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DOE OSTI2025

Describing Point Defect Topology in 2D Energy Materials Through Computer Vision

Point defects such as vacancies and impurity atoms strongly impact the performance of 2D materials. Traditional efforts often rely on manual detection, a process that is time-intensive, prone to human error, and challenging to scale. Here we leverage machine learning (ML) methods to identify and quantify vacancies within 2D transition metal carbides (Ti3C2, MXenes), aiming to expedite detection while improving accuracy. MXenes exhibit valuable defect-defined electrochemical properties, but we currently lack statistical understanding of defect topology needed to fully harness these materials. We employ a convolutional neural network for semantic segmentation of experimental MXene images, opening an opportunity to conduct a rigorous statistical study on defect hierarchy while investigating local relaxation in the lattice. We show how the integration of ML can yield fundamental insight into point defects, providing a powerful tool that will play an increasingly crucial role in the future of materials science.

2D materials↗

DOE OSTI2020

Characterizing Dislocation Defects in Dark Field X-ray Microscopy Images of Bulk Aluminum

Material defects play a large role in material response under shock loading, yet the process of how these defects initiate, propagate, and annihilate is not well understood. Using a newly developed diagnostic, dark field X-ray microscopy (DFXM), we can now visualize the behavior of dislocation defects in materials at the mesoscale under varying conditions. Using data from the European Synchrotron Radiation Facility, we apply a variety of image processing techniques to capture relevant features to locate and characterize size and orientation of dislocation defects in bulk aluminum DFXM images. Beyond simple visualization, this analysis drives statistical characterization of the defects and their dynamic response to further improve the relevant physics models.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Impact of Irradiation-induced Lattice Defects and Dopants on Thermal Transport in Oxide Nuclear Fuels

Advanced nuclear reactor concepts aim to use fuels that must withstand unprecedented temperature and radiation extremes. In these fuels, thermal energy transport under irradiation is directly related to fuel longevity, reactor safety, and is arguably one of the most important performance metrics. Here we provide a comprehensive, first-principles-informed treatment of phonon mediated thermal transport in a defect-bearing actinide oxide with direct comparison to experimental measurements. Pristine and proton irradiated thorium dioxide was chosen as a model system to treat the complexity of thermal transport in the presence of lattice defects. A thermal transport model is implemented using the linearized Boltzmann transport equation (LBTE) with input from first principles calculations and defect evolution models. The output of the LBTE is compared directly to mesoscopic measurements of thermal conductivity on length scales commensurate with defect accumulation. Parametric measurements of conductivity with irradiation dose and temperature reveal a monotonic decrease in conductivity with irradiation dose, in the range of 0.001 dpa to 0.1 dpa. Besides radiation-induced defects, doping the thorium dioxide crystal with small quantities of uranium atoms also results in a drastic reduction in thermal conductivity. Temperature-dependent measurements of thermal conductivity in uranium-doped thorium dioxide single crystals suggests a resonant scattering mechanism is responsible for the observed reduction. This comprehensive, atomistic- to meso-scale treatment provides the necessary basis to investigate thermal transport under irradiation in more complex systems that exhibit strong electron correlation. This is a poster presentation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2024

Broken Symmetry Optical Transitions in (6,5) Single-Walled Carbon Nanotubes Containing sp 3 Defects Revealed by First-Principles Theory

We present a first-principles many-body perturbation theory study of nitrophenyl-doped (6,5) single-walled nanotubes (SWCNTs) to understand how sp 3 doping impacts the excitonic properties. sp 3 -doped SWCNTs are promising as a class of optoelectronic materials with bright tunable photoluminescence, long spin coherence, and single-photon emission (SPE), motivating the study of spin excitations. We predict that the dopant results in a single unpaired spin localized around the defect site, which induces multiple low-energy excitonic peaks. By comparing optical absorption and photoluminescence from experiment and theory, we identify the transitions responsible for the red-shifted, defect-induced E 11 * peak, which has demonstrated SPE for some dopants; the presence of this state is due to both the symmetry-breaking associated with the defect and the presence of the defect-induced in-gap state. Furthermore, we find an asymmetry between the contribution of the two spin channels, suggesting that this system has potential for spin-selective optical transitions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

The Role of Defect Geometry in Localized Emission from Monolayer Tungsten Dichalcogenides

