Building nanoplatelet α-MoO3 films: A high quality crystal anisotropic 2D material for integration.

[Display omitted] • A successful methodology to produce large 2D α-MoO 3 nanoplatelets with the [0 1 0] crystallographic direction parallel to the normal of the film surface, and with their crystallographic directions [1 0 0] and [0 0 1] randomly distributed in-plane has been developed. • The synthetized α-MoO 3 nanoplatelets show no overlapping in-plane, and collectively form a dense network that optically behave as an anisotropic film both in the visible and medium infrared. • The anisotropic dielectric function of the nanoplatelet α-MoO 3 films as determined by spectroscopic ellipsometry analysis is reported. • These innovative nanoplatelet α-MoO 3 films behave as a 2D functional nanostructures suitable for the development of multilayer optoelectronic devices. The successful development of nanoplatelet α-MoO 3 −films with wavelength-dependent in-plane and out-of-plane birefringence both in the visible and in the medium infrared is demonstrated. The films are prepared by a two-step process starting from structurally amorphous and continuous substoichiometric MoO 3-X followed by isothermal annealing at low temperature (250 °C) to yield the formation of a dense network of large α-MoO 3 2D nanoplatelets lying in-plane with no overlapping. These α-MoO 3 crystals form a film with excellent thickness uniformity (20 nm) and are oriented with the [0 1 0] crystallographic direction parallel to the substrate normal. Finally, we report the film anisotropic optical complex refractive index, both parallel and perpendicular to the plane the full spectral range from 0.7 to 5 eV as determined by spectroscopic ellipsometry, and their characteristic in-plane phonon mode in the IR from FTIR measurements. These results show a promising pathway to the creation of highly functional anisotropic α-MoO 3 2D films suitable for the development of integrated nanostructured photonic components. [ABSTRACT FROM AUTHOR]