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Refractory high-entropy alloys (RHEAs) represented by WTaCrV are excellent candidates for future nuclear reactor structures. Both the preexisting edge dislocations (EDs) and screw dislocations (SDs) can significantly impact the irradiation performance of RHEAs. To explore the influence of preexisting dislocations on the generation and evolution of irradiation point defects in the RHEA WTaCrV, the interactions between preexisting dislocations (including EDs and SDs) and displacement cascades are studied by molecular dynamics simulations in this work. In addition, the results of the RHEA WTaCrV without preexisting dislocations and of pure W with preexisting dislocations are included for comparison. It is found that the presence of preexisting dislocations leads to a significant increase in the number of remained point defects after the cascades. However, the absorption of vacancies by dislocation cores in the RHEA WTaCrV is more significant than that in the pure W. Therefore, preexisting dislocations can reduce the possibility of void formation and act as sites for recombination of vacancies and interstitials in the subsequent long-term evolution. For the preexisting EDs in the RHEA WTaCrV, the local pinning of EDs, the attraction of vacancies, and the severe lattice distortion jointly cause the bowing out of EDs, which is conductive to accommodate vacancies. For the preexisting SDs, the abundant cross kinks tend to bind vacancies or interstitials, promoting the motion of SDs as well as the annihilation of point defects. In this sense, the preexisting dislocations in the RHEA WTaCrV can significantly enhance the irradiation resistance. The results of this research can provide design guidance for regulating the anti-irradiation performance of RHEAs. [ABSTRACT FROM AUTHOR]

Rare earth substitution in cuprate superconductors has sparked intense interest, driving progress in both fundamental research and advanced technology. In this investigation, we focus on SmBa 2 Cu 3 O 7 − δ (SmBCO), synthesized via the top-seeded melt growth method, with an aim to understand the corresponding vortex phases. Despite the minimal impact on transition temperature (T c) when yttrium in YBa 2 Cu 3 O 7 − δ is replaced by Sm, the critical current density (J c) remains exceptionally high under intense magnetic fields. Introducing Sm 2 Ba 1 Cu 1 O 5 (Sm-211) phase as point defects significantly boosts the pinning potential (U) and pinning force (F p ) and enhances their stability against external magnetic fields. Contrary to other superconductors, the SmBCO sample displays a notable peak effect in the magnetic field-dependent J c , driven by point defects introduced by the Sm-211 phase, which prompts vortex lattice softening and initiates a transition from an ordered to a disordered vortex glass phase, leading to the emergence of a second magnetization peak. Analysis suggests that the primary pinning mechanism in SmBCO involves a combination of normal point and Δ κ pinning. Additionally, investigations of the vortex glass phase beneath the thermally activated flux flow regime indicate that vortices in SmBCO may freeze into a state akin to a 2D vortex glass state. This study leads to a detailed phase diagram that clarifies the evolution of vortex phases in SmBCO. [ABSTRACT FROM AUTHOR]

This study investigates the effects of electron beam irradiation on the lasing characteristics of optically pumped CdSe quantum dot (QD) lasers grown on GaAs substrates using molecular beam epitaxy. The experimental setup allows the creation of two types of CdSe QDs with distinct size differences, with and without electron beam irradiation during the epitaxy. Lasing wavelengths were observed at 534 nm in the non-irradiated region and between 548 and 557 nm in the irradiated regions, depending on the electron beam irradiation conditions, achieving multi-wavelength lasing in the green-yellow ranges on a single chip. Internal laser parameters were evaluated for both irradiated and non-irradiated regions across different cavity lengths. Photoluminescence (PL) spectra revealed significantly higher integrated PL intensity in the irradiated regions compared to the non-irradiated regions, attributed to reduced point defects. However, at the lasing threshold, the impact of these defects is negligible. Lasing spectra exhibited a notable blue shift in the irradiated regions with an increase in threshold intensity due to the state-filling effect, which also causes a decrease in internal quantum efficiency. The modal gain and transparent intensity were evaluated, showing lower gain values in the irradiated regions, consistent with the observed broadening of the PL spectrum. These findings highlight the dynamic nature of the state-filling effect and its impact on lasing performance, providing insights into the mechanisms affecting CdSe QD lasers under electron beam irradiation in green-yellow spectrum range. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry data for samples of a 52 year old plutonium alloy with 3.3 at. % Ga that were heated beyond the melting point is analyzed using transition state theory to find activation energies for the δ to ɛ and ɛ to liquid phase transitions. A Bayesian statistical method involving a Gaussian process model is used to find mean values and confidence intervals for the activation energies. The activation energy for the δ to ɛ phase transition increases by 3.3 ± 3.8% per decade, relative to the case when all age related plutonium lattice point defects have been removed through annealing. The corresponding increase in activation energy for the ɛ to liquid transition is shown to be 7.1 ± 1.8% per decade. It is postulated that the change in activation energy with age for both phase transitions is caused, in part, by the accumulation of the same type of lattice point defects associated with the observed increase in elastic bulk modulus over time. [ABSTRACT FROM AUTHOR]

Point defects are thermodynamically stabilized in all crystalline materials, with increased densities negatively impacting the properties and performance of transition metal dichalcogenides (TMDs). While recent point defect reduction methods have led to considerable improvements in the optoelectronic properties of TMDs, there is a clear need for theoretical work to establish the lower limit of defect densities, as represented by thermal equilibrium. To that end, an ab initio and thermodynamic analysis of the equilibrium densities of intrinsic point defects in MoSe2 and WSe2 is presented. The intrinsic defect formation energies at the limits of the selenium and metal-rich regimes are determined by density functional theory (DFT) and then augmented with elemental chemical potential functions to determine temperature- and pressure-dependent formation energies. Equilibrium defect densities are determined for MSe, SeM, vM, and vSe, where M and v, respectively, represent the metal and the vacancy, as a function of synthesis temperature and pressure. The effects of vibrational free energy contributions and treatment of the DFT exchange–correlation potential are found to be non-negligible. Calculated equilibrium densities are several orders of magnitude below reported defect densities in TMDs made by chemical vapor deposition, chemical vapor transport, and flux methods, thereby establishing that current synthesis methods are either kinetically limited or impurity dominated. [ABSTRACT FROM AUTHOR]

