Metastable materials often vanish from the laboratory bench before researchers can study them. They form only briefly, quickly transforming into more stable structures as atoms rearrange toward thermodynamic equilibrium. Now, researchers in China have reported a way to capture one of these elusive phases in a form large enough for practical experiments. Using a two-step chemical conversion process, the team has produced wafer-scale films of W₆Te₆, a quasi-one-dimensional van der Waals material with a distinctive atomic architecture and potentially unusual electronic and transport properties.
The work, led by Yeliang Wang and Xiaolong Xu of Beijing Institute of Technology, addresses a long-standing challenge in the synthesis of W₆Te₆. Conventional tellurization, in which tungsten is directly exposed to a tellurium-containing environment, strongly favors the formation of thermodynamically stable WTe₂. Although W₆Te₆ is predicted to host intriguing physical behavior, the material is metastable, meaning that it is energetically less favorable than competing phases. Under ordinary growth conditions, the atoms rapidly follow the lower-energy route to WTe₂, leaving little opportunity for W₆Te₆ to emerge.
The researchers overcame this problem by introducing an intermediate template made from tungsten disulfide, or WS₂. Their kinetically controlled anion-exchange strategy begins with a tungsten film deposited by magnetron sputtering. The film is first sulfurized, converting it into a 2H-WS₂ structure. It is then exposed to tellurium under carefully controlled conditions. During this second step, sulfur anions are gradually replaced by tellurium anions, transforming the template into W₆Te₆ rather than allowing tungsten to react explosively and directly with tellurium.
The success of the method depends on controlling reaction kinetics rather than simply seeking the most thermodynamically stable product. Strong W–S bonds in WS₂ create an activation barrier that slows the exchange process. This barrier is crucial: it prevents the rapid structural collapse associated with direct tungsten tellurization and creates a temporary window in which the metastable W₆Te₆ phase can be trapped. By adjusting the reaction temperature, duration, and chemical environment, the team was able to guide the material through a sequence of intermediate states instead of allowing it to jump immediately to WTe₂.
The WS₂ template itself plays an important structural role. Rather than forming conventional layers with broad, relatively inert basal planes, the sulfurized film develops a vertically aligned grain structure. This orientation exposes a large number of reactive layer edges, where atoms have dangling bonds and can participate readily in anion exchange. At the same time, it minimizes the chemically passive basal surfaces that would otherwise hinder conversion. The result is a template designed at the nanoscale to make the slow, controlled replacement of sulfur by tellurium possible across a much larger film.
Microscopy provided direct evidence that the approach produced the intended structure. Atomic-resolution high-angle annular dark-field scanning transmission electron microscopy revealed the characteristic quasi-one-dimensional chains of W₆Te₆. Each chain consists of an inner arrangement of six tungsten atoms surrounded by an outer sheath of six tellurium atoms. These covalently bonded units are assembled into a larger solid through van der Waals interactions, giving the material a combination of strong internal bonding and relatively weak interchain coupling. That architecture may generate pronounced directional differences in charge transport, optical response, and other physical properties.
Chemical mapping further supported the structural identification. Large-area energy-dispersive X-ray measurements showed a uniform distribution of tungsten and tellurium throughout the converted film. Quantitative analysis produced a W:Te atomic ratio close to 1:1, consistent with the nominal W₆Te₆ composition. The researchers also systematically varied the synthesis conditions to construct a growth phase diagram. The map distinguished regions containing unreacted WS₂, partially converted material, and phase-pure W₆Te₆, providing a practical guide for reproducing the desired phase instead of relying on trial and error.
Using the optimized conditions, the team produced a one-inch wafer-scale W₆Te₆ film. Raman point mapping across the entire wafer showed highly consistent spectral signatures, indicating that the material’s structure was uniform over macroscopic distances. This scale is especially significant because many metastable low-dimensional materials have previously been limited to tiny flakes or isolated crystallites, making device fabrication and statistical measurements difficult. The researchers also demonstrated that the conversion is compatible with standard photolithography. Pre-patterned tungsten structures could be sulfurized and then tellurized while retaining their designed shapes, suggesting that the process may be integrated with established semiconductor manufacturing workflows.
The reported strategy could therefore extend beyond W₆Te₆. By using a chemically engineered intermediate to slow and redirect an otherwise unfavorable reaction, the method offers a general route toward metastable van der Waals materials that are inaccessible through direct synthesis. Large-area, patternable films would allow researchers to investigate the predicted physics of quasi-one-dimensional systems under realistic device conditions and could accelerate the search for materials with highly anisotropic electrical, optical, or sensing characteristics. The study, published in Nano Research on July 4, 2026, presents kinetic control not merely as a way to improve synthesis, but as a tool for making fleeting atomic phases available for systematic scientific exploration.
Subject of Research: Wafer-scale synthesis of metastable quasi-one-dimensional van der Waals material W₆Te₆ using a kinetically controlled two-step anion-exchange strategy.
Article Title: A two-step anion-exchange strategy via a WS₂ template enables the 1-inch wafer-scale growth of metastable quasi-1D van der Waals material W₆Te₆
News Publication Date: 4-Jul-2026
Web References: https://doi.org/10.26599/NR.2026.94908711; Nano Research
References: Wang, Y., Xu, X. et al., “A two-step anion-exchange strategy via a WS₂ template enables the 1-inch wafer-scale growth of metastable quasi-1D van der Waals material W₆Te₆,” Nano Research, DOI: 10.26599/NR.2026.94908711.
Image Credits: Nano Research, Tsinghua University Press
Keywords
W₆Te₆, tungsten telluride, WS₂ template, anion exchange, metastable materials, quasi-one-dimensional materials, van der Waals materials, wafer-scale synthesis, nanotechnology, materials science, Raman mapping, photolithography
