Synthesis of (BiSe)_1+δ(Bi₂Se₃)_1+γ(BiSe)_1+δTiSe₂ by Directed Self-Assembly of a Designed Precursor

Abstract

The synthesis, structure, and properties of a new three-constituent heterostructure containing BiSe, Bi2Se3, and TiSe2 layers, each with a different structural motif, are reported. (BiSe)1+δ(Bi2Se3)1+γ(BiSe)1+δTiSe2, where δ and γ are the misfit parameters representing the differences in the in-plane packing density of the constituents, forms via a self-assembly process during low-temperature annealing from precursors with a range of compositions and repeat period thicknesses. This indicates that the compound exists in a relatively broad and deep free-energy minima in the energy landscape. The formation was followed as a function of annealing temperature using X-ray diffraction to determine optimum annealing temperatures and stability range. High-resolution electron microscopy images revealed the layering sequence of the constituents and a supercell within the BiSe layers created by periodic anti-phase boundaries. Temperature-dependent electrical transport measurements show unexpected changes in carrier mobility and concentration relative to (BiSe)1.15TiSe2. This study suggests that new ternary and multinary phases containing fragments of known binary phases can be synthesized via precursors that mimic the desired product and that the properties of these new phases with ultrathin constituent thicknesses will probably be different from that expected based on composite behavior.