Jain and his co-authors made their quantum dots from the semiconductor copper sulfide, a material that is known to support numerous copper-deficient stoichiometries. Initially, the copper sulfide nanocrystals were synthesized using a common hot injection method. While this yielded nanocrystals that were intrinsically self-doped with p-type charge carriers, there was no control over the amount of charge vacancies or carriers.
"We were able to overcome this limitation by using a room-temperature ion exchange method to synthesize the copper sulfide nanocrystals," Jain says. "This freezes the nanocrystals into a relatively vacancy-free state, which we can then dope in a controlled manner using common chemical oxidants."
By introducing enough free electrical charge carriers via dopants and vacancies, Jain and his colleagues were able to achieve LSPRs in the near-infrared range of the electromagnetic spectrum. The extension of plasmonics to include semiconductors as well as metals offers a number of significant advantages, as Jain explains.
"Unlike a metal, the concentration of free charge carriers in a semiconductor can be actively controlled by doping, temperature, and/or phase transitions," he says. "Therefore, the frequency and intensity of LSPRs in dopable quantum dots can be dynamically tuned. The LSPRs of a metal, on the other hand, once engineered through a choice of nanostructure parameters, such as shape and size, is permanently locked-in."
Jain envisions quantum dots as being integrated into a variety of future film and chip-based photonic devices that can be actively switched or controlled, and also being applied to such optical applications as in vivo imaging. In addition, the strong coupling that is possible between photonic and electronic modes in such doped quantum dots holds exciting potential for applications in solar photovoltaics and artificial photosynthesis
"In photovoltaic and a
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory