Sunday, March 14, 2010

A big theory for tiny things

Much of the theory for plasmonics is derived from Maxwell's electromagnetic theory, a theory which works incredibly well for systems that are very large compared to the atoms that make up the comprising media and to the wavelength of the light. However, plasmonics deals with the phenomena that occur in nanoscale devices, which often are smaller than the wavelength of the light and can contain a few thousand atoms. In the case of surface-enhanced Raman scattering, single molecule detection is even possible.

I wonder if the researchers in plasmonics are ever unsettled by the fact that they are using a theory that is based on the concept of effective material properties (permittivity and permeability) to describe media that aren't quite effective materials. This state of affairs seems to suggest that we should expect deviations from the predictions of Maxwell's equations in plasmonics experiments, but does this now take away much of the credibility in the results in these experiments? Consider this question: how does a researcher sell her novel plasmonics device or experiment to reviewers and grant committees if it is expected not to work as, well, expected?

Taking a more positive viewpoint, perhaps this is what makes a field exciting for experimentalists. Here there is a phenomena for which a complete theory does not exist. Experiments are needed to establish the working principles from which a theory can evolve.