Light-emitting triangles may have applications in optical technology
06 February 2013
Scientists have used tungstenite to produce monolayer sheets of stacked sulphur and tungsten atoms in a honeycomb pattern of triangles with unusual photoluminescent properties.
Triangular single layers of tungsten disulphide have been synthesised by Penn State researchers. The edges of the triangles exhibit extraordinary photoluminescence, while the interior area does not (image: Terrones lab, Penn State University)
According to team leader Professor Mauricio Terrones of Penn State University, the triangular structures have potential applications in optical technology such aslight detectors and lasers.
Creating monolayers - single, one-atom-thick layers - is of special interest to scientists because the chemical properties of minerals and other substances are known to change depending on their atomic thickness, opening the door to potentially useful applications of multi-layered materials of various thicknesses.
Monolayer graphene was first achieved by exfoliating the material, layer by layer, with Scotch tape, until a single atom of thickness was attained. Now, for the first time, Terrones and his team have used a controlled thermal reduction-sulphurisation method (chemical vapour deposition) to accomplish the same feat with the rare mineral, tungstenite.
The scientists began by depositing tiny crystals of tungsten oxide, which are less than one nanometer in height, and they then passed the crystals through sulphur vapour at 850 degrees Celsius. This process led to individual layers composed of one atom in thickness. The resulting structure (tungsten disulphide) is a honeycomb pattern of triangles consisting of tungsten atoms bonded with sulphur atoms.
"One of the most exciting properties of the tungsten disulphide monolayer is its photoluminescence," Terrones said. "One interesting discovery from our work is the fact that we see the strongest photoluminescence at the edges of the triangles, right where the chemistry of the atoms changes, with much less photoluminescence occurring in the center of the triangles. We also have found that these new monolayers luminesce at room temperature. So no special temperature requirements are needed for the material to exhibit this property."
Terrones' colleague, Professor Vincent Crespi, describes the images of the photoluminescence as "beautiful". "The triangles light up all around their edges like little holiday ornaments - holiday ornaments with potentially transformative, long-term applications in nano-optics," he adds.
The research has many potential applications in the fields of optical light detection, the production of light-emitting diodes, and even laser technology. The researchers also plan to try the chemical-vapour-deposition technology to grow innovative monolayers using other layered materials with potentially useful applications.