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

At the heart of this breakthrough lies a carefully engineered metal oxide compound composed of strontium, iron, and cobalt, denoted as SrFe₀.₅Co₀.₅O₂.₅. The material’s architecture permits selective reduction and oxidation processes wherein cobalt ions undergo a reversible valence change, making it uniquely capable of oxygen uptake and release without compromising its crystal lattice. This sophisticated mechanism enables the crystal to mimic respiratory behavior—akin to inhaling and exhaling oxygen molecules on command. Such dynamic oxygen modulation is pivotal for solid oxide fuel cells and other energy systems, where controlled oxygen ion transport governs device efficiency and durability.

Professor Hyoungjeen Jeen of Pusan National University spearheaded the research initiative, bringing together a multidisciplinary team to dissect the fundamental chemistry and physics underpinning this material’s operation. Collaborating with Professor Hiromichi Ohta of Hokkaido University, the researchers employed advanced epitaxial growth techniques to fabricate the crystal with high precision, ensuring epitaxial quality crucial for elucidating the complex reductive and oxidative phenomena. Their findings, published in the esteemed journal Nature Communications (August 15, 2025), underscore a rare balance between chemical reactivity and structural resilience seldom observed in metal oxides.

This strontium-iron-cobalt oxide crystal leverages cobalt’s unique electronic configuration, which facilitates the selective reduction process. Unlike conventional oxygen storage materials that indiscriminately accommodate changes in metal oxidation states—often destabilizing the crystalline framework—this compound retains its periodic lattice by limiting redox activity to cobalt ions alone. This selectivity engenders a novel, stable phase post-reduction, heretofore unseen in similar perovskite-related oxides. The new crystal phase demonstrates robust reversibility, recovering its initial structure upon oxygen reinsertion, thereby validating its practical viability for cycling applications.

Oxygen mobility and exchange underpin many ecosphere technologies, from energy generation to environmental control. Solid oxide fuel cells (SOFCs), for instance, rely heavily on oxygen ion transport within ceramic layers to efficiently convert hydrogen fuel into electrical energy. The capacity of SrFe₀.₅Co₀.₅O₂.₅ to modulate oxygen content at moderate temperatures enhances fuel cell operation by reducing thermal strain and prolonging operational longevity. Moreover, the oxygen-breathing ability aligns closely with emerging concepts in thermal transistors—devices that modulate heat flow with unprecedented precision, analogous to electronic transistors controlling current.

Beyond energy, the smart material’s dynamic oxygen handling can revolutionize adaptive architecture and electronics. Smart windows that can adjust their thermal transmittance based on oxygen-induced phase transitions will optimize building energy consumption, reducing reliance on air conditioning and heating. Similarly, electronic components fabricated with these materials promise breakthroughs in stability and functionality by leveraging in-situ tunable oxygen stoichiometry. The reversible oxygen exchange presents a versatile platform for designing devices that respond in real time to environmental or operational stimuli.

Previous materials exhibiting oxygen storage or diffusion characteristics often suffered from structural degradation or required excessively high temperatures—sometimes exceeding 700°C—to activate oxygen exchange. These limitations hindered their scalability and practical application. In contrast, the newly reported SrFe₀.₅Co₀.₅O₂.₅ crystal operates robustly at considerably lower temperatures, maintaining its phase integrity even after numerous oxygen insertion and extraction cycles. This thermal threshold significantly streamlines the integration of these materials into existing technologies, facilitating reduced energy input and improved safety.

The research team employed state-of-the-art characterization techniques, including synchrotron X-ray diffraction and electron microscopy, to resolve the subtle phase transitions triggered by oxygen mobility. Their meticulous analysis showed that only cobalt ions undergo reduction from Co³⁺ to Co²⁺ during oxygen release, while iron and strontium ions remain chemically inert within the lattice. This selective reduction is critical for maintaining the host framework’s rigidity. Such insights not only elucidate the fundamental redox chemistry at play but also pave the way for targeted engineering of similar materials with customized oxygen exchange profiles.

