That bottleneck may finally be easing. A team led by Wei Zhai, Zhenyu Shi, Rui Tao, Zijian Li, Zhuangchai Lai and Hua Zhang, working across the City University of Hong Kong, The Hong Kong Polytechnic University and partner institutions, has published a detailed protocol in Nature Protocols describing a salt-assisted method that reliably converts ordinary 2H-phase crystals into phase-pure, highly crystalline 1T′-phase materials. The procedure covers a broad compositional palette, including MoS2, MoSe2, WS2, WSe2 and the mixed-chalcogen alloys MoS2xSe2(1−x) and WS2xSe2(1−x), and it does so at a scale that previous approaches could only dream of: gram quantities per batch, with individual crystals reaching hundreds of micrometers across.

The elegance of the method lies in its simplicity. Rather than building 1T′ crystals from scratch under exotic conditions, the protocol starts with commercially available 2H-phase transition metal dichalcogenides and co-anneals them with elemental chalcogen powders, such as sulfur or selenium, together with common alkali metal salts such as potassium oxalate hydrate or potassium carbonate. The reaction is carried out in a sliding tube furnace under a hydrogen-argon atmosphere. When the mixture is heated, the alkali metal salts act as the trigger for a remarkable structural transformation, coaxing the atomic layers of the stable 2H phase to slide and distort into the metastable 1T′ configuration. The chalcogen vapor maintains the correct chemical environment, preventing decomposition while the phase change proceeds.

Understanding why this works requires a brief tour of the underlying crystallography. In the 2H phase, each metal atom sits in a trigonal prismatic coordination environment, and the layers stack in a specific sequence that renders the material a semiconductor. The 1T′ phase, by contrast, features octahedral coordination with a periodic lateral displacement of the metal atoms, breaking the symmetry in a way that produces metallic conductivity. Because the 1T′ arrangement is metastable, it does not form spontaneously under ordinary synthesis conditions; it must be kinetically trapped. Alkali metal ions appear to facilitate this trapping by intercalating between the layers, weakening the interlayer bonding and lowering the energetic barrier for the intralayer atomic rearrangement. Subsequent deintercalation of these ions leaves behind the transformed lattice, now locked into its new metastable geometry.

The published protocol walks researchers through every stage of this process with unusual care. It specifies the setup of the sliding tube furnace, a configuration that allows the reactants to be rapidly moved into and out of the hot zone, giving precise control over reaction timing. It details the loading of the 2H-phase starting materials, the chalcogen powders and the salt, the purging and establishment of the hydrogen-argon atmosphere, the heating profile and the post-reaction washing steps that remove residual salts and recover the transformed crystals. The entire procedure takes approximately 37 hours and 20 minutes from start to finish, a time investment that is modest compared with the weeks of trial and error that often accompany attempts to grow metastable phases by conventional routes.

Equally important is the protocol’s emphasis on verification. Phase purity is not assumed; it is demonstrated. The authors prescribe a characterization workflow built on three complementary techniques. Raman spectroscopy probes the vibrational fingerprints of the lattice, which differ distinctly between the 2H and 1T′ arrangements. X-ray photoelectron spectroscopy examines the chemical states of the metal and chalcogen atoms, confirming that the transformation is complete and that no residual intercalants or decomposition products remain. X-ray diffraction provides the definitive structural verdict, revealing the characteristic peak positions of the 1T′ lattice and the absence of any detectable 2H-phase remnants. Together, these measurements give researchers the confidence that the material they are studying is genuinely the phase they intended to make.

The significance of gram-scale availability is difficult to overstate. Much of the early literature on metastable transition metal dichalcogenides relied on chemically exfoliated nanosheets produced through lithium intercalation, a method dating back to the 1980s that yields small, often defective flakes with variable phase content. Colloidal synthesis routes later offered better control but typically produced nanometer-scale particles rather than the large, well-ordered crystals needed for fundamental physics experiments and device fabrication. Hydrothermal and solution-phase approaches to 1T′ WSe2 and related compounds expanded the toolkit further, yet crystal size and phase purity remained persistent limitations. With crystals hundreds of micrometers wide available in gram batches, experiments that were previously impractical, such as building van der Waals heterostructures from 1T′ layers, performing detailed transport measurements, or loading industrial-scale electrocatalyst electrodes, become routine possibilities.