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices. [ABSTRACT FROM AUTHOR]

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices. [ABSTRACT FROM AUTHOR]

With density functional theory (DFT), it is possible to calculate the formation energy of charged point defects and in turn to predict a range of experimentally relevant quantities, such as defect concentrations, charge transition levels, or recombination rates. While prior efforts have led to marked improvements in the accuracy of such calculations, comparatively modest effort has been directed at quantifying their uncertainties. However, in the broader DFT research space, the development of Bayesian Error Estimation Functionals (BEEF) has enabled uncertainty quantification (UQ) for other properties. In this paper, we investigate the utility of BEEF as a tool for UQ of defect formation energies. We build a pipeline for propagating BEEF energies through a formation-energy calculation and test it on intrinsic defects in several materials systems spanning a variety of chemistries, bandgaps, and crystal structures, comparing to prior published results where available. We also assess the impact of aligning to a deep-level transition rather than to the VBM (valence band maximum). We observe negligible dependence of the estimated uncertainty upon a supercell size, though the relationship may be obfuscated by the fact that finite-size corrections cannot be computed separately for each member of the BEEF ensemble. Additionally, we find an increase in estimated uncertainty with respect to the absolute charge of a defect and the relaxation around the defect site without deep-level alignment, but this trend is absent when the alignment is applied. While further investigation is warranted, our results suggest that BEEF could be a useful method for UQ in defect calculations. [ABSTRACT FROM AUTHOR]

Three-dimensional topological semimetals are a class of electronic materials in which their bulk and surface states contain linear band touching nodes near the Fermi level. Like semiconductors, their properties will be affected by point and extended defects in their crystal structures, although the extent to which defects and disorders influence topological semimetals may differ in key ways due to their unique electronic structures. In this Tutorial, we provide an overview of the defects in topological semimetals, covering both computational and experimental methods for exploring defect-property relationships. We also include a discussion on open questions that still need to be explored further. [ABSTRACT FROM AUTHOR]

Mass transport in bulk spinel ferrites NiFe2O4 is studied computationally using the kinetic activation–relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Diffusion mechanisms—difficult to observe with molecular dynamics—are described by k-ART. Point defects are assumed to be responsible for ionic diffusion; thus, both cation and anion defects are investigated. This work focuses on vacancies and interstitials by comparing their properties with two Buckingham potential parameterizations: one with nominal charges and the other with partial charges. Both potentials are corrected at short distances, thus allowing interstitial diffusion and avoiding the catastrophic infinite energies appearing with Buckingham at short distances. The energy landscape along different pathways is described in detail. Both potentials predict the same mechanisms but different migration energies. Mechanisms by which a normal spinel is transformed to an inverse spinel via cation diffusion are unveiled, and diffusion coefficients are predicted. We find that interstitial Ni diffusion involves the movement of two Ni ions and that O interstitials trigger a collective diffusion of O ions, while an O vacancy diffuses by an O ion moving to the center of a cuboctahedron. [ABSTRACT FROM AUTHOR]

The degradation of β-Ga2O3-based devices' performance may occur when they are bombarded by charged particles in aerospace, astronomy, and nuclear-related applications. It is significant to explore the influence of irradiation on the microstructure of β-Ga2O3 and to reveal the internal relationship between the damage mechanisms and physical characteristics. Thus, we explored the low-energy recoil events of β-Ga2O3 based on the first-principles calculations in the present study. The threshold displacement energies (Eds) significantly depended on the recoil directions and the primary knock-on atoms. Eds of Ga atoms are generally larger than those of O atoms, indicating that the displacements of O atoms dominate under electron irradiation. In the neutral state, the formation energy of VO(I) is lower than that of VO(II) and VO(III), while in the +2 charge state, the case is a reversal. The formation energy of Oint(II) defect is high, and thus its equilibrium concentration is low, indicating that the Oint(II) defect is unlikely to be relevant for the thermal-mechanical properties of β-Ga2O3. The charged VO and Oint defects deteriorate the ability to resist external compression more profoundly, while defective β-Ga2O3 with lower Young's modulus is expected to possess higher elastic compliance than pristine β-Ga2O3. The lattice thermal conductivity of β-Ga2O3 decreases with increasing temperature and the charged point defects generally result in the decreasing lattice thermal conductivity more profoundly than neutral point defects. The presented results provide underlying mechanisms for defect generation in β-Ga2O3 and advance the fundamental understanding of the radiation resistances of semiconductor materials. [ABSTRACT FROM AUTHOR]

The degradation of β-Ga2O3-based devices' performance may occur when they are bombarded by charged particles in aerospace, astronomy, and nuclear-related applications. It is significant to explore the influence of irradiation on the microstructure of β-Ga2O3 and to reveal the internal relationship between the damage mechanisms and physical characteristics. Thus, we explored the low-energy recoil events of β-Ga2O3 based on the first-principles calculations in the present study. The threshold displacement energies (Eds) significantly depended on the recoil directions and the primary knock-on atoms. Eds of Ga atoms are generally larger than those of O atoms, indicating that the displacements of O atoms dominate under electron irradiation. In the neutral state, the formation energy of VO(I) is lower than that of VO(II) and VO(III), while in the +2 charge state, the case is a reversal. The formation energy of Oint(II) defect is high, and thus its equilibrium concentration is low, indicating that the Oint(II) defect is unlikely to be relevant for the thermal-mechanical properties of β-Ga2O3. The charged VO and Oint defects deteriorate the ability to resist external compression more profoundly, while defective β-Ga2O3 with lower Young's modulus is expected to possess higher elastic compliance than pristine β-Ga2O3. The lattice thermal conductivity of β-Ga2O3 decreases with increasing temperature and the charged point defects generally result in the decreasing lattice thermal conductivity more profoundly than neutral point defects. The presented results provide underlying mechanisms for defect generation in β-Ga2O3 and advance the fundamental understanding of the radiation resistances of semiconductor materials. [ABSTRACT FROM AUTHOR]

α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3. [ABSTRACT FROM AUTHOR]

α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3. [ABSTRACT FROM AUTHOR]

III-nitride materials, such as GaN and its alloys, are essential for modern microelectronics and optoelectronics due to their unique properties. Focused ion beam (FIB) techniques play a crucial role in their prototyping and characterization at the micro- and nanoscale. However, conventional FIB milling with Ga ions presents challenges, including surface amorphization and point defect introduction, prompting the exploration of alternative ion sources. Xenon-based inductively coupled plasma or plasma FIB has emerged as a promising alternative, offering reduced damage and better sample property preservation. Despite extensive research on FIB-induced damage in GaN, systematic comparisons between Ga and Xe ion milling on the luminescence characteristics of GaN remain limited. This study aims to fill this gap by evaluating and comparing the extent of FIB-induced damage caused by Ga and Xe ions in wurtzite and zincblende GaN through cathodoluminescence measurements. Our findings indicate that Xe ion milling yields higher integrated intensities compared to Ga ion milling, attributed to shallower implantation depths and reduced lattice disorder. We also observe a decrease in integrated intensity with increasing ion beam acceleration voltage for both wurtzite and zincblende GaN layers. This study provides valuable insights into optimizing FIB-based sample preparation techniques for III-nitride materials, with implications for enhancing device performance and reliability. [ABSTRACT FROM AUTHOR]

Point defect color centers acting as single-photon emitters are promising for quantum technology applications and have been extensively studied, e.g., in the 4H polytype of silicon carbide (SiC). However, the physics of such color centers in other SiC polytypes is much less explored. Herein, we study the formation and thermal stability of such color centers in 6H-SiC using photoluminescence spectroscopy. The emissions from typical single-photon emitters, such as silicon vacancies, divacancies, and carbon antisite-vacancy pairs in 6H-SiC, were monitored as a function of the proton irradiation fluence and post-irradiation annealing, and compared to that in 4H-SiC. Overall, at the background of similarities between the emission behavior in 4H- and 6H-SiC polytypes, we observed prominent differences; e.g., for the thermal stability of the carbon antisite-vacancy pair, which exhibited maximized emissions upon 300 and 900 ° C anneals in 4H- and 6H-SiC, respectively. Moreover, we observed a range of defect emission signatures not previously reported for 6H-SiC in the literature and discussed their potential origin in the context of the thermal stability. For example, among the PL-lines in 6H-SiC, we detected periodically repeatable emission signatures, resembling the so-called L-lines recently reported in 4H-SiC, even though their exact origin has not yet been settled in the literature. Thus, we use color centers comparison in different polytypes to better understand the nature of the single-photon emitters in SiC. [ABSTRACT FROM AUTHOR]

Previously, we demonstrated hysteretic and persistent changes of resistivity in two-terminal electronic devices based on charge trapping and detrapping at immobile metastable defects [Yin et al., Phys. Rev. Appl. 15, 014014 (2021)]; we termed these defect-level switching (DLS) devices. DLS devices feature all-electronic resistive switching and thus are volatile because of the "voltage-time" dilemma. However, the dynamics of volatile resistive switches may be valuable for emerging applications such as selectors in crosspoint memory and neuromorphic computing concepts. To design circuits using these volatile resistive switches, accurate modeling is essential. In this work, we develop an accurate and analytical model to describe the switching in DLS devices, based on the established theories of point defect metastability in Cu(In,Ga)Se2 (CIGS) and II–VI semiconductors. The analytical nature of our model allows for time-efficient simulations of dynamical behavior of DLS devices. We model the time durations of SET and RESET programming pulses, which can be exponentially shortened with respect to the pulse amplitude. We also demonstrate the concept of inverse design: given desired resistance states, the width and amplitude of the programming signal can be chosen accordingly. [ABSTRACT FROM AUTHOR]

Transparent conducting oxides with p-type conductivity hold immense potential for various electronic applications. The role of native point defects in delafossite CuMO 2 (M = Al, Ga, In) as the source of p-type conductivity has been widely acknowledged. However, understanding the primary defects governing the electrical properties and devising strategies for improvement remains a critical challenge. In this study, we employ range-separated hybrid density functional calculations to elucidate the impact of acceptor defects and their interactions with hydrogen on electrical conductivity. Our findings demonstrate that hydrogen plays a pivotal role in controlling p-type conductivity in these oxides. Our investigation reveals that the interactions between hydrogen interstitial H i and copper vacancy V C u lead to the formation of stable complexes that are electrically inactive. Considerable binding energies are observed for H i – V C u complexes, indicating that they are highly bound complexes with low formation energy and, thus, high concentrations under both O-rich and O-poor conditions. A second hydrogen can be bound to V C u to form 2H i – V C u complexes, which are thermodynamically stable and function as a single donor. Furthermore, hydrogen can bind with the antisite acceptor defects, Cu M , forming H i – Cu M complexes. However, the lower binding energies associated with these complexes suggest likely dissociation into isolated H i and Cu M at relatively low temperatures. By shedding light on the strong influence of hydrogen passivation of acceptor defects, this study offers valuable insights into p-type conductivity in delafossite CuMO 2. [ABSTRACT FROM AUTHOR]

