Electrification of polymer microfluidics by green femtosecond reductive laser sintering of copper(II) oxide

To date, femtosecond reductive laser sintering of copper(II) oxide for the maskless and vacuum-free production of conductive copper has been investigated using infrared lasers. Optical measurements of the precursor and copper layers conducted in this study demonstrate higher absorptance for shorter wavelengths, thus motivating an investigation of the influence of the laser wavelength. The fundamental near-infrared wavelength of 1030 nm of an amplified femtosecond laser is compared with the second harmonic wavelength of 515 nm under otherwise equivalent process conditions. As a holistic parameter variation approach, structure formation mapping identifies appropriate parameter ranges. The fabrication and investigation of two-dimensional copper electrodes are conducted utilizing the electrical 4-tip method, optical and scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The use of 515 nm leads to a 33% decrease in sheet resistance, accompanied by a simultaneous threefold acceleration in scan speed. Increasing the repetition rate to 600 kHz maintains this trend, and a minimum sheet resistance of 98 m Ω /sq is achieved at a scan speed of 150 mm/s. A commercial injection-molded microfluidic device is electrified ex post by generating a copper heating structure manufactured using reductive laser sintering. Thermographic imaging reveals that temperatures in excess of 110 ∘ C can be attained, thereby effectively heating the fluid flowing through the device. This finding establishes the foundation for a range of prospective future lab-on-chip applications.