Robust raspberry-like metallo-dielectric nanoclusters of critical sizes as SERS substrates

Aurélie Le Beulze, Sergio Gomez-Graña, Hélène Gehan, Stéphane Mornet, Serge Ravaine, Miguel A. Correa-Duarte, Luca Guerrini, Ramon A. Alvarez-Puebla, Etienne Duguet, Etienne Pertreux, Aurélien Crut, Paolo Maioli, Fabrice Vallée, Natalia del Fatti, Ovidiu Ersen, and Mona Treguer-Delapierre

Nanoscale 2017, 9, 5725‒5736

Raspberry-like nano-objects made of large plasmonic satellites (>10 nm) covering a central dielectric particle have many potential applications as photonic materials, superlenses and (bio-) sensors, but their synthesis remains challenging. Herein, we show how to build stable and robust raspberry-like nano-systems with close-packed satellites, by combining monodisperse silica particles (80 or 100 nm diameter) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10–50 nm). The spectral characteristics of their associated plasmonic resonances (wavelength, linewidth, extinction cross-section) and the electromagnetic coupling between satellites were observed using the spatial modulation spectroscopy technique and interpreted through a numerical model. The composite nano-objects exhibit numerous hot spots at satellite junctions, resulting in excellent surface-enhanced Raman scattering (SERS) performance. The SERS efficiency of the raspberry-like clusters is highly dependent on their structure.