Updated reference data and an analytic parameterisation of elastic electron and X-ray scattering are presented for all 118 neutral atoms. The reference electron densities for the multi-electron elements Z=2–118 are computed with the relativistic B-spline Dirac–Fock code atomx, while hydrogen is constructed from the exact relativistic one-electron Dirac 1s solution; the electron scattering factor f_e(g), X-ray scattering factor f_x(g) and radial moments are derived from these densities. The reported parameterisation extends the fixed-size Lobato–Van Dyck hydrogenic expansion while retaining closed-form expressions for f_x(g), ρ(r), the electrostatic potential V(r) and the projected potential V(R). These extensions are an element-adaptive basis size n_t(Z), a simultaneous real- and reciprocal-space fit, an exact ⟨ r^4⟩ constraint in place of the non-relativistic Kato cusp, and a charge-carrying Dirac–Padé basis term that adds a polynomial-times-exponential shape channel without replacing the hydrogenic basis by a tabulated Dirac radial function or assigning the term to a physical shell. For the same total parameter count, the Dirac–Padé-enriched basis improves on the parameter-matched non-relativistic basis for 111 of the 118 elements, lowering the mean total cost by 39%. Relative to a controlled fixed five-term refit on the same reference grid and objective, the element-adaptive bases improve the median reciprocal-space deviations by about three to four orders of magnitude and resolve shell structure in 4πr^2ρ(r) that the fixed five-term basis cannot. The largest changes occur near the nucleus and in the reciprocal-space tail beyond the legacy 12 inverse angstroms range, which is directly relevant to quantitative high-angle scattering and electron-diffraction measurements.

Twisting two atomic layers produces a geometric moire pattern, but bonding-induced interfacial reconstruction fundamentally transforms this into an ordered dislocation network - a distinction obscured in weakly-bonded van der Waals systems. Although in-plane topological vortex nanostructures arising from twisting-induced lateral strain modulation have been linked to periodic moire patterns in freestanding perovskite layers and 2D bilayers, their coupling to the interfacial dislocation network in twisted layers remains unresolved. Here we demonstrate that twisting freestanding SrTiO3 layers undergo interfacial reconstruction into a network of screw dislocations, accompanied by the emergence of in-plane topological vortices. Unlike in previous reports, these vortices are associated with the periodicity of the dislocation network rather than with geometric moire patterns. Four-dimensional scanning transmission electron microscopy (4D-STEM) reveals long-range ordered vortex-antivortex arrays with nearly continuous polarisation rotation. A machine-learning interatomic potential, trained on first-principles calculations, together with phase-field modelling, confirms that competing strains within the dislocation network stabilize polar vortex-antivortex pairs and drive the emergence of an electronic superlattice with a well-defined periodicity. Our results establish twist-controlled dislocation networks as a new and versatile route to designing local polar and electronic structures in oxide materials.

Colloidal cesium lead bromide (CsPbBr3) nanocrystals (NCs) are excellent candidates for various photonic and optoelectronic applications due to their bright and stable green emission. Here, we establish arm length control as a central structural parameter that governs both the optical properties of individual CsPbBr3 NCs and their self-assembly behavior. Armed NCs, featuring a cubic core with multiple protruding arms, are synthesized by controlling seed size, concentration, and injection temperature, while arm length is tuned via cesium oleate concentration. Prolonged storage in toluene is shown to lead to a time-dependent morphological evolution from armed NCs to 26-faceted rhombicuboctahedra, with short-armed structures as intermediates. NCs with a longer arm length yield enhanced radiative efficiency, extended photoluminescence (PL) lifetimes, and suppressed blinking, making such NCs suitable for light-emitting devices and quantum photonic applications. In contrast, short-armed NCs exhibit faster recombination, stronger PL intermittency, and increased surface accessibility, which are favorable for sensing and high-speed single-photon emission. The arm length also governs self-assembly behavior, hereby opening new possibilities for applications. Armed NCs form densely 3D-packed assemblies with tunable configurations. This work demonstrates how arm length tuning expands the functional potential of CsPbBr3 NCs by linking morphological control to both optical response and self-assembly characteristics.

