Distributions of electric fields in two-dimensional arrays of gold nanodisks on a Si3N4 membrane, with light incident through the membrane, are modeled with the aim of determining array geometries for effective plasmon-mediated Brillouin light scattering ("surface-enhanced Brillouin scattering," SEBS) from phonons or magnons in a specimen placed in contact with such an array. Particular attention is devoted to average intensities and high-wavevector components of the fields in a plane 2 nm from the circular nanodisk/vacuum interface, which is anticipated to be in the vicinity of the surface of a specimen. Dipole-like and quadrupole-like surface-plasmon modes of the nanodisks are found to be simultaneously excited by 532 nm light, and these modes contribute components of the fields that are approximately in phase and out of phase with the incident light, respectively. For nanodisks with diameters of 50 nm, the average intensity near the circular nanodisk/vacuum interface increases as the angle of the incident light approaches the normal of the Si3N4 surface, because of enhanced excitation of the dipole mode. At low angles of incidence relative to the Si3N4 normal, average intensities increase with decreasing array spacing, primarily because of the corresponding changes in fractional coverage area of the gold. The highest average intensities (with near-normal incidence and 70 nm array periodicity) are found to be ~3 times that of the incident light. More significantly, higher wavevector components (multiples of the reciprocal lattice vector) of the fields are found to have intensities comparable to the incident light. This finding provides evidence for the feasibility of using surface plasmons in nanodisk or nanoline arrays to mediate Brillouin scattering from phonons or magnons with wavelengths of tens of nanometers, which would extend the range of Brillouin-scattering metrology by an order of magnitude.
Citation: Journal of Physical Chemistry C
Pub Type: Journals
Brilloun light scattering, dipole resonance, discrete dipole approximation, electric fields, nanodisk arrays, quadrupole resonance, surface-enhanced Brillouin scattering, surface plasmons