Lasers Deposit MgB2
COLLEGE PARK, Md. -- High-temperature superconductors have been around for 15 years, but the levitating trains and zero-loss power lines that these materials promised have yet to make an appearance. Nevertheless, investigations into the applications of superconductivity continue. For example, lasers are enabling researchers to create thin films of magnesium diboride that will advance the study of this new superconductor and that could find a place in fast and novel superconducting electronics.
Pulsed laser deposition enables researchers to produce thin films of the superconductor magnesium diboride. Films produced in an in situ process exhibit a superconducting critical temperature of approximately 27 K.
Satish B. Ogale and his colleagues at the University of Maryland, in conjunction with researchers at the Department of Energy's Ames Laboratory and Iowa State University in Ames, have deposited thin films of magnesium diboride by alternating layers of Mg and MgB2 or B using pulsed laser deposition with a Lambda Physik excimer laser. The 1-µm-thick films are deposited on a substrate of SrTiO3 at high temperature and at a pressure of 10-7 t, with the 1.5-J/cm2 KrF laser firing at 10 Hz. The resulting sandwich is fused under heat.
Early high-temperature superconductors were complex, making them difficult to understand in theory and hard to work with in practice, so the discovery of superconductivity in magnesium diboride has generated tremendous excitement since it was reported in January. MgB2 is a simple, binary, intermetallic material, and while its superconducting critical temperature (Tc) of 39 K is approximately 100 K cooler than the world record, it is high enough to be commercially useful.
The best films have exhibited a Tc of approximately 27 K, which is lower than that of the bulk material. Ogale said the phenomenon might be due to oxidation of the magnesium, carbon contamination or the existence of some other phase of the material. An alternative ex situ growth process, in which deposited boron is annealed in magnesium vapor, has yielded films with a Tc equal to that of the bulk.
Impact on photonics
Basic research continues, with the goal of understanding the material and improving the thin-film characteristics. Commercial applications would require films of high quality and high Tc. If these can be produced economically, laser-deposited superconductor films may have an impact on photonic devices, such as ultrafast switches, Ogale said.
The team reported its results in the July 9 issue of Applied Physics Letters.
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