Transition metal oxides exhibit a wide range of tunable electronic properties arising from the complex interplay of charge, spin, and lattice degrees of freedom, governed by their d orbital configurations, making them particularly interesting for oxide electronics and (electro)catalysis. Perovskite oxide heterointerfaces offer a promising route to engineer these orbital states. In this work, we tune the Co 3d orbital occupancy in LaCoO_3 from a partial d^7 to a partial d^5 state through interfacial engineering with LaTiO_3, LaMnO_3, LaAlO_3 and LaNiO_3. Using X-ray absorption spectroscopy combined with charge transfer multiplet calculations, we identify differences in the Co valence and spin state for the series of oxide heterostructures. LaTiO_3 and LaMnO_3 interfaces result in interfacial charge transfer towards LaCoO_3, resulting in a partial d^7 orbital occupancy, while a LaNiO_3 interface results in a partial Co d^5 occupancy. Strikingly, a LaAlO_3 spacer layer between LaNiO_3 and LaCoO_3 results in a Co d^6 low spin state. These results indicate that the Co spin state, like the valence state, is governed by the interfacial environment. High-resolution scanning transmission electron microscopy imaging reveals a clear connection between strain and spin configuration, emphasizing the importance of structural control at oxide interfaces. Overall, this work demonstrates that interfacial engineering simultaneously governs orbital occupancy and spin state in correlated oxides, advancing spin-engineering strategies in correlated oxides and offering new insights for the rational design of functional oxide heterostructures.

Halide exchange in lead‐based halide perovskites has been studied extensively. While mixed Cl/Br or Br/I alloy compositions can be formed with no miscibility gaps, this is precluded for mixed Cl/I compositions, due to the large difference in Cl − and I − ionic radii. Here, perovskite‐chalcohalide CsPbCl 3 –Pb 4 S 3 Cl 2 nanocrystal heterostructures are exploited to study the Cl→I exchange and to isolate new types of intermediate structures. The epitaxial interface between the Pb 4 S 3 Cl 2 chalcohalide and the CsPbCl 3 perovskite significantly influences the intermediate stages of halide exchange in the perovskite domain, leading to coexisting CsPbCl 3 and CsPbI 3 domains, thereby delivering segmented CsPbI 3 –CsPbCl 3 –Pb 4 S 3 Cl 2 , energetically favorable heterostructures, with partial I‐alloying of the CsPbCl 3 domain and at the perovskite–chalcohalide interface. The I:CsPbCl 3 domain between CsPbI 3 and Pb 4 S 3 Cl 2 enables a gradual lattice expansion across the heterostructure. This design accommodates interfacial strain, with a 5.6% mismatch at the CsPbCl 3 –CsPbI 3 interface and a 3.4% mismatch at the perovskite–chalcohalide interface. Full halide exchange leads to CsPbI 3 –Pb 4 S 3 Cl 2 heterostructures. Both in intermediate and fully exchanged heterostructures, the CsPbI 3 domain is emissive. In the intermediate structures, the band alignment between the two perovskite domains is type‐I, with the carriers photogenerated in the CsPbCl 3 domain quickly transferring to the CsPbI 3 domain, where they can recombine radiatively.

