Femtosecond laser direct-writing technique using multi-photon process has received attention to fabricate two- and three-dimensional microstructures. We have reported direct writing of non-noble metals such as Cu and Ni using femtosecond laser reduction of glyoxylic acid metal complex. However, metal alloys have not been fabricated using the technique in air. In this presentation, Cu-Ni alloy microstructures were directly written using femtosecond laser reduction of glyoxylic acid Cu/Ni mixed complex.

First, glyoxylic acid Cu and Ni complexes were respectively prepared using glyoxylic acid and metallic salts such as Cu and Ni formates. Then, glyoxylic acid Cu and Ni mixed complexes were mixed with 2-amino-ethanol and ethanol. Next, the mixed complex was spin-coated on glass substrates. Finally, the femtosecond laser pulses operating with the pulse duration of 100 fs, the wavelength of 515 nm, and the repetition frequency of 40 MHz, were focused onto the complex using an objective lens with the numerical aperture of 0.45.

The absorption property of the mixed complex was investigated. Although the absorption at the femtosecond laser wavelength of 515 nm was weak, the intense absorption was exhibited at the half of the laser wavelength. These results indicate that multi-photon absorption process was expected to occur. The Cu-Ni alloys were precipitated without significant oxidation in air at the laser scanning speed of 10 mm/s and the pulse energy of 1.29-2.15 nJ. When the minimum line width was ~20 µm at the pulse energy of 1.29 nJ and scanning speed of 10 mm/s. The wider line width than the diameter of the focal spot was formed by thermal diffusion, indicating that the Cu-Ni alloy precipitation was induced by thermochemical reduction of the glyoxylic acid Cu/Ni mixed complex. The Cu-Ni alloy exhibited negative Seebeck coefficient, which was consistent with that of the bulk Cu-Ni. By considering to the thermal conductivity of the substrate to reduce the effect of heat accumulation, finer line patterns of the alloy will be obtained using the direct writing technique in air.