The researchers report TlFe1.6Se2, a layered material in which atomically thin FeSe sheets are periodically embedded inside a bulk host. The concept is to inherit the superior thermoelectric power factor associated with ultrathin FeSe while simultaneously suppressing heat flow in the surrounding crystal.

In their approach, the embedded FeSe layers coexist with ordered iron (Fe) vacancies. These vacancies act as built-in “phonon scatterers.” By disrupting local bonding and creating a complex lattice landscape, the vacancies strongly reduce the mobility of heat-carrying vibrations, lowering lattice thermal conductivity.

Electrical performance improves at the same time. The team finds that Seebeck coefficient values exceed 100 μV K−1 in the Fe-vacancy-ordered phase, delivering a thermoelectric power factor roughly five times larger than in the vacancy-disordered phase. The enhancement is linked to electronic structure changes induced by the vacancy ordering.

A key feature is a reversible temperature-driven transition near 180 °C, where the vacancy arrangement shifts from ordered to disordered. This dynamic behavior further strengthens phonon scattering and pushes thermal conductivity down to about 0.2 W m−1 K−1—at the level of, or lower than, leading thermoelectrics.

The results highlight a “low-dimensional functionality in bulk form” strategy: instead of building devices from films alone, the material embeds the benefits of two-dimensional physics inside a practical bulk crystal. Heavy thallium (Tl) atoms and the complex layered stacking additionally contribute by reducing phonon velocities and increasing scattering.

The publication also suggests broader applicability. Related alkali-intercalated FeSe systems containing potassium, rubidium, or cesium may offer tunable vacancy concentrations, providing a pathway to further optimize thermoelectric performance.

Overall, TlFe1.6Se2 demonstrates that power factor and thermal suppression can be engineered together through structural design—offering a viral, concept-forward blueprint for next-generation waste-heat converters.

Keywords
Thermoelectricity; FeSe; Vacancy ordering; Lattice thermal conductivity; Seebeck coefficient; Power factor; Layered crystals; Phonon scattering

Subject of Research: Not applicable
Article Title: Simultaneous enhancement of power factor and suppression of thermal conductivity in bulk TlFe1.6Se2 via embedded atomically thin FeSe layers
News Publication Date: 30-Apr-2026
Web References: https://pubs.rsc.org/ta/article/14/37/24666/1243050/Simultaneous-enhancement-of-power-factor-and
References: 10.1039/D6TA02075E
Image Credits: Institute of Science Tokyo

For decades, precise control of atoms has been predominantly confined to systems such as laser-cooled atoms in optical traps, ion traps, and scanning probe microscopy techniques. These modalities have enabled extraordinary insights and technological breakthroughs, especially in quantum information processing and the study of fundamental condensed matter phenomena. However, extending this atomic precision manipulation into the inherently complex and densely packed three-dimensional architecture of bulk solids has been a monumental challenge. The intricate interatomic interactions and dense lattice environment have historically obscured efforts to programmatically reposition single atoms within a crystal without inducing collateral damage.

The advancement reported here circumvents these long-standing obstacles by harnessing the power of a precisely controlled electron beam within a scanning transmission electron microscope (STEM) framework. This tool, long appreciated for its ability to visualize atomic structures, is now also exploited as a dynamic instrument capable of steering individual chromium (Cr) atoms embedded in a layered magnetic semiconductor, chromium sulfide bromide (CrSBr). Working on a spatial precision less than 20 picometers—more than one hundred times smaller than the width of an atom—the researchers successfully nudged Cr atoms from substitutional lattice sites into specific interstitial positions.

This controlled atomic translocation results in the formation of vacancy–interstitial defect complexes, which collectively assemble into a regular impurity lattice within the host crystal. Impressively, the team demonstrated the ability to orchestrate the creation of over 40,000 programmed defects spanning a volume of approximately 150 nm by 100 nm by 13 nm within minutes. Such a mesoscale defect superlattice is robust at ambient conditions and remains stable even after removal from the microscope environment, confirming the potential for practical applications well beyond controlled laboratory settings.

Beyond the engineering novelty, this mesoscale artificial lattice represents a new class of engineered quantum matter. The embedded impurity states within the crystal are predicted, through advanced quantum mechanical calculations, to exhibit rich interactions. These include not only localized optical transitions within individual defects but also kinetic coupling and Coulomb interactions spanning multiple impurities. Such correlated many-body states open expansive opportunities for quantum simulation of complex Hamiltonians, potentially allowing researchers to model phenomena previously inaccessible in conventional materials or cold atom setups.

Key to the predictive control achieved in this study was the comprehensive tracking of Cr atom displacements induced by electron beam interactions. By finely tuning beam parameters and scanning protocols, the occurrence of stochastic or damaging events was minimized. This enabled reproducible atomic repositioning with high fidelity—a crucial step toward scalable atomic manufacturing. The underlying atomic motion mechanisms were elucidated by a combination of in situ STEM imaging, statistical analysis of displacement trajectories, and first-principles calculations.