Local and high-resolution structural investigation of metal-organic frameworks (MOFs) is essential for understanding the role of defects and incorporated elements. In this paper, we characterize the structure of metalated versions of (Hf)PCN-222(H2) and locate the position of the additional metal atoms. Transmission electron microscopy (TEM) is a powerful technique for this purpose, but MOFs are highly sensitive to the electron beam. To avoid structural alterations, it is therefore crucial to establish the maximum electron dose that can be applied. In this study, we apply a systematic workflow to measure the critical electron dose, enabling the identification of the optimal technique for extracting reliable information about the local structure of MOFs. We examined the electron beam stability of benchmarked (Zr)NU-1000, (Hf)PCN-222(H2) and its metalated versions, (Hf)PCN-222(Fe) and (Hf)PCN-222(Pd), and identified factors influencing the stability under the electron beam. After the threshold for electron dose was established, we applied low-dose, four-dimensional scanning transmission electron microscopy (4D-STEM). We then compared annular bright field (ABF), annular dark field (ADF), and real-time integrated center of mass (riCOM) images that could be extracted from the 4D dataset. The riCOM technique successfully revealed the structure of investigated MOFs with minimal beam-induced alterations and provides insights into local features, including organic linkers and additional metalation elements.

Metal halide perovskites (MHPs) are emerging as promising materials for optoelectronic and photovoltaic applications due to their favorable electronic properties, including a tunable bandgap. However, achieving high stability for these materials remains a critical challenge, particularly for CsPbI3, whose photoactive phases spontaneously convert into a nonphotoactive yellow orthorhombic δ-phase under ambient conditions. This transformation results in a significant increase in bandgap and a loss of photoactive functionality. In this study, we investigate the impact of Zn2+ and Cd2+ dopants on the phase stability of CsPbI3 nanocrystals (NCs), emphasizing the formation of Ruddlesden-Popper (RP) planar defects, which are frequently observed during compositional tuning. Using transmission electron microscopy (TEM), we follow the temporal evolution of the phase transformation, where black-phase NCs agglomerate and form elongated microtubes with a yellow-phase crystal structure. Our observations demonstrate that doped samples are significantly more stable, while the dopants are key factors in the formation of the RP-like defects with specific atomic arrangements. Using a combination of quantitative TEM and molecular dynamics (MD) simulations we characterize the structure and composition of as-found RP-like defects and elucidate their role in stabilizing the photoactive phases of CsPbI3 through decreased phase transition kinetics.

Halide exchange in lead-based halide perovskites has been studied extensively. While mixed Cl/Br or Br/I alloy compositions can be formed with no miscibility gaps, this is precluded for mixed Cl/I compositions, due to the large difference in Cl- and I- ionic radii. Here, perovskite-chalcohalide CsPbCl3-Pb4S3Cl2 nanocrystal heterostructures are exploited to study the Cl→I exchange and to isolate new types of intermediate structures. The epitaxial interface between the Pb4S3Cl2 chalcohalide and the CsPbCl3 perovskite significantly influences the intermediate stages of halide exchange in the perovskite domain, leading to coexisting CsPbCl3 and CsPbI3 domains, thereby delivering segmented CsPbI3-CsPbCl3-Pb4S3Cl2, energetically favorable heterostructures, with partial I-alloying of the CsPbCl3 domain and at the perovskite-chalcohalide interface. The I:CsPbCl3 domain between CsPbI3 and Pb4S3Cl2 enables a gradual lattice expansion across the heterostructure. This design accommodates interfacial strain, with a 5.6% mismatch at the CsPbCl3-CsPbI3 interface and a 3.4% mismatch at the perovskite-chalcohalide interface. Full halide exchange leads to CsPbI3-Pb4S3Cl2 heterostructures. Both in intermediate and fully exchanged heterostructures, the CsPbI3 domain is emissive. In the intermediate structures, the band alignment between the two perovskite domains is type-I, with the carriers photogenerated in the CsPbCl3 domain quickly transferring to the CsPbI3 domain, where they can recombine radiatively.

