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Physics Condensed Matter Materials Science

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Sunday 2 November

Materials Science · Cross-listed from physics.bio-ph

New avenues for characterizing individual mineralized collagen fibrils with transmission electron microscopy

Tatiana Kochetkova, Stephanie M. Ribet, Lilian M. Vogl et al. (+5 more)

Bone serves as a remarkable example of nature's architectured material with its unique blend of strength and toughness, all at a lightweight design. Given the hierarchical nature of these materials, it is essential to understand the governing mechanisms and organization of its constituents across length scales for bio-inspired structural design. Despite recent advances in transmission electron miscoscopy (TEM) that have allowed us to witness the fascinating arrangement of bone at micro-down to the nano-scale, we are still missing the details about the structural organization and mechanical properties of the main building blocks of bone – mineralized collagen fibrils (MCFs). Here, we propose a novel approach for extracting individual MCFs from nature's model material via a dropcasting procedure. By isolating the MCFs onto TEM-compatible substrates, we visualized the arrangement of organic and mineral phases within the individual MCFs at the nanoscale. Using a 4D-STEM approach, the orientation of individual mineral crystals within the MCFs was examined. Furthermore, we conducted first-of-its-kind in situ tensile experiments, revealing exceptional tensile strains of at least 8%, demonstrating the intricate relationship between structural organization and the mechanical behavior of MCFs. The capabilities of TEM allow us to resolve MCF organization and composition down to the nanoscale level. This new knowledge of the ultrastructure of the bone-building blocks and the proposed sample extraction and in situ mechanical testing opens up new avenues for research into nature's inspired material design.
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All authors Tatiana Kochetkova, Stephanie M. Ribet, Lilian M. Vogl, Daniele Casari, Rohan Dhall, Philippe K. Zysset, Andrew M. Minor, Peter Schweizer

Materials Science

Gate Dielectric Engineering with an Ultrathin Silicon-oxide Interfacial Dipole Layer for Low-Leakage Oxide-Semiconductor Memories

Fabia F. Athena, Jonathan Hartanto, Matthias Passlack et al. (+11 more)

We demonstrate a gate dielectric engineering approach leveraging an ultrathin, atomic layer deposited (ALD) silicon oxide interfacial layer (SiL) between the amorphous oxide semiconductor (AOS) channel and the high-k gate dielectric. SiL positively shifts the threshold voltage (V$_T$) of AOS transistors, providing at least four distinct $V_T$ levels with a maximum increase of 500 mV. It achieves stable $V_T$ control without significantly degrading critical device parameters such as mobility, on-state current, all while keeping the process temperature below 225 $^{\circ}$C and requiring no additional heat treatment to activate the dipole. Positive-bias temperature instability tests at 85 $^{\circ}$C indicate a significant reduction in negative $V_{T}$ shifts for SiL-integrated devices, highlighting enhanced reliability. Incorporating this SiL gate stack into two-transistor gain-cell (GC) memory maintains a more stable storage node voltage ($V_{SN}$) (reduces $V_{SN}$ drop by 67%), by limiting unwanted charge losses. SiL-engineered GCs also reach retention times up to 10,000 s at room temperature and reduce standby leakage current by three orders of magnitude relative to baseline device, substantially lowering refresh energy consumption.
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All authors Fabia F. Athena, Jonathan Hartanto, Matthias Passlack, Jack C. Evans, Jimmy Qin, Didem Dede, Koustav Jana, Shuhan Liu, Tara Peña, Eric Pop, Greg Pitner, Iuliana P. Radu, Paul C. McIntyre, H.-S. Philip Wong

Materials Science

Characterising Atomic-Scale Surface Disorder on 2D Materials Using Neutral Atoms

Chenyang Zhao, Sam M. Lambrick, Ke Wang et al. (+5 more)

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2, have the potential to be widely used in electronic devices and sensors due to their high carrier mobility and tunable band structure. In 2D TMD devices, surface and interface cleanness can critically impact the performance and reproducibility. Even sample surfaces prepared under ultra-high vacuum (UHV) can be contaminated, causing disorder. On such samples, trace levels of submonolayer contamination remain largely overlooked, and conventional surface characterisation techniques have limited capability in detecting such adsorbates. Here, we apply scanning helium microscopy (SHeM), a non-destructive and ultra-sensitive technique, to investigate the surface cleanness of 2D MoS2. Our measurements reveal that even minute amounts of adventitious carbon induce atomic-scale disorder across MoS2 surfaces, leading to the disappearance of helium diffraction. By tracking helium reflectivity over time, we quantify the decay of surface order across different microscopic regions and find that flat areas are more susceptible to contamination than regions near edges. These findings highlight the fragility of surface order in 2D materials, even under UHV, and establish SHeM as a powerful tool for non-damaging microscopic 2D material cleanness characterisation. The approach offers a new route to wafer-scale characterisation of 2D material quality.
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All authors Chenyang Zhao, Sam M. Lambrick, Ke Wang, Shaoliang Guan, Aleksandar Radic, David J. Ward, Andrew P. Jardine, Boyao Liu

Materials Science

A CN complex as an alternative to the T center in Si

J. K. Nangoi, M. E. Turiansky and C. G. Van de Walle

We present a first-principles study of a carbon-nitrogen (CN) impurity complex in silicon as an isoelectronic alternative to the T center [(CCH)$_\mathrm{Si}$]. The latter has been pursued for applications in quantum information science, yet its sensitivity to the presence of hydrogen is still problematic. Our proposed complex has no hydrogen, thereby eliminating this issue. First, we show that the CN complex is stable against decomposition into substitutional and interstitial defects. Next, we show that due to being isoelectronic to the T center, the CN complex has a similar electronic structure, and therefore could be used in similar applications. We assess several low-energy configurations of the CN complex, finding (CN)$_\mathrm{Si}$ to be stable and have the largest Debye-Waller factor. We predict a zero-phonon line (ZPL) of 828 meV (in the telecom S-band) and a radiative lifetime of 4.2 $\mu$s, comparable to the T center. Due to the presence of a bound exciton, choice of the exchange-correlation functional and also supercell-size scaling of the ZPL and transition dipole moment require special scrutiny; we rigorously justify our extrapolation schemes that allow computing values in the dilute limit.
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Materials Science · Cross-listed from physics.med-ph

Magnetic Materials for Transcranial Magnetic Stimulation (TMS)

Max Koehler, Akshata Sangle and Stefan M. Goetz

Various coils for transcranial magnetic stimulation (TMS) are widely available for clinical and research use. These coils are almost all designed as air coils, which require large levels of energy to achieve a given magnetic flux density and in turn electric field strength, whereas in other sectors, such as power electronics or electrical machines, magnetic materials have been used for a long time to achieve higher efficiencies. We tested the impact on the electric and magnetic properties of different soft magnetic materials, including various ferrite cores, laminated sheet materials of nonisotropic corn-oriented silicon-steel, non-oriented silicon-steel, as well as cobalt-iron, and soft magnetic compound powder cores with insulated particles. Every material led to a reduction in coil current and voltage for the same target electric field strength. For the same field energy, every material yielded lower losses. Most common materials saturated already at very low currents. More material in thicker layers could shift the saturation point but at the cost of high weight. Due to their low saturation flux density, ferrites appear unsuitable for the high amplitude requirements of TMS. Laminated sheet materials and powder cores reduce the pulse energy, but the laminated sheet material adds more weight for the same effect than powder cores. Thus, appropriate magnetic materials can reduce the required pulse energy. Saturation flux density is the most relevant parameter, whereas the permeability beyond a certain base level is practically irrelevant. Most importantly, the weight of a magnetic-core coil may always be increased compared to an air coil for the same target field.
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Saturday 1 November

Materials Science · Cross-listed from cond-mat.soft

Influence of carbon nanocone structure on ultra-efficient water flow

Bruno H. S. Mendonça, Elizane E. de Moraes, João P. K. Abal et al. (+3 more)

In this study, using nonequilibrium molecular dynamics simulation, the water flow in carbon nanocones is studied using the TIP4P/2005 rigid water model. The results demonstrate a nonuniform dependence of the flow on the cone apex angle and the diameter of the opening where the flow is established, leading to a significant increase in the flow in some cases. The effects of cone diameter and pressure gradient are investigated to explain flow behavior with different system structures. We observed that some cones can optimize the water flow precisely. Nanocones with a larger opening facilitate the sliding of water, significantly increasing the flow, thus being promising membranes for technological use in water impurity separation processes. Nanocones with narrower opening angles limited water mobility due to excessive confinement. This phenomenon is linked to the ability of water to form a larger hydrogen-bond network in typical systems with diameters of this size, obtaining a single-layer water structure. Nanocones act as selective nanofilters capable of allowing water molecules to pass through while blocking salts and impurities. The conical shape of their structures creates a directed flow that improves separation efficiency. Membranes based on carbon nanocones are becoming promising for clean, smart, and efficient technologies. The combination of transport speed, selectivity, and structural control put them ahead of other nanostructures for various purposes.
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All authors Bruno H. S. Mendonça, Elizane E. de Moraes, João P. K. Abal, João V. L. Valle, Tássylla O. Fonseca, Hélio Chacham

Materials Science

Nuclear spin-free 70Ge/28Si70Ge quantum well heterostructures grown on industrial SiGe-buffered wafers

P. Daoust, N. Rotaru, D. Biswas et al. (+9 more)

The coherence of hole spin qubits in germanium planar heterostructures is limited by the hyperfine coupling to the nuclear spin bath due to 29Si and 73Ge isotopes. Thus, removing these nuclear spin-full isotopes is essential to extend the hyperfine-limited coherence times needed to implement robust quantum processors. This work demonstrates the epitaxial growth of device-grade nuclear spin-free 70Ge/28Si70Ge heterostructures on industrial SiGe buffers while minimizing the amounts of highly purified 70GeH4 and 28SiH4 used. The obtained 70Ge/28Si70Ge heterostructures exhibit a dislocation density of 5.3 x 10e6 cm-2 and an isotopic purity exceeding 99.99%, with carbon and oxygen impurities below the detection sensitivity, as revealed by atom probe tomography. Magnetotransport measurements on gated Hall bars demonstrate effective gate control of hole density in nuclear spin-free quantum wells. Negative threshold gate voltages confirm the absence of intentional doping in the wells, while Hall and Shubnikov-de Haas analyses yield consistent carrier densities (1.4 x 10e11 cm-2) and high mobilities (2.4 x 10e5 cm2/Vs). Mobility trends reveal interfacetrap- limited scattering and percolation concentration below 7 x 10e10 cm-2. These analyses, along with atomic-level studies, confirm the high quality of epitaxial 70Ge/28Si70Ge heterostructures and their relevance as a platform for long-coherence spin qubits.
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All authors P. Daoust, N. Rotaru, D. Biswas, S. Koelling, E. Rahier, A. Dubé-Valade, P. Del Vecchio, M. S. Edwards, M. Tanvir, E. Sajadi, J. Salfi, O. Moutanabbir

Materials Science · Cross-listed from physics.chem-ph

Delta-learned force fields for nonbonded interactions: Addressing the strength mismatch between covalent-nonbonded interaction for global models

Leonardo Cázares-Trejo, Marco Loreto-Silva and Huziel E. Sauceda

Noncovalent interactions–vdW dispersion, hydrogen/halogen bonding, ion-$\pi$, and $\pi$-stacking–govern structure, dynamics, and emergent phenomena in materials and molecular systems, yet accurately learning them alongside covalent forces remains a core challenge for machine-learned force fields (MLFFs). This challenge is acute for global models that use Coulomb-matrix (CM) descriptors compared under Euclidean/Frobenius metrics in multifragment settings. We show that the mismatch between predominantly covalent force labels and the CM's overrepresentation of intermolecular features biases single-model training and degrades force-field fidelity. To address this, we introduce \textit{$\Delta$-sGDML}, a scale-aware formulation within the sGDML framework that explicitly decouples intra- and intermolecular physics by training fragment-specific models alongside a dedicated binding model, then composing them at inference. Across benzene dimers, host-guest complexes (C$_{60}$@buckycatcher, NO$_3^-$@i-corona[6]arene), benzene-water, and benzene-Na$^+$, \mbox{$\Delta$-sGDML} delivers consistent gains over a single global model, with fragment-resolved force-error reductions up to 75%, without loss of energy accuracy. Furthermore, molecular-dynamics simulations further confirm that the $\Delta$-model yields a reliable force field for C$_{60}$@buckycatcher, producing stable trajectories across a wide range of temperatures (10-400~K), unlike the single global model, which loses stability above $\sim$200~K. The method offers a practical route to homogenize per-fragment errors and recover reliable noncovalent physics in global MLFFs.
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Materials Science

The stability and topological behaviors in lanthanide antiperovskite nitrides: a high-throughput study

Shuxiang Zhou, Kevin Vallejo and Krzysztof Gofryk

Antiperovskite (APV) nitrides exhibit a diverse range of electronic properties, including superconductivity, magnetic effects, and nontrivial topological behaviors. In this study, we propose a new family of APV nitrides by incorporating 4$f$-electron metals, known for strong electron correlations, localized magnetic moments, and spin-orbit coupling, to further explore the unique properties of APVs. A high-throughput density functional theory (DFT) calculation was utilized to identify stable lanthanide APV nitride compounds. To address the challenge of strong electron correlation, we developed a double-screening framework that assumes either a fully itinerant or localized nature of the $f$-electrons during calculations. Using this approach, we systematically identified 37 stable lanthanide APV nitride compounds from both thermodynamic and dynamical perspectives. Furthermore, we report nontrivial topological behaviors observed among these stable lanthanide APV nitride compounds, as computed by DFT. Notably, Dirac and semi-Dirac cones are observed near the Fermi level for Er$_3$TlN. This study opens a pathway to investigate lanthanide APVs, revealing potential novel physical properties by leveraging the rich physics of both APVs and $f$-electrons.
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Materials Science

Ferroelectricity-driven altermagnetism in two-dimensional van der Waals multiferroics

Bo Zhao, Fu Li, Wei Ren et al. (+2 more)

Altermagnets (AMs) are a recently identified class of unconventional collinear compensated antiferromagnets that exhibit momentum-dependent spin splitting despite having zero net magnetization. This unconventional magnetic order gives rise to a range of phenomena, including the anomalous Hall effect, chiral magnons, and nonlinear photocurrents. Here, using spin space group (SSG) symmetry analysis and first-principles calculations, we demonstrate an efficient strategy to control altermagnetism in two-dimensional multiferroics through ferroelectric polarization and interlayer sliding. For material realization, we find that monolayer and bilayer FeCuP2S6 exhibit finite spin splitting when ferroelectric sublattices are connected by nonsymmorphic screw-axis operations rather than pure translation or inversion symmetry. Interlayer sliding further enables reversible switching or suppression of spin splitting through modifications of the SSG. Our calculations further reveal that the anomalous Hall response serves as a direct probe of these spin-split states. These findings establish two-dimensional van der Waals multiferroics as promising platforms for realizing electrically controllable altermagnetism and advancing next-generation spintronic and magnetoelectric technologies.
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All authors Bo Zhao, Fu Li, Wei Ren, Hao Wang, Hongbin Zhang

Materials Science · Cross-listed from cond-mat.mes-hall

Tuning the Electronic Structure of Graphene by Controlling Spatial Confinement

Mohammadamir Bazrafshan and Thomas. D. Kühne

The electronic properties of a material depend on the spatial freedom of the electron wavefunction. A well-known example is graphite, which is a conventional gapless semiconductor, while a single layer of it, graphene, exhibits extremely high electronic conductivity. Nevertheless, graphene ribbons can have different physical properties, such as a tunable band gap, ranging from gapless to a large band gap semiconductor. The purpose of this study is to investigate the electronic structure of few-layer graphene composed of a layer of graphene nanoribbons and graphene sheet(s), where quasi-one-dimensional nanoribbons can interact with a two-dimensional sheet of graphite. Using the tight-binding model for graphite, we show how different configurations of such heterostructures can affect the electronic structure, which is different from that of their components. Our results show that systems composed of semiconducting AGNRs can not be seen as two separate systems. Namely, a local gap of ~0.6 eV at the Dirac point for dispersive bands can be opened in a bilayer configuration composed of a layer of gapless armchair nanoribbon stacked on graphene. We demonstrate that the band steepness in these structures can be tuned, highlighting their potential for electronic applications.
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Materials Science