Deposition of Mo S 2 on Au(111) alters the electronic properties of Mo S 2 . In this study, we investigate the free-standing MoS 2 monolayer and the MoS 2 /Au(111) heterostructure, with and without strain, as well as defects of interest in memristive and neuromorphic applications. We focus on the so-called atomristor devices based on monolayer materials that achieve resistive switching characteristics with the adsorption and desorption of metal adatoms. Our study confirms that the formation of midgap states is the primary mechanism behind the resistive switching. Our results show that strain lowers the adsorption/desorption energies of Au+defect structures of interest, leading to more favorable switching energies, but simultaneously reduces the switching ratio between states of differing conductivities. The presence of the Au(111) substrate additionally introduces non-uniform amounts of strain and charge transfer to the MoS 2 monolayer. We propose that the induced strain contributes to the experimentally observed n - to p -type transition and Ohmic to Schottky transition in the MoS 2 monolayer. The charge transfer leads to a permanent polarization at the interface, which can be tuned by strain. Our study has important implications on the role of the electrode as being a source of the observed variability in memristive devices and as an additional degree of freedom for tuning the switching characteristics of the memristor device. [ABSTRACT FROM AUTHOR]

Quartz-based minerals in earth's crust are well-known to contain water-related defects within their volume-constrained lattice, and they are responsible for strength-loss. Experimental observations of natural α -quartz indicate that such defects appear as hydroxyl groups attached to Si atoms, called Griggs defect (Si-OH), and molecular water (H 2 O) located at the interstitial sites. However, factors contributing to the formation of Griggs and interstitial H 2 O defects remain unclear. For example, the role of point defects like vacancy sites (O 2 − and Si 4 + ), and substitutional (Al 3 + ) and interstitial (Li + , K + , Ca 2 + , Mg 2 + , etc.) ions has remained largely unexplored. Here, we performed ab initio molecular dynamics at 300 K to examine the energetics and structure of water-related defects in volume-constrained α -quartz. Several configurations were systematically interrogated by incorporating interstitial H 2 O, O 2 − and Si 4 + vacancies, substitutional Al 3 + , and interstitial Li + , Ca 2 + and Mg 2 + ions within α -quartz. Interstitial H 2 O defect was found to be energetically favorable in the presence of Substitutional Al 3 + , and interstitial Ca 2 + , Mg 2 + , and Li 1 + . In the presence of O 2 − and Si 4 + vacancies, H 2 O showed a strong tendency to dissociate into OH—to form Griggs defect—and a proton; even in the presence of substitutional and interstitial ions. These ions distorted the α -quartz lattice and, in the extreme case, disrupted long-range order to form local amorphous domains; consistent with experimental reports. Our study provides an initial framework for understanding the impact of water within the crystal lattice of an anhydrous silicate mineral such as quartz. We provide not only thermodynamic and process-related information on observed defects, but also provides guidelines for future studies of water's impact on the behavior of silicate minerals. [ABSTRACT FROM AUTHOR]

Tetrahedrally bonded III-N and related alloys are useful for a wide range of applications from optoelectronics to dielectric electromechanics. Heterostructural AlN-based alloys offer unique properties for piezoelectrics, ferroelectrics, and other emerging applications. Atomic-scale point defects and impurities can strongly affect the functional properties of materials, and therefore, it is crucial to understand the nature of these defects and the mechanisms through which their concentrations may be controlled in AlN-based alloys. In this study, we employ density functional theory with alloy modeling and point defect calculations to investigate native point defects and unintentional impurities in Al 1 − x Gd x N alloys. Among the native defects that introduce deep midgap states, nitrogen vacancies (V N ) are predicted to be in the highest concentration, especially under N-poor growth conditions. We predict and experimentally demonstrate that V N formation can be suppressed in thin films through growth in N-rich environments. We also find that Al 1 − x Gd x N alloys are prone to high levels of unintentional O incorporation, which indirectly leads to even higher concentrations of deep defects. Growth under N-rich/reducing conditions is predicted to minimize and partially alleviate the effects of O incorporation. The results of this study provide valuable insights into the defect behavior in wurtzite nitride-based alloys, which can guide their design and optimization for various applications. [ABSTRACT FROM AUTHOR]

Point defects have a strong influence on the physical properties of materials, often dominating the electronic and optical behavior in semiconductors and insulators. The simulation and analysis of point defects is, therefore, crucial for understanding the growth and operation of materials, especially for optoelectronics applications. In this work, we present a general-purpose Python framework for the analysis of point defects in crystalline materials as well as a generalized workflow for their treatment with high-throughput simulations. The distinguishing feature of our approach is an emphasis on a unique, unit cell, structure-only, definition of point defects which decouples the defect definition, and the specific supercell representation used to simulate the defect. This allows the results of first-principles calculations to be aggregated into a database without extensive provenance information and is a crucial step in building a persistent database of point defects that can grow over time, a key component toward realizing the idea of a "defect genome" that can yield more complex relationships governing the behavior of defects in materials. We demonstrate several examples of the approach for three technologically relevant materials and highlight current pitfalls that must be considered when employing these methodologies as well as their potential solutions. [ABSTRACT FROM AUTHOR]

Nanopore/pillar formation on a Ge substrate can be induced by ion irradiation, which activates the ion beam sputtering and self-organization of point defects. Considering that the size and morphology of nanostructures are dependent on damage production, the irradiation parameters significantly affect nanostructuring. Here, the projected range of incident ions was selected as a parameter to be investigated. The projected range was modified by adding an Au buffer layer on the surface of the substrate, enabling the ions to stop in a shallower layer. The experimental results showed that the deposited Au layer affected the size and morphology of the nanostructures produced by ion irradiation. As a unique morphology, network-like structures were observed on the Au-deposited substrates. These structures were larger than ordinary porous structures. [ABSTRACT FROM AUTHOR]

