Molybdenum Trioxide on Anatase TiO2(101) - Formation of Monodispersed (MoO3)1 Monomers from Oligomeric (MoO3)n Clusters

Complex oxide systems with hierarchical order are of critical importance in material science and catalysis. Despite their immense potential, their design and synthesis are rather difficult. In this study we demonstrate how the deposition of small oligomeric (MoO₃)_1-6 clusters, which can be formed by the sublimation of MoO₃ powders, leads to the formation of locally ordered layers of (MoO₃)₁ monomers on anatase TiO₂(101). Using both high-resolution imaging and theoretical calculations, we show that at room temperature, such oligomers undergo spontaneous dissociation to their monomeric units. In initial stages of the deposition, this is reflected by the observation of one to six neighboring (MoO₃)₁ monomers that parallel the size distribution of the oligomers. A transient mobility of such oligomers on both bare TiO₂(101) and (MoO₃)₁ covered areas is key to the formation of a complete layer with a saturation coverage of one (MoO₃)₁ per two undercoordinated surface Ti sites. We further show that such layers are stable to 500 K, making them highly suitable for a broad range of applications.