A team of North Dakota State University researchers, led by NDSU physics student Joseph Granlie, NDSU Professor Erik Hobbie (physics), and NDSU Associate Professor Dmitri Kilin (chemistry and biochemistry), have made a new discovery that holds promise for enhancing the brightness and efficiency of blue and green light emitted from silicon carbide nanocrystals, also known as SiC quantum dots. These particles would have wide-ranging applications including lighting, displays, solar energy, and medical imaging. Like silicon, silicon carbide is durable, earth abundant, and nontoxic. By focusing their study on silicon carbide nanocrystals, the team aimed to address a common obstacle: impurities that impede the nanocrystals' ability to emit light effectively.
 
Their findings revealed that certain impurities, especially oxygen in certain forms, might have only a minimal effect on the ability of the nanocrystals to emit light. This contrasts with what is known for pure silicon, where oxygen is almost always detrimental to light emission from quantum dots. The team discovered this using advanced computer simulations developed at NDSU and supported by an NSF CAREER award (Kilin) to scrutinize how these impurities form during creation of the nanocrystals. By studying the building blocks of the particles, they identified the most likely bonding patterns between atoms of silicon, carbon, and oxygen, and then examined the brightness of emission in the different scenarios.
 
“This work is interesting on two levels,” said Hobbie. “First, it explains the emission that people have observed from SiC nanocrystals made by breaking down bulk material in strong acids, which to date is almost the only way emitting SiC nanocrystals have been made. Such material will have high levels of oxygen impurity. Second, we know from our work with silicon quantum dots that nanocrystals built from the bottom up using molecular precursors are of much higher quality than those made by breaking down bulk material. At NDSU, we are actively engaged in making bright SiC quantum dots from the ground up, using liquid precursors in nonthermal plasmas. This work suggests that in certain cases, oxygen might not be as detrimental as we initially thought.”
 
The team’s research was featured as the cover story of Volume 14, Issue 26 of The Journal of Physical Chemistry Letters, a scientific journal known for its publication of cutting-edge research in the form of concise letters.