Structure and Defect Identification at Self-Assembled Islands of CO₂ Using Scanning Probe Microscopy

Understanding how carbon dioxide (CO₂) behaves and interacts with surfaces is paramount for the development of sensors and materials to attempt CO₂ mitigation and catalysis. Here, we combine simultaneous atomic force microscopy (AFM) and scanning tunneling microscopy (STM) using CO-functionalized probes with density functional theory (DFT)-based simulations to gain fundamental insight into the behavior of physisorbed CO₂ molecules on a gold(111) surface that also contains one-dimensional metal-organic chains formed by 1,4-phenylene diisocyanide (PDI) bridged by gold (Au) adatoms. We resolve the structure of self-assembled CO₂ islands, both confined between the PDI-Au chains as well as free-standing on the surface and reveal a chiral arrangement of CO₂ molecules in a windmill-like structure that encloses a standing-up CO₂ molecule and other foreign species existing at the surface. We identify these species by the comparison of height-dependent AFM and STM imaging with DFT-calculated images and clarify the origin of the kagome tiling exhibited by this surface system. Our results show the complementarity of AFM and STM using functionalized probes and their potential, when combined with DFT, to explore greenhouse gas molecules at surface-supported model systems.