In two-dimensional transition metal dichalcogenides such as tungsten diselenide (WSe 2 ), single photon emission has been broadly attributed to exciton localization from atomic point defects, yet the precise microscopic origins are unclear. This work introduces an empirically grounded computational framework that explains the origins of facile single photon emission in WSe 2 . High-resolution microscopy identifies native defect geometries in monolayer WSe 2 lattices from which the model is built. Here, the qualitative effects of chalcogen type, defect geometry, and mechanical strain on the electronic structure are individually assessed using density functional theory, and a specific divacancy configuration emerges as the candidate for localized single-electron transitions that match observed spectral energies. Spectroscopy and photon correlation measurements further validate this model, establishing a self-consistent link between defect geometry, electronic structure, and quantum emission.

defect emission↗

DOE OSTI2017

Electronic Transport and Ferroelectric Switching in Ion-Bombarded, Defect-Engineered BiFeO 3 Thin Films

Despite continued interest in the multiferroic BiFeO 3 for a diverse range of applications, use of this material is limited by its poor electrical leakage. This work demonstrates some of the most resistive BiFeO 3 thin films reported to date via defect engineering achieved via high-energy ion bombardment. High leakage in as-grown BiFeO 3 thin films is shown to be due to the presence of moderately shallow isolated trap states, which form during growth. Ion bombardment is shown to be an effective way to reduce this free carrier transport (by up to ≈4 orders of magnitude) by trapping the charge carriers in bombardment-induced, deep-lying defect complexes and clusters. The ion bombardment is also found to give rise to an increased resistance to switching as a result of an increase in defect concentration. This study demonstrates a systematic ion-dose-dependent increase in the coercivity, extension of the defect-related creep regime, increase in the pinning activation energy, decrease in the switching speed, and broadening of the field distribution of switching. Ultimately, the use of such defect-engineering routes to control materials will require identification of an optimum range of ion dosage to achieve maximum enhancement in resistivity with minimum impact on ferroelectric switching.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Operando Interaction and Transformation of Metastable Defects in Layered Oxides for Na‐Ion Batteries

Non-equilibrium defects often dictate the macroscopic properties of materials. They largely define the reversibility and kinetics of processes in intercalation hosts in rechargeable batteries. Recently, imaging methods have demonstrated that transient dislocations briefly appear in intercalation hosts during ion diffusion. Despite new discoveries, the understanding of impact, formation and self-healing mechanisms of transient defects, including and beyond dislocations, is lacking. Here, operando X-ray Bragg Coherent Diffractive Imaging (BCDI) and diffraction peak analysis capture the stages of formation of a unique metastable domain boundary, defect self-healing, and resolve the local impact of defects on ionic diffusion in Na x Ni 1-y MnyO 2 intercalation hosts in a charging sodium-ion battery. Results, applicable to a wide range of layered intercalation materials due to the shared nature of framework layers, elucidate new dynamics of transient defects and their connection to macroscopic properties, and suggest how to control the nanostructure dynamics.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Defect‐Mediated Ordering of Condensed Water Structures in Microporous Zeolites

Abstract Ab‐initio molecular dynamics simulations and transmission infrared spectroscopy are employed to characterize the structure of water networks in defect‐functionalized microporous zeolites. Thermodynamically stable phases of clustered water molecules are localized at some of the defects in zeolite Beta, which include catalytic sites such as framework Lewis acidic Sn atoms in closed and hydrolyzed‐open forms, as well as silanol nests. These water clusters compete with ideal gas‐like structures at low water densities and pore‐filling phases at higher water densities, with the equilibrium phase determined by the water chemical potential. The physical characteristics of these phases are determined by the defect identity, with the local binding and orientation of hydroxyl moieties around the defects playing a central role. The results suggest general principles for how the structure of polar solvents in microporous solid acids is influenced by local defect functionalization, and the thermodynamic stability of the condensed phases surrounding such sites, in turn, implies that the catalysis of Lewis acids will be influenced by local water ordering.

