Improve the Local Electric Field Enhancement of Au Cylindrical Nanohole by Pt Coating

Local electric field enhancement in a long cylindrical Au nanohole with Pt coating has been theoretically studied based on quasi-static model. Calculation results show that both the peak wavelength and local field factor in the nanohole are greatly dependent on the Pt coating thickness. Because of the Pt coating, a new local surface plasmon resonance (LSPR) band takes place in the ultraviolet wavelength below 400 nm, which also results in intense local electric field enhancement in the nanohole. As the Pt coating thickness is increased, the local field factor peak corresponding to the Pt shell red shifts and gets intense rapidly, which is much greater than that of Au shell. However, the increasing Pt thickness can also leads to the decrease of the local field factor when the dielectric constant of inner hole is much greater than that of outer environment. The local field factor in Pt shell is also sensitive to the Pt thickness and local dielectric environment. At the inner surface of the Pt shell, the increasing Pt thickness results in non-monotonic change of the local field factor when the dielectric constant of inner hole is equal or smaller than that of outer environment. Whereas at the outer surface of the Pt shell, the increasing Pt thickness always results in monotonic decrease of the local field factor, which is independent on the difference of the dielectric constant between inner hole and outer surrounding. This Pt coating-controlled local field enhancement in cylindrical Au@Pt nanohole presents design criteria and synthetic strategies toward local field effect-induced surface-enhanced Raman scattering (SERS), surface-enhanced fluorescence, and biosensing applications.