The applications that stand to benefit span an impressive range. In electrocatalysis, the metallic character of 1T′-phase materials makes them natural candidates for the hydrogen evolution reaction, the cathodic half of water splitting that underpins green hydrogen production. Previous work by members of the same team demonstrated that the phase of the support material dramatically influences how platinum catalysts grow and perform on molybdenum disulfide, achieving highly efficient hydrogen evolution when the metal deposited on metallic-phase surfaces. In electronics, 1T′ phases offer low-resistance contacts to semiconducting 2H layers, a strategy known as phase engineering that has been used to build better transistors. In photonics and sensing, 1T′ monolayers stabilized on gold nanowires have enabled ultrasensitive surface-enhanced Raman scattering detection. And in condensed matter physics, the metallic 1T′ phases of certain dichalcogenides host superconductivity, making high-purity crystals essential for studying emergent quantum phenomena.

The protocol also reflects a maturing view of what its authors call phase engineering of nanomaterials, a discipline that treats crystal phase as a design parameter on par with composition and dimensionality. Over the past decade, reviews in Chemical Reviews and Nature Reviews Chemistry have charted the rapid growth of this field, cataloguing unconventional phases across two-dimensional materials and the synthetic strategies developed to access them. The salt-assisted approach described here joins other recent innovations, including photoredox phase transformation driven by light, as part of a growing arsenal for navigating the energy landscapes of metastable matter. By codifying the method into a reproducible, step-by-step protocol, the team has effectively lowered the barrier to entry for laboratories worldwide.

For the broader materials community, the message is one of cautious optimism. Metastable phases have long been viewed as fragile curiosities, accessible only to specialists with finely tuned equipment and generous patience. A protocol that transforms shelf-stable commercial powders into gram quantities of phase-pure 1T′ crystals using a standard tube furnace and inexpensive salts suggests that these materials are ready to move from the margins of feasibility into the mainstream of research practice. Whether the next breakthrough comes in hydrogen catalysis, quantum devices or entirely unforeseen directions, the raw ingredients are now, quite literally, available by the gram.

Subject of Research: Salt-assisted synthesis of high phase-purity metastable 1T′-phase group VIB transition metal dichalcogenide crystals

Article Title: Salt-assisted synthesis of high phase-purity metastable 1T′-phase group VIB transition metal dichalcogenides

Article References: Zhai, W., Shi, Z., Tao, R., Li, Z., Dong, D., Tang, J., Wang, W., Wang, L., Yang, H., Zhai, L., Ruan, X., Wu, Y., Wang, J., Yao, Y., Zhao, C., He, Q., Lai, Z., & Zhang, H. (2026). Salt-assisted synthesis of high phase-purity metastable 1T′-phase group VIB transition metal dichalcogenides. Nature Protocols. https://doi.org/10.1038/s41596-026-01429-8

Image Credits: AI Generated

DOI: 10.1038/s41596-026-01429-8

Keywords: transition metal dichalcogenides, 1T′ phase, phase engineering, salt-assisted synthesis, metastable materials, two-dimensional materials, hydrogen evolution, electrocatalysis, MoS2, WS2, crystal growth, Nature Protocols

The fundamental process behind the team’s research is rooted in the unique characteristics of diarylethene crystals. When these crystals are exposed to ultraviolet (UV) light, they not only change color but also undergo significant morphological transformations. These shape changes add complexity to the methodologies employed in their manipulation and control. What makes this research particularly fascinating is how the team, consisting of graduate student Mami Isobe, lecturer Daichi Kitagawa, and Professor Seiya Kobatake, utilized sublimation to pattern these crystals on a substrate.