Crystalline and glassy tellurides of silicon

Dmytro Bletskan

This monograph presents the results of experimental and theoretical studies of binary and ternary crystalline and glassy silicon tellurides. It provides a detailed description of the methods for synthesizing and growing bulk and nanostructured binary crystals of Si2Te3, SiTe2, and ternary crystals known in the M-Si-Te systems (M = Na, K, Cu, Ag, Al, In), as well as sodium-silicon and tellurium-silicon clathrates. Significant attention is paid to the results of investigations into their electronic structure, optical, electrical, photoelectric, and photoluminescent properties.The publication is intended for researchers and specialists in the fields of semiconductor materials science, physics, and semiconductor technology, as well as lecturers, postgraduate students, and students of relevant specialties.
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Materials Science

Compatibilities and supercompatibility conditions in shape memory alloys determined from correspondence, metrics and symmetries

Cyril Cayron

The phenomenological theory of martensite crystallography (PTMC) developed in the 1950s explains the main crystallographic and microstructural features of martensite in shape memory alloys, such as the habit planes of bi-variant laminate martensite product, and the transformation twins between the variants. It also permits to determine the austenite and martensite lattice parameters that allow supercompatibility, which has driven important research and development of new shape memory alloys with low hysteresis and high cyclability. Supercompatibility takes the form of three mathematical equations called cofactor conditions. The calculations are in great part based mathematical tools from continuum mechanics (polar decompositions and stretch tensors). They were recently replaced by pure crystallographic tools (metric tensors, group of symmetries and correspondence) in an alternative approach called correspondence theory (CT). The CT allows for the direct calculation of the transformation twins and their generic and non-generic characteristics. These twins ensure the compatibility at martensite/martensite (M/M) junction planes. Here, we show that the CT can also be used to determine the conditions of austenite/martensite (A/M) compatibility, and A/M/M supercompatibility.
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Materials Science

Altermagnetism and Anomalous Transport in Ag$^{2+}$ Fluorides: KAgF$_3$ and K$_2$AgF$_4$

Xiao Nan Chen, Sining Zhang, Zhengxuan Wang et al. (+2 more)

Compounds containing Ag$^{2+}$ ion with 4d$^9$ configuration will cause significant Jahn-Teller distortions and orbital ordering. Such orbital order is closely related to the magnetic coupling, according to Goodenough-Kanamori Ruels. Our first-principles calculations reveal that the ground state of KAgF$_3$ exhibits collinear A-type antiferromagnetic (A-AFM) ordering accompanied by C-type orbital ordering. In contrast, K$_2$AgF$_4$ adopts a collinear intralayer antiferromagnetic configuration coupled with ferromagnetic orbital ordering. The A-AFM KAgF$_3$ presents distinct altermagnetic responses, including: (i) prominent anomalous transport effects, such as anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and thermal anomalous Hall conductivity (TAHC); and (ii) strong magneto-optical responses, manifested through pronounced Kerr and Faraday effects. On the other hand, K$_2$AgF$_4$ behaves as a conventional collinear antiferromagnet preserving $\mathcal{PT}$ symmetry, hence precluding the emergence of an anomalous Hall response.
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All authors Xiao Nan Chen, Sining Zhang, Zhengxuan Wang, Minping Zhang, Guangtao Wang

Materials Science

Applicability of Electrical Conductivity Ratio Method to Complicated Band Structure and the Carrier Scattering Mechanisms of SnSe

Pan Ren, Junling Gao, Guiying Xu et al. (+7 more)

The electrical conductivity ratio (ECR) method can be used to analyze carrier scattering mechanism (CSM) without the need of magenetic transport measurements. In this work, the applicability of the ECR method in the analysis of complex energy band structures is discussed. Combined with the thermoelectric properties of SnSe, the feasibility using ECR method of ideal single band transport model to study the CSM of semiconductor materials with complicated band structure is studied. The results indicate that ECR method is not only applicable to idea band structure as reported before but also to the complicated band structure. The analysis results of the CSM of single crystal SnSe by ECR method using ideal single-band model agree with the carrier mobility temperature dependence in the nonphase transition temperature range. The CSM along three direction of single crystal SnSe are different because of its anisotropic crystal structure. The difference between dislocation scattering (DS) and charged impurity scattering (CIS) is that DS is always accompanied by polar optical phonon scattering (POP), such as the CSM of SnSe along b axis direction. The difference between CIS and DS can be more easily distinguished by the ECR method than the carrier mobility temperature dependent method. DS and POP might be one of the approaches to improve thermoelectric property because the scattering factor for DS or POP is larger than that of acoustic phonon scattering (APS) and alloy scattering (AS). For polycrystalline SnSe, the carrier scattering mechanisms varies with the crystal structure and the temperature. This indicates that the ECR method can better reflect the variation of carrier scattering mechanisms with temperature compared to the carrier mobility temperature dependence method.
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All authors Pan Ren, Junling Gao, Guiying Xu, Bohang Nan, Tao Guo, Quanxin Yang, Fanchen Meng, Myles McKenna, Jian He, Sitong Niu

