Defocus direct-writing properties of Cu micropatterns in femtosecond laser reduction of CuO nanoparticles

Abstract

We investigated defocus direct-writing properties of Cu micropatterns on planar poly(dimethylsiloxane) (PDMS) substrates in femtosecond laser reduction of CuO nanoparticles (NPs). The Cu lines written at defocus position of every 1 μm from -5 to 5 μm had almost uniform width, 20±1 μm, at a numerical aperture (NA) of 0.45. The crystal structures of the micropatterns which were formed at the defocus positions of -5, 0, and 5 μm were also evaluated. The micropatterns were formed at the pulse energy of 0.45 nJ, scan pitch of 5 μm, and various scan speed. Regardless of the defocus position, the degree of reduction of micropatterns exhibited the same properties. When scan speed was larger than 10 mm/s, Cu-rich micropatterns were obtained. When scan speed was 5 mm/s, Cu₂O-rich micropatterns were formed. Finally, Cu-based mesh micropatterns were fabricated at various laser scan pitch. When scan pitch was determined as 25 μm and 50 μm, Cu-rich mesh micropatterns were formed at 5 mm/s. The temperature coefficient of resistance of Cu-rich mesh micropatterns with the pitch of 25 μm was 0.005/°C, which was as small as expected values.