The silicon-hydrogen system is of key interest for solar-cell devices, including both crystalline and amorphous modifications. Elemental amorphous Si is now well understood, but the atomic-scale effects of hydrogenating the silicon matrix remain to be fully explored. Here, we present a machine-learned interatomic potential model based on the atomic cluster expansion (ACE) framework that can describe a wide range of Si-H phases, from crystalline and amorphous bulk structures to surfaces and molecules. We perform numerical and physical validation across a range of hydrogen concentrations and compare our results to experimental findings. Our work constitutes an advancement toward the exploration of large structural models of $a$-Si:H at realistic device scales.

This work presents a systematic study of the pressure evolution of the electronic structure of ZrSiS using bulk magnetotransport measurements under hydrostatic pressure and first-principles calculations. Magnetoresistance measured at four pressure points (0.25, 0.47, 1.55, and 2.10 GPa) exhibits clear Shubnikov-de Haas oscillations characterized by five dominant frequencies, $F_{\alpha }=17$, $F_{\beta }=37$, $F_{\gamma }=93$, $F_{\delta }=138$, and $F_{\epsilon }=242\mathrm{T}$, which remain nearly unchanged with increasing pressure. To probe the pressure evolution of the electronic states, the Berry phase $\left({\mathrm{\Phi }}_{\mathrm{B}}\right)$ was extracted from Landau level fan diagram analyses. The extracted ${\mathrm{\Phi }}_{\mathrm{B}}$ values for the $\alpha$ and $\epsilon$ orbits show a systematic evolution with pressure, changing from values close to $\pi$ at low pressure toward values approaching zero above $\sim 0.47$ GPa, suggesting a possible change in the electronic topology near this pressure. To further examine the evolution of the band topology, we calculated the topological invariants calculations. The results suggest nontrivial states at low pressures and a tendency toward trivial states at higher pressures, consistent with the experimentally observed evolution of the Berry phase. To further investigate the underlying electronic structure, first-principles calculations were performed up to 16 GPa. The calculated band structures reveal multiple Dirac crossings near the Fermi level derived primarily from Zr $d$ and S $p$ orbitals, which remain robust under pressure. Phonon dispersion calculations show no imaginary modes up to 16 GPa, confirming the dynamical stability of ZrSiS under hydrostatic compression. The combined experimental and theoretical results indicate that pressure modifies the electronic states without a pronounced reconstruction of the Fermi surface, highlighting the role of subtle changes in the electronic structure. These findings provide insight into pressure-driven electronic evolution in nodal-line semimetals and related quantum materials.

The electrochemical instability of Sn-based halide perovskites in aqueous media is commonly linked to surface electron accumulation and defect-assisted oxidation of ${\mathrm{Sn}}^{2+}$ to ${\mathrm{Sn}}^{4+}$. Here, we examine how interfacial coupling in a cesium tin chloride (${\mathrm{CsSnCl}}_3)$-molybdenum disulfide $\left({\mathrm{MoS}}_2\right)$ (CSC–MS, 10%) composite electrode influences charge distribution and electrochemical behavior. Electrochemical and spectroscopic measurements indicate trends consistent with effective electronic redistribution at the interface between $n$-type ${\mathrm{CsSnCl}}_3$ and $p$-type 2H-${\mathrm{MoS}}_2$, suggestive of a type-II–like alignment. Mott-Schottky analysis yields an apparent flat-band offset on the order of several hundred millivolts, which reflects an effective interfacial capacitance response rather than a uniquely defined junction potential in the heterogeneous composite electrode. Correlated trends in x-ray photoelectron spectroscopy, impedance spectroscopy, and kinetic analyses support reduced near-surface electron density in ${\mathrm{CsSnCl}}_3$ and an enhanced pseudocapacitive response. In addition, ${\mathrm{MoS}}_2$ contributes hydrophobic basal planes and electronically active edge states that cooperatively improve interfacial stability, electronic percolation, and charge transport. As a result, the composite exhibits a kinetically extended aqueous operating window approaching 2.3 V under scan conditions and mixed charge-storage behavior in which reversible ${\mathrm{Sn}}^{2+}/{\mathrm{Sn}}^{4+}$ redox processes are contributory but not exclusive. These results provide a physically consistent, though not uniquely resolved, picture of how interfacial coupling and composite engineering can enhance the aqueous pseudocapacitive performance of lead-free halide perovskite electrodes.

