Transfer-Free Conformal Graphene Coating on Pyramidal Microstructures Decorated with Silver Nanoparticles for Superior Raman Signal Enhancement.

Graphene, a two-dimensional nanomaterial with excellent physicochemical properties, has considerable potential to functionalize surfaces for diverse applications. However, reliable methods for preparing uniform conformal graphene on complex surfaces are still limited. In this study, we develop a practical strategy for the direct growth of conformal graphene coatings on silicon substrates textured with randomly distributed micropyramidal structures. The produced transfer-free graphene exhibits high uniformity (monolayer content ∼95%), low defect density, and excellent conformality, even across high-curvature features, such as micropyramid apexes. The graphene films not only faithfully replicate the underlying microstructures but also contribute to advantageous surface properties, including strong fluorescence quenching, excellent chemical stability, enhanced molecular adsorption, and improved charge-transfer interactions. All these properties are crucial for effective surface-enhanced Raman scattering (SERS). This graphene-coated pyramidal substrate enabled reproducible and stable SERS detection of rhodamine 6G (R6G), exhibiting high sensitivity with a detection limit of ∼10-6 M, excellent long-term stability over 30 days, and low spatial signal variation of ∼10% at the millimeter scale. By further decorating the graphene-coated pyramidal substrate with silver nanoparticles, the detection limit was improved to 5.5 × 10-9 M for R6G with a high analytical enhancement factor of 1.08 × 105. This enhanced performance arose from the synergistic interplay between the light-trapping capability of the microstructured surface, the chemical enhancement caused by the graphene interface, and the electromagnetic amplification provided by the plasmonic nanoparticles. These findings offer valuable insights into the design of high-performance SERS platforms. This study also presents a practical method for the direct synthesis of conformal graphene for surface functionalization that is promising for a wide range of applications in sensing, optoelectronics, and catalysis.