Regioselective C─H bond functionalization is pivotal in modern scientific exploration, offering solutions for achieving novel synthetic methodologies and pharmaceutical development. In this aspect, achieving exceptional regioselective functionalization, like para-selective products in electron-poor aromatics, diverges from traditional methods. Leveraging the advantages of atomically dispersed photocatalysts, we designed a robust photocatalyst for an unconventional regioselective aromatic C─H bond functionalization. This innovation enabled para-selective trifluoromethylations of electron-deficient metadirecting aromatics (─NO2, ─CF3, ─CN, etc.), which is entirely orthogonal to the traditional approaches. Mechanistic experiments and DFT analysis confirmed the interaction between Cu-atom and the aromatic substrate, alongside the photocatalyst's molecular arrangement, driving selective exposure of the para-selective functionalization. This strategic approach elucidated pathways for precise molecular transformations, advancing the frontier of regioselective C─H bond functionalization by using atomically dispersed photocatalysts in organic synthesis.

Secondary electron (SE) imaging offers a powerful complementary capabilities to conventional scanning transmission electron microscopy (STEM) by providing surface-sensitive, pseudo-3D topographic information. However, contrast interpretation of such images remains empirical due to complex interactions of emitted SE with the magnetic field in the objective field of TEM. Here, we propose an analytical physical model that takes into account the physics of SE emission and interaction of the emitted SEs with magnetic field. This enables more reliable image interpretation and potentially lay the foundation for novel 3D surface reconstruction algorithms.

In this paper, a methodology is presented to count the number of atoms in heterogeneous nanoparticles based on the combination of multiple annular dark field scanning transmission electron microscopy (ADF STEM) images. The different non-overlapping annular detector collection regions are selected based on the principles of optimal statistical experiment design for the atom-counting problem. To count the number of atoms, the total intensities of scattered electrons for each atomic column, the so-called scattering cross-sections, are simultaneously compared with simulated library values for the different detector regions by minimising the squared differences. The performance of the method is evaluated for simulated Ni@Pt and Au@Ag core-shell nanoparticles. Our approach turns out to be a dose efficient alternative for the investigation of beam-sensitive heterogeneous materials as compared to the combination of ADF STEM and energy dispersive X-ray spectroscopy.

To understand the structure-property relationship of nanostructures, reliably quantifying parameters, such as the number of atoms along the projection direction, is important. Advanced statistical methodologies have made it possible to count the number of atoms for monotype crystalline nanoparticles from a single ADF STEM image. Recent developments enable one to simultaneously acquire multiple ADF STEM images. Here, we present an extended statistics-based method for atom counting from a combination of multiple statistically independent ADF STEM images reconstructed from non-overlapping annular detector collection regions which improves the accuracy and allows one to retrieve precise atom-counts, especially for images acquired with low electron doses and multiple element structures.

The Bayesian genetic algorithm (BGA) is a powerful tool to reconstruct the 3D structure of mono-atomic single-crystalline metallic nanoparticles imaged using annular dark field scanning transmission electron microscopy. The number of atoms in a projected atomic column in the image is used as input to obtain an accurate and atomically precise reconstruction of the nanoparticle, taking prior knowledge and the finite precision of atom counting into account. However, as the number of parameters required to describe a nanoparticle with atomic detail rises quickly with the size of the studied particle, the computational costs of the BGA rise to prohibitively expensive levels. In this study, we investigate these computational costs and propose methods and control parameters for efficient application of the algorithm to nanoparticles of at least up to 10 nm in size.

Metal halide perovskites (MHP) are highly promising semiconductors. In this study, we focus on FAPbBr3 nanocrystals, which are of great interest for green light-emitting diodes. Structural parameters significantly impact the properties of MHPs and are linked to phase instability, which hampers long-term applications. Clearly, there is a need for local and precise characterization techniques at the atomic scale, such as transmission electron microscopy. Because of the high electron beam sensitivity of MHPs, these investigations are extremely challenging. Here, we applied a low-dose method based on four-dimensional scanning transmission electron microscopy. We quantified the observed elongation of the projections of the Br atomic columns, suggesting an alternation in the position of the Br atoms perpendicular to the Pb-Br-Pb bonds. Together with molecular dynamics simulations, these results remarkably reveal local distortions in an on-average cubic structure. Additionally, this study provides an approach to prospectively investigating the fundamental degradation mechanisms of MHPs.