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

The formation of two-dimensional metal-organic frameworks (MOFs) on the 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 topological surface states, potentially leading to a quantum anomalous Hall effect. However, achieving ordered MOFs on TI surfaces remains challenging because of the limited knowledge of self-assembly on these substrates. In this paper, we demonstrate the 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 formed. 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 into designing MOF/TI interfaces with tailored electronic and magnetic properties.