Photothermal Synthesis of Copper Sulfide Nanowires forDirect Lithography of Chalcogenides on a Chip

In the context of sustainability in industrial material and device production, research and development attachgreat importance to the reduction of power consumption in the form of heat. Here, we report on the thermal conversion ofelectrochemically synthesized nanowires of copper thiourea complex (CTC) to copper sulfide and the effective lowering ofthe 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 temperaturerequired for complete thermal conversion (180 °C). As a result, the optical absorption of these composite nanowires increasesin the visible range, suggesting the evolution of a substantial photothermal effect. When the CTC nanowires are pre-annealedto 110 °C, exposure to low-power green laser light completely transforms the CTC precursor into copper sulfide in secondsand without further external heating. This conversion is locally confined to the dimension of the laser spot which can befocused to 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