4H Silicon carbide (4H-SiC) is widely recognized as a highly promising material for high-voltage and high-power electronic applications due to its exceptional properties. The performance of devices based on 4H-SiC is often weakened by the presence of carbon-related point defects, particularly carbon vacancies (VC). The defects of VC introduce deep-level traps (e.g., Z1/2 and EH6/7) that deteriorate device functionality. Experimental and theoretical studies on VC have led to some conflicting results about the charge states of VC, especially for the charge state ordering of EH6/7. We now employ ab initio metadynamics (META) to systematically investigate configuration space including the direction and magnitude of bond distortion and identify the most stable structures of VC. Eventually, the charge states of VC in 4H-SiC are identified. The Z1 (EH6) and Z2 (EH7) indicate transitions from acceptor (donor) levels of VC, located on the h and k sublattice sites, respectively. Z1 and Z2 demonstrate negative-U ordering, characterized by U values of −0.16 and −0.37 eV, respectively. Conversely, EH6 and EH7 display positive-U ordering, with U values of 0.16 and 0.08 eV, respectively. The current results provide insights into the properties of VC in 4H-SiC, highlighting the effectiveness of META in the exploration of complex potential energy surfaces associated with point defects in solids. [ABSTRACT FROM AUTHOR]

In this work, we show how diffraction-based chemically sensitive dark-field transmission electron microscopy (DFTEM) reveals the presence of Bi hetero-antisites (BiGa) at the interface of Ga(As,Bi)/(Al,Ga)As quantum well (QW) structures grown by molecular beam epitaxy on GaAs(001). The presence of BiGa is demonstrated by the striking appearance of "dark-lines" at the interfaces under two-beam DFTEM imaging conditions using the (002) diffraction spot. Additional analytical scanning (S)TEM procedures reveal Ga depletion and Bi accumulation at the exact position of the dark-lines, consistent with BiGa at this location. The precise location of the dark-lines agrees with the position of growth interruptions made to adjust substrate temperature and the As/Ga flux ratio and, most importantly, the realization of a Bi pre-treatment before QW growth. We believe the Bi pre-treatment may have favored formation of BiGa hetero-antisites. We validate the use of g002 DFTEM for further investigations of the intricate bismuth incorporation into the lattice and its dependence on the growth conditions. Finally, g002 DFTEM imaging is positioned as a very powerful technique for the detection of point defects in general in materials with the zinc-blende crystal structure, beyond dilute bismide alloys. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping. [ABSTRACT FROM AUTHOR]

We investigate the native point defects in the long-wavelength infrared (LWIR) detector material H g 0.75 C d 0.25 Te using a dielectric-dependent hybrid density functional combined with spin–orbit coupling. Characterizing these point defects is essential as they are responsible for intrinsic doping and nonradiative recombination centers in the detector material. The dielectric-dependent hybrid functional allows for an accurate description of the bandgap (E g) for Hg 1 − x Cd x Te (MCT) over the entire compositional range, a level of accuracy challenging with standard hybrid functionals. Our comprehensive examination of the native point defects confirms that cation vacancies V Hg (Cd) are the primary sources of p -type conductivity in the LWIR material given their low defect formation energies and the presence of a shallow acceptor level (− /0) near the valence-band maximum. In addition to the shallow acceptor level, the cation vacancies exhibit a deep charge transition level (2 − / −) situated near the midgap, characteristic of nonradiative recombination centers. Our results indicate that Hg interstitial could also be a deep center in the LWIR MCT through a metastable configuration under the Hg-rich growth conditions. While an isolated Te antisite does not show deep levels, the formation of V Hg –Te Hg defect complex introduces a deep acceptor level within the bandgap. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDs) hold immense promise as ultrathin-body semiconductors for cutting-edge electronics and optoelectronics. In particular, their sustained charge mobility even at atomic-level thickness as well as their absence of surface dangling bonds, versatile band structures, and silicon-compatibility integration make them a prime candidate for device applications in both academic and industrial domains. Despite such high expectations, group-VI TMDs reportedly exhibit a range of enigmatic properties, such as substantial contact resistance, Fermi level pinning, and limited unipolar charge transport, which are all rooted in their inherent defects. In other words, intrinsic physical properties resulting from their native defects extend their influence beyond the material level. Bridging point-defect-induced material properties and their behavior at the device level, this Perspective sheds light on the significance of crystalline defects beyond a rather simple defect–property relationship. As a distinctive approach, we briefly review the well-established defect model of conventional III–V semiconductors and further apply it to the emergent defect behaviors of 2D TMDs such as their defect-induced gap states. Within the main discussion, we survey a range of behaviors caused by the most prevalent intrinsic defect, namely, vacancies, within 2D TMDs, and their implications for electronic and optoelectronic properties when employed at the device level. This review presents an in-depth summary of complexities in material properties as well as device characteristics arising from intrinsic point defects and provides a solid foundation for the cross-links among native defects and material/device properties. [ABSTRACT FROM AUTHOR]

Mixed thorium/uranium dioxide, (Th,U)O2, is under consideration for advanced nuclear fuel applications. Investigating the point defect structure and energy in this oxide is important for predicting its behavior as fuel. In this work, we use first-principles calculations based on the generalized gradient approximation (GGA)+Hubbard U approach to investigate the internal energy and entropy of the formation of point defects in Th1−xUxO2 at various compositions below x ≤ 0.5. Point defects including O vacancies, O interstitials, Th vacancies, Th interstitials, U vacancies, and U interstitials have all been considered with their charges ranging from neutral to the maximum nominal values. The observed trends have been explained in terms of electronic density of states. The valence band maxima of crystals that contain defects play a crucial role and exhibit variations depending on the U content and the applied charge. The temperature dependence of internal energy and entropy of formation of defects have also been examined. The internal energy of formation of defects was found to exhibit slowly varying or constant values with respect to changes in the U content, except at low values of x and low temperatures. The entropy of formation of defects was observed to decrease with increasing U content. It was additionally observed that the entropy of formation of vacancies increases with temperature, while that of interstitials decreases. This investigation further revealed that at 0 K, the cation vacancies and anion interstitials become increasingly favorable with increasing U content, while cation interstitials and anion vacancies become less favorable. [ABSTRACT FROM AUTHOR]

