Raman amplification in the ultra-small limit of Ag nanoparticles on SiO2 and graphene: Size and inter-particle distance effects

Size, shape and hot spots are crucial to optimize Raman amplification from metallic nanoparticle (NPs). The am-plification from radius = 1.8 ± 0.4 nm ultra-small silver NPs was explored. Increasing NP density redshifts andwidens their plasmon that, according to simulations for NPs arrays, is originated by the reduction of the interparticle distance, d, becoming remarkable for d ≤ R. Inter-particle interaction red-shifts (N130 nm) and widens(N90 nm) the standard plasmon of non-interacting spherical particles. Graphene partly delocalizes the carriersenhancing the NIR spectral weight. Raman amplification of graphene phonons is moderate and depends smoothly on d while that of Rhodamine 6G (R6G) varies almost exponentially due to their location at hot-spots that depend strongly on d. The experimental correlation between amplification and plasmon position iswell reproduced by simulations. The amplification originated by the ultra-small NPs is compared to that of larger particles, granular silver films with 7

localized surface plasmon resonances; silver nanoparticle (arrays); surface enhanced raman scattering

Raman amplification in the ultra-small limit of Ag nanoparticles on SiO2 and graphene: Size and inter-particle distance effects Articles