| Transition metal carbides/nitrides(MXenes)are a newly developing class of two-dimensional(2D)materials with technically robust properties that can be finely tuned by planar surface functionalization.In this thesis,the effects of oxygen(O-)functionalization on the tensile mechanical characteristics of 2D Ti2C and Ti3C2 MXenes are explored by molecular dynamic(MD)simulation with first-principle based ReaxFF forcefield.Main results are summarized as follows:(1)2D Ti2C sheet shows unique tensile mechanical behaviors that pronouncedly vary with the content of O-functionalization and stretching direction.Upon both armchair and zigzag loading directions,there is an apparent crossover in the Young’s modulus,failure strength and failure strain.Under armchair directional load,a structural transition of 1T to 1T’ phase occurs in the Ti2C region,which has been observed in many transition metal dichalcogenides.Upon zigzag directional straining,however,two distinct structural transformations take place in pristine and fully O-functionalized Ti2C sheets,respectively.As the load is removed,those three structural transformations are reversible.(2)2D Ti2C2Ox sheets are more structurally stable MXenes than Ti2COx ones.Subjected to zigzag-directional load,Ti2C2 MXene is able to show hardening behaviors,while Ti2COx sheets exhibit tensile responses including linear,softening and sudden drop of loading stress.Similar to the case of Ti2COx,there is crossover in tensile properties of Ti3C2Ox sheets;with increasing the content of O-functionalization,failure strength and failure strain initially decreases but then increases,while the tensile Young’s modulus monotonically increases.Tensile properties of Ti3C2Ox sheets under zigzag-directional load are more robust than under armchair-directional load.Moreover,tensile Young’s modulus and failure strength of Ti2C2Ox are higher than those of Ti2COx sheets,but it is opposite for failure strain. |