This remarkable control over individual atomic defects in a three-dimensional solid effectively bridges the gap between atomic-scale fabrication and mesoscopic engineering. Unlike prior demonstrations that either manipulated single atoms sporadically or only on surface layers, the presented methodology integrates atom-level precision with the scalability necessary for realistic device architectures. The technique’s compatibility with existing characterization platforms also suggests swift adoption within both applied and fundamental research environments.

Potential applications extend far beyond the realm of fundamental physics. Deterministic placement of defect centers with atomic precision in wide-bandgap semiconductors could revolutionize quantum photonics by enabling the scalable creation of single-photon emitters and spin qubits in deterministic arrays. The controlled engineering of impurity lattices may also underpin future generations of quantum simulators, capable of emulating strongly correlated electron systems or exotic quasiparticles. Furthermore, atomically precise doping and defect patterning can lead to unprecedented tuning of material properties such as magnetism, conductivity, and catalytic activity.

The implications for manufacturing are profound as well. Introducing an atom-by-atom manufacturing paradigm capable of manipulating thousands of atoms reproducibly within bulk crystals might unleash a new era of nanoelectronics, where devices are built from the ground up with atomic exactitude. This approach contrasts starkly with traditional lithography, which fundamentally operates on much larger scales and with less precision. In this context, the work offers a blueprint for “atomic-scale foundries,” integrating electronics, photonics, and quantum functionalities within engineered materials.

The foundation of this work lies in the nuanced understanding of electron beam–matter interactions. Historically, electron irradiation in microscopes was considered primarily destructive, causing unwanted atomic displacements and contamination. However, by tailoring beam energy and positioning at sub-angstrom scales, the researchers turned this challenge into an opportunity, transforming the electron beam from a passive probe into an active writing tool capable of deterministic defect engineering. This paradigm shift illustrates the evolving role of electron microscopy from characterization to fabrication.

Moreover, the chosen material system—CrSBr—exemplifies a magnetic van der Waals layered semiconductor with intrinsic order and electronic properties amenable to defect engineering. The magnetic nature of Cr dopant atoms, combined with the lattice’s structural anisotropy, offers a fertile platform to explore spin–orbit coupling, magneto-optical phenomena, and interactions between localized magnetic moments. Such control can pave the way toward integrated spintronic devices and quantum sensors with tunable properties defined atom-by-atom.

The scalability and robustness of the engineered defect arrays at room temperature further enhance their applicability. Many quantum phenomena require cryogenic environments that complicate practical deployment. Here, ambient stability ensures that engineered quantum states can persist in operational conditions, obviating the need for elaborate cooling systems and enabling integration into commercial technologies. This opens promising avenues for robust quantum networking and information storage architectures.

Given the microscopic precision, rapid engineering speed—realizing tens of thousands of atomic modifications within minutes—demonstrates the feasibility of practical industrial relevance. Automated beam steering combined with advanced image recognition algorithms could accelerate the development of complex defect architectures tailored to specific quantum or electronic functionalities, heralding an era of “precision defect photonics and electronics.”

In conclusion, this pioneering work establishes a versatile and generalizable platform for atomic-scale defect engineering in three-dimensional solids. By combining the spatial precision of electron beam manipulation with a deep understanding of beam–matter physics, researchers have unlocked a pathway toward engineered mesoscale quantum materials. The resulting artificial impurity lattices serve as a model system for exploring new quantum phases, while simultaneously providing a technological toolkit for next-generation device fabrication. With continued advancements, this approach may revolutionize both fundamental quantum science and its translation into practical technologies, driving the atomic-scale manufacturing revolution to new heights.

Article Title: Mesoscale atomic engineering in a crystal lattice

Article References:
Klein, J., Roccapriore, K.M., Weile, M. et al. Mesoscale atomic engineering in a crystal lattice. Nature (2026). https://doi.org/10.1038/s41586-026-10431-9

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10431-9

Nanocrystals are foundational to modern technology, embedded in devices that range from the processors in computers and smartphones to the vivid displays of TVs and mobile screens. These particles form the backbone of sensitive diagnostic tools such as gold-nanoparticle sensors that detect COVID-19 or confirm pregnancies. Furthermore, nanocrystals play a crucial role in catalytic converters within automobile exhaust systems, where their high reactivity helps mitigate environmental pollution. This exploitation of their catalytic prowess arises from their high surface area, which significantly accelerates chemical reactions without consuming the catalyst itself.

A groundbreaking leap in this domain comes from the work of Matteo Cargnello, an associate professor of chemical engineering at Stanford University’s School of Engineering, and his collaborators. Their research focuses on transcending the traditional single-metal nanocrystals, known for their well-studied properties, towards more intricate systems in which multiple metals coalesce within a single particle. The challenge here is staggering: to achieve uniformity and precise control over particle composition when combining five distinct metals into one nanocrystal — a feat that until now bordered on the impossible due to the vastly different chemical behaviors of each component.

