ightning strikes a tree on a cold night in Indonesia almost 2 million years ago. Several branches burst into flames. A few fall burning to the ground. A shivering ape-man (Homo erectus) bravely picks up a branch burning at one end. He basks in its heat until he burns himself and screams in pain. Man has discovered fire.
Thousands of years later, women cook meat in clay pots suspended over fire. Humans have learned to use fire not only to cook but also to harden clay into pots, giving rise to the pottery industry. Thousands more years pass. A new use for fire has been found: extracting copper from rocks. The age of metals is born.
What do these examples from prehistory and early recorded history show? According to ORNL's Doug Mashburn, "The combination of a materials processing technique, such as fire, and accessible materials, such as clay and rock, spawns new industries, such as potterymaking and metalworking. Such technological advances proceed in a cyclical synergistic fashion."
"New industries arise from the use of newly discovered or invented processing methods and newly discovered accessible materials. As each industry grows, it hones the process, makes the new materials widely available, and eventually enables the next cycle. Each cycle significantly expands the range of materials accessible."
Fast forward to the inventions of mechanical power and precision rotating machinery in the 19th century. These innovations, Mashburn says, were enabled by the existence of a well-developed metals-processing industry. The harnessing of electricity was made possible by the existence of industries to produce and shape copper and iron into wires, magnets, and other components. The inventions of the dynamo for generating electricity and the electric motor for using it depended upon the precision rotating machinery industry, which was made possible by the availability of affordable and appropriate metals.
A significant jump in materials access came with the combination of electricity and vacuum. "Practical use of vacuum depended on both precision machinery and mechanical power," Mashburn says. "Invention of the hot filament electric light was enabled by the harnessing of vacuum and electricity. The combination of vacuum and electricity in the form of an electron beam opened up possibilities of discovering and accessing many new materials, such as refractory metals, superalloys, refractory ceramics, and large pure crystals."
Electricity and vacuum together have also made possible the evaporation and deposition of material as optical films for high-performance mirrors, lenses, and windows. These new optical components enabled the invention and development of the laser. A unique materials-processing tool, quite different from fire or electricity, the laser is still being perfected and folded into industry.
The invention of the pulsed laser has enabled laser ablation deposition, an extremely versatile processing technique. "Because of its ability to 'boil off' atoms and rapidly assemble them into thin films," Mashburn says, "laser ablation opens the door for a quantum leap in materials access."
According to the Handbook of Chemistry and Physics, 4000 inorganic compounds are available in more than microscopic quantities today. These materials can be made by using traditional processing technologies, mainly heating, which segregates out some elements rather than incorporating them into the structure of materials.
"Because laser ablation removes so many processing limitations, we can now contemplate the synthesis of previously impossible compounds," Mashburn says. "By combining oxides of the 60 different metallic elements in groups of three, simple math shows that the possibilities exceed 100,000 compounds. If we consider more complex combinations of more than three elements, such as the high-temperature superconducting yttrium-barium-copper oxide, the possibilities are far greater. And then if we consider such combinations of metals with fluorine, sulfur, chlorine, and so on, it is clear that the 4000 existing compounds make up only a tiny corner of the huge continent of possibilities. How many more complex materials as exciting as the new superconductors are still awaiting discovery?"
The laser ablation technique, already showing distinct promise for such an exploration, is in its infancy. Mashburn expects that new advances--including his own innovations--will improve lasers, ablation chamber designs, the physics and control of the ablation process, and monitoring of both the ablation process and the deposited material.
Just as a lightning strike may have sparked the discovery of fire, a laser beam striking a target could launch the discovery of astounding new materials--and the creation of whole new industries.--Carolyn Krause
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