Bukowski, Brandon C.↗

DOE OSTI2021

Interfacial Defect of Lithium Metal in Solid‐State Batteries

Abstract All‐solid‐state battery with Li metal anode is a promising rechargeable battery technology with high energy density and improved safety. Currently, the application of Li metal anode is plagued by the failure at the interfaces between lithium metal and solid electrolyte (SE). However, little is known about the defects at Li–SE interfaces and their effects on Li cycling, impeding further improvement of Li metal anodes. Herein, by performing large‐scale atomistic modeling of Li metal interfaces with common SEs, we discover that lithium metal forms an interfacial defect layer of nanometer‐thin disordered lithium at the Li–SE interfaces. This interfacial defect Li layer is highly detrimental, leading to interfacial failure such as pore formation and contact loss during Li stripping. By systematically studying and comparing incoherent, coherent, and semi‐coherent Li–SE interfaces, we find that the interface with good lattice coherence has reduced Li defects at the interface and has suppressed interfacial failure during Li cycling. Our finding discovered the critical roles of atomistic lithium defects at interfaces for the interfacial failure of Li metal anode, and motivates future atomistic‐level interfacial engineering for Li metal anode in solid‐state batteries.

Yang, Menghao↗

DOE OSTI2026

Controlling Nb(IV) Defects in SrNbO 2 N Oxygen Evolution Photocatalyst by Ammonolysis With Dinitrogen–Ammonia Mixtures

Strontium niobium oxynitride (SrNbO 2 N) is a promising, corrosion resistant semiconductor for the visible light-driven water splitting reaction, a non-photovoltaic pathway to green hydrogen fuel. However, SrNbO 2 N materials made by ammonolysis usually contain Nb 4+ defect states that cause electron–hole recombination. Here, in this work, we demonstrate that such defects can be minimized by synthesizing SrNbO 2 N from metal oxides in a mixed 13%:87% (vol) NH 3 /N 2 atmosphere. According to electron paramagnetic resonance (EPR), SrNbO 2 N made in pure NH 3 contains paramagnetic impurities with g = 2.002 and 2.195, which can be assigned to lattice and surface Nb 4+ defects. These states also cause broad optical absorptions centered at 800 and 1020 nm, respectively, and the lattice defect produces a 1.55–1.63 eV signal in surface photovoltage spectra. The improved SrNbO 2 N contains five times fewer lattice Nb 4+ defects (8.95 × 10 15 cm −3 ), based on the integrated EPR signal intensity, and supports a water oxidation photocurrent of 1.07 mA cm −2 at 1.23 V versus RHE under simulated sunlight and an apparent quantum efficiency of 5.1% at 400 nm during photocatalytic oxygen evolution. Based on earlier results with LaTiO 2 N and BaTaO 2 N, dilution of NH 3 during synthesis appears generally beneficial to transition metal oxynitrides.

electron paramagnetic resonance↗

DOE OSTI2018

Defect Parameters Contour Mapping: A Powerful Tool for Lifetime Spectroscopy Data Analysis

Temperature‐ and injection‐dependent lifetime spectroscopy (TIDLS) is extensively used for the characterization of defects in silicon material for photovoltaic applications. By coupling TIDLS measurements with Shockley–Read–Hall recombination models, the most important defects’ parameters can be assessed including the defect energy level E t and the capture cross section ratio k . However, while proving extremely helpful in a variety of studies aiming at the characterization of contaminated silicon, a generalized approach for the analysis of industrially‐relevant material has not yet emerged. In this contribution, we examine in detail the recently introduced defect parameters contour mapping (DPCM) methodology for TIDLS data analysis as a tool for direct visualization of possible lifetime limiting defects. Herein, we showcase the DPCM method's potential by applying it to two representative case studies selected from literature and we demonstrate that, even when data are scarce, invaluable information is obtained in an easy and intuitive way without any a priori assumption needed. We then apply the DPCM method to simulated TIDLS data to evaluate the general characteristics of its response and the optimal conditions for its application. This analysis proves that the temperature dependence of lifetime is the most critical information required toward a really univocal identification of metal impurities.

Bernardini, Simone↗

DOE OSTI2024

Role of Selenium in CdZnTeSe as a Defect Engineering Agent

Cadmium zinc telluride (CdZnTe) with 10 atomic % Zn has been the material of choice for room-temperature semiconductor compact X- and gamma-ray detector applications for over three decades. Despite its commercial success as the most desirable room-temperature semiconductor radiation detection material, CdZnTe (CZT) suffers from a lack of compositional homogeneity on both the micro- and macroscales and the presence of high concentrations of performance-limiting defects such as subgrain boundary networks (dislocation walls) and secondary phases (Te-rich inclusions). Random distributions of these defects in the CZT matrix result in the spatial inhomogeneity of the material’s charge-transport properties. The recently discovered quaternary Cd x Zn 1-x Te 1-y Se y (CZTS) has experienced remarkable advances in its material properties, with highly reduced defects and higher compositional homogeneity. This book chapter focuses on the presence of performance-limiting defects in CZT that have thus far hindered the yield and cost of high-quality detectors and restricted their widespread deployment for a variety of potential applications, particularly for their use as large-volume gamma detectors, where the demands on material perfection are significantly greater. This chapter also provides an overview of the recent developments in the quaternary material CZTS, particularly the effects of selenium (Se) in the CZTS matrix on the defect engineering of the quaternary alloy material and the advancement of CZTS as a potential next-generation detector operable at room temperature.

