Fe-DCA Metal-Organic Frameworks on the Bi2Se3(0001) Topological Insulator Surface

The formation of two-dimensional metal-organic frameworks (MOFs) on an inert surface of a topological insulator (TI) is a pathway to engineer quantum materials with exotic properties. MOFs featuring ferromagnetically coupled metal atoms are theoretically predicted to induce an exchange gap in the TI surface band structure, potentially leading to a quantum anomalous Hall effect. However, achieving ordered MOFs on TI surfaces remains challenging due to the limited knowledge of self-assembly on these substrates. In this paper, we demonstrate self-assembly of Fe atoms and dicyanoanthracene (DCA) molecules into 2D MOFs on the Bi2Se3(0001) surface at room temperature, investigated via a combination of low-energy electron microscopy and diffraction (LEEM/LEED), scanning tunneling microscopy (STM), and ab initio calculations based on density functional theory (DFT). Two competing Fe-DCA phases form. The first phase corresponds to a close-packed Fe1DCA3 structure. In contrast, the second phase exhibits a larger unit cell with no match to either known or DFT-calculated systems, indicating a more complex bonding environment. These findings advance the understanding of the growth of MOFs on a strong topological insulator surface and provide insights for designing MOFs/TI interfaces with tailored electronic and magnetic properties.