Super hot, superconducting thin film.By making copper-oxide materials one layer of atoms at a time, Japanese materials scientists have created thin films that hint at record-high transition temperatures for superconductors. In recent years, researchers have failed to push transition temperatures -- above which a material ceases to conduct electricity with no resistance -- much higher than 125 kelvins. So like other scientists, Tomoji Kawai of Osaka University Home to many elite and renowned alumni of CEOs, lawyers, doctors, scientists, bureaucrats, and a Nobel laureate, as well as to many advanced research centers, Osaka University is considered one of the most prestigious universities in Japan and Asia. and his co-workers have sought a better understanding of super-conductivity by controlling ever more precisely the structure and composition of copper-oxide thin films. For the research, this Japanese group uses a technique called laser molecular-beam epitaxy Molecular beam epitaxy (MBE), is one of several methods of depositing single crystals. It was invented in the late 1960s at Bell Telephone Laboratories by J. R. Arthur and Alfred Y. Cho. . First, the researchers put the ingredients for the superconductor A material that has little resistance to the flow of electricity. Traditional superconductors operate at absolute zero (-459.67 degrees Fahrenheit or -273.15 degrees Celsius). Experiments in the 1980s raised the temperature to -321 degrees Fahrenheit. into a reaction chamber. Atoms knocked off these ingredients by the laser then settle onto a substrate The base layer of a structure such as a chip, multichip module (MCM), printed circuit board or disk platter. Silicon is the most widely used substrate for chips. Fiberglass (FR4) is mostly used for printed circuit boards, and ceramic is used for MCMs. and build up into a thin film. The researchers control the chemical makeup of the film by varying the timing and number of pulses aimed at each ingredient. The reasearchers can stack up any number of layers of copper-oxide molecules. They have discovered that they can adjust the spacing between the layers of this so-called infinite-layer structure by sandwiching calcium and strontium strontium (strŏn`shēəm) [from Strontian, a Scottish town], a metallic chemical element; symbol Sr; at. no. 38; at. wt. 87.62; m.p. 769°C;; b.p. 1,384°C;; sp. gr. 2.6 at 20°C;; valence +2. atoms in different proportions between the layers. These sandwiched atoms prompt oxygen to squeeze in as well. The addition of oxygen improves superconducting su·per·con·duct·ing adj. Having, exhibiting, or capable of superconductivity: "a revolutionary superconducting magnetic propulsion system" Colin Nickerson. properties, says Kawai. He and his coleagues also found that lowering the temperature of the film's substrate improves transition temperatures. Thus, by inserting calcium as well as strontium between the layers and lowering the substrate temperature, they observed reliable indications of superconductivity superconductivity, abnormally high electrical conductivity of certain substances. The phenomenon was discovered in 1911 by Kamerlingh Onnes, who found that the resistance of mercury dropped suddenly to zero at a temperature of about 4.2°K;. up to 120 kelvins, he reports. That transition temperature represents a record for these layered copper-oxide materials, he adds. Kawai and his group have also observed unusual magnetic and resistance behavior in the film at 180 kelvins. But before he will believe that those observations suggest higher superconducting transition temperatures, "I need to see 150 kelvins." Kawai says. |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion