The appeal of TMDs begins with their unusual structure. With the general formula MX2, where M is a transition metal such as molybdenum, tungsten, niobium, or tantalum and X is sulfur, selenium, or tellurium, each monolayer consists of a sheet of metal atoms sandwiched between two sheets of chalcogen atoms. Adjacent layers are held together only by weak van der Waals forces, which means bulk crystals can be peeled into single-atom-thick sheets. This architecture yields enormous surface-area-to-volume ratios, coordinatively unsaturated edge atoms with dangling bonds that serve as natural binding sites for reactive intermediates, and interlayer galleries that can host rapid ion transport. These are precisely the features that electrochemical energy devices demand.

Yet pristine TMDs carry intrinsic handicaps. The thermodynamically stable 2H phase is semiconducting, which limits charge transport; the basal plane is chemically inert and contributes little to catalysis; and narrow interlayer spacing slows ion intercalation. Exfoliated nanosheets also tend to restack during device fabrication, degrading stability and cycling performance. The review’s central message is that these limitations are not dealbreakers but design opportunities, addressable through a toolkit that includes defect engineering, heteroatom doping and alloying, strain engineering, atomic-scale modulation, nanostructure design, interlayer and phase control, and heterostructure fabrication.

Defect engineering has proven especially powerful. Sulfur vacancies in molybdenum disulfide create donor states within the band gap and expose undercoordinated metal atoms that bind hydrogen favorably. One highlighted study used high-throughput density functional theory calculations to identify the optimal vacancy configuration, then developed a hydrogen peroxide chemical etching method to distribute single sulfur vacancies uniformly across MoS2 nanosheets. The resulting catalyst achieved a hydrogen evolution overpotential of just 131 millivolts at 10 milliamperes per square centimeter, with a Tafel slope near 48 millivolts per decade and excellent stability. The authors caution, however, that defects cut both ways: they can also act as scattering centers and trap states that degrade carrier mobility, so passivation of harmful defects must accompany the deliberate introduction of useful ones.

Doping and alloying offer complementary control over electronic structure. When researchers doped MoS2 with zinc using a fusion heat method, X-ray photoelectron spectroscopy revealed binding energy shifts of roughly 0.47 and 0.40 electron volts for the Mo 3d and S 2p levels, indicating increased electron density that accelerates the hydrogen discharge step. Bimetallic strategies push further: cobalt-doped MoS2 works bifunctionally in both acidic and alkaline water splitting, while ruthenium doping wrapped in carbon nanotubes activates the otherwise inert 2H basal plane. Alloying enables continuous band gap tuning, with CVD-grown MoS2(1-x)Se2x films showing more than ten percent band gap modulation and quaternary alloys spanning 1.60 to 2.03 electron volts. Remarkably, doping can even trigger phase transitions, as rhenium concentrations above 40 percent stabilize the metallic 1T-prime phase of MoSe2.

Strain engineering adds another dimension. Because TMD monolayers can withstand more than 20 percent elastic distortion, mechanical deformation directly reshapes their band structure. Computational work predicted that only 0.3 to 3 percent uniaxial tensile strain converts 1H-MoTe2 into the quasi-metallic 1T-prime phase at room temperature, and experiments confirmed strain-induced band gap tuning in MoS2. The most striking results come from combining strain with vacancies: when sulfur vacancies in monolayer 2H-MoS2 were simultaneously strained, gap states shifted toward the Fermi level, yielding near-optimal hydrogen adsorption free energy. The combined system showed a Tafel slope of 60 millivolts per decade versus 98 for pristine MoS2, and the turnover frequency of its molybdenum atoms exceeded even that of conventional edge sites.

Phase engineering targets the most consequential lever of all. The metallic 1T phase of MoS2 conducts electricity roughly ten million times better than the semiconducting 2H phase and is hydrophilic, both critical for electrochemistry. Chemically exfoliated 1T-MoS2 reaches benchmark hydrogen evolution current densities at around 187 to 195 millivolts versus RHE, compared with more than 300 millivolts for the 2H phase, with Tafel slopes dropping from about 110 to the mid-40s. Because 1T is metastable and reverts to 2H near 92 degrees Celsius, researchers have developed stabilization tricks including sulfur intercalation, metal cation insertion, and palladium doping that partially converts the phase and slashes Tafel slopes from 157 to as low as 62 millivolts per decade.

Heterostructures and single-atom catalysts round out the toolkit. Coupling MoS2 with WTe2 creates a low Schottky barrier at the interface that shortens electron transport paths from micrometers to roughly 700 picometers, dramatically improving charge injection. Covalent 0D-2D hybrids of Co9S8 nanoparticles bonded to MoS2 through Co-S-Mo links render molybdenum sites electron-rich and activate the basal plane across all pH values. Meanwhile, isolated nickel atoms anchored on MoS2 nanofibers cut hydrogen evolution overpotentials from 263 to 161 millivolts, and nickel-oxygen sites engineered onto 1T-MoS2 achieved an onset potential near 0 volts with an overpotential of only 46 millivolts in alkaline media. In photocatalysis, single-layer 1T-MoS2 paired with nitrogen-doped graphene produced hydrogen roughly 600 times faster than comparable 2H systems under visible light.

Energy storage results are equally compelling. Vertically aligned metallic MoS2 on graphene delivered initial lithium-ion capacities near 1700 milliampere-hours per gram, while carbon-free metallic nanotube anodes retained the 1T phase for at least 120 days in air. For sodium-ion batteries, freestanding 1T-MoS2 grown on hollow graphene foam sustained stable capacities around 313 milliampere-hours per gram over 200 cycles. Supercapacitors built from restacked 1T-MoS2 films achieved volumetric capacitances of 400 to 650 farads per cubic centimeter, retaining over 93 percent of initial capacitance after 5000 cycles, and water-coupled metallic MoS2 with nanochannels reached 150 farads per gram even without conductive additives. The review concludes that scalable synthesis, long-term phase stability, and clear structure-property correlations remain the key hurdles, and it points to artificial intelligence-assisted materials discovery as the accelerant that could carry these engineered atomically thin catalysts from laboratory demonstrations to industrial deployment.

Subject of Research: Materials engineering strategies for tuning metallic two-dimensional transition metal dichalcogenides for energy conversion and storage

Article Title: Recent advances in tuning the properties of metallic 2D transition-metal dichalcogenides for energy conversion and storage

Article References: Ha, J., Park, G., Kang, G., Kang, J., Bak, H., Lee, D., Lee, H., Cho, K., & Kim, Y. (2026). Recent advances in tuning the properties of metallic 2D transition-metal dichalcogenides for energy conversion and storage. Advances in Industrial and Engineering Chemistry, 2(1), Article 5. https://doi.org/10.1007/s44405-026-00045-0

Image Credits: AI Generated

DOI: 10.1007/s44405-026-00045-0

Keywords: transition metal dichalcogenides, two-dimensional materials, hydrogen evolution reaction, phase engineering, defect engineering, heteroatom doping, strain engineering, heterostructures, lithium-ion batteries, supercapacitors, electrocatalysis, energy storage

Van der Waals forces—weak, non-covalent interactions that arise from transient electric dipoles—have traditionally been viewed as secondary to stronger chemical bonds in materials science. However, the latest research underscores their profound influence when employed strategically during epitaxial growth processes. Epitaxy, the method of depositing a crystalline film onto a crystalline substrate, conventionally requires the two materials to be chemically bonded, necessitating precise lattice matching. The innovation here is utilizing van der Waals forces instead, allowing the layers to maintain distinct orientations without chemical bonding, creating a new level of structural freedom.

The research team set their sights on the interface between tin selenide (SnSe), a ferroelectric semiconductor known for its promising electronic properties, and molybdenum disulfide (MoS₂), a two-dimensional transition metal dichalcogenide renowned for device integration compatibility. The pairing was deliberate; MoS₂’s nearly identical lattice structure to SnSe optimizes the van der Waals interaction strength, providing a comparative foundation against prior experiments involving substrates like graphene, where weaker interactions prevailed.

Their meticulous experimentation revealed that these van der Waals forces profoundly dictate three crucial aspects of the SnSe thin films: thickness, strain state, and domain architecture. Thickness, in this context, refers to the quantifiable number of atomic layers comprising the material. Strain state details how these atomic layers deform—whether stretched or compressed—under the influence of the substrate’s atomic lattice. Domain architecture pertains to spatial regions within the ferroelectric film exhibiting uniform polarization directions, essentially defining the functional electronic domains.