Sublimation is a phase transition process where a solid transforms directly into vapor without passing through the liquid phase. In the context of this research, powdered diarylethene crystals were sublimated onto a substrate, allowing the researchers to control the orientation and position of these crystals with exceptional precision. This control extends to the creation of functional structures, including minute crystals formed on convex shapes, thereby demonstrating the potential for intricate designs that can respond to environmental stimuli.

The team successfully produced convex structures with dimensions in the range of several microns in height and several microns in width, designed in the shape of straight lines and numerals ranging from 0 to 20. This design showcases not only the versatility of the method but also emphasizes how tailored configurations can yield unique photomechanical responses. The ability to design structures of various shapes signifies a significant advancement in the domain of material science, where form can dictate function.

One of the key expectations from this research is the application of the crystal patterning method to other sectors, particularly semiconductor materials and pharmaceuticals. Organic compounds similar to diarylethene have found a significant footing in these domains, and the insights gained from this study may lead to enhanced functionalities and novel applications. Graduate student Mami Isobe commented on the anticipation surrounding this method, reflecting a broader excitement about the possibilities it holds for future material developments.

Professor Kobatake’s remarks highlight the ambition to expand upon this research further. He expressed a desire to analyze how different sizes and shapes of the convex structures influence crystal growth and orientation. This exploration aims to unveil quantitative explanations of the underlying principles driving crystal pattern formation. Such insights could unlock new methodologies for crystal engineering, which is pivotal in various scientific fields.

The publication of these findings in the journal Small Methods signifies their relevance in the scientific community. It adds to the ongoing discourse in material science, especially regarding the fundamental interactions between light and matter at the microstructural level. The ability to manipulate such systems opens a door to numerous possibilities in research that extends beyond the current scope.

Moreover, the study showcases the potential of pattern formation techniques, paving the way for advancements in organic electronics and optoelectronics. As the field moves forward, the interest in photomechanical materials is likely to grow, especially with the increasing integration of smart materials in technology. These materials can provide intelligent responses to environmental changes, thus enhancing functionality in multiple applications.

The implications of this research are far-reaching. By controlling the orientation of diarylethene crystals at such a fine scale, researchers are opening up possibilities for the next generation of responsive materials. Such advancements are crucial in developing systems that require specific responses to stimuli such as light, heat, or electric fields. The work done by the Osaka Metropolitan University team provides a springboard for future investigations into the fundamental properties of materials and their applications in technology.

This research also invites the attention of industries looking to innovate in smart material technologies. As companies seek to enhance the capabilities of their devices and systems, understanding how molecular orientation impacts performance will be essential. The findings demonstrated by the Osaka Metropolitan University team will undoubtedly inspire further research aimed at harnessing the properties of crystals engineered for specific applications.

The imperative now for scientists and researchers in this domain is to comprehend the principles unveiled through this study and adapt them to various practical scenarios. The exploration of new materials and methods will drive much of the future technological landscape, particularly as we seek to integrate more sophisticated functions into everyday devices. As industries prepare for the adoption of these materials, a wave of innovation is likely on the horizon, driven by the very principles of molecular science explored in this research.

In summary, the work conducted by Osaka Metropolitan University represents a significant milestone in the field of photomechanical materials. Combining precision in crystal manipulation with the fundamental properties of diarylethene offers transformative possibilities for future materials science applications. Researchers and industries alike will benefit from understanding and utilizing the techniques developed through this pioneering study.

Subject of Research: Photomechanical materials, specifically diarylethene crystals; crystal patterning methods.
Article Title: Patterning of Photochromic Diarylethene Crystals by Sublimation for Morphological Controls.
News Publication Date: 19-Jan-2025.
Web References: Osaka Metropolitan University.
References: DOI.
Image Credits: Credit: Osaka Metropolitan University.
Keywords: Diarylethene, photomechanical materials, crystal patterning, sublimation method, semiconductor, pharmaceuticals, molecular structure, organic compounds, crystal growth, shape control, responsive materials, material science.