Fundamental Limitation: How Through-Thickness Heterogeneity in Laser-Reduced Graphene Oxide Compromises Sensor...

Laser-induced reduction of graphene oxide (GO) is a promising technique for the rapid, single-step fabrication of porous carbon electrodes for electronic devices. However, the translation of this method into reliable, high-performance applications is often constrained by a lack of understanding of the material's inherent structural and chemical heterogeneity. This study presents a parametric investigation into the pulsed CO₂ laser reduction of free-standing GO membranes to deconvolve the relationship between processing parameters, material properties, and device stability. Through detailed morphological (SEM), chemical (XPS, FTIR), and structural (XRD, Raman) characterization, we identify the optimal laser power (2.4 W) to produce a highly porous, "peony-like" rGO architecture with a high surface area of 234 m²/g. Crucially, we provide definitive evidence of a "top-down" reduction mechanism, where high-quality lattice restoration via thermal disproportionation is restricted to the surface layers. This inherent through-thickness heterogeneity creates a "buried" hydrophilic reservoir that acts as a functional bottleneck, leading to the observed baseline drift and moisture-driven instability in sensing applications. The residual GO layer strongly absorbs water molecules, leading to an extremely slow and incomplete recovery, rendering the material unsuitable for practical sensing applications. These findings highlight a fundamental limitation of direct laser writing for creating uniform functional materials and underscore the critical role that through-thickness heterogeneity plays in device performance and stability.