Each of these structural dimensions exerts a measurable impact on the electronic and ferroelectric behavior of the tin selenide thin films. By controlling the van der Waals forces at the heterointerface, the team effectively tuned the domain configurations and manipulated strain distributions — parameters integral to optimizing device performance, such as switching speeds and energy consumption.

A particularly remarkable finding was that employing a monolayer of MoS₂ as the substrate led to the growth of SnSe films with notably larger lateral dimensions compared to previous approaches, facilitating the production of high-quality films with fewer defects. This enhancement not only promises improved device reliability but also suggests the feasibility of scaling up production, a persistent challenge in materials engineering.

Dr. Yin Liu, a co-corresponding author and assistant professor at North Carolina State University, highlighted the novelty of the work: “The van der Waals force’s tunability allows us to overcome previous epitaxial limitations and tailor the ferroelectric thin films in ways previously unattainable. The structural freedom introduced by these forces means we can control properties at the atomic level without compromising crystalline quality.”

This research also challenges the long-standing paradigm that strong chemical bonding and rigid lattice matching are prerequisites for epitaxial growth, showing that van der Waals forces can offer an alternative yet effective mechanism to influence thin-film properties. It introduces a new design principle that could be exploited in diverse fields, from low-power electronics to quantum computing architectures, where precise material control is paramount.

Furthermore, the ability to modulate strain via van der Waals epitaxy could unlock unprecedented electronic functionalities. Strain engineering is known to influence band structures in semiconductors, and the team’s ability to control strain across nanoscopic dimensions opens doors to tailoring electronic bandgaps, carrier mobilities, and polarization behaviors with exceptional precision.

The interdisciplinary nature of this advancement, involving contributions from experts at institutions like University of Florida, Pennsylvania State University, Argonne National Laboratory, and Texas A&M University, underscores the collaborative effort required to push the frontiers of materials science. Their combined expertise enabled a comprehensive exploration of not only the material synthesis but also the nuanced structural-electronic interplays.

Underpinning this innovation is the application of cutting-edge experimental techniques capable of resolving atomic-scale interactions and domain structures within these epitaxial layers. This granular insight is essential for validating theoretical models and propelling practical applications.

Looking forward, the study prompts a reevaluation of substrate selection criteria in ferroelectric thin film deposition, elevating the role of van der Waals interactions as a decisive factor rather than a mere secondary consideration. It advocates for the exploration of other two-dimensional materials with tunable interaction strengths to customize thin-film properties further.

In summary, the demonstrated control over ferroelectric tin selenide films via van der Waals epitaxial interactions represents a paradigm shift in thin-film materials engineering. By unlocking tunable thickness, strain, and domain organization, this approach charts a promising route for next-generation electronics characterized by enhanced performance metrics and sustainable energy consumption.

As the electronics industry faces relentless demands for miniaturization and efficiency, such fundamental materials research offers critical avenues for achieving those goals. The demonstrated heteroepitaxial strategy not only expands the toolkit for materials scientists but also ignites new possibilities for device innovations that could redefine technological capabilities in the coming decades.

This pioneering work is published in the journal ACS Nano under the title “Heteroepitaxial control of thickness, strain, and domain architecture in few-layer ferroelectric tin monochalcogenides,” with lead contribution from Ph.D. student Yueyin Wang and senior guidance from co-corresponding authors Yin Liu and Honggyu Kim. The study received generous funding from the National Science Foundation, the Department of Energy, and the American Chemical Society Petroleum Research Fund.

Subject of Research: Ferroelectric thin films and van der Waals epitaxy in heterostructured materials

Article Title: Heteroepitaxial control of thickness, strain, and domain architecture in few-layer ferroelectric tin monochalcogenides

News Publication Date: 3-Jun-2026

Web References: 10.1021/acsnano.6c02795

References: ACS Nano, Volume on ferroelectric thin films and van der Waals epitaxy

Keywords: van der Waals forces, ferroelectric thin films, epitaxy, tin selenide, molybdenum disulfide, strain engineering, domain architecture, 2D materials, electronic devices, materials science, thin-film heterostructures, semiconductor technology