Cu-based fine patterns were directly fabricated using femtosecond laser reduction of Cu<sub>2</sub>O nanospheres (NSs) via nonlinear optical absorption. Cu<sub>2</sub>O NS solution films, containing Cu<sub>2</sub>O NSs, polyvinylpyrrolidone (PVP), and 2-propanol, were prepared by spin-coating of the Cu<sub>2</sub>O NS solution on glass substrates or Cu-coated glass substrates. Finer line patterns were formed by scanning the focused femtosecond laser pulses. The absorption of the Cu<sub>2</sub>O NS solution film at wavelength of the femtosecond laser pulses, 780 nm, was low, whereas the intense absorption at wavelength of 390 nm was observed. Finer patterns were obtained on the Cu-coated glass substrates than on the glass substrates. The minimum line width of 0.6 μm was obtained on the Cu-sputtered film, which was smaller than the focal spot diameter of 1.3 μm. The heat accumulation is lower on the Cu-sputtered films due to their high thermal conductivity, resulting that the line width with the sub diffraction limit was achieved. The electrical conductivity of the patterns on the glass substrates was evaluated to be 4.1×10<sup>6</sup> S/m at scanning speed of 200 μm/s and pulse energy of 0.312 nJ, which is close to that of bulk copper.
Copper (Cu)-based micropatterns were fabricated on polymer substrates using femtosecond laser reduction of copper (II) oxide (CuO) nanoparticles. CuO nanoparticle solution, which consisted of CuO nanoparticles, ethylene glycol as a reductant agent, and polyvinylpyrrolidone as a dispersant, was spin-coated on poly(dimethylsiloxane) (PDMS) substrates and was irradiated by focused femtosecond laser pulses to fabricate Cu-based micropatterns. When the laser pulses were raster-scanned onto the solution, CuO nanoparticles were reduced and sintered. Cu-rich and copper (I)-oxide (Cu2O)-rich micropatterns were formed at laser scanning speeds of 15 mm/s and 0.5 mm/s, respectively, and at a pulse energy of 0.54 nJ. Cu-rich electrically conductive micropatterns were obtained without significant damages on the substrates. On the other hand, Cu<sub>2</sub>O-rich micropatterns exhibited no electrical conductivity, indicating that microcracks were generated on the micropatterns by thermal expansion and shrinking of the substrates. We demonstrated a direct-writing of Cu-rich micro-temperature sensors on PDMS substrates using the foregoing laser irradiation condition. The resistance of the fabricated sensors increased with increasing temperature, which is consistent with that of Cu. This direct-writing technique is useful for fabricating Cu-polymer composite microstructures.
Cu-based micro-temperature sensors were directly fabricated on poly(dimethylsiloxane) (PDMS) blood vessel models in EVE using a combined process of spray coating and femtosecond laser reduction of CuO nanoparticles. CuO nanoparticle solution coated on a PDMS blood vessel model are thermally reduced and sintered by focused femtosecond laser pulses in atmosphere to write the sensors. After removing the non-irradiated CuO nanoparticles, Cu-based microtemperature sensors are formed. The sensors are thermistor-type ones whose temperature dependences of the resistance are used for measuring temperature inside the blood vessel model. This fabrication technique is useful for direct-writing of Cu-based microsensors and actuators on arbitrary nonplanar substrates.
We propose a novel method of fabricating metallic glass thin films using a carousel type sputtering system. In conventional methods of fabricating metallic glass thin films using alloy targets, control of the alloy composition is difficult. However, since r.f. power for each target can be controlled independently in the proposed system, it is easy to control the alloy composition. Thin films of various alloy compositions are fabricated. In this work, near-equiatomic CuZr thin films are fabricated by the sputtering system with rotational speeds of the substrate holder ranging from 10 to 50 rpm. Small-angle XRD revealed that the specimen fabricated with rotation at 10 rpm had a multilayer structure. The specimen fabricated with rotation at 50 rpm exhibited a glass transition temperature of 672 K, a crystallization temperature of 715 K, and a supercooled liquid region of 43 K. However, although the XRD results indicated that the specimen fabricated with rotation at 30 rpm was in an amorphous state, it exhibited solid-state amorphization rather than glass transition before the crystallization in DSC measurement. Thus, the specimen did not become a metallic glass. Clearly, sputtering rate is a very important parameter in the fabrication of metallic glass thin films by the proposed sputtering system. These results have shown the proposed method to be effective in fabricating metallic glass thin films.