Scanning Probe Microscopy of Graphene Sensors Before and After Nitrogen Exposure

Developing high-performance, miniaturized 2D material platforms requires a deep, multiscale understanding of gas-surface interactions and localized electronic behavior. In this study, we demonstrate an integrated experimental methodology that combines in situ environmental scanning electron microscopy (ESEM) with ex situ scanning probe microscopy (SPM) to analyze monolayer graphene field-effect transistor (GFET) sensors before and after controlled nitrogen (N₂) exposure. In situ electrical measurements performed inside the ESEM chamber show a continuous, monotonic increase in graphene channel resistance (up to approximately 5%, reaching 6.30 kΩ at 160 Pa) as N₂ vapor displaces residual atmospheric contaminants. On the micro and nanoscale, ex situ SPM characterization confirms that the gross topography and structural integrity of the diagonal contact-graphene boundary remain intact post-exposure. The initial highly heterogeneous, "charge-puddle-like" work-function landscape-characterized by a low-potential diagonal band-is replaced by a visually smoother, spatially uniform potential profile after N₂ treatment. This shift is primarily attributed to the displacement, desorption, and spatial reorganization of preadsorbed environmental p-dopants (such as water vapor and oxygen molecules) by N₂ gas.