Effect of CuO nanoparticle size distribution on Cu-based patterns fabricated via femtosecond laser-pulse-induced thermochemical reduction

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Copper-direct writing using laser reductive sintering of CuO nanoparticles has received significant interest for printing technology. We investigated the effect of the particle size distribution in CuO nanoparticle inks on patterns fabricated using femtosecond laser-pulse-induced thermochemical reduction. First, Gaussian- and bimodal-type inks were prepared using commercially available and chemically synthesized nanoparticles, respectively. Both types of inks on glass substrates with a thickness of approximately 10 µm were estimated to be absorbed 80% of the irradiated near-infrared femtosecond laser pulses, as indicated by both absorption coefficients. The bimodal-type ink increased the density of the patterns, as expected using the packing theory. However, the patterns comprised non-reduced CuO and Cu2O, as well as residual polyvinylpyrrolidone. In contrast, the patterns fabricated using the Gaussian-type ink were well-reduced to Cu and exhibited a low density and high surface area. In addition, the patterns were advantageous for electrochemical applications, which exhibited intense peaks corresponding to the reduction of CuO and Cu2O surface oxides back to metallic copper in comparison of the patterns fabricated using the bimodal-type ink, regardless of laser irradiation conditions.