Growth of out-of-plane standing MoTe$_{2(1-x)}$Se$_{2x}$/MoSe$_2$ composite flake films by sol-gel nucleation of MoO$_y$ and isothermal closed space telluro-selenization

Abstract

This study describes the sol-gel processing of MoO_y on Si (100) to subsequently achieve out-of-plane MoTe₂/MoSe₂ flake composite films by an isothermal closed space vapor transformation. The oxide precursor films have been prepared from a Mo isopropoxide solution in isopropanol and acid catalysis induced by HCl. Thermal annealing at 200, 400 and 600°C enhanced the condensation after xerogel formation. An x-ray absorption analysis demonstrates that films condensed at 200°C are at an intermediate chemical state between MoO₃ and MoO₂. To achieve MoTe₂/MoSe₂ composite films, the precursor oxide films were reduced in H₂ and exposed to the chalcogenides by isothermal closed space vapor transport at 600°C. The multilayered nanocomposite films grow with an out-of-plane flake-like structure and an evident integration of Se in the MoTe₂ phase according to a MoTe_2(1-x)Se_2x alloy, with an estimation of $x$ of 0.25. The alloy and the orientation of the flakes is consistent with the bands present in the Raman spectrum. These films are attractive for applications requiring high surface area interfaces favoring gas or ion exchange reactions with transition metal dichalcogenides.