The team selected ruthenium, a precious metal celebrated for its catalytic activity, as the foundational element. Ruthenium’s cost and scarcity drive the search for ways to reduce its usage without compromising functionality. To this end, the scientists introduced four additional metals—iron, cobalt, nickel, and copper—into the mix. Each of these metals is more abundant and inexpensive, but combining them into a homogeneous nanoparticle presented a formidable challenge. Disparate reduction kinetics and affinities promised a chaotic assembly with numerous heterogeneous products.

Contrary to widespread expectations that more complexity produces greater synthetic disorder, the researchers unveiled a paradoxical phenomenon. The inclusion of multiple metals, particularly when scaling up from two or three to five metals, actually enhanced the uniformity of the resulting nanocrystals. Rather than a mixture of inconsistent particles, a single, well-defined five-metal particle emerged with a remarkable consistency in both size and elemental composition. This discovery flips prior assumptions on their head and introduces unprecedented control in heterometallic nanocrystal synthesis.

Delving deeper, the team traced the synthesis mechanism to the pivotal role of copper. Among the base metals incorporated, copper displayed the highest nobility, meaning it reduces to its metallic state most readily under the reaction conditions. This early reduction allows copper to deposit first onto ruthenium seed particles. Intriguingly, copper and ruthenium do not blend homogeneously but instead form a heterodimer with distinct domains within a single nanoparticle. This side-by-side configuration effectively creates a scaffold for subsequent metal deposition rather than a random alloy.

The sequential orchestration of metal deposition follows the affinities and reduction kinetics of the individual elements. Cobalt and nickel, which prefer to interact with ruthenium and copper respectively, form intermediate shells enveloping the core. Iron, which reduces with much greater difficulty under the reaction conditions, arrives last to encapsulate the particle in an outer layer. This results in an onion-like architecture: ruthenium at the center, flanked by copper, then cobalt and nickel layers, and finally crowned by an iron-rich exterior. Such self-assembly exemplifies how elemental immiscibility can paradoxically give rise to ordered multi-metallic nanostructures.

The ramifications of this breakthrough extend beyond synthesis into practical catalytic performance. The team tested these five-metal nanocrystals for the decomposition of ammonia, a reaction with significant industrial and energy-related importance. Ammonia, widely produced as a fertilizer precursor, is gaining traction as a hydrogen storage medium due to hydrogen gas’s challenging storage and transportation requirements. Ammonia’s chemical decomposition at the delivery destination releases hydrogen and nitrogen, but this reaction typically requires extreme temperatures and robust catalysis.

Remarkably, the multimetallic nanocrystals exhibited catalytic activity four times higher than that of pure ruthenium under identical reaction conditions. Even more impressive was their stability: after enduring 12 hours at a searing 900°C, these catalysts maintained their structural integrity and performance, whereas single-metal ruthenium particles showed significant degradation. The five-metal structures resisted sintering, a common failure mode where particles agglomerate and lose surface area, thus preserving their activity and longevity under harsh conditions.

This work marks a critical advance toward industrially relevant catalysts optimized for hydrogen energy infrastructure and cleaner chemical processes. The German chemical company BASF, a co-funder and collaborator in the project, is currently assessing the catalysts under conditions that closely mimic real-world industrial operations. Their progression from laboratory curiosity to commercial viability could transform how catalysts are engineered for sustainable energy applications.

Professor Cargnello’s decade-long relationship with BASF exemplifies an encouraging paradigm in which fundamental discoveries at academic institutions translate effectively into largescale technologies. If the performance observed in controlled settings holds under practical scenarios, the implications for energy, environmental chemistry, and catalysis could be transformative. This collaboration underscores the importance of integrating scientific discovery with industry partnerships to accelerate innovation.

Beyond the immediate catalytic applications, the principles elucidated through this research provide a new blueprint for the design of complex nanomaterials. By understanding the interplay of chemical reactivity, elemental affinities, and reduction kinetics, researchers now have the tools to rationally assemble multi-element nanocrystals with unprecedented consistency and functionality. This methodology promises to broaden the horizon of tailored materials in nanotechnology, unlocking capabilities in fields ranging from electronics to medicine.

In a discipline where atomic-scale control over even a handful of elements is a formidable challenge, achieving robust and uniform five-metal nanocrystals signals a paradigm shift. It invites a reimagining of materials synthesis where complexity does not equate to disorder but instead fosters order and precision. These findings craft a new narrative for the future of nanomaterials, where interdisciplinary insights carve paths toward sustainable technologies.

Such advances cement the role of nanocrystals not just as passive materials but as active, meticulously engineered players in the quest to address global challenges. The nuanced dance between metals at the nanoscale illuminated by this research exemplifies how profound complexity can emerge from simplicity when guided by the principles of chemistry and physics.

Subject of Research: Multimetallic Nanocrystal Synthesis and Catalysis
Article Title: Competitive reactivity drives size- and composition-focusing in multimetallic nanocrystals
News Publication Date: 7-May-2026
Web References: Science DOI 10.1126/science.aea8044

Keywords

Nanocrystals, Catalysis, Chemical Engineering, Multimetallic Nanoparticles, Ruthenium, Ammonia Decomposition, Hydrogen Energy, Nanomaterials, Self-Assembly, Heterodimers, Industrial Catalysts, Surface Chemistry