  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. Herein, the critical role of
oxygen (O-) functionalization on the tensile mechanical characteristics of
thinnest 2D Ti2C MXene is explored by molecular dynamic (MD) simulation with
first-principle based ReaxFF forcefield. It is demonstrated that Ti2C sheet
shows unique tensile mechanical behaviors that pronouncedly vary with the
content of O-functionalization and stretching direction. Upon both loading
directions, there is an apparent crossover in the Young's modulus, failure
strength and failure strain. Intriguingly, 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, and they are
critically understood by analysis of the bond configurations. The study
provides important insights into mechanical behaviors and structural
transformations of functionalized MXenes.

Materials Science