Parameter-controllable microchannel reactor for enhanced deposition of copper sulfide thin films

A microchannel reactor was designed and fabricated based on the unique fluid-flow and mass transfer characteristics in a closely parallel channel for the deposition of copper sulfide (CuxS) thin films. The configuration of the microchannel allows the flow pattern to be confined uniformly across the channel width and length, thereby resulting in a uniform deposited thin film covering the whole surface of the substrate. A parametric study of the deposition of CuxS thin films was performed, including the effects of deposition time (2-10 min), flow rate (2-6 ml/min) and reaction temperature (60-80 °C). It was observed that the basic characteristics of CuxS films, such as morphology, film thickness, film composition and optical band gap, were highly affected by all deposition parameters. We were able to attain smooth, dense and adherent CuxS film with homogeneous grains at a high growth rate of 1.8 μm/h, by optimizing the controllable parameters. The optimized condition was at temperature of 80 °C, flow rate of 6 ml/min and deposition time of 4 min. The results showed that the film formation by heterogeneous nucleation and growth on the substrate is promoted over homogeneous reaction in the solution phase, which is strongly due to the incorporation of the optimal channel design in a micro-scale structure together with the controlled deposition parameters. This method can overcome the issue of the deposition in limited area and can be scaled for large-area substrates with good uniformity of CuxS films.