Combined dielectric and plasmon resonance for giant enhancement of Raman scattering

Combined dielectric/metal resonators for colossal enhancement of inelastic light scattering are developed and their properties are investigated. It is shown that a record enhancement factor of $2 \times 10^8$ can be obtained using these structures. The dielectric resonators are fabricated on Si/SiO$_2$ substrates where periodic arrays of square $10$- to $200$-nm-high dielectric pillars are produced via electron-beam lithography and plasma etching. The lateral size a of the pillars varies between $50$ and $1500$ nm, and their period in the array is $2a$. To make a combined dielectric/metal resonator, a nanostructured layer of silver is deposited onto the fabricated periodic dielectric structure by thermal evaporation. It is established that, for a fixed height of the dielectric pillars, the Raman scattering enhancement factor experiences pronounced oscillations as a function of the period (and size) of the pillars. It is shown that these oscillations are determined by the modes of the dielectric resonator and governed by the relation between the excitation laser wavelength and the planar size of the dielectric pillars.