The new work follows a paper published in September about the lab's creation of nano antennas that concentrate and magnify light up to 1,000 times. That paper focused on the intensity of laser light shot into a gap between the tips of two gold nanowires.
This time, Natelson and Ward spread molecules -- either oligophenylene vinylene or 1-dodecanethiol -- on the surface of a gold nanowire and then broke the wire, leaving a nanoscale gap. When they were fortunate enough to find molecules in the gap -- "the sweet spot" being where the metal wires are closest, Natelson said -- they'd power up and read the resulting spectra.
The experiments were carried out in a vacuum with materials cooled to 80 kelvins (-315 degrees Fahrenheit). The researchers found they could easily detect temperature fluctuations of up to 20 degrees in the molecules.
On the macro level, Natelson said, "You're usually looking at something that's essentially cold. You send in light, it dumps some of the energy into the thing you're looking at and the light comes out with less energy than when you started. With Raman scattering, you can actually see particular molecular vibrational modes."
But the opposite can happen if the atoms are already vibrating with stored energy. "The light can grab some of that and come out with more energy than when it started," he explained.
The effect is most dramatic when current is supplied through the nanowires. "As we crank up the current through this junction, we can watch these different vibrations shaking more and more. We can watch this thing heat up."
Natelson, named by Discover magazine in 2008 as one of the nation's top 20 scientists under age 40, said the experiments show not only how molecules wedged into the nanogap heat up, but also their interaction with the metal wires. "The vibrations show up as sharp peaks in the spectra," he said. "They
|Contact: David Ruth|