Annealing Rate as a Crucial Parameter Controlling the Photoelectrochemical Properties of AuCu Mosaic Core-Shell Nanoparticles

Thermal processing is an essential step during the synthesis of various metal nanostructures and for tailoring their morphology, optical, and electrochemical properties. Herein, a profound impact of the annealing rate and time on photoactivity of gold-copper nanostructures by changes in the position and alignment of energy levels and surface states is reported. AuCu nanoparticles (NPs) are fabricated by sputtering of thin metal layers on the Ti nanopatterned foil followed by slow (0.67 degrees C s(-1)) or fast (30 degrees C s(-1)) treatment in the rapid thermal annealing furnace and then utilized as photoanodes. Photocurrent in the visible range of the slow-heated AuCu materials is 77 times higher, whereas for the fast heated 24 times higher than for pure Ti platform. On the other hand, the fast-heated material exhibits higher photon-to-current efficiency, longer recombination rate which reaches 10s, and higher carrier transport rate of 150 mu s. Based on the simulated projected local density of states analysis and the characteristics of intensity-modulated spectra, this phenomenon is attributed to the presence of deeper midgap states in the electronic band structure for the fast-heated samples. Furthermore, photocurrent is enhanced by the presence of Au inside NPs, which increases tunneling across copper oxides junction.