HOUSTON (March 12, 2010) Calculations are fine, but seeing is believing. That's the thought behind a new paper by Rice University students who decided to put to the test calculations made more than a century ago.
In 1908, the German physicist Gustav Mie came up with an elegant set of equations to describe the interaction of electromagnetic waves with a spherical metal particle. The theory has been a touchstone ever since for researchers seeking to quantify how nanoscale plasmonic particles scatter radiation.
"The Mie theory is used extensively whenever you deal with nanoparticles and their optical properties," said Alexei Tcherniak, a Rice graduate student and primary author of the new paper in the online edition of Nano Letters this month. "That's the foundation of every calculation."
Tcherniak and Stephan Link, a Rice assistant professor of chemistry and electrical and computer engineering, co-authored the paper with former graduate student Ji Won Ha and current Rice graduate students Liane Slaughter and Sergio Dominguez-Medina.
Better characterization of single nanoparticles is important to researchers pursuing microscopic optical sensors, subwavelength "super lenses," catalysis and photothermal cancer therapies that use nanoparticles.
"Since technology is moving toward single-particle detection, we wanted to see whether Mie's predictions would hold," Tcherniak said. "Average properties fall exactly on the predictions of Mie theory. But we show that individual particles deviate quite a bit." Particles that differ in size can return similar signals because they vary in shape and orientation on the substrate, with which they also interact. Mie's theory, developed for spherical particles in solution long before single-particle spectroscopy, did not consider these factors.
The project began as a sideline in the students' attempt to track single nanoparticles in solution. It became their primary
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