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Besides the high flexibility and strong anisotropic elastic properties of phosphorene, oxidation is so important to tune its elastic properties and extending the corresponding applications. Phosphorene half-oxides can be stretched becoming ideal for devices requiring flexibility [79]. Moreover, the degree of oxidation influences significantly the elastic parameters [30–80]. The polar plot of Young modulus and Poisson ratios reveals that the maximal values are attempted for armchair-strain resulting super flexible structures. However, it is hard to implement zigzag deformation direction that shows minimal values of elastic parameters (see Figures 1.13a, b). Importantly, the Poisson ratios of and conformers take negative values for some ranges of angles, which lead to an auxetic behavior (see [79]). Moreover, in all the conformers, the Poisson ratio is lower than 0.5, which correspond to incompressible materials. Stress-strain responses, under the armchair and zigzag tensile strain, show that half oxidation leads to much higher critical points, compared to pure phosphorene. It is found that both the dangling and bridge structures resist to a large axial deformation up to 27%–39% along the AC-axis with respect to the ZZ one. More precisely, the maximum values coincide with the dangling structures P₄O_U, P₂O_D, and P₃O_U which can resist a tensile strain up to 30%, 33%, and 39%, respectively, showing a high flexibility in the armchair direction. This result is owing to the high buckled honeycomb structures that exhibit these configurations in this direction. The mechanical flexibility of half-oxidized phosphorene make these structures an ideal candidate for wearable optoelectronic devices.

Figure 1.12 Excitons wave functions. Black balls represent the holes.

Figure 1.13 Part of polar plots of (a) Young modulus, (b) Poisson ratios.

Under half oxidation, the Debye temperature of phosphorene increases, with a maximum value reached in the ZZ-axis relative to AC. The high Debye temperature values indicate an important thermal conductivity in these new derivatives lattice lattice [79]. Furthermore, the curves describing the normal electrical polarization of the PO configurations in terms of applied strain are linear. With respect to pure phosphorene, the piezoelectric stress parameters increase under 50% oxidation while the piezoelectric strain coefficients d11 are three times lower than 2D BP [80].

When axial deformation is implemented, the electronic features of the POs become modulated. The band gap of dangling and bridge structures increases with low tensile strain, then it reduces to achieve a metallic state for large deformations. Besides, both groups of POs can maintain the semi-conductor behavior along the armchair direction for a strain ranging from 20% to 40% [81]. One can deduce that the adjustment of the phosphorene oxides features makes this class of materials potential candidates for advanced devices.