Materials Science

Atomic-Scale Roughness of Freestanding Oxide Membranes Revealed by Electron Ptychography

Huaicheng Yuan, Yu-Chen Liu, Li-Shu Wang et al. (+3 more)

Freestanding oxide films offer significant potential for integrating exotic quantum functionalities with semiconductor technologies. However, their performance is critically limited by surface roughness and interfacial imperfection caused by dangling bonds, which disrupt coherent interactions and suppress quantum phenomena at heterointerfaces. To address the challenge of structural characterization of surfaces and interfaces, we develop a metrological approach achieving atomic-scale precision in mapping the topography of both free surfaces and buried interfaces within ultrathin oxide heterostructures leveraging three-dimensional structures reconstructed from multislice electron ptychography. This method also allows for counting the number of atoms, even including light elements such as oxygen, along the electron trajectory in electron microscopy, leading to the identification of surface termination in oxide films. The planar-view of measurement geometry, allowing for large field-of-view imaging, provides remarkably rich information and high statistics about the atomic-scale structural inhomogeneities in freestanding membranes. This quantitative analysis provides unprecedented capabilities for correlating structural imperfection with quantum device performance, offering critical insights for engineering robust heterointerfaces in next-generation oxide electronics.
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All authors Huaicheng Yuan, Yu-Chen Liu, Li-Shu Wang, Zehao Dong, Jan-Chi Yang, Zhen Chen

Materials Science

Alternative treatment of relativistic effects in linear augmented plane wave (LAPW) method: application to Ac, Th, ThO2 and UO2

A. V. Nikolaev, U. N. Kurelchuk and E. V. Tkalya

We examine the influence of the relativistic effects within the linear augmented plane wave method (LAPW) for solids and propose a few alternative ways to accurately take them into account: (1) we introduce new radial dependencies for LAPW (Bloch-type) basis functions, based on two actual radial solutions of the Dirac equation for j=l-1/2 and j=l+1/2 states. The proposed radial 6p functions receive more weight from the Dirac p-1/2 solution and, due to this, can on average correctly describe completely filled $6p$ bands even without the additional p-1/2 local atomic function, as is done in the LAPW+p-1/2 method; (2) the canonical LAPW matrix elements for the spherically symmetric component of the potential, assuming non-relativistic radial wave functions, should be corrected; (3) we argue that for a realistic spin-orbit (SO) energy splitting of the semicore 6p-states the spin-orbit interaction constant zeta(p) should be calculated with the 6p-3/2 radial component, because the value of zeta(p) obtained with the canonical mixing of the 6p-1/2 and 6p-3/2 components overestimates the SO splitting. Different ways of taking into account relativistic effects can change the equilibrium lattice constant up to 0.15 A and the elastic modulus up to 26 GPa. We find that in the full treatment of the spin-orbit coupling UO2 has a small gap of forbidden states (0.2-0.4 eV) at the Fermi level, which persists for all k-vectors and, therefore, UO2 should be classified as a semimetal. We also discuss the peculiarities of the electron band structure of actinium, which result in an overestimation of its lattice constant.
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Materials Science

Elastic and Strain–Tunable Electronic and Optical Properties of La2AlGaO6 Hybrid Perovskite: A First-Principles Study

Chaithanya Purushottam Bhat, Jyoti Dagar, Ashwin K. Godbole et al. (+1 more)

Perovskite materials, known for their structural versatility and multifunctional properties, continue to draw interest for advanced electronic and optoelectronic applications. In this study, we investigate the elastic and strain–engineered mechanical, electronic properties and optical properties of the orthorhombic La2AlGaO6 (LAGO) hybrid perovskite using first–principles quantum mechanical calculations based on density functional theory (DFT). Structural optimizations were performed using both the local density approximation (LDA) and the generalized gradient approximation (GGA). The mechanical stability of LAGO was confirmed through the Born–Huang criteria, and key elastic constants (C11, C12, C33, C44, and C66) were evaluated. These constants were further used to derive mechanical parameters such as Young's modulus, bulk modulus, shear modulus, Poisson's ratio, Cauchy's pressure, and anisotropic factor, offering insights into the material's ductility, hardness, and elastic anisotropy. Crucially, we explored the influence of biaxial strain on the electronic band structure, DOS/PDOS, and Fermi energy, revealing significant band gap modulation under compressive and tensile strain, and hence, varying the optical properties. The coupling between elastic response and electronic structure highlights LAGO's potential for tunable device applications, where mechanical stimuli can be employed to tailor its electronic functionality.
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All authors Chaithanya Purushottam Bhat, Jyoti Dagar, Ashwin K. Godbole, Debashis Bandyopadhyay

Materials Science

Narrow magneto-optical transitions in Erbium implanted silicon carbide-on-insulator

Alexey Lyasota, Joshua Bader, Shao Qi Lim et al. (+5 more)

Solid state spin photon interfaces operating in the near telecom and telecom bands are a key resource for long distance quantum communication and scalable quantum networks. However, their optical transitions often suffer from spectral diffusion that hampers the generation of coherent spin photon entanglement. Here we demonstrate narrow magneto-optical transitions of erbium dopants implanted into thin film silicon carbide (SiC)-on-insulator, a viable platform for industrially scalable quantum networks. Using high-resolution resonant spectroscopy and spectral hole burning at cryogenic temperatures, we reveal sub megahertz homogeneous linewidths and identify two lattice sites that best stabilise the emitters. We further characterise their optical lifetimes and magneto-optical response, establishing erbium doped SiC-on-insulator as a robust and scalable platform for on-chip quantum networks.
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All authors Alexey Lyasota, Joshua Bader, Shao Qi Lim, Brett C. Johnson, Jeffrey C. McCallum, Qing Li, Sven Rogge, Stefania Castelletto

