Expanding the Concept of van der Waals Heterostructures to Interwoven 3D Structures

Abstract

Several members of a new family of heterostructures [(LaSe)1.17]1V n(1+y)+1Se2n+2 with n = 1, 2, and 3 were prepared using a diffusion constrained, kinetically controlled synthesis approach. Specular diffraction patterns collected as a function of annealing temperature show the evolution of designed precursors into highly ordered heterostructures. Scanning transmission electron microscopy (STEM) images reveal that the structure of n = 3 consists of rock salt structured LaSe bilayers alternating with vanadium selenide layers of varying thickness, which are structurally closely related to V3Se4. Interplanar distances obtained from the STEM images were successfully used as the starting point for Rietveld refinements of the specular diffraction patterns of these crystallographically aligned compounds. Utilizing this unorthodox combined approach to extract detailed structural information unambiguously, we demonstrated that these thin film compounds are the first examples of chalcogenide-based heterostructures, where the bulk structures of both building blocks lack a van der Waals gap, yet a nonepitaxial incommensurate interface forms. Moreover, the refinement results of the n = 2 and 3 heterostructures suggest that the structure of the V–Se layers can be varied ranging from VSe2 to VSe depending on the film composition. The electrical resistivity of the [(LaSe)1.17]1V n(1+y)+1Se2n+2 heterostructures changes systematically from semiconducting toward metallic behavior with increasing n, showcasing the ability to tune physical properties by precisely controlling the layer sequence in these heterostructures.

Compositional Phase Change of Early Transition Metal Diselenide (VSe2 and TiSe2) Ultrathin Films by Postgrowth Annealing

“…These materials may be combined by van der Waals epitaxy and thus create a new direction for van der Waals heterostructures. Use of intercalation-compound building blocks, such as V 3 Se 4 , has already been demonstrated for bulk van der Waals materials, 50 suggesting that thin film growth of such van der Waals heterostructures is plausible.…”

Molecular Beam Epitaxy of Transition Metal (Ti-, V-, and Cr-) Tellurides: From Monolayer Ditellurides to Multilayer Self-Intercalation Compounds

“…Similarly, the growth of layered materials has been demonstrated on intercalation compound substrates (MBE grown Cr 2 Te 3 ) . Moreover, intercalation compounds, like V 3 Se 4 , have been incorporated in a bulk van der Waals materials . These studies indicate that few-layer intercalation compounds, terminated by TMDC layers, are an extension of van der Waals materials and can be useful “building-blocks” for MBE-grown van der Waals heterostructures.…”

Synthesis of Metastable Inorganic Solids with Extended Structures

“…[79][80][81][82][83][84] New families of homologous compounds (shown in Figure 26) have been prepared with transition metal dichalcogenide layers alternating with layers of Bi2Se3 and Bi2Te3, [85,86] GeSe2, [87] and V3Se4. [88] These metastable compounds are prepared using precursors as described for misfit layer homologs discussed previously. Key to the synthesis is preparing the precursors such that each elemental bilayer contains the appropriate number of atoms to form a structural unit of the desired constituent.…”