Developed by a team of researchers, energy-momentum spectroscopy allows scientists to better understand how light is emitted from layered nanomaterials and other thin films, possibly leading to better LEDs and solar cells.
A multi-university research team has used a new spectroscopic method to gain a key insight into how light is emitted from layered nanomaterials and other thin films.
The technique, called energy-momentum spectroscopy, enables researchers to look at the light emerging from a thin film and determine whether it is coming from emitters oriented along the plane of the film or from emitters oriented perpendicular to the film. Knowing the orientations of emitters could help engineers make better use of thin-film materials in optical devices like LEDs or solar cells.
The research, published online on March 3 in Nature Nanotechnology, was a collaborative effort of Brown University, Case Western Reserve University,
“The key difference in our technique is we’re looking at the energy as well as the angle and polarization at which light is emitted,” said Rashid Zia, assistant professor of engineering at Brown University and one of the study’s lead authors. “We can relate these different angles to distinct orientations of emitters in the film. At some angles and polarizations, we see only the light emission from in-plane emitters, while at other angles and polarizations we see only light originating from out-of-plane emitters.”
The researchers demonstrated their technique on two important thin-film materials, molybdenum disulfide (MoS2) and PTCDA. Each represents a class of materials that shows promise for optical applications. MoS2 is a two-dimensional material similar to
“If you were making an LED using these layered materials and you knew that the electronic excitations were happening across an interface,” Zia said, “then there’s a specific way you want to design the structure to get all of that light out and increase its overall efficiency.”
The same concept could apply to light-absorbing devices like solar cells. By understanding how the electronic excitations happen in the material, it could be possible to structure it in a way that coverts more incoming light to electricity.
“One of the exciting things about this research is how it brought together people with different expertise,” Zia said. “Our group’s expertise at Brown is in developing new forms of spectroscopy and studying the electronic origin of light emission. The Kymissis group at Columbia has a great deal of expertise in organic DOI: 10.1038/nnano.2013.20
Other authors on the paper were Sinan Karaveli (Brown), Theanne Schiros (Columbia), Keliang He (Case Western), Shyuan Yang (Columbia), Ioannis Kymissis (Columbia) and Jie Shan (Case Western). Funding for the work was provided by the Air Force Ofﬁce of Scientiﬁc Research, the Department of Energy, the National Science Foundation, and the Nanoelectronic Research Initiative of the Semiconductor Research Corporation.
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