In Situ Synthesis of Molybdenum Carbide Nanoparticles Incorporated into Laser-Patterned Nitrogen-Doped Carbon for Room Temperature VOC Sensing

Carbon laser-patterning (CLaP) is emerging as a new tool for the precise and selective synthesis of functional carbon-based materials for on-chip applications. The aim of this work is to demonstrate the applicability of laser-patterned nitrogen-doped carbon (LP-NC) for resistive gas-sensing applications. Films of pre-carbonized organic nanoparticles on polyethylenetherephthalate are carbonized with a CO₂-laser. Upon laser-irradiation a compositional and morphological gradient in the films is generated with a carbon content of 92% near the top surface. The specific surface areas of the LP-NC are increased by introducing sodium iodide (NaI) as a porogen. Electronic conductivity and surface area measurements corroborate the deeper penetration of the laser-energy into the film in the presence of NaI. Furthermore, impregnation of LP-NC with MoC_1−x (<10 nm) nanoparticles is achieved by addition of ammonium heptamolybdate into the precursor film. The resulting doping-sensitive nano-grain boundaries between p-type carbon and metallic MoC_1−x lead to an improvement of the volatile organic compounds sensing response of ΔR/R₀ = −3.7% or −0.8% for 1250 ppm acetone or 900 ppm toluene at room temperature, respectively, which is competitive with carbon-based sensor materials. Further advances in sensitivity and in situ functionalization are expected to make CLaP a useful method for printing selective sensor arrays.