Understanding the mechanical behavior of nanotwinned materials in alloys is essential, particularly in relation to solute-influenced twin boundary (TB) migration. This research employs atomistic simulations and theoretical analysis to explore the influence of solute atoms on TB migration in CuAg alloys. Contrary to conventional beliefs, simulations reveal that solute Ag atoms enhance TB migration, challenging established perceptions. Nudged elastic band calculations confirm that Ag solutes substantially reduce energy barriers, shedding light on the mechanism driving solute-enhanced TB migration. This work opens novel avenues for investigating point defect impacts on TB mobility, offering insights into alloy element roles in grain boundary migration and polycrystalline material properties. [ABSTRACT FROM AUTHOR]

Annealing Mg-implanted homoepitaxial GaN at temperatures above 1400 °C eliminates the formation of inversion domains and leads to improved dopant activation efficiency. Extended defects, in the form of inversion domains, contain electrically inactive Mg after post-implantation annealing at temperatures as high as 1300 °C (one GPa N2 overpressure), which results in a low dopant activation efficiency. Triple-axis x-ray data reveal that implant-induced strain is fully relieved after annealing at 1300 °C for 10 min, indicating that strain-inducing point defects formed during implantation have reconfigured and inversion domains are formed. However, annealing at temperatures of 1400–1500 °C (one GPa N2 overpressure) eliminates the presence of the inversion domains. While residual defects, such as dislocation loops, still exist after annealing at and above 1400 °C, chemical analysis at multiple dislocation loops shows no sign of Mg segregation. Meanwhile, an overall decreasing trend in the dislocation loop density is observed after annealing at the higher temperatures and longer times. Additionally, once inversion domains are formed and the samples are cooled to room temperature, they are shown to dissolve with subsequent annealing above 1400 °C. While such defects have been observed before, the important finding that such defects can be dissolved with a short, higher temperature step is key. Earlier work [Breckenridge et al., J. Appl. Phys. Lett. 118, 022101 (2021)] addressing electrical measurements of these types of samples showed that annealing at 1400 °C leads to a dopant activation efficiency that is an order of magnitude higher than that observed at 1300 °C. This work complements earlier work by identifying the inversion domains, which incorporate Mg, and points to the benefits, in terms of defect density and p-type dopant activation, of using higher temperature (>1400 °C) annealing cycles to activate Mg in GaN, even if the Mg-containing inversion domains had been formed during lower temperature annealing. [ABSTRACT FROM AUTHOR]

Mg-doped, graded AlGaN films showed the formation of an impurity band and high, temperature-invariant p-conductivity even for doping levels well below the Mott transition. However, compensating point defects disrupted the impurity band, resulting in an Anderson transition from the impurity band to valence band conduction and a more than tenfold reduction in room-temperature conductivity. This is the first demonstration of Anderson-like localization in AlGaN films. [ABSTRACT FROM AUTHOR]

The combination of optical and mechanical properties of calcium lanthanum sulfide (CLS) makes it an attractive material for optical applications. CLS is a γ -phase La2S3/CaS solid solution above 50:50 La2S3/CaS. Experiments have characterized the effect of composition on the structural, thermal, and optical properties. However, the effect of impurities and other defects, such as porosity, on resulting properties is difficult to deconvolute. We used the density functional theory (DFT) simulations to characterize the effect of La2S3/CaS relative fractions on structural, electronic, mechanical, and vibrational properties of single crystalline CLS solid solutions. We find a decrease in the stiffness with CaS fraction and confirm the experimentally observed increase in the lattice parameter with La2S3 fraction. We also characterized the point defects, including sulfur vacancies, oxygen substituting sulfur, oxygen, and sulfur impurities on lanthanum sublattice vacant sites, and sulfur substituting calcium (vS, OS, OLa, and SLa, respectively). Our defect studies in 90:10 CLS find the neutral charge state configuration to be energetically favorable for all tested configurations except for the sulfur vacancies (vS). [ABSTRACT FROM AUTHOR]

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films after nanosecond pulse laser annealing. For the as-deposited Cu film, we identified the coexistence of two different vacancy-type defects, vacancy clusters (such as V16) and monovacancy-type defects, coupled with impurities. An enlargement in the vacancy size was observed after the laser annealing process. The size of these defects was estimated to be close to V30, and such defects could not be formed by conventional furnace annealing. After furnace annealing at 400 °C, the size of the larger vacancy clusters decreased, but that of the smaller vacancies increased. The observed change in the sizes of vacancies is considered to be related to interactions between vacancies and impurities. The depth profile of the defects varied by changing the laser energy density and the number of laser shots. The impact of laser annealing on the vacancy-type defects was observed even after furnace annealing at 800 °C. Because the presence of point defects in electroplated Cu directly correlates with electromigration and grain growth, the ability of laser annealing to introduce large vacancy clusters in the localized region shows the potential of nanosecond laser annealing as a low-thermal budget process tool for back-end-of-line materials. [ABSTRACT FROM AUTHOR]

The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+δ) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700–900 °C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 °C exhibited intense diffraction peaks along the growth direction corresponding to (000ℓ) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+δ film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+δ can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 °C) and has the potential to be used as a template for III-nitride growth on Si substrates. [ABSTRACT FROM AUTHOR]

Interstitial atoms usually diffuse much faster than vacancies, which is often the root cause for the ineffective recombination of point defects in metals under irradiation. Here, via ab initio modeling of single-defect diffusion behavior in the equiatomic NiCoCrFe(Pd) alloy, we demonstrate an alloy design strategy that can reduce the diffusivity difference between the two types of point defects. The two diffusivities become almost equal after substituting the NiCoCrFe base alloy with Pd. The underlying mechanism is that Pd, with a much larger atomic size (hence larger compressibility) than the rest of the constituents, not only heightens the activation energy barrier (Ea) for interstitial motion by narrowing the diffusion channels but simultaneously also reduces Ea for vacancies due to less energy penalty required for bond length change between the initial and the saddle states. Our findings have a broad implication that the dynamics of point defects can be manipulated by taking advantage of the atomic size disparity, to facilitate point-defect annihilation that suppresses void formation and swelling, thereby improving radiation tolerance.

