ION IMPLANTATION OF MATERIALS
What do computer chips and artificial hips have in common? Both have been significantly improved by the application of ion beam processing, which had its beginnings in Oak Ridge.
Ion beam technology was first employed on a large scale at the Y-12 Plant in the electromagnetic separation of uranium isotopes for the atomic bomb that helped end World War II. Since the mid-1940s, ORNL has made major advances in developing ion sources for physics and fusion experiments and in using ion beams for materials processing. Using calutrons, accelerators, and other devices, researchers developed techniques for producing high-current beams of ions of numerous elements for use by industry for ion implantationinjecting ions (charged atoms) near the surface of a material surface to modify its properties.
ORNL helped the electronics industry when Gerald Alton and others used the calutrons to show that electrical junctions can be formed in silicon by the direct implantation of boron and phosphorus ions. Thousands of semiconductor samples were implanted in Oak Ridge for industry in the early development of integrated circuits for electronic applications.
The 1962 discovery by ORNL's Mark Robinson and Dean Oen of ion channeling and its effects in crystals greatly improved the understanding of the interaction of ion beams with solids and advanced the use of ion beams for characterizing, analyzing, and processing materials. The ion channeling effect was discovered theoretically by a computer simulation that showed ions shooting through the "channels" between rows and planes of atoms in crystalline materials. The actual existence of ion channeling was later demonstrated experimentally at a Canadian laboratory and later at ORNL.
The channeling effect is critical in ion implantation because it affects ion depth in crystals, which is crucial for making effective semiconductor chips that form the heart of laptop computers, automatic cameras, and other electronic devices. Because of the importance of the crystal lattice in the transport of ions in solids and in radiation damage phenomena, Robinson developed the computer code MARLOWE, which continues to be the standard for the simulation of ion beam interactions with crystalline matter.
In the early 1970s, Bill Appleton initiated an experimental effort using ion beams for implantation and other processes for modifying semiconductors, metals, insulators, and ceramics to improve their surface properties. Since then, ORNL researchers have used ion implantation to produce new materials for electronic, optical, and tribological uses. New implantation techniques have been developed to deposit thin films and fabricate improved optical waveguides.
Artificial hip joints can last much longer if implanted with nitrogen ions, according to ORNL research. Jim Williams, Bill Appleton Ray Buchanon (guest scientist from the University of Alabama at Birmingham), and others in the Solid State Division discovered that implanting surgical alloys used in prosthetic implants made them tougher and more resistant to wear by corrosion. The technology was developed and transferred to industry. By the early 1990s ion implantation was used on about half of the artificial hips and knees sold in the United States, with a potential savings of about $100 million a year by preventing rework of failed joints.
Because of the enthusiastic following of collaborators from universities and industry, ORNL in 1980 formed the Surface Modification and Characterization Research Center. Ion implantation facilities were expanded, and by 1990 the center had four accelerators for high-current, high-energy implantation and low-energy ion beam deposition. Each year about 100 scientists from universities, industries, and national laboratories engage in cooperative research projects at the center. Through research and collaboration, ORNL's work in ion implantation can be expected to be a source of many new exciting applications in science and technology.
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