Hydrogen isotope transport in plasma-facing components is a critical issue for nuclear fusion devices, as it directly affects fuel retention, permeation, and material integrity. In ITER-like divertor designs, tungsten monoblocks are bonded to copper-based heat sinks, forming W/Cu interfaces that play a key role in hydrogen migration from the plasma-facing surface toward the coolant. At the atomic scale, such interfacial regions present additional challenges, as interstitial diffusion is inherently more complex than in bulk materials due to asymmetries in the energy landscape and modified atomic coordination. This asymmetry restricts the development of macroscopic kinetic models, as it requires considering a large number of flux balance equations. Consequently, metallic interfaces are often assumed to be in local thermodynamic equilibrium, ensuring chemical potential continuity. These assumptions, widely employed in macroscopic rate equations codes, are examined in this study. A methodology is proposed to reduce the number of equations needed for flux balance across metallic interfaces, eliminating the necessity of assuming local thermodynamic equilibrium or chemical potential continuity while enabling implementation in reaction diffusion codes. Given its relevance for nuclear fusion devices, we apply the approach to hydrogen diffusion at the tungsten/copper interface as a case study. The resulting reduced kinetic model accurately reproduces both the time to reach steady-state conditions and the hydrogen concentration profile.

The unique optoelectronic properties of organic semiconductors make them attractive candidates for functional electronic devices. Organic molecules exhibiting singlet fission—a process in which a photoexcited singlet exciton converts into two triplet excitons—hold particular promise for enhancing the efficiency of organic optoelectronic devices. Once generated, triplet excitons decay either through triplet-triplet annihilation (TTA) or interaction with trap states. Identifying these decay pathways is essential for understanding and controlling the performance of organic semiconductors. Modulated photocurrent (MPC) spectroscopy is a useful technique for extracting information about various parameters of the trap states of inorganic and organic semiconductors. Recently, it was shown that in organic semiconductors the MPC is highly sensitive to exciton-trap interactions, where excitons dissociate into mobile holes. Here, using this approach, we present a new spectroscopic method based on MPC for extracting both the triplet exciton density and the density of traps involved in their dissociation in two-terminal organic devices: rubrene single crystals and pentacene thin films. Furthermore, we show that the characteristic dependence of triplet exciton density on the light generation rate enables the separation of different decay pathways. Our results reveal that triplet exciton decay is dominated by TTA in rubrene crystals, while in pentacene films it primarily proceeds via triplet-trap interactions.

The structural and scintillation properties of pure and Ce-doped ${\mathrm{Y}}_3{\mathrm{Sc}}_x{\mathrm{Al}}_{5-x}{\mathrm{O}}_{12}$ $(x=0, 0.05, 1.16, \text{and} 2)$ crystals were systematically investigated. High-resolution ${}^{45}\mathrm{Sc}$ and ${}^{27}\mathrm{Al}$ magic angle spinning nuclear magnetic resonance spectroscopy revealed that $\mathrm{S}{\mathrm{c}}^{3+}$ ions predominantly occupy octahedral sites, effectively replacing $\mathrm{A}{\mathrm{l}}^{3+}$ ions, while antisite Sc at Y dodecahedral positions remains below 0.2 at.%. Sc incorporation into ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ induces strong exciton emission at 320–324 nm, nearly 10 times higher than that of reference ${\mathrm{Bi}}_4{\mathrm{Ge}}_3{\mathrm{O}}_{12}$ (BGO) crystal, even at low Sc concentrations (5 at.%). $\mathrm{C}{\mathrm{e}}^{3+}$ doping introduces characteristic $5d^1\to 4f$ emission at 518 nm, accelerates scintillation decay, and in combination with $\mathrm{M}{\mathrm{g}}^{2+}$ codoping, promotes the formation of $\mathrm{C}{\mathrm{e}}^{4+}$ ions that enable a fast radiative de-excitation pathway. ${\mathrm{Y}}_3{\mathrm{Sc}}_2{\mathrm{Al}}_3{\mathrm{O}}_{12}$: Ce exhibits a maximum scintillation light yield of 80–84% relative to BGO with a mean decay time of 85–110 ns. Thermostimulated liminescence and electron paramagnetic resonance studies indicate that holes are mainly trapped at oxygen ions near Sc ions (${\mathrm{O}}^{-}$ centers), while electrons are primarily localized at Sc antisite ions near oxygen vacancies ($\mathrm{S}{\mathrm{c}}^{2+}\text{–}{\mathrm{V}}_{\mathrm{O}}$ centers), affecting scintillation kinetics. Density functional theory calculations confirm that $\mathrm{S}{\mathrm{c}}^{3+}$ at the dodecahedral site forms a deep electron trap. These results highlight the key role of Sc and Ce in tuning emission, decay dynamics, and defect-mediated processes in Sc-admixed multicomponent garnet scintillators.

