Dimensional transformation of chemical bonding during crystallization in a layered chalcogenide material

Two-dimensional (2D) van der Waals (vdW) materials possess a crystal structure in which a covalently-bonded few atomic-layer motif forms a single unit with individual motifs being weakly bound to each other by vdW forces. Cr2Ge2Te6 is known as a 2D vdW ferromagnetic insulator as well as a potential phase change material for non-volatile memory applications. Here, we provide evidence for a dimensional transformation in the chemical bonding from a randomly bonded three-dimensional (3D) disordered amorphous phase to a 2D bonded vdW crystalline phase. A counterintuitive metastable quasi-layered state during crystallization that exhibits both long-range order and short-range disorder with respect to atomic alignment clearly distinguishes the system from conventional materials. This unusual behavior is thought to originate from the 2D nature of the crystalline phase. These observations provide insight into the crystallization mechanism of layered materials in general, and consequently, will be useful for the realization of 2D vdW material-based functional nanoelectronic device applications.

Automated summary

The study demonstrates a dimensional transformation in chemical bonding from a randomly bonded three-dimensional disordered amorphous phase to a 2D bonded vdW crystalline phase, as well as the emergence of a counterintuitive metastable quasi-layered state during crystallization.