Internal and external morphology-dependent plasmonic resonance in monolithic nanoporous gold nanoparticles

We report morphology-dependent plasmonic resonance in monolithic nanoporous gold nanoparticles with a nanoscale internal porous network produced by the combination of lithographic patterning and dealloying. Timed dealloying and post-dealloying thermal annealing techniques have been employed to precisely control the morphological evolution. We found that prolonged dealloying time caused further pore coarsening to increase by similar to 4 nm, whereas thermal annealing induced both pore coalescence and disk shrinkage, which eventually led to pore elimination. Both types of morphological changes caused a blueshift in the major plasmonic extinction band of up to 200 nm, in contrast to the redshift (similar to 50 nm) observed in semi-infinite NPG thin films. In addition, a greater blueshift was observed in a higher Au atomic content starting alloy. The tunable plasmonic properties have great potential in surface-enhanced spectroscopy and optical sensing.