Materials Science

Impact of Oxygen Plasma Surface Treatment on Photoresist Adhesion in BaTiO3-Based Photonic Device Fabrication

Weiyou Kong, Weijia Kong, Lukas Chrostowski et al. (+1 more)

Oxygen-plasma pre-cleans are routine before fabrication, but on BaTiO3 thin films we observed catastrophic photoresist lift-off during mild rinsing and sonication. To explain the failure, we combined optical microscopy, EDS, and XPS. EDS showed no meaningful bulk stoichiometry change, whereas XPS revealed a nanometer-scale, plasma-induced shift in surface chemistry: hydroxylation and carbonate formation consistent with a BaCO3-rich interphase at the resist/BaTiO3 boundary. This chemically weak interphase, recreated upon each plasma step and removable by simple solvent cleaning, provides the mechanism for delamination. The key takeaway for practitioners is process guidance: avoid uncritical O2-plasma use on BTO; if cleaning is required, use alternative chemistries (e.g., UV-ozone) or carefully tuned plasma windows that preserve adhesion. More broadly, the study illustrates how lightweight analytics at the surface (correlative microscopy + surface spectroscopy) can pinpoint the root cause of yield-limiting defects in oxide photonics and translate directly into higher-reliability process recipes.
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All authors Weiyou Kong, Weijia Kong, Lukas Chrostowski, Xin Xin

Friday 31 October

Materials Science · Cross-listed from cond-mat.mes-hall

Resolving the phase of a Dirac topological state via interferometric photoemission

Shiri Gvishi, Ittai Sidilkover, Yun Yen et al. (+10 more)

The electronic wavefunction is at the heart of physical phenomena, defining the frontiers of quantum materials research. While the amplitude of the electron wavefunction in crystals can be measured with state-of-the-art probes in unprecedented resolution, its phase has remained largely inaccessible, obscuring rich electronic information. Here we develop a quantum-path electron interferometer based on time- and angle-resolved photoemission spectroscopy, that enables the reconstruction of phase information associated with electronic states, as encoded in the photoemission transition amplitudes - with energy and momentum resolution. We demonstrate the scheme by resolving the phase along the Dirac electronic band of a prototypical topological insulator and observe a resonance-associated phase jump as well as a momentum and phase synchronized inversion revealing the helicity of the Dirac cone. We show the interferometer can be optically controlled by the polarization of the absorbed light, allowing a differential measurement of the phase - a crucial component for extracting phase information from an interferogram. This photo-electron-interferometer provides direct experimental access to the phase of electronic transition amplitudes. Its implementation relies on experimentally accessible conditions - such as the presence of a suitable intermediate state and polarization-selective coupling - and can therefore be extended to a wide class of materials.
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All authors Shiri Gvishi, Ittai Sidilkover, Yun Yen, Shaked Rosenstein, Nir Hen Levin, Adi Perelmuter, Omer Pasternak, Costel R. Rotundu, Ido Biran, Semën Gorfman, Naaman Amer, Michael Sentef, Hadas Soifer

Materials Science · Cross-listed from cond-mat.soft

AI-Driven Design of poly(ethylene terephthalate)-replacement copolymers

Chiho Kim, Wei Xiong, Akhlak Mahmood et al. (+2 more)

Poly(ethylene terephthalate) (PET), a widely used thermoplastic in packaging, textiles, and engineering applications, is valued for its strength, clarity, and chemical resistance. Increasing environmental impact concerns and regulatory pressures drive the search for alternatives with comparable or superior performance. We present an AI-driven polymer design pipeline employing virtual forward synthesis (VFS) to generate PET-replacement copolymers. Inspired by the esterification route of PET synthesis, we systematically combined a down-selected set of Toxic Substances Control Act (TSCA)-listed monomers to create 12,100 PET-like polymers. Machine learning models predicted glass transition temperature (Tg), band gap, and tendency to crystallize, for all designs. Multi-objective screening identified 1,108 candidates predicted to match or exceed PET in $T_{\rm g}$ and band gap, including the “rediscovery” of other known commercial PET-alternate polymers (e.g., PETG, Tritan, Ecozen) that provide retrospective validation of our design pipeline, demonstrating a capability to rapidly design experimentally feasible polymers at a scale. Furthermore, selected, entirely new (previously unknown) candidates designed here have been synthesized and characterized, providing a definitive validation of the design framework.
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All authors Chiho Kim, Wei Xiong, Akhlak Mahmood, Rampi Ramprasad, Huan Tran

Materials Science · Cross-listed from physics.chem-ph

Resolving the Marcus-Rehm-Weller Paradox in Electron Transfer

Ethan Abraham

Marcus theory famously predicts that electron-transfer rates decrease once the thermodynamic driving force exceeds the reorganization energy. Yet many systems instead exhibit Rehm-Weller kinetics characterized by rate saturation rather than decrease. Here we show that these apparently contradictory phenomenologies emerge as opposite physical limits of the same two-state quantum Hamiltonian. In the normal region, the model recovers both Marcus and Rehm-Weller behavior. In the inverted region, however, it predicts Marcus's decreasing rate in the nonadiabatic limit but Rehm-Weller saturation in the adiabatic limit. Using physically realistic reorganization energies and electronic coupling values, we show that Rehm-Weller's data can be quantitatively reproduced within a microscopic quantum model without invoking phenomenological corrections.
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Materials Science · Cross-listed from physics.ins-det

