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We achieve direct electrical readout of the wavelength and polarization dependence of the plasmon resonance in individual gold nanogap antennas by positioning a graphene nanoconstriction within the gap as a localized photodetector. The polarization sensitivities can be as large as 99%, while the plasmon-induced photocurrent enhancement is 2-100. The plasmon peak frequency, polarization sensitivity, and photocurrent enhancement all vary between devices, indicating the degree to which the plasmon resonance is sensitive to nanometer-scale irregularities.

The extinction spectra of a three-layered metal nanoshell, which consists of a particle with a dielectric core, a middle Ag (Au) layer, and an outer Au (Ag) shell, have been investigated by means of the Mie theory. With a decrease in the outer shell thickness or the middle layer thickness, the wavelengths of the localized surface plasmon resonance (LSPR) for SiO2–Ag–Au (SiO2–Au–Ag) nanoshells show distinct redshifts and the full widths at half maximum (FWHMs) for the dipole peaks in the extinction spectra decrease first and then increase. We have further investigated the influence of the embedding medium on the LSPRs for SiO2–Ag–Au and SiO2–Au–Ag nanoshells and found that the resonance wavelengths of the particles show redshift and the FWHM of the dipole peak increases with increasing the dielectric constant of the embedding medium. The calculated results indicate that the LSPR of the three-layered gold-silver nanoshells can be controlled to the near-infrared region by changing the geometry, which has practical biomedical application. [ABSTRACT FROM AUTHOR]

Abstract: The electric field enhancements in Au/Ag and Ag/Au core/shell nanoparticles have been investigated by means of quasi-static theory. The maximum enhancements of outside fields for Au/Ag and Ag/Au nanoshells occur along the incident polarization at plasmon resonance wavelength. It is surprised that the largest field enhancement in the shell of Ag/Au nanoshell occurs along the polarization direction, while that for Au/Ag nanoshell is perpendicular to the incident polarization. At off-resonance wavelength 1000 nm, the general shape of the field pattern is similar to that in resonance case except for much weaker amplitude. Furthermore, for the seamless nanoshells, the maximum enhancements of the electric field increase by increasing the shell thickness. As the shell thickness is small, the hot spots play an important role in the enhancement of the local electric field. [Copyright &y& Elsevier]

The weak peak at ultraviolet region observed by Zhu and Zhang in gold nanoshells should not be ascribed to the coupling of the “quadruple resonance,” which may be interpreted in terms of the contributions of the interband transitions in the Au layer. In addition, the quasistatic theory used by Zhu and Zhang is not suitable for investigation of the optical properties of gold nanoshells when the total radius of the shell is larger than the quasistatic limit. Furthermore, it is obvious that the strength and position of the local field factor peak should vary with the radial distance and the polar angle. [ABSTRACT FROM AUTHOR]