Editorial: E beams touch all phases of materials technology
The discovery of electrons happened more than a century ago. Research in the late 1800s by pioneering scientists/physicists showed that a cathode discharge (cathode rays) consists of streams of negatively electrified particles, now called electrons. One of the first applications of these high-energy beams was to melt refractory metals in a process patented by M. von Pirani in 1907, but not much else was done with this new-found phenomenon, and even EB melting technology didn't reach commercial importance until about 50 years ago. Since the 1950s though, electron-beam technology has made many tough materials processing jobs feasible, from melting to joining, coating, surface modification, and others (see "Electron-Beam Technology Makes Tough Metal-Processing Jobs Easy" in this issue on p 30).
While the author notes that EB technology has a bright future and will grow and continue to contribute in industrial processes, electron beams also will be instrumental in creating new materials. Electron beams are being used at the DOE Materials Science and Engineering Div. to characterize materials structure and composition including research on the arrangement and identity of atoms and molecules in materials; specifically the development of quantitative characterization techniques, theories, and models describing how atoms and molecules are arranged and the mechanisms by which the arrangements are created and evolve.
The activity is driven by the need for quantitative characterization and understanding of materials structure and its evolution over atomic to micron length scales. Advancements include the ability to image light elements (such as nitrogen) within a matrix of heavy elements; a high-resolution method to map the spatial distribution of valence electrons in high-temperature superconductors, using electron holography to image grain boundary potentials in a dielectric; and development of a three-dimensional atom probe to study impurities and precipitation. Four user centers including Argonne National Laboratory, Lawrence Berkely National Laboratory, Oak Ridge National Laboratory and the Frederick Seitz MRL at University of Illinois are the only facilities in the U.S. with electron beam microcharacterization capabilities available to outside users from the physical science community in academia, government laboratories, and industry.
Sophisticated, highly integrated synthesis, characterization, and modeling efforts are expected to lead to the development of unique new analysis tools and breakthroughs in materials, such as self-assembled nanostructured materials, bulk metallic glasses, and magnetic materials. An understanding of the mechanisms by which grain boundaries in metals and ceramics influence the properties and behavior of these materials will emerge, which should revolutionize their structural design.
After many years of discussion and dispute following the discovery of cathode rays as to whether the rays were waves in the ether (some sort of invisible light) or streams of negatively charged particles shot off with great speed from the surface of the cathode, they came to be recognized (as noted in an early 20th century physics book) as "?treams of electrons shot off from the surface of the cathode with speeds which may reach the stupendous value of 100,000 miles per second." Little did the pioneers involved in that research including Sir William Crookes (1832-1919), Sir Joseph Thomson (1856-1940) and several others know how stupendous would be the contribution of beams of electrons to mankind.