Modular Design via Multiple Anion Chemistry of the High Mobility van der Waals Semiconductor Bi₄O₄SeCl₂

Making new van der Waals materials with electronic or magnetic functionality is a chemical design challenge for the development of two-dimensional nanoelectronic and energy conversion devices. We present the synthesis and properties of the van der Waals material Bi₄O₄SeCl₂, which is a 1:1 superlattice of the structural units present in the van der Waals insulator BiOCl and the three-dimensionally connected semiconductor Bi₂O₂Se. The presence of three anions gives the new structure both the bridging selenide anion sites that connect pairs of Bi₂O₂ layers in Bi₂O₂Se and the terminal chloride sites that produce the van der Waals gap in BiOCl. This retains the electronic properties of Bi₂O₂Se while reducing the dimensionality of the bonding network connecting the Bi₂O₂Se units to allow exfoliation of Bi₄O₄SeCl₂ to 1.4 nm height. The superlattice structure is stabilized by the configurational entropy of anion disorder across the terminal and bridging sites. The reduction in connective dimensionality with retention of electronic functionality stems from the expanded anion compositional diversity.