Photothermal Synthesis of Copper Sulfide Nanowires for Direct Lithography of Chalcogenides on a Chip

In the context of sustainability in industrial material and device production, research and development exhibit great importance to the reduction of power consumption in the form of heat. Here, we report on the thermal conversion of electrochemically synthesized nanowires of the copper thiourea complex (CTC) to copper sulfide and the effective lowering of the applied process temperature by irradiation with visible light. Our structural and spectroscopic studies revealed that copper sulfide nanocrystals start to form inside the CTC nanowires at 95 °C, which corresponds to roughly half the temperature required for complete thermal conversion (180 °C). As a result, the optical absorption of these composite nanowires increases in the visible range, suggesting the evolution of a substantial photothermal effect. When the CTC nanowires are pre-annealed to 110 °C, exposure to low-power green laser light completely transforms the CTC precursor into copper sulfide in seconds and without further external heating. This conversion is locally confined to the dimension of the laser spot, which can be focused to the micrometer size. When applied in a direct photolithography mode, this new approach opens for the design of copper sulfide-based microdevices for photovoltaics and thermoelectrics.