Reversibility—a hallmark of any sustainable oxygen storage or operating system—is impressively demonstrated in this crystal. By cycling the material through controlled oxygen atmospheres, the researchers showed that it consistently regains its initial crystalline structure and oxygen content without performance degradation. This cycling endurance, unprecedented for materials operating at modest temperatures, heralds a new category of “oxygen lung” materials that could underpin autonomous and energy-efficient devices capable of adaptive self-regulation.

This development resonates broadly with the global push towards cleaner, smarter technologies. By controlling oxygen with precision and stability, devices based on this material could drastically reduce greenhouse gas emissions inherent in traditional energy harvesting methods. Additionally, its ability to accommodate reversible oxygen flux may inspire innovations in sensors, catalysis, and energy storage systems. The interdisciplinary nature of this discovery—intersecting physics, chemistry, and engineering—underscores the vitality of collaborative research for addressing complex global challenges.

Looking ahead, opportunities abound for tailoring this material’s properties via chemical doping, strain engineering, and nanoscale patterning to further optimize oxygen kinetics and thermal stability. Integrating such materials into prototype devices will test their efficacy beyond laboratory conditions and catalyze their translation from experimental novelty to commercial reality. The convergence of innovative crystal chemistry and device engineering promises to unlock new functionalities unattainable with conventional materials.

In summary, the SrFe₀.₅Co₀.₅O₂.₅ crystal embodies a pioneering step forward in the development of smart materials capable of reversible oxygen management under mild conditions. This advancement not only enriches the fundamental understanding of solid-state redox chemistry but also lays foundational groundwork for transformative applications in clean energy, electronics, and environmentally responsive infrastructure. As the world intensifies its energy transition efforts, materials with innate adaptability like this oxygen-breathing crystal will be indispensable allies in crafting sustainable technological landscapes.

Subject of Research:
Development of a reversible oxygen-breathing crystal material with potential applications in clean energy, electronics, and thermal management.

Article Title:
Selective reduction in epitaxial SrFe0.5Co0.5O2.5 and its reversibility.

News Publication Date:
15-Aug-2025

Web References:
https://doi.org/10.1038/s41467-025-62612-1

References:
Joonhyuk Lee, Hyoungjeen Jeen, et al. “Selective reduction in epitaxial SrFe0.5Co0.5O2.5 and its reversibility,” Nature Communications, August 15, 2025.

Image Credits:
Prof. Hyoungjeen Jeen, Pusan National University, Korea.

Keywords

Materials science, Crystallography, Chemistry, Physics, Nanotechnology, Engineering, Energy, Electrical engineering, Electrochemistry, Electronics

At the heart of this research lies the exploration of magnetoelectric compounds, materials where electric and magnetic properties intertwine intimately. This interplay paves the way to manipulate magnetic states without relying on traditional magnetic fields, which typically require significant energy input. Instead, the electrical control exemplified in these materials opens pathways toward drastically reduced power consumption in electronic components—an urgently needed breakthrough as data centers and AI computing platforms increasingly strain global energy resources.

The focal point of the experiment is an unusual crystalline substance called copper oxyselenide (Cu₂OSeO₃), characterized by its olive-green hue and unique magnetic properties at low temperatures. Within this material, atomic spins—essentially tiny magnetic moments attributable to electrons—organize into elaborate nanoscale patterns such as helices and cones. These magnetic textures extend far beyond the atomic lattice scale, permitting substantial adaptability since their configurations are not rigidly fixed to the underlying crystal symmetry.

Prior investigations have established the existence of such magnetic arrangements, but their controllability has been limited by the constraints imposed by external magnetic fields. PSI’s team, however, has achieved a landmark by applying a finely tuned electric field that alters the propagation direction of these magnetic textures, effectively steering them in a continuous and deterministic manner. This electric field-mediated steering transcends previous limitations by enabling a process termed magnetoelectric deflection, in which the magnetic spirals shift orientation without mechanical or magnetic intervention.

To visualize this delicate effect, the team harnessed the exceptional capabilities of the Swiss Spallation Neutron Source (SINQ), specifically employing the Small-Angle Neutron Scattering (SANS) technique on the SANS-I beamline. This method leverages streams of neutrons to map the spatial arrangement and directional propagation of magnetic structures at nanoscale resolution. The experiment was designed with a custom sample environment, allowing high electric fields to be applied in situ while probing magnetic configurations, revealing real-time responses of the magnetic textures under varying conditions.