Cation self-diffusion plays a key role in the microstructure evolution of a wide range of materials, including oxide nuclear fuels. Growing evidence indicates that small defect clusters can make a substantial contribution to cation transport in these oxides. Quantifying this contribution is nevertheless challenging because of complex defect chemistry, strong correlations between cation and anion migration, and the existence of multiple competing migration mechanisms. In this work, we compute bulk cation self-diffusion coefficients in stoichiometric ${\mathrm{UO}}_2$ and ${\mathrm{PuO}}_2$ by explicitly accounting for small vacancy clusters (cation–anion divacancies and Schottky defects) in addition to isolated cation vacancies. Our approach combines a systematic exploration of cluster migration pathways using ART-nouveau with the calculation of cluster transport coefficients through the KineCluE code, which rigorously incorporates the influence of local atomic environments and kinetic correlations on defect migration. These transport coefficients are then coupled with equilibrium cluster concentrations to obtain self-diffusion coefficients directly comparable with experimental data. We find that small vacancy clusters are significantly more mobile than isolated cation vacancies and dominate the overall diffusion process. In ${\mathrm{UO}}_2$, the resulting self-diffusion coefficients are consistent with the most reliable experimental datasets, whereas in ${\mathrm{PuO}}_2$ the predictions are discussed in light of the limited data currently available. Although vacancy clusters exhibit higher mobility in ${\mathrm{PuO}}_2$, the overall self-diffusion coefficient is lower than in ${\mathrm{UO}}_2$ because of the larger cation vacancy formation energy predicted by our defect model. Beyond actinide oxides, this work demonstrates how defect clusters can be systematically integrated into diffusion calculations and provides transferable insights and input data for fuel behavior models.

It is known that cuprate artificial high-$T_C$ superlattices (AHTS) with period $d$, composed of quantum wells confining interface space charge in stoichiometric Mott insulator layers ($S$), with thickness $L$, at the interface with overdoped normal metallic cuprate layers ($N$) show a superconducting dome by tuning the geometric $L$ over $d$ ratio of the SNSN superlattice with the top predicted by quantum material design engineering quantum size effects. Here we report high-field magnetotransport measurements up to 41 Tesla of AHTS across the entire superconducting dome. The results show the universal upward-concave behavior of the temperature-dependent upper critical magnetic field in low-$T_C$ samples at the rising edge and drop edge of the dome, providing strong evidence consistent with two-band superconductivity in agreement with multigap theory used for quantum design of the SNSN superlattices. The measured superconducting coherence length demonstrates that atomic-scale engineering controls not only the critical temperature but also the intrinsic pair size at Fano-Feshbach resonances physics paving the way toward next-generation quantum devices and shedding light on unconventional superconductivity.

