Structural Design And Growth Simulation Of Transition Metal Carbide MC(M=Ti,Zr,Hf) Monolayer Materials

Two-dimensional(2D)transition metal carbides(TMCs)have emerged as a new family of 2D materials due to their exceptional mechanical properties,chemical stability,ultra-hardness,high melting points,and good conductivity,making them highly promising for applications in coatings,aerospace,catalysis,energy conversion and storage.However,most of the inherent 2D TMCs structures are of the MXene type,possessing metallic properties that greatly limit their applications in optoelectronic devices.Therefore,it is necessary for researchers to expand their application range and enrich the 2D TMCs family beyond the MXene type,to obtain fascinating physical properties such as bandgap and/or unique topological features.Furthermore,it is important to conduct growth simulations to explore the effects of different growth environments on thin film growth,which can guide experiments more directly.We employed first-principles calculations and molecular dynamics simulations to investigate the structural design and growth simulation of two sets of 2D MC(M=Ti,Zr,Hf)materials.The specific research contents are as follows:(1)Two sets of tetragonal β-and hexagonal γ-MC structures were obtained through structural search and theoretical design,which were found to be more stable than the α-phase.Moreover,the single-layer β-MC has a higher binding energy than γ-MC.Based on theoretical calculations,the structural stability and electronic/optical properties of 2D MC were studied.The β-MC is a group of semimetallic structures with two nodal loops,namely the inner and outer rings surrounding the Fermi level.On the other hand,the single-layer γ-Zr C(Ti C,Hf C)has a bandgap of 1.24 e V(1.59,1.57 e V)and high optical absorption ability.Overall,these excellent mechanical,semimetallic,and optical properties suggest the potential applications of 2D MCs in the next generation of spintronics and optoelectronics technologies.(2)The β-Ti C structure was selected for study,and a machine learning approach was employed to obtain a potential function that approximates the accuracy of density functional theory(DFT).Molecular dynamics simulations were then used to investigate the growth process of Ti C on the Si C(100)substrate and explore the influence of growth conditions on crystal structure.We found that the growth mode of Ti C changes from three-dimensional island growth to two-dimensional layer-by-layer growth as the temperature increases.These results are significant for further understanding the growth mechanism and optimizing the preparation process of 2D TMCs.