Open AccessReversing the size-dependence of surface plasmon resonances
Author(s) -
Sheng Peng,
Jeffrey M. McMahon,
George C. Schatz,
Stephen K. Gray,
Yugang Sun
Publication year - 2010
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.1007524107
Subject(s) - plasmon , particle size , range (aeronautics) , molecular physics , surface plasmon resonance , absorption (acoustics) , surface plasmon , colloid , blueshift , nanoparticle , particle (ecology) , mie scattering , chemistry , materials science , chemical physics , optics , nanotechnology , physics , scattering , light scattering , photoluminescence , oceanography , geology , composite material
The size-dependence of surface plasmon resonances (SPRs) is poorly understood in the small particle limit due to complex physical/chemical effects and uncertainties in experimental samples. In this article, we report an approach for synthesizing an ideal class of colloidal Ag nanoparticles with highly uniform morphologies and narrow size distributions. Optical measurements and theoretical analyses for particle diameters in thed ≈ 2–20 nm range are presented. The SPR absorption band exhibits an exceptional behavior: As size decreases fromd ≈ 20 nm it blue-shifts but then turns over neard ≈ 12 nm and strongly red-shifts. A multilayer Mie theory model agrees well with the observations, indicating that lowered electron conductivity in the outermost atomic layer, due to chemical interactions, is the cause of the red-shift. We corroborate this picture by experimentally demonstrating precise chemical control of the SPR peak positions via ligand exchange.