Single-atom catalysts (SACs) hold great promise for CO-selective NO reduction (CO-SCR) due to their maximal metal atom utilization and the tunable adsorption of reactants and intermediates. However, optimizing SACs remains a major challenge because it requires a delicate balance of adsorption strengths, which are governed by complex atomic-scale interactions. Here, we combine first-principles calculations with interpretable AI to systematically investigate over 200 transition metal (TM)-doped metal oxides for CO-SCR using a hierarchical learning workflow, which delivers both higher training accuracy and better predictive performance than the conventional nonhierarchical approach. Through thermodynamic screening, we significantly reduce the candidate pool to 20 promising SACs and ultimately identify Mn-doped $\mathrm{Zr}{\mathrm{O}}_2\left(111\right)$ as the most effective catalyst based on both thermodynamic and kinetic criteria. While no single catalyst feature shows a direct correlation with activity, our hierarchical learning approach uncovers nonlinear combinations of features, such as $d$-band center, atomic radius, and charge state, that reliably predict performance. In addition, subgroup discovery data mining reveals physically meaningful strategies for optimizing catalytic properties. This work demonstrates the value of integrating first-principles theory with hierarchical learning to accelerate the discovery of efficient catalysts for environmentally important reactions.

Rhombohedral-stacked transition metal dichalcogenides (TMDs) break inversion symmetry between adjacent layers, giving rise to an intrinsic out-of-plane ferroelectric polarization. Controlling the formation of this stacking polytype is therefore essential for harnessing ferroelectric effects in two-dimensional materials. In this work, we demonstrate the epitaxial growth of rhombohedral bilayer tungsten diselenide (3R-${\mathrm{WSe}}_2$) on a cubic W(110) single crystal by molecular beam epitaxy. We show that selenium passivation of the substrate is key to enable a quasi-van der Waals epitaxy, effectively suppressing strong interfacial bonding and promoting the growth of quasi free-standing bilayer films. The 3R stacking order is confirmed through a combination of Raman spectroscopy and high-resolution angle-resolved photoemission spectroscopy (ARPES), supported by density functional theory (DFT) calculations. ARPES and DFT reveals an indirect-gap electronic structure with the valence-band maximum at the Γ point, as well as a pronounced spin-orbit-driven splitting of $520\pm 20$ meV at the K point. Analysis of the measured dispersions yields hole effective masses of $0.46\pm 0.04m_e$ and $0.75\pm 0.06m_e$ for the upper and lower valence bands at K point, respectively. These results establish a robust route for synthesizing quasi-free-standing 3R-${\mathrm{WSe}}_2$ and provide a platform for exploring the electronic, optical, and ferroelectric functionalities that emerge from inversion-symmetry breaking in layered TMDs. Our findings further highlight the potential of cubic substrates for deterministic fabrication of rhombohedral TMD heterostructures and ferroelectric devices at the nanoscale.

We explore the molecular beam epitaxy synthesis of superconducting aluminum thin films grown on c-plane sapphire substrates at cryogenic temperatures of 6 K and compare their behavior with films synthesized at room temperature. We demonstrate that cryogenic growth increases structural disorder, producing crystalline grains that modify the optical, electrical, and superconducting properties of aluminum. We observe that cryogenic deposition changes the color of aluminum from fully reflective to yellow and correlate the pseudodielectric function and reflectance with structural changes in the film. We find that smaller grain sizes enhance the superconductivity of aluminum, increasing its critical temperature and critical field. We then estimate the superconducting gap and coherence length of Cooper pairs in aluminum in the presence of disorder. Finally, we fabricate superconducting microwave resonators on these films and find that, independently of the growth temperature, the system is dominated by two-level system loss with similar quality factors in the high- and low-power regimes. We further measure a higher kinetic inductance in the cryogenically grown films.

