van der Waals Nanoreactors

TL;DR

This paper introduces van der Waals stacks as nanoreactors for synthesizing high-quality single crystals of quantum materials at the microscale, enabling new possibilities in quantum material research.

Contribution

It presents a novel nanochemical synthesis method using vdW stacks to grow single crystals, including elemental and compound types, with high crystalline quality and broad applicability.

Findings

Successfully synthesized single crystals of tellurium and Pd-Te compounds.

Confirmed high crystalline quality via atomic-resolution microscopy.

Observed superconductivity in PdTe1-x with x ~ 0.18 at 3.8 K.

Abstract

Advancing the chemical synthesis of crystals is important for both fundamental research and practical applications of quantum materials. While established bulk-phase and thin-film growth methods have enabled enormous progress, synthesizing single crystals suitable for quantum electronic discoveries remains challenging for many emerging materials. Here, 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 such as hexagonal boron nitride (hBN), we achieve nanoconfined synthesis with the resulting crystals remaining encapsulated. As proof of concept, we synthesized isolated single crystals of elemental tellurium and distinct types of Pd-Te compounds. Structural characterization, including atomic-resolution scanning transmission electron microscopy, confirms the high crystalline quality of the products. We confirm the intrinsic semiconducting gap of tellurium and observe that non-stoichiometric PdTe1-x with a significantly reduced Te content (x ~ 0.18, a regime not previously achieved) retains uniform crystallinity and exhibits superconductivity below a critical temperature of 3.8 K. This nanochemical synthesis is broadly generalizable, chip-integrable, well-suited to a wide range of processing conditions, and compatible with nanofabrication routines for constructing devices. The concept of vdW nanoreactors offers a powerful and versatile pathway to expand the accessible landscape of quantum materials.