Al 2 O 3 with the desired electrical insulating properties and thermal shock resistivity has been extensively applied in the field of solid oxide fuel cells and oxygen sensors. However, degradation of the insulating Al 2 O 3 layer is an intractable issue in practical applications. In this study, different point defect structures of Al 2 O 3 were realized with the substitutional doping effect of ZrO 2 and MgO. The MgO dopant provides positively charged oxygen vacancies, whereas the ZrO 2 dopant tends to trigger negatively charged vacancy formation at Al3+ sites. The oxygen vacancy concentration of Al 2 O 3 exhibits the following trend: MgO-doped Al 2 O 3 > Al 2 O 3 > ZrO 2 -doped Al 2 O 3. Furthermore, the densification morphology, insulating properties, and oxygen vacancy migration of Al 2 O 3 have been confirmed to be largely affected by the extrinsic factors. This study indicates that oxygen vacancy migration depends on the applied electric field at high temperatures. As the voltage and temperature increase, oxygen vacancy migration shows obvious electric-field-dependent characteristics, and its aggregation macroscopically shows hole defects. The defect position of Al 2 O 3 is nonstoichiometric Al 2 O 3-x with poor crystallinity. Therefore, it is believed that the oxygen vacancy migration triggered by the second phase directly determines the insulation performance and causes the degradation of Al 2 O 3 materials. [ABSTRACT FROM AUTHOR]

Defect chemistry that results in the thermal processing of dielectric and piezoelectric films, crystals and ceramics ultimately controls the properties and long‐term performance of materials and devices. This paper reviews several thermochemical defect reactions using important perovskite base composition dielectrics including Pb(Zr,Ti)O3, (Na,K)NbO3, (Bi0.5Na0.5)TiO3‒BaTiO3, and Ca(Hf,Ti,Mn)O3. Within this group of perovskite‐based functional materials, we note ways the point defects can be formed to create non‐stoichiometric compositions changing the overall cation‐to‐anion ratios during the synthesis process. These reactions can be developed with the loss of volatile species such as metal and oxygen ions. The relative concentrations of these can impact the over conductions in terms of the mixed contributions of ionic conductivity from the oxygen vacancies and the electronic conductivity, along with microstructure and properties in some cases. [ABSTRACT FROM AUTHOR]

In this study, the influence of foreign and native point defects in magnesium oxide on the sintering process is examined. We have introduced dopants into magnesium oxide, with cations that share similar sizes but possess varying charges to minimize the direct impact of strain. The selected foreign cations were as follows: (1) Li1+, an acceptor that enhances the concentration of oxygen vacancies; (2) Sc3+, a donor that enhances the concentration of magnesium (metal) vacancies; and (3) Zn2+, an isovalent dopant. The results reveal that oxygen vacancies introduced by lithium doping greatly decrease the sintering temperature of magnesium oxide compared to the magnesium vacancies' effect (scandium doping). Zinc doping was found to increase the surface oxygen vacancies with only a minor effect on the sintering temperature. Enhancing the oxygen vacancy concentration by lithium doping creates an additional mechanism for sintering because the anion sublattice is the backbone of the material, and oxygen ion diffusion is the rate‐limiting step. Scandium doping also has a sintering–promoting effect, yet a minor one. The doping factor analysis is considered and implies that aliovalent dopants do not affect the concentration of the fast‐diffusing species, which are native vacancy associates. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO3, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO3−δ with δ ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO3, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO3−δ with δ ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

The point cloud keypoint detection algorithm like USIP that uses downsampling first and then fine-tuning the sampling points cannot effectively detect the defect part of the single view defect point cloud, resulting in the inability to output the keypoints of the defect part. Therefore, this paper proposes the twin structure key point detection algorithm named TSKPD based on the idea of contrastive learning, which uses two single-view defect point clouds to synthesize relatively more complete key points for learning, so as to promote the network model to learn the features of the complete point cloud. The robustness of key point detection of point cloud is effectively improved, and the detection of single view defect point cloud is realized. The test results on ModelNet40 and ShapeNet datasets show that the coverage rate of TSKPD on the missing part of the single view defect point cloud is 12.62 higher than the existing optimal algorithm. [ABSTRACT FROM AUTHOR]

A model for studying displacement damage in irradiated HfO2 ferroelectric thin films was developed using deep learning and a repulsive table, combining the accuracy of density functional theory with the efficiency of molecular dynamics. This model accurately predicts the properties of various HfO2 phases, such as PO (Pca21), T (P42/nmc), AO (Pbca), and M (P21/c), and describes the atom collision-separation process during irradiation. The displacement threshold energies for the Hf atoms, three-coordinated O atoms, and four-coordinated O atoms are 57.72, 41.93, and 32.89 eV, respectively. The defect formation probabilities (DFPs) for the O primary knock-on atoms (PKAs) and Hf PKAs increase with energy, reaching 1. Below 80.27 eV, the O PKAs are more likely to form point defects than the Hf PKAs. Above this energy, the Hf PKAs have a higher DFP because the O PKAs form replacement loops more easily, inhibiting the generation of point defects. This study provides a comprehensive understanding of defect formation, which is crucial for increasing the reliability of HfO2 ferroelectric devices under irradiation. [ABSTRACT FROM AUTHOR]

We present a detailed study on the optical properties of GaAsBi/GaAs multiple quantum well structure, optimized for the active area for vertical-external-cavity surface-emitting lasers. The quantum structure was grown by molecular beam epitaxy with every other barrier made thinner to have a homogeneous structure with high photoluminescence (PL) intensity. PL measurements were carried out in a wide temperature range from 4 to 300 K. The PL band of 1.085 eV was attributed to the optical transition in QWs with 8.0%Bi. The S-shaped temperature dependence of PL peak positions showed high localization effect of 30 meV. The internal quantum efficiency (IQE) was evaluated for the bismide structures with a modified ABB* method, which includes contribution from trap-assisted Auger recombination. The calculations showed low IQE of <0.025% for GaAs0.92Bi0.08/GaAs 12 QWs structure, which was explained by the low growth temperature, resulting in a high density of point defects in the material. [ABSTRACT FROM AUTHOR]