Quantifying the Full Damage Profile of Focused Ion Beams via 4D-STEM Precession Electron Diffraction and PSNR Metrics

M.G. Masteghin, Z.P. Aslam, A.P. Brown et al. (+4 more)

Focused ion beams (FIBs) are widely used in nanofabrication for applications such as circuit repair, ultra-thin lamella preparation, strain engineering, and quantum device prototyping. Although the lateral spread of the ion beam is often overlooked, it becomes critical in precision tasks such as impurity placement in host substrates, where accurate knowledge of the ion-matter interaction profile is essential. Existing techniques typically characterise only the beam core, where most ions land, thus underestimating the full extent of the point spread function (PSF). In this work, we use four-dimensional scanning transmission electron microscopy (4D-STEM) to resolve the ion beam tail at defect densities equivalent to $<$0.1 ions nm$^{-2}$. Convergent beam electron diffraction (CBED) patterns were collected in calibration regions with known ion fluence and compared to patterns acquired around static dwell spots exposed to a 30 keV Ga$^{+}$ beam for 1-10 s. Cross-correlation using peak signal-to-noise ratio (PSNR) revealed that 4D-STEM datasets are ultra-sensitive for defect quantification and more robust against scanning artefacts than conventional dark-field imaging. This approach is complementary to image resolution methods enabling a comprehensive profiling of ion-induced damage even at low-dose regimes, offering a more accurate representation of FIB performance and supporting application tailoring beyond the conventional resolution metrics focused solely on the beam core.
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All authors M.G. Masteghin, Z.P. Aslam, A.P. Brown, M.J. Whiting, S.K. Clowes, R.P. Webb, D.C. Cox

Materials Science

Temperature-driven polarization rotation and triclinic phase at morphotropic phase boundary of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Alexei A. Bokov, Haiyan Guo and Zuo-Guang Ye

Information about the crystal structures in the range of morphotropic phase boundary of ferroelectric perovskite solid solutions is important for understanding their intricate properties which result in wide opportunities for practical applications. However, for the (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solution system this information is contradictory. Different composition-temperature phase diagrams have been reported for this system in literature based on the investigations of single crystals and ceramics using various experimental techniques. In this work we apply polarized light microscopy (PLM), X-ray diffraction (XRD) and dielectric spectroscopy to study the crystal structure and phase transitions in the 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystal. We confirm the monoclinic MB symmetry (space group Cm) of the room-temperature phase. According to PLM, it transforms with increasing temperature into a triclinic (Tr) phase rather than the previously reported monoclinic MC or tetragonal phase. XRD data are consistent with the presence of Tr phase. The Tr phase transforms to the monoclinic MC (Pm) phase and then to the cubic phase. Ergodic relaxor behavior is observed above the Curie temperature. The unit cell in the MC phase is pseudotetragonal with the lattice parameters a = b < c and small monoclinic angle. In the MB phase the direction of spontaneous polarization is temperature independent and close to the <111> pseudocubic direction. In the Tr and MC phases it changes with temperature so that near the Curie point it is close to [001] axis. No significant anomalies in the dielectric properties or changes in the domain structure are observed at the MB to Tr and Tr to MC phase transitions. The domain structure changes dramatically when the temperature varies within the Tr phase, causing a sharp change in birefringence.
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Materials Science

Ambient-Induced Selenium Segregation and Nanoparticle Formation in 2H-HfSe2: An Experimental and Theoretical Study

Stefany P. Carvalho, Guilherme S. L. Fabris, Ana Carolina F. de Brito et al. (+7 more)

We investigate the air-induced degradation of few-layer hafnium diselenide (HfSe$_2$) through combined experimental and theoretical approaches. AFM and SEM reveal the formation of selenium-rich spherical features upon ambient exposure, while EDS confirms Se segregation. Ab initio molecular dynamics simulations show that Se atoms migrate to flake edges and that O/O$_2$ exposure leads to selective Hf oxidation, breaking Se–Hf bonds and expelling Se atoms. No stable Se–O bonds are observed, indicating structural reorganization rather than oxidation. These findings emphasize the material's instability in air and the importance of encapsulation for preserving HfSe$_2$ in practical applications. Scanning tunneling spectroscopy confirms the semiconducting character of the nanoparticles, with an electronic bandgap compatible with that of elemental Se. These results highlight the critical role of lattice defects and oxidation dynamics in the degradation process and underscore the need for encapsulation strategies to preserve the integrity of HfSe$_2$-based devices.
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All authors Stefany P. Carvalho, Guilherme S. L. Fabris, Ana Carolina F. de Brito, Raphael B. de Oliveira, Wesley Kardex C. de Oliveira, Catalina Ruano-Merchan, Carlos A. R. Costa, Luiz F. Zagonel, Douglas Galvao, Ingrid D. Barcelos

