Digitally Tuned Copper Composites: From Oxide-Free Encapsulation to Graphene Hybrids

We present a tunable manufacturing platform for copper nanoparticles (CuNPs) on polyethylene terephthalate (PET) that addresses the critical challenge of processing this air-sensitive material under ambient conditions. By precisely controlling laser parameters, we demonstrate that a single CuNPs-PET precursor can produce two distinct functional composites. Low laser powers result in a purely metallic composite within the polymer matrix by simultaneously sintering and encapsulating CuNPs. In contrast, higher laser powers shift the process toward polymer carbonization and graphitization, creating a durable copper-assisted laser-induced graphene (Cu-LIG) hybrid embedded in PET. High-speed visualization enables real-time analysis of the mechanisms involved, revealing the sintering, encapsulation, and integration of CuNPs into the polymer. Chemical and structural analyses show that the laser process also reduces native copper oxide on pristine NPs, resulting in a metallic copper composite with a sheet resistance as low as 0.13 Ω sq^-1 and significant stability under harsh conditions, including exposure to high relative humidity (RH) levels above 95% for several days. We demonstrate practical applications of these composites by creating highly robust, flexible devices, including thermocouples with a Seebeck coefficient of 14.6 μV °C^-1 and high-load capacitive pressure sensors. This work redefines laser processing as a versatile approach for digitally selecting material functionality, advancing the manufacturing of flexible electronics.