Abstract
Direct writing of cobalt/cobalt oxide composites has attracted attention for its potential use in catalysts and detectors in microsensors. In this study, cobalt-based composite patterns were selectively formed on glass, polyethylene naphthalate (PEN), and polyethylene terephthalate (PET) substrates via the femtosecond laser reductive sintering of Co3O4 nanoparticles in an ambient atmosphere. A Co3O4 nanoparticle ink, including the nanoparticles, ethylene glycol as a reductant, and polyvinylpyrrolidone as a dispersant, was spin-coated onto the substrates. Near-infrared femtosecond laser pulses were then focused and scanned across the ink films to form the patterns. The non-sintered nanoparticles were subsequently removed from the substrate. The resulting sintered patterns were found to be made up of Co/CoO composites on the glass substrates, utilizing various pulse energies and scanning speeds, and the Co/CoO/Co3O4 composites were fabricated on both the PEN and PET substrates. These results suggest that the polymer substrates with low thermal resistance react with the ink during the reductive sintering process and oxidize the patterns more easily compared with the patterns on the glass substrates. Such a direct writing technique of cobalt/cobalt oxide composites is useful for the spatially selective printing of catalysts and detectors in functional microsensors.
Highlights
There is considerable interest in the use of laser direct writing technologies in the fabrication of metal patterns for printed electronics because the techniques permit photolithographyfree electrode fabrication
The minimum pulse energy on polyethylene naphthalate (PEN) substrates required for the continuous line patterning was higher than that on polyethylene terephthalate (PET) substrates
The finer patterns were formed on glass substrates even though the pulse energy was higher than that on PEN and PET. These results indicate that the low thermal conductivity of PEN and PET achieved a higher temperature than that on glass substrates
Summary
There is considerable interest in the use of laser direct writing technologies in the fabrication of metal patterns for printed electronics because the techniques permit photolithographyfree electrode fabrication. Many techniques, including inkjet, flexo, gravure, and screen printing, have been developed for the printed electronics process, the advantage of laser direct writing is that the patterning and the metallization can be performed simultaneously via the sintering or reductive sintering of nanoparticle inks. Cu nanoparticle inks have previously been coated and selectively sintered via irradiating continuous-wave and pulsed lasers on substrates [2,3,4]. Cu electroconductive patterns were formed on substrates after removing the non-sintered nanoparticles. An optimal laser scanning condition existed to obtain high electrical conductivity, which prevents the patterns from re-oxidizing or losses of energy [2]
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