Materials Science · Cross-listed from math.NA

Approximating Young Measures With Deep Neural Networks

Rayehe Karimi Mahabadi, Jianfeng Lu and Hossein Salahshoor

Parametrized measures (or Young measures) enable to reformulate non-convex variational problems as convex problems at the cost of enlarging the search space from space of functions to space of measures. To benefit from such machinery, we need powerful tools for approximating measures. We develop a deep neural network approximation of Young measures in this paper. The key idea is to write the Young measure as push-forward of Gaussian measures, and reformulate the problem of finding Young measures to finding the corresponding push-forward. We approximate the push-forward map using deep neural networks by encoding the reformulated variational problem in the loss function. After developing the framework, we demonstrate the approach in several numerical examples. We hope this framework and our illustrative computational experiments provide a pathway for approximating Young measures in their wide range of applications from modeling complex microstructure in materials to non-cooperative games.
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Materials Science

Interface-mediated softening and deformation mechanics in amorphous/ amorphous nanolaminates

Vivek Devulapalli, Fedor F. Klimashin, Manuel Bärtschi et al. (+4 more)

Interfaces govern the unique mechanical response of amorphous multilayers. Here, we examine nanoindentation hardness and deformation behaviour of amorphous-amorphous Ta$_2$O$_5$/SiO$_2$ nanolaminates with bilayer thicknesses ranging from 2 nm to 334 nm. Whilst monolithic SiO$_2$ exhibits catastrophic failure through a single dominant shear band, multilayer architectures demonstrate varied deformation mechanisms. Hardness decreases with reduced bilayer thickness, from 7.7 GPa at 334 nm to 5.5 GPa at 2 nm spacing, contrasting with crystalline systems, which strengthen with decreasing spacing. Cross-sectional transmission electron microscopy reveals that fine bilayer spacings promote closely spaced vertical shear bands with bilayer compression, while coarser spacings show fewer, widely spaced shear bands with chemical intermixing. Scanning electron diffraction mapping demonstrates significant densification beneath indents. The high interface density facilitates strain accommodation that prevents catastrophic failure typical of brittle amorphous materials.
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All authors Vivek Devulapalli, Fedor F. Klimashin, Manuel Bärtschi, Stephan Waldner, Silvia Schwyn Thöny, Johann Michler, Xavier Maeder

Materials Science

Transfer learning discovery of molecular modulators for perovskite solar cells

Haoming Yan, Xinyu Chen, Yanran Wang et al. (+10 more)

The discovery of effective molecular modulators is essential for advancing perovskite solar cells (PSCs), but the research process is hindered by the vastness of chemical space and the time-consuming and expensive trial-and-error experimental screening. Concurrently, machine learning (ML) offers significant potential for accelerating materials discovery. However, applying ML to PSCs remains a major challenge due to data scarcity and limitations of traditional quantitative structure-property relationship (QSPR) models. Here, we apply a chemical informed transfer learning framework based on pre-trained deep neural networks, which achieves high accuracy in predicting the molecular modulator's effect on the power conversion efficiency (PCE) of PSCs. This framework is established through systematical benchmarking of diverse molecular representations, enabling lowcost and high-throughput virtual screening over 79,043 commercially available molecules. Furthermore, we leverage interpretability techniques to visualize the learned chemical representation and experimentally characterize the resulting modulator-perovskite interactions. The top molecular modulators identified by the framework are subsequently validated experimentally, delivering a remarkably improved champion PCE of 26.91% in PSCs.
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All authors Haoming Yan, Xinyu Chen, Yanran Wang, Zhengchao Luo, Weizheng Huang, Hongshuai Wang, Peng Chen, Yuzhi Zhang, Weijie Sun, Jinzhuo Wang, Qihuang Gong, Rui Zhu, Lichen Zhao

Materials Science

Constructing a bifunctional platform based on Mn2+-doped Mg2Y8(SiO4)6O2 phosphors for multi-parameter optical thermometry and manometry

Zhiyu Pei, Shuailing Ma, Maja Szymczak et al. (+4 more)

Series of the Mn2+-doped Mg2Y8(SiO4)6O2 phosphors were synthesized. Upon excitation at 408 nm, these phosphors exhibited intense orange emission originating from Mn2+, with concentration quenching observed beyond x = 0.07, and they also demonstrated excellent thermal stability. For optical thermometry, two independent parameters, emission band centroid ({\lambda}) and lifetime, were employed as thermal indicators, yielding sensitivities of d{\lambda}/dT = 0.053 nm K-1 and SR = 0.86% K-1, respectively. High-pressure in-situ X-ray diffraction revealed that the phosphors retained structural integrity under compression, accompanied by a progressive lattice contraction. With increasing pressure (0.13-10.89 GPa), a spectral red-shift was observed, corresponding to a pressure sensitivity of d{\lambda}/dp = 4.75 nm GPa-1. Additionally, pressure-dependent shifts in color coordinates allowed the development of a colorimetric manometric response, achieving a relative sensitivity of 3.27% GPa-1. Remarkably, the pressure-induced spectral shift of Mn2+ emission, characterized by low thermal cross-sensitivity, enabled a highly reliable ratiometric manometric strategy, with a relative sensitivity of 72% GPa-1. Notably, the system delivered the highest TIMF reported to date above 3 GPa, peaking at 1940 K GPa-1 at 7 GPa. These results position Mn2+-doped Mg2Y8(SiO4)6O2 phosphors as a highly promising bifunctional material for next-generation, multi-parameter optical sensing applications under extreme conditions.
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All authors Zhiyu Pei, Shuailing Ma, Maja Szymczak, Lukasz Marciniak, Tian Cui, Laihui Luo, Peng Du