Thermoplasmonics in thin metal films

A. Passian, A. L. Lereu, R. H. Farahi, T. L. Ferrell, T. Thundat

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

1 Scopus citations

Abstract

Optical excitation of collective electronic oscillations in the surface region of thin metal films has provided a platform for the observation of a range of fascinating phenomena. Here, the non-radiative decay of surface plasmons is shown to be of consequence to the local thermal state of the supporting film. In this case, a temperature dependent dielectric function may be used to model the observed behavior. Utilizing such surface plasmon (SP) assisted thermal processes, we have investigated various forms of all-optical modulation. The thermo-plasmonic effect may be observed during excitation of surface plasmons using a single beam of photons in analogy with self-lensing (but without a physical change of state). However, in order to investigate the modulation further, we have studied a coupling scheme involving multiple photon energies. We show that simultaneous excitation of surface plasmons at multiple photon energies allows the transfer of information from one beam to many others and vice versa at modulation frequencies up to 10 kHz. For high frequency modulation, we propose an excitation scheme based on surface plasmon interference. We establish the formation of such an "electronic" grating in a thin gold film by recording the corresponding SP fringes in the tunneling region utilizing a photon scanning tunneling microscope (PSTM). The mechanism of the underlying coupling is characterized by determining the magnitude of the coupling as a function of the modulation frequency (time scale) as well as the power levels of the exciting beams. A nonlinear behavior is observed in both cases. Furthermore, in a pump-probe configuration, we map the surface plasmon excitation region into a region of modified dielectric properties. An incoming laser beam traversing this region, will undergo phase variations such that in the far field it may be diffracted into concentric rings similar to Newton's rings. These results have the potential of opening up new frontiers based on surface plasmon assisted couplings in thin films. We discuss one such scenario, where the microscale temperature gradient, on the free surface of a gold thin film facilitates the manipulation of picoliter liquid droplets. To stimulate further discussions, other possible applications are proposed and future investigations are discussed.

Original languageEnglish
Title of host publicationTrends in Thin Solid Films Research
PublisherNova Science Publishers, Inc.
Pages69-109
Number of pages41
ISBN (Print)9781600214554
StatePublished - 2007

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