Mingyu Zhao

Band structure engineering in a MoS2/PbI2 van der Waals heterostructure via an external electric field

Band structure engineering in a MoS2/PbI2 van der Waals (vdW) heterostructure under an external electric field (Efield) is investigated using density functional theory (DFT). It is demonstrated that the MoS2/PbI2 vdW heterostructure has a type-II heterojunction with a direct bandgap, and thus the lowest energy electron-hole pairs are spatially separated. Meanwhile, the band structure could be effectively modulated under an Efield and the bandgap shows linear variations with the Efield, indicating a giant Stark effect. This gets further support from the band edges of MoS2 and PbI2 in the heterostructure. Moreover, the MoS2/PbI2 vdW heterostructure experiences transitions from type-II to type-I and then to type-II under various Efields. Our calculated results pave the way for experimental research and provide a new perspective for the application of the vdW heterostructure in electronic and optoelectronic devices.

Effects of applied strain and electric field on small-molecule sensing by stanene monolayers

We focus on the electronic structures of small gas molecule (such as CO, H2O, NH3, NO, and NO2)-adsorbed stanene monolayers by first-principles method. The results show that H2O, NH3, and CO molecules are physisorbed on stanene monolayer, while NO and NO2 molecules are found to be chemisorbed on stanene with quite large charge transfer, sizable adsorption energy, and strong covalent (Sn–O) bonds. Moreover, our spin–orbit coupling calculations show that the band gaps of the molecule-adsorbed stanene monolayers can be tuned effectively. In particular, our results also show that when the biaxial strains and electric field are applied, the adsorption energies and charge transfer between gas molecules and stanene monolayers change dramatically, which indicates that external factors on stanene monolayers are highly preferred. These results indicate that stanene is promising for wide-ranging applications as superior gas sensors and electrical devices.

The electronic and diffusion properties of metal adatoms on graphene sheets: a first-principles study

We use first-principles calculations to investigate the geometric, electronic and magnetic properties of metal adatoms on two typical graphene substrates (monolayer and bilayer). Firstly, we study the adsorption behaviors and the doping effects of metal atoms on pristine and defective bilayer graphene sheets (PBG and DBG). It is found that the metal doping in DBG sheets is more stable than that in PBG sheets, since there are stronger covalent bonds between metal atoms and the dangling bonds of the carbon atoms. Compared to the unsupported graphene sheets, the Pt(111) supported graphene substrates have some effect on the stability of metal adatoms. Besides, the diffusion pathways of metal adatoms move from the upper pristine layer to the sublayer with large energy barriers, which is more difficult than that on the upper layer of DBG and the intercalated reaction from the upper layer to the sublayer, so the metal adatoms tend to penetrate into the graphene overlayer through the defective site. Moreover, the different metal adatoms can effectively regulate the electronic and magnetic properties of graphene sheets. This work provides valuable information on understanding the formation mechanisms of metal doping in graphene sheets, which would be vital for designing new functional metal–graphene composites.

Effect of an external electric field on the electronic properties of SnS2/PbI2 van der Waals heterostructures

The future development of optoelectronic devices will require an advanced control technology in electronic properties, for example by an external electric field (Efield). Here we demonstrate an approach that the heterostructure based on van der Waals (vdW) heterobilayer built by monolayer SnS2 and PbI2 has a well-controlled electronic properties with Efield. A type-II staggered-gap band alignment is achieved from the SnS2/PbI2 vdW heterostructure with which SnS2 dominated the lowest energy holes as well as the lowest energy electrons are separated in PbI2. The charge redistribution with an Efield is mainly on the surface of SnS2 layer and PbI2 and the numbers of polarized electrons on the monolayers display a linear evaluation with external Efield. The band structure under different Efield experiences not only a transition from semiconductor to metal but also conversions between type-I straddling-band alignment and type-II staggered-gap, which results in different spatial distribution of the lowest energy electrons and holes. Moreover, when the Efield is between −0.06 V A−1 and −0.34 V A−1, the material manifests a varied direct bandgap which is more favor to optoelectronics and solar cell. Consequently, this vdW heterobilayer with well-controlled manner shows expectation for huge potential in optics and electronics.

CO oxidation over BC3 nanosheet: a theoretical study

ABSTRACT Metal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The electronic structure and catalytic property of BC3 sheet are investigated by using first-principles calculations. It is found that the BC3 sheet as the active surface can effectively regulate the adsorptive stability of reactive gases. Besides, the possible reaction processes for CO oxidation on the BC3 sheet are comparably analysed through different reaction mechanisms, which include the Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and termolecular Eley–Rideal (TER). In the CO oxidation reactions, the decomposition of O2 molecule as the starting state (0.40 eV) is an energetically more favourable process than those of other processes, the Eley–Rideal (ER) reactions (2Oads+2CO→CO2) are more prone to take place with lower energy barriers (< 0.20 eV) on the BC3 sheet. These results provide an important guidance on exploring the highly efficiency metal-free catalyst for CO oxidation. GRAPHICAL ABSTRACT

Strain effects on the magnetism of transition metal-doped MoTe2 monolayer

Abstract Using first-principles calculations, we investigated the electronic and magnetic performance of MoTe2 monolayer doped by transition metal (TM) Ti, V, Cr, Mn, Fe, Co and Ni atoms as well as strain effects. The dopants of Ti, V, Mn, Fe, Co and Ni atoms can induce magnetic moments in MoTe2 monolayer, and the magnetic moments mainly originate from the localizing unpaired TM-3d electrons. Mn- and Fe-doped MoTe2 nanostructures show the half-metallic character with 100% spin polarization near the Fermi level. The elastic strain applied on TM-doped MoTe2 monolayer systems leads to the redistribution of the electrons in TM-3d states, which results in the magnetic state transition in doped systems. The magnetic moments of Ti-, Co- and Ni-substituted MoTe2 sheets monotonously increase with the increase in strain, while the magnetic moment of V-substituted MoTe2 sheet has an oscillatory variation with the increase in strain. The Hubbard potential U has no significant effect on our main conclusions. The research results offer an important theoretical support for further application of strain-driven spin devices on MoTe2 nanostructures.

The adsorption properties of CHx species on metal modified graphene

The adsorption geometries of CHx species (x = 0, 1, 2, 3 and 4) on the metal embedded graphene (M–graphene) substrates and the change in electronic structure and magnetic property of systems are an...