Linear and nonlinear optical properties of gold nanospheres immobilized on a metallic surface
Abstract
We studied linear and nonlinear optical properties of surface-immobilized gold nanospheres (SIGNs) above a metallic surface with a gap distance of a few nanometers. The nanogap is supported by self-assembled monolayers (SAMs); they are used as spacers. A localized surface plasmon resonance (LPR) band (λ=600-700nm) redshifted from the LPR band of isolated gold nanospheres (λ∼520nm) is observed in the p -polarized reflection absorption spectra with oblique incidence. This band originates from the electromagnetic interaction of the gold nanospheres with their images produced in the metallic substrate. The amount of redshift depends on the gap distance, which is controlled by the thickness of the SAMs. These optical properties can be simulated using theoretical calculations obtained by considering multipolar interactions based on a quasistatic approximation. Further, in SIGNs above a metal, we observed a significantly enhanced optical second-harmonic generation (SHG). The field enhancement factor was found to be greater than 10 at 1064nm . This is due to an increase in local electric fields in SIGN systems at both fundamental and SHG wavelengths (λ2ω=532nm) . Local electric field calculations imply that the SHG from the nanogap does not dominate even under the LPR condition because the nanogap region is almost centrosymmetrical.
- Publication:
-
Physical Review B
- Pub Date:
- July 2006
- DOI:
- 10.1103/PhysRevB.74.035416
- Bibcode:
- 2006PhRvB..74c5416A
- Keywords:
-
- 78.67.Bf;
- 42.65.-k;
- 78.40.-q;
- 78.68.+m;
- Nanocrystals and nanoparticles;
- Nonlinear optics;
- Absorption and reflection spectra: visible and ultraviolet;
- Optical properties of surfaces