Chemistry of Materials最新文献

Atomic layer etching (ALE) enables atomic-scale removal of thin films through self-limiting reactions, and robust ALE processes for high-κ oxides are essential for semiconductor applications. Here, we report the ALE of HfO₂ and ZrO₂ using a novel NbF₅/TiCl₄ precursor combination. HfO₂ films retained structural quality after ALE, with minimal impurity incorporation and preservation of density, roughness, and refractive index. In contrast, ZrO₂ etched more rapidly but showed surface degradation and higher impurity levels. Density functional theory calculations support these findings by indicating that ZrO₂ more readily undergoes the ligand-exchange step, which is consistent with its faster etching. ALE was further applied to HfO₂ films in 3D nanohole structures, revealing crystallinity- and location-selective etching in complex geometries. These results highlight the importance of developing selective ALE processes for high-κ oxides, underscoring their potential for precise patterning and integration in advanced semiconductor manufacturing.

Ionic liquids (ILs) possess exceptional physicochemical properties, such as negligible vapor pressure, wide electrochemical stability windows, and tunable molecular architectures, making them attractive candidates for advanced electrolyte applications. These properties arise from intricate ionic correlations and variable ionicity between cations and anions, which govern thermal stability, electrical conductivity, and other key behaviors. In this work, we employ the neuroevolution potential (NEP) framework to develop machine learning-based force fields for a series of imidazole ILs with four distinct anions. The NEP models are rigorously validated against density functional theory (DFT) calculations, showing excellent agreement in energies and forces, and outperforming classical force fields in reproducing structural properties. Molecular dynamics simulations based on the NEP accurately predicted physical properties, including density, self-diffusion coefficients, and viscosity, in close agreement with experimental measurements. Importantly, the ML-driven NEP framework enables simulations of much larger system sizes and longer time scales than are feasible with DFT, while achieving significant speedups over classical force fields. Analysis of ionicity revealed values near 1/3, consistent with previous studies, and provided molecular-level insights into the interplay between ionicity and structural features. This study highlights the potential of machine learning-driven force fields for efficient, accurate, and scalable modeling of complex IL systems, providing practical guidance for designing IL-based electrolytes with tailored properties.

Amorphous calcium carbonate phases are common intermediates in multistep crystallization processes. In many cases, it was shown that these dense and liquid-like phases function as transient metastable precursors that transform into mature crystalline phases. However, some biological systems consist of inorganic condensates that serve only as ion carriers and dissolve prior to the formation of the mineral. In this work, we study the chemical conditions that regulate the release of calcium ions from polymer condensates toward the formation of calcium carbonate. It is shown that the presence of bicarbonate ions tunes the stability of biogenic and bioinspired polymer–Ca condensates. In specific conditions of the carbonate system, condensate dissolution is induced, affecting calcium carbonate supersaturation and crystallization kinetics. This behavior recapitulates observations on the roles of such condensates in vivo, suggesting that bicarbonate ions indirectly affect mineralization by turning inorganic condensates from mineral precursors into sacrificial ion pools.

The potential of hybrid improper ferroelectrics (HIFs) in electronic and spintronic devices hinges on their ability to switch polarization. Although the coupling between octahedral rotation and tilt is well established, the factors that govern switching barriers remain elusive. In this study, we explore this area to demonstrate the critical role of causal reasoning in uncovering the mechanisms to control the ferroelectric switching barrier in HIFs. By combining causal discovery, causal interventions, and first-principles simulations, we identify tolerance factor, A-site cation radii mismatch, epitaxial strain, and octahedral rotation/tilt as key parameters and quantify how their interplay directly influences switching barrier. Three key insights emerge from our work: (a) the analysis identifies the structural descriptors controlling polarization reversal across a broad family of A-site-layered double perovskites and superlattices, (b) it uncovers nontrivial, material-specific rotation-tilt mechanisms, including a counterintuitive cooperative pathway where both rotation and tilt change while lowering the barrier, an effect mostly inaccessible to conventional Landau or first-principles-based approaches and (c) it maps these material-specific mechanisms to experimentally realizable parameters, showing that epitaxial strain from orthorhombic substrates (e.g., NdScO₃, NdGaO₃) selectively tunes octahedral distortions to achieve barrier reduction across varied compositions. These results establish actionable, materials-by-design principles linking composition, structure, and strain to polarization switching, while highlighting the potential of causal reasoning to guide intelligent, mechanism-driven strategies for engineering complex functional oxides.

Ytterbium doped cesium lead halide materials exhibit a property known as quantum cutting which allows for greater than 100% photoluminescent quantum yields (PLQYs). The local atomic structure of the defects responsible for these properties and the effectiveness of the doping for producing the desired PLQYs is not readily discerned using techniques requiring long-range order. In this work we prepared 2.5, 5, 10, and 20% Yb³⁺ doped CsPbCl₃ powders using mechanosynthesis under distinct stoichiometric ratio conditions and characterized the defect incorporation and its effects on local atomic disorder using solid-state nuclear magnetic resonance (SSNMR) spectroscopy. We then correlate our observations to the observed PLQYs for each of the prepared samples. All samples prepared were found to be in an orthorhombic phase and no lattice shrinking was observed upon increased Yb³⁺ doping. An increase in doping concentrations was accompanied by a decrease in ¹³³Cs NMR spin–lattice relaxation times T₁ consistent with a paramagnetic relaxation enhancement effect induced by Yb³⁺ incorporation into the perovskite lattice. Through a comparison of synthesis methods, PLQY and NMR T₁ parameters we found that incorporated defects favorable for PLQY in mechanosynthesized samples are more likely to form in the presence of excess lead and excess chloride ions. The maximum PLQY values obtained for each set of samples correlated with T₁ parameters in the range of 13 to 35 s. In addition, we found that the observed PLQY in 5% doped samples was optimized after 1 to 2 h of interval grinding in stainless steel jars. Further grinding beyond 2 h led to a reduction in particle size below 1 μm as well as a reduction in PLQY and spin relaxation times.

