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/Al2O3 hybrid porous NPs with controlled porosity and composition ratio are fabricated through plasma-enhanced atomic layer deposition of Al2O3 into the porous structure. In the Au/Al2O3 hybrid porous NPs, both Au and Al2O3 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.
ABSTRACT
Fluorescent gold nanoparticles with high quantum yield are highly desirable for optical imaging in the fields of biology and materials science. We investigate the one-photon photoluminescence (PL) properties of individual gold nanobipyramids (GNBs) and find they are analogous to those of the extensively studied gold nanorods (GNRs). By combining PL and atomic force microscopy (AFM) measurements with discrete dipole approximation (DDA) simulations, we obtain the PL quantum yield of single GNRs and GNBs. Compared to GNRs in the similar surface plasmon resonance range, the PL quantum yield of GNBs is found to be doubled. The stronger field intensity around GNBs can explain their higher PL quantum yields. Our research would provide deeper understanding of the mechanism of PL from gold nanoparticles as well as be beneficial for finding out optical imaging labels with high contrast.
