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Less than two years ago, scientists discovered that magnesium diboride (MgB2)--a relatively simple and readily available metallic compound--can conduct electricity with next to no resistance. Moreover, its superconductivity occurs at temperatures around 39 degrees Kelvin, which is much higher than those required for similar superconductors. But efforts to make superconducting circuits out of the compound have so far met with limited success. Now a new technique described in the current issue of the journal Nature Materials may pave the way to fabricating devices based on MgB2.
Superconducting devices require multiple layers of thin films to be grown on a single surface. One current method of making MgB2 films results in sheets with good superconducting properties but rough surfaces, which make layering them difficult. A second method makes smoother films, but the potential for contamination is high. In the new work, Xiaoxing Xi of Pennsylvania State University and his colleagues heated chips of magnesium to more than 700 degrees Celsius in the presence of hydrogen gas. When they added diborane gas (a mixture of boron and hydrogen), a film of MgB2 began to grow on a sapphire surface within the reaction chamber. The presence of hydrogen is key, the researchers report, because it stops the formation of magnesium oxide, which contaminates the films and lowers their superconductivity. Their film (see image) exhibited similar superconducting properties as bulk MgB2 does.
Although the findings are encouraging for new technologies based on MgB2, the process is not yet ready for commercialization. So far, the scientists have been able to manufacture only one film at a time. "But because the system is currently so simple," writes John Rowell of the Materials Research Institute at Northwestern University in an accompanying commentary, "it is easy to imagine modifications that would allow the sequential deposition of multiple superconductors, insulators and other materials, as required for a successful multilayer film technology."
