Tunable Chemochromism and Elastic Properties in Intercalated MoO₃: Au-, Cr-, Fe-, Ge-, Mn-, and Ni-MoO₃

Chemical tunability of the elastic constants of α-MoO₃, a two-dimensional layered oxide, is demonstrated with mutability on the order of tens of GPa, simply by choice of a metal intercalant including Au, Cr, Fe, Ge, Mn, and Ni. Using Brillouin laser light scattering from confined acoustic phonons in nanometer-thick materials, the in-plane angular dispersion of the quantized acoustic phonon branches of 2D layered, intercalated MoO₃ is measured and used to determine the bulk modulus (K), Young's moduli (E₁₁, E₂₂, and E₃₃), each of the nine independent elastic tensor elements (c), and the thickness. Intercalation of metals generally reduces the anisotropy in MoO₃ except in Ge-MoO₃, for which the in-plane longitudinal elastic anisotropy is unaffected. Chemochromism from transparent white (MoO₃ and Fe-MoO₃) to near black (Ni-MoO₃) to brilliant dark blue (Ge-MoO₃) is demonstrated and is associated with a reduction in electronic band gap with intercalation and an increase in absorption >600 nm for some intercalants (Cr-, Ge-, and Mn-MoO₃).