Rice lab clocks “hot” electrons

Fri, 01/31/2014 - 7:48am

Rice Univ. researchers have successfully measured the time it takes electrons generated by plasmons to move from a gold nanorod to graphene. From left, Rice chemist Stephan Link and graduate students Lin-Yung Wang and Anneli Hoggard. Image: Jeff Fitlow/Rice Univ.Plasmonic nanoparticles developed at Rice Univ. are becoming known for their ability to turn light into heat, but how to use them to generate electricity is not nearly as well understood.





Dark-field scattering and photoluminescence spectroscopy of more than 200 nanoparticles helped them determine that it takes about 160 femtosec (quadrillionths of a second) for an electron to transfer from the particle to highly conducting graphene, the single-atom-thick form of carbon.


The plasmon resonance of gold nanorods on graphene is broadened compared with gold nanorods on quartz, according to a new study by Rice Univ. scientists. The additional peak width was attributed to excited electron transfer between gold nanorods and graphene. Image: Anneli Hoggard/Rice Univ.If the energy input is intense enough, the output can be intense as well. In one practical example demonstrated at Rice, plasmon excitation in gold nanoparticles produces heat that instantly turns even ice-cold water into steam.




The Rice researchers found graphene broadened the nanorods’ surface plasmon response—and shortened its lifetime—by accepting hot electrons. By acting as an electron acceptor, the graphene accelerated damping of the plasmons. The difference in damping between the quartz and graphene samples provided a means to calculate the electrons’ transfer time.

A visualization of how electrons generated by plasmons in a gold nanorod transfer to a sheet of graphene. The measurements were made through spectroscopic analysis of hundreds of particles. The research will help scientists strategize on ways to gather and store electrons from plasmonic particles. Image: Anneli Hoggard/Rice Univ.“The plasmon resonance is determined by the size and the shape of the nanoparticle,” Hoggard said. “And it usually appears as a single peak for gold nanorods. But there are important parameters about the peak: The position and the width of the peak can give us information about the particle itself, or the type of environment it’s in. So we looked at how the width of the peak changes when nanoparticles are introduced into an electron-accepting environment, which in this case is graphene.”






Using the Plasmon Linewidth To Calculate the Time and Efficiency of Electron Transfer between Gold Nanorods and Graphene

Source: Rice Univ.


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