Surface plasmon amplification by stimulated emission of radiation has been modeled for the first time in an all-carbon system by researchers in Australia. The "spaser" technology might be exploited in flexible electronics devices that could one day be printed on to textiles to create smart clothing, for instance.
A spaser is effectively a nanoscale laser and the effect was first described more than a decade ago by David Bergman (Tel Aviv University, Israel) and Mark Stockman (Georgia State University, Atlanta, USA). It was not until the 2009 work of researchers at Purdue, Norfolk State and Cornell universities that demonstrated a 44-nanometer spaser using a nanoparticle with a gold core surrounded by a dyed silica gain medium. Spasers emit a beam of light through the vibration of free electrons, rather than the space-consuming electromagnetic wave emission process of a conventional laser.
Now, Chanaka Rupasinghe, Malin Premaratne and Ivan Rukhlenko of Monash University's Department of Electrical and Computer Systems Engineering (ECSE) in Clayton, Victoria, suggest that a carbon spaser would have several advantages over other approaches. Rupasinghe et al, ACS Nano, 2014, 8(3), pp 2431-2438; DOI: 10.1021/nn406015d] "Other spasers designed to date are made of gold or silver nanoparticles and semiconductor quantum dots while our device would be comprised of a graphene nanoflake resonator and a carbon nanotube gain element," explains Rupasinghe.
By using carbon instead of precious metals it should be possible to build a spaser that is less fragile and even flexible. It might also be able to operate at raised temperatures as well as avoiding the environmental concerns of sourcing precious metals. Rupasinghe muses that it might one day be possible to print circuitry, such as that needed for a mobile phone, on to clothing based on carbon, spaser-based device. Spasers offer an alternative to the current transistor-based paradigm for microelectronics, microprocessors, memory, and displays. They could also circumvent many of the miniaturization and bandwidth limitations of current systems.
The team's modeling suggests that a graphene and carbon nanotubes device can demonstrate non-radiative energy transfer between these two components, exciting localized fields on the graphene resonator. Such optical interactions are very fast and energy efficient. The researchers explain that such a spaser can generate high-intensity electric fields concentrated into a nanoscale space. Such a field is much stronger than that generated by illuminating metal nanoparticles by a laser.
The team calculated the localized fields of the plasmon modes and the matrix elements of the Plasmon-exciton interaction and was thus able to find the optimal geometric and material parameters of the spaser that would yield the highest plasmon generation rate. "The results obtained may prove useful in designing robust and ultracompact coherent sources of surface plasmons for plasmonic nanocircuits," they say. "We plan to apply this model in nanoplasmonic circuit design and come up with fully carbon-made processor architectures. Also plan to work on possible cancer treatment techniques based on spaser phenomena," Rupasinghe told Materials Today.
David Bradley blogs at http://www.sciencebase.com and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".