Nanoscale chemical characterization of functionalized graphene by heterodyne AFM-IR and chemical force microscopy

Nanoscale analysis is of critical importance for understanding and engineering the functional properties of advanced materials, particularly in applications requiring precise control of surface chemistry. In this work, we present a powerful strategy to probe the nanoscale heterogeneity of chemical functional species on graphene by combining heterodyne AFM-based infrared (AFM-IR) microscopy and chemical force microscopy (CFM). AFM-IR provides nanoscale-resolved chemical fingerprint information, enabling direct characterization of surface functional species, while complementary CFM reveals specific surface chemical interaction at the nanoscale with surface morphology. This combined approach successfully visualizes the nanoscale heterogeneity of chemical functional species on graphene introduced by a liquid-phase photoinduced covalent modification (PICM) method. Specifically, our results reveal that oxidative functional groups such as carboxyl, hydroxyl, and epoxide groups are relatively uniformly distributed across the PICM-modified regions. In contrast, methoxy groups form nanosized domains concentrated at the center of the PICM regions. This study represents the first successful molecular fingerprint visualization of nanoscale heterogeneity in functional groups introduced on graphene surfaces. As this method is fundamentally applicable to a wide range of sample systems-including other 2D atomic layer materials, polymers, and biological samples-, our work provides significant implications for both basic science and industrial applications.