Structural, electronic, and chemical manifestations of weak molecule–substrate coupling on Bi2Se3 compared with Ag, Au, and graphene

Modifying topological insulator (TI) surfaces with metal-organic layers offers a pathway to a material that displays the quantum anomalous Hall effect. However, knowledge of the molecular nanoarchitectonics on weakly interacting TI surfaces remains limited, which hinders the experimental realization of organic layers with the required properties. Here, we combine low-energy electron microscopy and diffraction, STM, XPS, and DFT calculations to investigate the adsorption of 4,4’-biphenyl-dicarboxylic acid (BDA) on the Bi 2 Se 3 (0001) and compare it with Ag(100), Ag(111), Au(111), and graphene substrates. We identify four manifestations of weak molecule–substrate coupling: (i) Upon deposition, the BDA molecule stays intact and is physisorbed. (ii) The intact nature of BDA is preserved at elevated temperatures. (iii) The electronic energy levels of BDA are decoupled from substrate polarization effects. (iv) There is a weak positional preference of the BDA molecular phase with respect to the substrate. Bi 2 Se 3 exhibits uniquely weak structural, electronic, and chemical interactions with BDA, meeting all these points, whereas the other substrates fail to meet one or several of these points. These insights provide a quantitative framework for understanding weak molecule–substrate coupling across a range of 2D materials and metallic surfaces, informing the design of molecular architectures on non-metallic substrates for quantum and functional nanomaterials with potential applications in quantum nanoelectronics.