SURFACE ENHANCED BRILLOUIN SCATTERING (PLASMONS, POLARITONS, ACOUSTIC WAVES, PHONONS)
Abstract
Surface plasmons play a central role in a host of interesting surface-enhanced, nonlinear optical phenomena which have been intensively studied in recent years. Much of the enhancement is attributed to the increased electric fields associated with surface plasmons at metal (silver) surfaces. The magnitude of the enhancement is a function of several factors: (i) the structure of the surface: the enhancement can be extraordinarily large (>10('6)) for localized surface plasmons on 'rough' silver surfaces, but apparently much more modest for extended surface plasmons on 'smooth' silver surfaces, (ii) the particular nonlinear phenomenon, and (iii) adsorbed chemical species, especially in the case of surface enhanced Raman scattering (SERS) and even second harmonic generation. The motivation of this work was to explore the surface plasmon enhancement of Brillouin scattering (SEBS) from thermal equilibrium surface acoustic waves (SAW) of the silver itself. We deliberately chose Brillouin scattering because it permits an unambiguous determination of the surface plasmon enhancement factor. Unique to this situation, chemical factors can play no role. We explored two cases: (1) for 'rough' surfaces, specifically on silver island covered GaAs substrates, where no appreciable enhancement was observed, and (2) for 'smooth' surfaces where we successfully obtained SEBS from silver films ((TURNEQ)450 (ANGSTROM) thick) deposited on a glass substrate. The extended surface plasmons were generated by the attenuated total reflection (ATR) Kretschmann method, at the silver-air interface. An unambiguous method for determining the magnitude of the enhancement ((TURN)25x) was developed for one particular form of surface plasmon-phonon interaction. Much larger enhancement factors were qualitatively observed for other forms of interaction. A theoretical analysis gave excellent agreement with both the quantitative and qualitative measurements. The analysis was based on the complex dielectric constant (epsilon)(,Ag) of silver derived from the resonant interaction of the surface plasmons and SAW. Finally, we explain the successful observation of SEBS on 'smooth' surfaces versus the failure on 'rough' surfaces.
Degree
Ph.D.
Subject Area
Condensation
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