The Lewis acidic etching route is an efficient method for preparing MXenes with tunable properties through redox reaction between Lewis acidic salts (such as CuCl₂ and CoCl₂) and the A-layer elements (such as Al, Ga, Sn, and Si) in the MAX phase. However, the etching pathways and phase transition are still lacking in-depth exploration. This work employs in situ time-resolved synchrotron radiation X-ray diffraction (SRXRD) to unveil the contrasted etching processes of Nb₂AlC in different molten salts. It is demonstrated that CuCl₂ etching leads to a transformation from Nb₂AlC to Nb₂CuC and ultimately yields Nb₂CT_x MXene; no intercalation of molten salts into the MXene interlayers is found in the process, while CoCl₂ drives Lewis acidic corrosion, resulting from Nb₂AlC to Nb₂CoC, subsequently decomposing into NbC. Similar NbC layers form during etching with FeCl₂/NiCl₂, indicating that the redox potential of molten salts alone cannot predict the final Lewis acidic etching outcomes. Therefore, two distinct Lewis acidic reactions, including MXene formation etching and carbide decomposition, are identified. This study provides fundamental insights into the selectivity of Lewis acidic reaction routes via in situ X-ray techniques, which is of great significance for the controllable synthesis and specific applications of MXenes.

The design of multimetallic catalysts is a promising strategy for advancing the catalytic synthesis of carbon nanotubes (CNTs). Various element combinations have been explored, and among them, molybdenum (Mo) has been widely studied as a cocatalyst. However, conventional catalyst preparation methods often lead to nonuniform metal distribution, making it difficult to determine the role of Mo. Layered double hydroxides (LDHs), which provide a uniform distribution of metal cations, offer a promising alternative for controlled catalyst design. In this study, cobalt–magnesium–aluminum (CoMgAl) LDHs with varying molecular Mo content were synthesized to investigate the role of Mo in CNT growth. Phase analysis of Mo revealed that Mo₂C forms beyond a specific Mo threshold, significantly enhancing CNT yield. Mo₂C acts as a carbon reservoir, stabilizing Co particles and preventing deactivation. CNT synthesis was further examined using iron (Fe) and Fe–Co LDH systems, confirming that the role of Mo₂C is independent of the active metal. The results demonstrate that Mo₂C formation is essential for optimizing CNT growth, providing a deeper mechanistic understanding of Mo’s catalytic function. This study highlights the advantages of Mo species-intercalated LDH catalysts for achieving high-yield CNT synthesis and offers insights into multimetallic catalyst design.

Melt-grown, highly crystalline CsPbBr₃ has been intensely investigated as a semiconductor for direct hard radiation detection. While the phase purity and crystallinity of the CsPbBr₃ ingots are assessed by X-ray diffraction and optical microscopy, the overall quality of the material is ultimately judged by the performance of the final device. The iterative evaluation of crystal quality would greatly benefit from broadening readily accessible structural methods. In this work, we establish nuclear quadrupole resonance (NQR) spectroscopy as a versatile, noninvasive technique for evaluating the quality of melt-grown CsPbBr₃ ingots. We show that in addition to its inherent utility for probing the local environment around a quadrupolar nucleus, NQR spectroscopy is highly sensitive to crystal orientation and crystallinity, as further supported by ab initio calculations. The key spectroscopic descriptors (linewidth and integrals) can thus be correlated with both macroscopic and microscopic structural features, thereby establishing a robust and rapid method for evaluating crystal quality. Customized resonators can accommodate large ingots and enable measurements directly in the quartz ampule used for melt growth, as well as semiautomated spatial mapping of spectroscopic features across the ingots. For instance, we show that removing the impurities collected near the top of the ingot and subsequent recrystallization improve the homogeneity and overall crystallinity of the samples, highlighting the need for multiple purification steps. We also observe that different crystallographic orientations of crystal domains along the ingot are obtained and preserved in cut crystal disks. These findings pave the way for integrating NQR spectroscopy as a practical, noninvasive tool for in-line or in-situ crystal quality control and guided sample selection.

The NaFeNb(PO₄)₃, NFNP, material has been designed as a candidate anode material for sodium-ion batteries, as in its pristine form it combines the presence of Fe(III) and Nb(V)─available for possible reduction upon Na insertion─allowing for the formal introduction of 3 Na ions at reasonable potentials, and the robust NASICON structure with open channels for Na migration. The NFNP material has been successfully obtained by the solid-state route and fully characterized in terms of structure and transport properties by means of diffraction, XAS, and DFT analysis. Although promising, the electrochemical testing reveals that the initially satisfactory results in terms of capacity and Coulombic efficiencies fade upon cycling. The in-depth operando investigation, with the implementation of in situ XRD and XAS, unveiled a phase transition upon cycling; this involves the formation and accumulation of a low-symmetry secondary phase delivering lower capacity related to the Nb redox couples.