Stack-flipping strategy for in-situ visualization of surface contaminants: Optimizing rinsing protocols for clean graphene transfer and enhanced electrical performance

Abstract

Graphene, as a promising 2D material with outstanding thermal, optical, mechanical, and electronic properties, shows great potential for next-generation device applications. During the wet transfer process of CVD monolayer graphene, acid/alkali cleaning agents are gradually used to facilitate the complete removal of polymeric support layers, for example PMMA, enabling a clean transfer of graphene. However, a comprehensive understanding of potential surface contaminants during this process, particularly the key factor influencing subsequent PMMA removal and the ultimate cleanliness of graphene, remains limited. Here, we report a facile stack flipping strategy to directly expose the surface of the etched PMMA/graphene film, enabling in-situ visualization and analysis of the residual contaminants under various rinsing conditions, including deionized (DI) water, acid, and salt solutions. Through systematic characterization and analysis, the key influencing factor and underlying mechanism governing the impact of acid/alkali solution treatments on the surface cleanliness of transferred graphene have been elucidated. Notably, graphene field-effect transistors (GFETs) fabricated using acid rinsing protocols exhibited a distinct negative shift in Dirac point voltage and demonstrated superior carrier mobility compared to devices prepared via the conventional transfer method. The proposed approach demonstrates great promise for enhancing quality control in graphene transfer, thereby facilitating its integration into high-performance (opto)electronic device applications.