van der Waals Nanochemical Reactors.

Synthesizing single crystals suitable for quantum electronic discoveries remains challenging for many emerging materials. We introduce van der Waals (vdW) stacks as nanochemical reactors for single-crystal synthesis and demonstrate their broad applicability in growing both elemental and compound crystals at the micrometer scale. By encapsulating atomically thin reactants that are stacked compactly with inert vdW layers, we achieve nanoconfined synthesis with the resulting crystals remaining encapsulated. As a proof of concept, we synthesized isolated single crystals of elemental tellurium and distinct types of Pd-Te compounds. Structural characterization confirms the high crystalline quality of the products. We observe the intrinsic semiconducting gap of tellurium and superconductivity in nonstoichiometric PdTe1-x with a significantly reduced Te content. The concept of vdW nanoreactors is broadly generalizable, chip-integrable, well-suited to a wide range of processing conditions, and compatible with nanofabrication, offering a versatile pathway to expand the accessible landscape of quantum materials.