Electron Microscopy
The phrase "electron microscopy" usually conjures up ideas of high magnification images of biological specimens or perfectly formed crystals. Indeed these are the major uses of commercial instruments, but to a physicist, electron microscopy may also be interpreted as a method of using electrons to better view a specimen at the molecular or even atomic level. Interpreted in this broad manner, there is a large number of unsolved problems of considerable interest.
The instrument itself presents problems of great interest to a physicist. What options are available in using electrons to create an image? Are there any new possibilities for imaging? What are the theoretical and practical limitations? These questions raise many scientific issues, some of which have been consistent challenges for decades. For example, there is the question of resolution. The highest resolving power yet attained cannot resolve the spacing between atoms in solids, and the limit of resolution is set by well-established theoretical studies of lenses. Albert Crewe has developed ideas for overcoming these limitations. Two such concepts have proven feasible theoretically, but are impractical. A third possibility has been devised very recently and appears to be very promising. Work on this project is continuing both theoretically and in the laboratory.
Resolution is not enough, however; one also needs contrast. Our invention of the high resolution scanning microscope appears to have solved this problem for the time being, and isolated heavy atoms are now imaged. This has enabled us to study the natural motion of atoms on surfaces.
Biological materials present yet another challenge, this time in image analysis. It is known that such materials are easily damaged by electrons so that the only recourse is to use low electron currents where the damage is small but the image is poor. Digital image analysis techniques must be developed to extract the information from such images. This kind of work is still in its infancy, and new methods are being developed. EFI faculty also have developed some new mathematical procedures for 3D reconstruction from 2D projections.
This area combines knowledge from a wide variety of fields: theoretical and practical electron optics, the interaction of fast electrons with matter, high vacuum and specimen preparation techniques, Fourier transform optics, and image theory. By extending knowledge in these areas, instruments may be created that will solve problems in biology and material sciences.