Dirac-cone induced metallic conductivity in Cu 3 (HHTP) 2 : high-quality MOF thin films fabricated via ML-driven robotic synthesis

Abstract

Metal-organic frameworks have garnered interest for over 25 years in energy and electronics, yet their adoption in devices has been hindered by low electrical conductivity, largely attributed to activated transport. Our study demonstrates a significant shift, revealing metallic conductivity in Cu₃(HHTP)₂ thin films-240 S m^-1 at room temperature and 300 S m^-1 at 100 K, a departure from its presumed semiconductive nature. Achieved through robotic, AI-based layer-by-layer assembly in a self-driving laboratory, this method produces SURMOFs with minimal defects, optimized <i>via</i> rapid surrogate characterization techniques. Our research, supported by both electronic structure calculations and experimental verification, identifies a persistent Dirac cone in the hexagonal <i>D</i>_6h symmetry of 2D sheets as crucial for the observed metallic behavior. Notably, even with ABAB stacking in the bulk, this Dirac cone feature maintains metallic conductivity, enhancing at lower temperatures. This breakthrough not only clarifies the conduction mechanism in Cu₃(HHTP)₂ but also highlights the SDL's potential in developing high-quality MOF thin films for future applications. Our findings indicate that tailoring the Dirac cone's energy could lead to a new class of highly conductive, metallic MOFs.