Roy, Utpal N.↗

DOE OSTI2017

Surface defects and chiral algebras

Here, we investigate superconformal surface defects in four-dimensional N = 2 superconformal theories. Each such defect gives rise to a module of the associated chiral algebra and the surface defect Schur index is the character of this module. Various natural chiral algebra operations such as Drinfield-Sokolov reduction and spectral flow can be interpreted as constructions involving four-dimensional surface defects. We compute the index of these defects in the free hypermultiplet theory and Argyres-Douglas theories, using both infrared techniques involving BPS states, as well as renormalization group flows onto Higgs branches. We find perfect agreement with the predicted characters, in each case.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Kinetic control of phase evolution and defect-mediated recombination in AACVD-grown copper antimony sulphide thin films

Copper antimony sulphide (CAS) is a multinary chalcogenide semiconductor in which small deviations from stoichiometry can drive phase competition and strong defect-mediated modulation of optoelectronic properties. However, the systematic roles of copper precursor fraction and deposition time in governing phase evolution, off-stoichiometry, and recombination dynamics in aerosol-assisted chemical vapour deposition (AACVD)-grown undoped CAS thin films remain insufficiently understood. In this work, undoped CAS thin films were deposited by AACVD using Cu(dedtc)2 and Sb(dedtc)3 single-source precursors at 550 °C and a carrier gas flow rate of 150 sccm, while the Cu(dedtc)2 mole fraction (x = 0.15 – 0.55) and deposition time (1 – 2 hours) were systematically varied to probe how growth kinetics influence phase composition, microstructure, and defect-mediated optical properties without post-deposition annealing or extrinsic doping. Increasing copper precursor content drives phase evolution toward tetrahedrite-dominant CAS films at intermediate Cu(dedtc)2 mole fractions, with the film deposited at x = 0.35 exhibiting the strongest tetrahedrite character within the parameter space examined. The films are also copper-rich, antimony-poor, and sulphur-deficient, consistent with off-stoichiometric growth and intrinsic defect formation, plausibly including copper interstitials, Cu-on-Sb antisites, and sulphur vacancies. These growth-dependent compositional deviations are accompanied by tunable indirect optical bandgaps of approximately 1.60 – 2.18 eV and weak visible photoluminescence governed by defect-mediated recombination. Time-resolved photoluminescence reveals bi-exponential decay behaviour with lifetimes of approximately 0.1 – 3.6 ns, with emission dominated by slower donor–acceptor pair recombination and a smaller contribution from faster trap-assisted pathways. Collectively, these results establish an explicit kinetic process–structure–defect–property relationship for AACVD-grown CAS thin films and provide a growth–structure–property framework relevant to future optimization of CAS-based optoelectronic and energy materials.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Influence of structural defects on charge density waves in 1T-TaS2

Abstract The influence of intrinsic defects of 1T-TaS 2 on charge density waves (CDWs) is studied using scanning tunneling microscopy and spectroscopy (STM, STS), angle-resolved photoelectron spectroscopy (ARPES), and density functional theory (DFT). We identify several types of structural defects and find that most have a local character limited to a single CDW site, with a single exception which effectively behaves as a dopant, leading to band-bending and affecting multiple neighboring sites. While only one type of defect can be observed by STM topographic imaging, all defects are easily resolved in STS mapping. Our results indicate modulation of the Mott band gap commensurate with the CDW and breaking of the three-fold symmetry of electronic states. DFT calculations (with included Coulomb interactions) are used to investigate the electronic structure, focusing on both sulfur vacancy and oxygen-sulfur substitution. The sulfur vacancy system, characterized with a metallic behavior, is identified as the origin of one of the experimentally observed defects. Additionally, the effect of oxidation of 1T-TaS 2 depends on the substitution site, leading to the heterogeneity of electronic properties.

