We investigate the electronic structure and work function modulation of α-Fe₂O₃ films by strain based on the density functional method. We find that the band gap of clean α-Fe₂O₃ films is a function of the strain and is influenced significantly by the element termination on the surface. The p_x and p_y orbitals keep close to Fermi level and account for a pronounced narrowing band gap under compressive strain, while unoccupied d_z2 orbitals from conduction band minimum draw nearer to Fermi level and are responsible for the pronounced narrowing band gap under tensile strain. The spin polarized surface state, arising from localized dangling-bond states, is insensitive to strain, while the bulk band, especially for p_z orbital, arising from extended Bloch states, is very sensitive to strain, which plays an important role for work function decreasing (increasing) under compressive (tensile) strain in Fe termination films. In particular, the work function in O terminated films is insensitive to strain because p_z orbitals are less sensitive to strain than that of Fe termination films. Our findings confirm that the strain is an effective means to manipulate electronic structures and corrosion potential.

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.

The prevention of hydrogen penetration into steels can effectively protect steels from hydrogen damage. In this study, we investigated the effect of a monolayer MoS₂ coating on hydrogen prevention using first-principles calculations. We found that monolayer MoS₂ can effectively inhibit the dissociative adsorption of hydrogen molecules on an Fe(111) surface by forming a S–H bond. MoS₂ coating acts as an energy barrier, interrupting hydrogen penetration. Furthermore, compared with the H-adsorbed Fe(111) film, the work function of the MoS₂-coated film significantly increases under both equilibrium and strained conditions, indicating that the strained Fe(111) film with the MoS₂ coating also becomes more corrosion resistant. The results reveal that MoS₂ film is an effective coating to prevent hydrogen damage in steels.