2-D mesoparticulate arrays of α-Cr₂O₃

An inexpensive low-temperature aqueous thin film processing technique is presented for the fabrication of large two-dimensional (2-D) arrays of α-Cr₂O₃ without template, surfactant, or applied external field. The arrays consist of well-defined, monodispersed, and noninteracting crystalline spherical mesoparticles (250 nm) that are grown directly onto single crystalline silicon wafers (Si or SiO₂) or polycrystalline transparent conducting oxide (TCO) substrates by heteronucleation. Their UV-visible optical absorption properties are consistent with the electronic transitions of Cr³⁺ ions in D_3d symmetry but significantly blue-shifted compared to single crystal or polydispersed α-Cr₂O₃ samples. Such arrays could be of interest for theoretical and experimental studies of the unique nonreciprocal optical effects observed in α-Cr₂O₃.