Electron Microscope Studies of Organic Crystals

[摘要] This thesis is arranged in two parts; after an introductory chapter on the theory of image formation in the electron microscope, Chapters 2 to 5 are concerned with the problem of radiation damage to the specimen in the microscope, and Chapters 6 and 7 describe studies of crystalline paraffins by electron microscopy. Radiation damage to the specimen has long been recognised as a major hindrance to image-formation and diffraction studies in electron microscopy, especially of organic and biological material. Changes may occur in the structure of the specimen under the beam, leading to a false picture of the material, or the structure may be destroyed altogether before any detail can be recorded. Among the methods commonly used to counteract radiation damage are: cooling the specimen stage of the microscope in the hope of "freezing in" severed radicals, using minimum dose techniques in combination with image processing to extract information from low-contrast negatives, and coating the specimen with a thin layer of an amorphous conducting material such as evaporated carbon. In this study, the effect of combining some of these techniques is investigated, in particular the protective effect of an encapsulating carbon coat at various temperatures - room temperature down to 10K. A group of compounds which is highly sensistive to radiation damage is that of the crystalline paraffins. An understanding of the behaviour of long-chain paraffins may be important to the elucidation of the structures of some polymers and biological lipids, especially when the effect of the presence of chains of more than one length is taken into account. In the second section of the thesis, high resolution images have been taken of crystals of pure paraffins and of their solid solutions, in two orientations: the long axis may be viewed directly at room temperature, but image processing has been applied to the projection of the small (ab) unit cell face. Defects in the crystal lattice planes have been observed, and the variation in the interlamellar spacing according to the composition of solid solutions has been measured.

[发布机构] University:University of Glasgow

[关键词] Organic chemistry, Analytical chemistry