Jonathan White, beamline scientist at PSI, emphasized the experimental ingenuity involved, noting that capturing magnetoelectric deflection demands the unparalleled resolution and flexibility afforded by SANS-I. The measurement’s sensitivity enabled the detection of minute adjustments in magnetic propagation vectors, a testament to how advanced instrumentation can unlock subtle, yet fundamentally transformative physical phenomena.

Delving deeper into the physics, the research unveiled that the response of the magnetic textures to electric fields is not monolithic but manifests in three distinctly separable regimes. At low electric field strengths, the textures exhibit a smooth, linear deflection, subtly reorienting in accordance with the applied field. With medium electric fields, the system enters a complex, nonlinear response domain, suggesting the interplay of competing energy terms and emergent interactions not captured by simplistic models. Most remarkably, high field strengths instigate abrupt 90-degree flips in the magnetic texture’s propagation direction, signaling a threshold-driven transition that could be harnessed for binary switching applications.

These findings hold profound technological implications. According to Sam Moody, a leading postdoctoral researcher and the study’s principal author, the ability to toggle between diverse response regimes through precise electric and magnetic field modulation could underpin next-generation device architectures. For example, hybrid devices leveraging these controllable magnetic trajectory flips might deliver ultra-fast, energy-efficient memory and sensor functionalities without the heat dissipation or complexity typical of current technologies.

Fundamental to the excitement surrounding this discovery is its promise to enable magnetism manipulation with unprecedented energy efficiency. Electric fields can be applied with minimal power overhead compared to magnetic fields, offering a sustainable alternative for information storage and magnetic logic operations. Such energy-conscious approaches are critical as the electronics industry confronts physical limits and environmental concerns associated with escalating data processing demands.

Additionally, the flexibility with which copper oxyselenide’s magnetic textures can be tuned introduces a versatile platform for exploring new physics and device paradigms. The observed nonlinear and threshold behaviors hint at rich underlying interactions guided by spin-orbit coupling, magnetoelectric coupling, and perhaps emergent multi-scale phenomena. These avenues open fertile ground for interdisciplinary research spanning condensed matter physics, materials engineering, and device science.

Importantly, the PSI team’s innovative combination of experimental design and high-precision neutron scattering paves the way for translating fundamental discoveries into real-world applications. By controlling magnetic spiral trajectories deterministically via electric fields, a class of low-power, high-speed nanomagnetic devices may soon be realized—devices aligned with global efforts to create greener, smarter computing infrastructure.

Beyond computing, the implications of such magnetoelectric control extend into energy conversion technologies and medical devices where finely tuned magnetic behavior at the nanoscale is essential. The magnetoelectric deflection technique could lead to enhanced sensors, actuators, and components that exploit magnetic responses optimized through electrical stimuli, radically expanding the scope of functional materials.

This seminal research symbolizes a crucial leap from observing exotic magnetic phenomena toward harnessing them in practical settings. As we witness escalating demands for energy efficiency and novel functionalities in electronic systems, magnetoelectric materials like copper oxyselenide exemplify the transformative potential residing in quantum materials and advanced experimentation techniques.

The work from PSI underscores how marrying cutting-edge neutron scattering science with creative engineering illuminates unseen realms of physics and nurtures technology innovations of tomorrow. These discoveries chart a compelling roadmap for sustained exploration and application of magnetoelectric effects in a variety of fields, heralding a new era of electrically controlled magnetism for precision and sustainability in technology.

Subject of Research: Not applicable
Article Title: Deterministic control of nanomagnetic spiral trajectories using an electric field
News Publication Date: 6-Jun-2025
Web References: 10.1038/s41467-025-60288-1
Image Credits: Paul Scherrer Institute / AI-assisted visualisation

Keywords

Magnetoelectric materials, electric field control, nanomagnetic spirals, copper oxyselenide, magnetoelectric deflection, small-angle neutron scattering, SANS-I beamline, Swiss Spallation Neutron Source, energy-efficient magnetism, spin textures, magnetic switching, advanced materials physics