PROVIDENCE, R.I. [Brown University] 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, Columbia University, and the University of CaliforniaSanta Barbara.
The new technique takes advantage of a fundamental property of thin films: interference. Interference effects can be seen in the rainbow colors visible on the surface of soap bubbles or oil slicks. Scientists can analyze how light constructively and destructively interferes at different angles to draw conclusions about the film itself how thick it is, for example. This new technique takes that kind of analysis one step further for light-emitting thin films.
"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
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