First-principles prediction of two-dimensional metal bis(dithiolene) complexes as promising gas sensors

Abstract

The recently synthesized two-dimensional metal bis(dithiolene) complex (MDT), a kind of metal–organic framework with a kagome lattice structure, has been found to be a promising material for electronic devices. Here we report the surface adsorption effects of gas molecules on the electronic properties and transport behaviors of two-dimensional MDT (M = Fe, Co, Ni, Pd, and Pt) films. The first-principles results reveal that the MDT nanosheets are selectively sensitive to different adsorbed molecules, such as CO, NO, and O₂ molecules. All the studied gas molecules can be chemically adsorbed on the ferromagnetic FeDT and CoDT nanosheets, whereas the non-magnetic PdDT and PtDT films are only sensitive to NO molecules, showing quite weak interaction with CO and O₂. The physisorption of CO on PdDT and PtDT originates from the mismatch of energy levels between the metal d_z² orbitals and the CO σ orbitals. In contrast, the Pd and Pt d_xz and d_yz orbitals can well align with the NO π* orbitals, causing strong chemisorption. More importantly, the adsorption of NO on PdDT and PtDT not only induces a magnetism of 1.0 μ_B for the two films but also greatly enhances the conductivity. In the case of PtDT, we observe a transition from the semiconducting to the metallic phase on NO adsorption. This significant change in the electronic structure can be understood from the adsorption-induced interfacial charge transfer and the strong orbital hybridization between the metal d states and the NO π* states. Our results suggest the potential application of the PdDT and PtDT nanosheets in gas sensing and spintronics.