Nanoporous Gold Nanoparticles and Au/Al₂O₃ Hybrid Nanoparticles with Large Tunability of Plasmonic Properties

Abstract

Nanoporous gold nanoparticles (NPG-NPs) with controlled particle size and pore size are fabricated via a combination of solid-state dewetting and a subsequent dealloying process. Because of the combined effects of size and porosity, the NPG-NPs exhibit greater plasmonic tunability and significantly higher local field enhancement as compared to solid NPs. The effects of the nanoscale porosity and pore size on the optical extinction are investigated for the NPG-NPs with different particle sizes experimentally and theoretically. The influences of both porosity and pore size on the plasmonic properties are very complicated and clearly different for small particles with dominated dipole mode and large particles with dominated quadrupole mode. Au/AlO hybrid porous NPs with controlled porosity and composition ratio are fabricated through plasma-enhanced atomic layer deposition of AlO into the porous structure. In the Au/AlO hybrid porous NPs, both Au and AlO components are bicontinuously percolated over the entire structure. A further red shift of the plasmon peak is observed in the hybrid NPs due to the change of the environmental refractive index. The high tunability of the plasmonic resonances in the NPG-NPs and the hybrid porous NPs can be very useful for many applications in sensing biological and organic molecules.

Plasmonic nanosponges

“…One is by changing the dealloying conditions, such as temperature, concentration of nitric acid, and dealloying time. Figure 1 shows the SEM images of gold nanosponges, where the ligament/pore sizes increase with increasing temperature and concentration of nitric acid [18]. An alternative approach is based on annealing induced coarsening of the as-dealloyed nanosponges [56].…”

“…The details about the statistic analysis of the particle size, pore size, and ligament size can be found in the Ref. [18].…”

“…For instance, it has been demonstrated that Au-Ag alloy nanosponges with SiO 2 shell possess the superior SERS activities [65]. There is a clear redshift of the plasmonic resonance for the Au/Al 2 O 3 hybrid nanosponges comparing to the gold nanosponges [18], and the thermal stability of the gold nanosponges has been clearly enhanced by the hybrid structures [66].…”

“…In addition to the large enhancement of local field, the gold nanosponges also exhibit a large tuneability of plasmonic resonances from visible to NIR range by controlling the porosity, particle size, particle form, and pore/ligament size [18][19][20]. The plasmonic properties can be tuned further by forming the structure of hybrid nanosponges [18,21].…”

“…The plasmonic properties can be tuned further by forming the structure of hybrid nanosponges [18,21]. The nanosponges show strong polarization dependence due to the structural anisotropy contributed from the constraint of the nanoporous structure within a limited nanosponge or particle size [22,23].…”