Creating self-assembled arrays of mono-oxo (MoO₃)₁ species on TiO₂(101) via deposition and decomposition of (MoO₃)_n oligomers.

Abstract

Hierarchically ordered oxides are of critical importance in material science and catalysis. Unfortunately, the design and synthesis of such systems remains a key challenge to realizing their potential. In this study, we demonstrate how the deposition of small oligomeric (MoO₃)_1-6 clusters-formed by the facile sublimation of MoO₃ powders-leads to the self-assembly of locally ordered arrays of immobilized mono-oxo (MoO₃)₁ species on anatase TiO₂(101). Using both high-resolution imaging and theoretical calculations, we reveal the dynamic behavior of the oligomers as they spontaneously decompose at room temperature, with the TiO₂ surface acting as a template for the growth of this hierarchically structured oxide. Transient mobility of the oligomers on both bare and (MoO₃)₁-covered TiO₂(101) areas is identified as key to the formation of a complete (MoO₃)₁ overlayer with a saturation coverage of one (MoO₃)₁ per two undercoordinated surface Ti sites. Simulations reveal a dynamic coupling of the reaction steps to the TiO₂ lattice fluctuations, the absence of which kinetically prevents decomposition. Further experimental and theoretical characterizations demonstrate that (MoO₃)₁ within this material are thermally stable up to 500 K and remain chemically identical with a single empty gap state produced within the TiO₂ band structure. Finally, we see that the constituent (MoO₃)₁ of this material show no proclivity for step and defect sites, suggesting they can reliably be grown on the (101) facet of TiO₂ nanoparticles without compromising their chemistry.