It's a UV light, semiconductor, sensor, superconductor, ferromagnet, optoelectronic device. Just add water.
In a remarkable chance landmark discovery, a team of researchers at four universities has discovered a mysterious material that emits ultraviolet light and has insulating, electrical conducting, semiconducting, superconducting, and ferromagnetic properties — all controlled by surface water. It happened while the researchers were studying a sample of lanthanum aluminate film on a strontinum titanate crystal. The sample mysteriously began to glow, emitting intense levels of ultraviolet light from its interior. After carefully reproducing the experimental conditions, they tracked down the unlikely switch that turns UV light on or off: surface water moisture.
The team of researchers from Drexel University, the University of Pennsylvania, the University of California at Berkeley, and Temple University also found that the interface between the materials’ two layers of electrical insulators also had an unusual electrical conducting state that, like UV, could also be altered by the water on the surface. On top of that, the material also exhibited superconducting, ferromagnetic ordering, and photoconductive properties. Even weirder, “we can also make [the effects] stronger by increasing the distance between the molecules and surface and the buried interface, by using thicker films for example,” said Drexel College of Engineering Professor Jonathan E. Spanier.
Puzzled, the researchers turned to their theory collaborators on the team: Penn’s Andrew M. Rappe, Fenggong Wang, and Diomedes Saldana-Grego. “Dissociation of water fragments on the oxide surface releases electrons that move to the buried interface, cancelling out the ionic charges,” Wang said. “This puts all the light emission at the same energy, giving the observed sharp photoluminescence.”
According to Rappe, this is the first report of the introduction of molecules to the surface controlling the emission of light — of any color — from a buried solid-surface interface. “The mechanism of a molecule landing and reacting, called dissociative chemisorption, as a way of controlling the onset and suppression of light is unlike any other previously reported,” Saldana-Grego added. The team recently published its findings in the American Chemical Society journal Nano Letters.
Via Dr. Stefan Gruenwald