3:45 PM - 4:00 PM
△ [7p-S45-9] Femtosecond laser writing of micropatterns using Cu2O nanospheres
Keywords:femtosecond laser, two photon absorption, microfabrication
Femtosecond laser writing via nonlinear optical absorption has received attention in three-dimensional (3D) microfabrication. The arbitrary 3D microstructures were fabricated by two-photon-absorption, which only occurs around the focal position when laser pulses are tightly focused into the photosensitive materials. Polymer-based microstructures using photopolymerization of photosensitive resin, metal microstructures using photoreduction of metal ions such as gold and silver have been proposed. However, the fabrication of Cu micropatterns using this technique was difficult because Cu ions have intense absorption at wavelength of near-infrared femtosecond laser pulses. In this study, we proposed to use Cu2O nanospheres (NSs), which exhibit relatively higher transparency at the wavelength, as a raw material for Cu microfabrication.
Cu2O NSs were prepared by polyol method. Copper nitrate (72 mM) and polyvinylpyrrolidone (288 mM) in ethylene glycol were simultaneously added and heated for 1 hour at 140°C. The suspension was centrifuged at 14500 rpm for 30 min to separate and wash Cu2O NSs, and they were dispersed into deionized (DI) water. The Cu2O NS solution was spin-coated on glass substrates. The glass substrates were treated by ultraviolet for surface modification. After spin-coating the solution on the glass substrates, the solution film was baked on a hot plate at 80°C to form Cu2O NSs film by evaporating DI water. Micropatterns were formed using a femtosecond laser direct writing system. The pulse duration, wavelength, repetition frequency of the femtosecond laser were 120 fs, 780 nm, and 80 MHz, respectively. The femtosecond laser pulses were focused onto the Cu2O NS solution film using an objective lens with the numerical aperture of 0.75. Nonlinear optical absorption property was evaluated using OA (Open-aperture) Z-scan technique. Crystal structures of the fabricated micropatterns were examined using X-ray diffraction (XRD) analysis
Cu2O NSs films exhibited two-photon-absorption in Z-scan analysis. The absorption linearly increased with the square of intensity. Two-photon absorption coefficient was estimated as 43-105 cm/GW. The FE-SEM image of the fabricated line patterns on the films showed the possibility of nonlinear absorption writing because its line width was close to or less than focal spot diameter of the femtosecond laser pulses (1.3 µm). To evaluate the crystal structures of the fabricated micropattern, we fabricated the 300 µm×900 µm pattern. The scan speed, pulse energy, and raster scan pitch were 100 µm/s, 0.31 nJ, and 2 µm, respectively. The result of XRD analysis indicated reduction of Cu2O NSs to Cu micropattern.
Cu2O NSs were prepared by polyol method. Copper nitrate (72 mM) and polyvinylpyrrolidone (288 mM) in ethylene glycol were simultaneously added and heated for 1 hour at 140°C. The suspension was centrifuged at 14500 rpm for 30 min to separate and wash Cu2O NSs, and they were dispersed into deionized (DI) water. The Cu2O NS solution was spin-coated on glass substrates. The glass substrates were treated by ultraviolet for surface modification. After spin-coating the solution on the glass substrates, the solution film was baked on a hot plate at 80°C to form Cu2O NSs film by evaporating DI water. Micropatterns were formed using a femtosecond laser direct writing system. The pulse duration, wavelength, repetition frequency of the femtosecond laser were 120 fs, 780 nm, and 80 MHz, respectively. The femtosecond laser pulses were focused onto the Cu2O NS solution film using an objective lens with the numerical aperture of 0.75. Nonlinear optical absorption property was evaluated using OA (Open-aperture) Z-scan technique. Crystal structures of the fabricated micropatterns were examined using X-ray diffraction (XRD) analysis
Cu2O NSs films exhibited two-photon-absorption in Z-scan analysis. The absorption linearly increased with the square of intensity. Two-photon absorption coefficient was estimated as 43-105 cm/GW. The FE-SEM image of the fabricated line patterns on the films showed the possibility of nonlinear absorption writing because its line width was close to or less than focal spot diameter of the femtosecond laser pulses (1.3 µm). To evaluate the crystal structures of the fabricated micropattern, we fabricated the 300 µm×900 µm pattern. The scan speed, pulse energy, and raster scan pitch were 100 µm/s, 0.31 nJ, and 2 µm, respectively. The result of XRD analysis indicated reduction of Cu2O NSs to Cu micropattern.