Crystals of the same compounds prepared from normal organic solvents as described in Subsection 3.5.3.2 have the long-chain axis normal to the carbon-grid plane and thus parallel to the electron beam. The advantage of the normal orientation is that the large interplanar spacing along the chain axis is more accessible to direct imaging in the electron microscope.
References
Fryer, J. R., McConnell, C. H., Dorset, D. L., Zemlin, F. & Zeitler, E. (1997). High resolution electron microscopy of molecular crystals. IV. Paraffins and their solid solutions. Proc. R. Soc. London, A453, 1929–1946.Google ScholarWittmann, J. C. & Lotz, B. (1990). Epitaxial crystal growth on organic and polymeric substrates. Electron Crystallography of Organic Molecules, edited by J. R. Fryer & D. L. Dorset, pp. 241–254. Dordrecht: Kluwer Academic Publishers. Google Scholar