Electrodeposition of thermally stable gold and silver nanoparticle ensembles through a thin alumina nanomask

Hemispheric gold or silver nanoparticle (Au and AgNP) ensembles were electrodeposited on a smooth ITO electrode through a thin Al2O3 nanomask. The nanomask reduced the deviation in the particle size and interparticle distance. The absorption peak based on localized surface plasmon resonance (LSPR) of the AuNP ensemble redshifted with increasing environmental refractive index, suggesting that the ensemble would be used as a LSPR sensor for chemical analysis and bioanalysis. The Al2O3 nanomask prevented the Au and AgNPs from thermal coalescence even at 500 degrees C, and consequently, it improved thermal stabilities of nanoparticle ensembles. The ensembles exhibit LSPR-based absorption peak in the visible region, even after annealing. The nanomask allowed AgNPs, which are thermally and chemically less stable than AuNPs, to be coated with sintered TiO2. The ITO/AgNP/TiO2 electrode thus obtained functions as a photocathode on the basis of photoinduced electron transfer from silver nanoparticles to TiO2.