Atomic volume differences determine the structure and phase stability of alloys. To assess the size mismatch, atomic volumes of pure elements, derived from their elemental crystalline states, are normally used as a reference. Using ab initio calculations, we show that substitutional transition metal solute atoms in bcc iron or tungsten exhibit sizes substantially different from their elemental volumes. Analysis of electronic structure suggests that the significant oversizing of substitutional solutes in bcc $\alpha$-iron is caused by the asymmetric filling of electronic states of solute atoms. This produces a strong local magnetovolume effect where, for example, the apparent sizes of platinum and palladium solute atoms are from 35% to 40% larger than their elemental volumes. The analysis of nonlocal variation of electronic structure in the neighborhood of a solute atom shows that in bcc tungsten, the atoms near a substitutional $3d$ transition metal solute atom shrink, whereas in bcc iron, atoms next to a substitutional site swell, further increasing the apparent relaxation volume of the solute atom. Constrained magnetic DFT calculations show that manganese, iron, and cobalt solute impurity atoms in tungsten retain their magnetic moments, with collinear spin-flip barriers of 0.20, 0.52, and 0.17 eV, respectively. In other instances, elements like Cr in $\alpha$-Fe are nominally undersized if the elemental volumes are compared, but in a solute form the relaxation volume of Cr is positive ($+20$% of its atomic volume), stemming from the electron transfer effect and variation of the effective volume of neighboring host Fe atoms. Simulations suggest that application of strong magnetic field might also affect the relaxation volume of transition metal solutes and their solubility.

When two-dimensional atomic layers of different materials are brought into close proximity to form van der Waals (vdW) heterostructures, interlayer interactions can strongly influence their physicochemical properties. These effects are particularly pronounced when the interface exhibits local order and near-perfect structural alignment, giving rise to moiré patterns. Using density-functional theory calculations, we investigate a bilayer heterostructure composed of hexagonal boron nitride (hBN) and silicon carbide (SiC). We predict that introducing a boron vacancy, $V_{\mathrm{B}}$, at specific lattice sites alters the interlayer interaction from weak vdW coupling to localized silicon-nitrogen covalent bonding. Motivated by this mechanism, we examine the binding of transition-metal adatoms and identify principles for enhancing surface reactivity and stabilizing isolated single-metal atoms. Machine-learning molecular dynamics at finite temperature further demonstrate rapid and effectively irreversible trapping of Cu at $V_{\mathrm{B}}$ sites, and show how the $V_{\mathrm{B}}$:Cu ratio governs the transition from single-atom isolation to vacancy-directed aggregation. These results suggest the hBN/SiC heterostructure as a versatile platform for atomically precise transition-metal functionalization, with implications for catalytic energy-conversion materials.

We present a comprehensive optical characterization of 200-nm-thick CrN(111) films grown simultaneously on ${\mathrm{Al}}_2{\mathrm{O}}_3\left(0001\right)$ and $\mathrm{AlN}\text{/}{\mathrm{Al}}_2{\mathrm{O}}_3\left(0001\right)$ using plasma-assisted molecular beam epitaxy. Spectroscopic ellipsometry, spanning the far-infrared to ultraviolet range ($0.04–5.5\mathrm{eV}$), is conducted at room temperature to determine the optical constants $n$ and $k$ of the films. Spectral fits reveal two interband transitions at approximately 0.35 and 0.60 eV. In the infrared range, the ellipsometry data also reveal a pronounced Reststrahlen band stemming from transversal and longitudinal optical phonons at approximately 403 and $629{\mathrm{cm}}^{-1}$, respectively. The relative static and high-frequency permittivities are estimated to be about 39 and 15, respectively. A Born effective charge of approximately 2.7, extracted from the far-infrared region, indicates that CrN is partially ionic.

The search for room-temperature ferromagnetic two-dimensional materials is crucial for the development of future functional spintronic devices. In this study, combining a global minimum search method of the free energy surfaces by the CALYPSO software, we have predicted a two-dimensional cobalt structure. First-principles calculations demonstrate that the structure is a stable ferromagnetic metal exhibiting in-plane magnetic anisotropy, with an estimated Curie temperature of 1001 K significantly exceeding room temperature. Furthermore, the structure shows remarkable resistance to external strain, maintaining its ferromagnetic ground state and excellent stability under biaxial strains ranging from −4% to 5%. These findings indicate that the structure holds promising application prospects in spintronic devices.