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A new understanding of why synthetic 2-D materials often perform orders of magnitude worse than predicted was reached by teams of researchers led by Penn State. They searched for ways to improve these materials' performance in future electronics, photonics, and memory storage applications.
Two-dimensional materials are films only an atom or two thick. Researchers make 2-D materials by the exfoliation method—peeling a slice of material off a larger bulk material—or by condensing a gas precursor onto a substrate. The former method provides higher quality materials, but is not useful for making devices. The second method is well established in industrial applications, but yields low performance 2-D films.
Researchers - Time - Quality - Materials - Chemical
The researchers demonstrated, for the first time, why the quality of 2-D materials grown by the chemical vapor deposition method have poor performance compared to their theoretical predictions. They report their results in a recent issue of Scientific Reports.
"We grew molybdenum disulfide, a very promising 2-D material, on a sapphire substrate," said Kehao Zhang, a doctoral candidate of Joshua Robinson, associate professor of materials science and engineering, Penn State. "Sapphire itself is aluminum oxide. When the aluminum is the top layer of the substrate, it likes to give up its electrons to the film. This heavy negative doping—electrons have negative charge—limits both the intensity and carrier lifetime for photoluminescence, two important properties for all optoelectronic applications, such as photovoltaics and photosensors."
Aluminum - Electrons - Film - Sapphire - Substrate
Once they determined that the aluminum was giving up electrons to the film, they used a sapphire substrate that was cut in such a way as to expose the oxygen rather than the aluminum on the surface. This enhanced the photoluminescence intensity and the carrier lifetime...
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