Some Unsolved Problems and Promising Methods in Electron Image Processing

Abstract

The greatest practical problem of high-resolution electron microscopy is undoubtedly that of radiation damage: certain struetures are fragile enough to be destroyed by an electron dose too low to form a useful image. This difficulty can be palliated if not solved by combining ultra-low-dose imaging witbimage averaging (see chapter by J. Frank in this volume) but not all specimens lend themselves to this treatment. A major break-through in the struggle against radiation damage, achieved by exploiting the very low-temperature environment inside a superconducting lens, has recently been described (Dietrich et al., 1979) and evidence showirighow effective this is presented elsewhere in this volume by I. Dietrich and J. Dubochet; the protection afforded when a liquid helium stage rather than a superconducting lens is employed is discussed in the paper by G.M. Parkinson et al. (this vol.). Further work will show whether Operation at a few kelvins is a general panacea and reveal any limitations to the protection. Nonetheless, however valuable very low-temperature operation may prove, other procedures such as averaging and the trace strueture analysis proposed by Hoppe (1975, 1978) will undoubtedly continue to be developed.