Chemistry↗

DOE OSTI2017

Enhanced diode-like operation mediated by an asymmetric non-Hermitian and nonlinear defect

In this work we study the nonreciprocal transport along two tight-binding chains which are connected by a single defect having an asymmetric non-Hermitian nonlinear off-diagonal coupling. The spectrum of transmission and reflection, the gain curve and the rectifying factor are analytically obtained using a backward iterative process. A set of discrete linear Schroedinger equations is used to model the wave propagation through the two Hermitian side chains, while a discrete nonlinear Ablowitz–Ladik equation governs their coupling by the single defect. We show that the emergence of a multistability window induced by the non-linear contribution, together with the biased transport promoted by a parity-breaking non-Hermiticity, generates an efficient rectification of the transmitted wave component. - Highlights: • Transmission along a quantum channel with a defect is analytically studied. • The defect has non-Hermitian, nonlinear and non-symmetric characteristics. • The transmission spectrum exhibits multistability regions. • The non-conventional properties of the defect lead to a diode-like behavior. • Multistability is shown to promote an enhanced rectification of the transmitted signal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Defective autophagy in vascular smooth muscle cells enhances atherosclerotic plaque instability

Highlights: • We investigated the role of autophagy in SMCs on plaque instability in vivo. • We conducted to form a tandem stenosis in the carotid artery. • Thrombus was frequently found in KO mice. • Plaque hemorrhage was frequently found in KO mice. • Defective autophagy in SMCs enhances plaque instability. Autophagy is considered as an evolutionarily conserved cellular catabolic process. Defective autophagy has been implicated in various human diseases, including cardiovascular diseases. Recently, we and others demonstrated that defective autophagy in vascular smooth muscle cells (SMCs) promotes the progression of atherosclerosis. In this study, we investigated the role of autophagy in SMCs on plaque instability in vivo. We generated mice with a defect atg7in which is an essential gene for autophagy, in SMCs by crossing Atg7{sup f/f} mice with transgelin (Tagln) Cre{sup +/0} mice (Atg7cKO). Then, Atg7cKO and apolipoprotein E (apoe)-deficient (apoeKO) mice were crossed to generate Atg7cKO:apoeKO mice. To generate a mouse model of plaque instability, we conducted to form a tandem stenosis in the carotid artery of Atg7cKO:apoeKO mice and their controls (apoeKO mice) at the age of 10 weeks. At 5 weeks after surgery, the percentage of cross-sectional stenosis area in the operated common carotid artery of Atg7cKO:apoeKO mice was significantly higher than that in apoeKO mice. In addition, thrombus, which was not observed in apoeKO mice, was frequently found in Atg7cKO:apoeKO mice. Furthermore, the number of Berlin blue staining-positive areas, which indicated intraplaque hemorrhage, was significantly higher in Atg7cKO:apoeKO mice than in control apoeKO mice. Taken together, our data suggest that defective autophagy in SMCs enhances plaque instability and the risk of plaque rupture.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2020

Migration energy barriers and diffusion anisotropy of point defects on tungsten surfaces

We report tungsten is one of the most promising candidates for plasma-facing materials in future fusion devices, owing to its high performance under extreme irradiation conditions. However, irradiation-induced surface morphology varies significantly, depending on the irradiation type, fluence, and flux. Therefore, it is critical to examine the dynamics of point defects on tungsten (W) surfaces to understand how irradiation affects surface morphology. In this study, we employ the Self-Evolving Atomistic Kinetic Monte Carlo (SEAKMC) method to search for potential migration paths of point defects on W (1 0 0), (1 1 0) and (1 1 1) surfaces. The first-principles calculations are then used to accurately determine the migration energy barriers. The obtained paths and barriers are incorporated into a kinetic Monte Carlo (KMC) model to determine trajectories and diffusivities, which are described by diffusion tensors to demonstrate their anisotropic features. Multiple diffusion mechanisms have been identified on different surfaces, with various anisotropy factors. Particularly, point defects on the W (1 1 0) surface have the highest diffusivities, with anisotropy factors independent of temperatures. In comparison, the anisotropy of the W (1 0 0) surface decreases as temperature increases, while the W (1 1 1) surface is isotropic for point defects. This study provides insights into defect transport properties on different surfaces, which are essential for understanding the early stages of irradiation-induced microstructural evolutions and surface morphology of tungsten.

36 MATERIALS SCIENCE↗