A theory for inelastic scattering of fast electrons in solids is developed, based on an extension of the theory of scattering in an electron gas. Values of the inverse mean free path and related optical potential can be computed quite conveniently. It appears that, particularly in the case of solids characterized by high atomic numbers, the contribution of inelastic scattering to the optical potential for fast electrons may have been considerably over-estimated by electron microscopists in the past.

Electron excitation and the optical potential in electron microscopy

A condensed description is given of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers It is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments Because of this, only qualitative predictions of behaviour in the electron microscope can be made A number of authors have described the changes in the image or diffraction pattern of particular specimen types during observation in the electron microscope and their work is reviewed here In general, contrast features in the image may disappear, due to loss of mass or crystallinity, or new features may appear due to distortion of ordered regions The effects of radiation damage on attainable resolution, and possible methods of improving the resolution are then discussed

Radiation damage and electron microscopy of organic polymers

A condensed description is given of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers. It is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments. Because of this, only qualitative predictions of behaviour in the electron microscope can be made. A number of authors have described the changes in the image or diffraction pattern of particular specimen types during observation in the electron microscope and their work is reviewed here. In general, contrast features in the image may disappear, due to loss of mass or crystallinity, or new features may appear due to distortion of ordered regions. The effects of radiation damage on attainable resolution, and possible methods of improving the resolution are then discussed. I. Introduction Specimens in the electron microscope are inevitably exposed to irradiation by electrons. A certain fraction of these electrons will interact with orbital electrons in the specimen and transfer energy to them. At normal accelerating voltages the excited states formed in metals and most other inorganic substances dissipate their energy as heat, and no permanent change occurs. In some inorganic salts and all organic substances, however, some fraction of the excited states decay to altered structures, giving permanent changes in the chemical and physical properties of the specimen. In general, some fraction of the mass is lost, the chemical composition changes and any long range order originally present is destroyed. When organic material provides the image contrast, the appearance of the specimen changes considerably during observation in the electron microscope, because of radiation damage. The impermanence of the original appearance limits the possible resolution. After considerable irradiation - which may only take a short time in the microscope - the specimen stabilizes in a new form, resistant to further radiation. All of the initial structure of interest may have been

http://rd.springer.com/content/pdf/10.1007%2FBF00540772.pdf

Review Radiation damage and electron microscopy of organic polymers

The cross-section for inelastic scattering of 80 keV electrons in thin films of evaporated carbon has been measured as a function of energy loss (from 10 to 600 eV) and scattering angle (up to 0·1 rad). The onergy-loss spectrum shows a broad peak around 24 eV, believed to arise mainly from plasmon oscillation of valence electrons. Losses between 50 and 280 eV are principally due to single interband transitions of the valence electrons, their intensity being proportional to (energy loss)−r , with r in the range 4 to 4·5. Their angular distribution shows a broad peak within the range 20—50 mrad (dependent on the energy loss) which can be explained using oither a wave-mechanical or a ballistic model. The cross-section for K-shell excitation (energy loss > 285 eV) was measured as a function of scattering angle; the results appear to be in good agreement with Bethe theory. Implications of inelastic scattering in transmission electron microscopy of carbon and organic materials are discussed with refore...

Inelastic scattering of 80 keV electrons in amorphous carbon

Rate control in dissolution of alkali feldspars—I. Study of residual feldspar grains by X-ray photoelectron spectroscopy

The distributions of electron energy loss (range 10–100 ev) from fima of evaporated carbon, have been studied for a range of film thicknesses from 165 to 835 A and a range of electron energies from 23 to 70 key. It is shown that these distributions may be fitted, and hence predicted, within a deviation of a few per cent, for energy losses less than about 200 ev and the mean free path λ for inelastic electron scattering is determined for each electron energy. These values of λ are in good agreement with the experimental values of Brunger and Menz (1965) and with theoretical values evaluated using the Bohm—Pines plasma oscillation theory.

R. E. Burge

Papers

Electron Energy Loss Spectra for Evaporated Carbon Films