The development of efficient photocatalysts is a mainstay for the advancement of photocatalytic technology. Heterojunction photocatalysts can overcome the inherent limitations of single photocatalysts, integrating the advantages of each component, and achieving efficient separation of photogenerated charges, making them a research focus in the field of photocatalysis. The role of point defects in photocatalytic reactions is diverse and can significantly influence the performance of photocatalysts. This review comprehensively summarizes the latest advancements in point defect engineering for the modulation of heterojunction photocatalysts. First, the types of point defects and their impact on photocatalytic processes are introduced. Subsequently, the common types of heterojunction photocatalysts are presented. Then, in accordance with recent research progress, the regulatory mechanisms of point defects within heterojunction photocatalysts are outlined, with a particular focus on their functions on surface/interfacial properties and photogenerated charge transfer processes. Finally, the challenges faced by point defect engineering in optimizing heterojunction photocatalysts and promising solutions are proposed. This review provides an in‐depth understanding of the role of point defect engineering in heterojunction photocatalysts, with the expectation of offering insights into the development of highly active photocatalytic materials. [ABSTRACT FROM AUTHOR]

ABSTRACT Objective Materials and Methods Results Conclusions Clinical Significance To investigate the surface roughness on cementoenamel junction after application of various rubber‐dam retraction clamps for different durations.Fifty‐four extracted human molar teeth were used. Various retraction clamps were placed on the cementoenamel junction. There are three main examination groups in the study. Group 1 (n = 6) included a polymer clamp (SoftClamp, Kerr Hawe, Switzerland), Group 2 (n = 6) included a metal clamp with a flat edge (Black Line RDCM7X, Hu‐Friedy Group, USA), and Group 3 (n = 6) included a metal clamp with a serrated edge (Fiesta Color Coded, Coltene, USA). All clamps were applied for 30 min, 1, and 2 h. Surface roughness measurements were performed using a profilometer before and after the clamp application and surface morphology was assessed through the SEM images. One‐way ANOVA was used to compare three or more groups. Percentage changes were evaluated using the Kruskal–Wallis test, followed by Dunn's test for post hoc analyses. The deemed significance was set at p < 0.05.Between the initial and the final roughness measurements, after 30 min of clamp application, only Group 3 showed significant increases in roughness (p = 0.001). After 1 and 2 h of clamp application, there were significant increases in roughness for all groups. No significant differences in percentage changes for all groups in 30 min and 2 h of application (p = 0.220 and p = 0.091, respectively). However, Group 1 presented significantly lower surface roughness in percentage after the 1 h of application (p = 0.040). No significant differences in the percentage changes in roughness were observed within the groups for 30 min, 1, and 2 h applications (p = 0.220, p = 0.884, and p = 0.755 for Groups 1, 2, and 3, respectively). In SEM analysis, deep point microstructure defects were seen as the clamp application time increased.Rubber‐dam clamp application may cause damage to the cementoenamel junction area. However, the level of damage is clamp‐type‐dependent. Slight scratch‐type damages were observed on teeth with plastic clamps, while metal clamps generally caused cracks. The increase in the duration of the same rubber‐dam clamp application was not considered an effective factor regarding the damage.During rubber‐dam isolation, clamp type and duration of the application may cause damage to the tooth surface or progress an existing defect. Examining the teeth before selecting the clamp might be beneficial for minimizing dental tissue damage. [ABSTRACT FROM AUTHOR]

Epitaxial strain is known to significantly influence the structural and functional properties of oxide thin films. However, its impact on point defect concentration has been less explored. Due to the challenges in experimentally measuring thin-film stoichiometry, computational studies become crucial. In this work, we use first-principles calculations based on density functional theory to investigate the formation and stability of Bi vacancies and Bi-O vacancy pairs in BiFeO3 (BFO) under (111) epitaxial strain. Our results demonstrate that compressive strain (−4%) decreases the formation enthalpy of Bi vacancies by 0.88 eV, whereas tensile strain (4%) increases it by 0.39 eV. Out-of-plane (OP) Bi-O vacancy pairs exhibit enhanced stability under both compressive and tensile strain, with formation enthalpy reductions of 1.49 eV and 1.05 eV, respectively. In contrast, in-plane (IP) vacancy pairs are stabilized under compressive strain but are insensitive to tensile strain. Finally, we discuss how these findings influence Bi stoichiometry during thin-film growth and the role of local strain fields in the formation of conducting domain walls. [ABSTRACT FROM AUTHOR]

While scaling down resistive random access memory devices can bring many benefits, it also introduces uncertainties during operation. One example is the wide distribution of the resistances in the low‐resistance state (LRS) when the device is connected by a small current compliance (Ic$I_{\text{c}}$) in the microampere range. During the operation under such small Ic$I_{\text{c}}$, it is believed that the stochastic migration of oxygen vacancies in the oxide layer plays an important role for the variability. To this regard, the model where oxygen vacancies are treated as point defects and the kinetic Monte Carlo method is applied for the stochastic migration of vacancies is extended. The relation between the macroscopic observations in measurements and the microscopic vacancy distribution are discussed. It turns out that three representative configurations are sufficient to describe the vacancy distribution in the LRS. The large spread of the resistance seen in the cycle‐to‐cycle statistics is then due to the change from one of the configuration to the other. The origin for the change between configurations is discussed in terms of the anisotropic zero‐field energy barrier of the diffusion of vacancies. [ABSTRACT FROM AUTHOR]

High-pressure effects can be used to effectively optimize the thermoelectric performance of wide-bandgap oxides. We build upon this finding to show that the synergistic effects of doping with aluminum and graphene composite give excellent thermoelectric performance under high pressure. By employing the parabolic band model, the Pisarenko curves are derived at different pressures, coupled with the band structure of Al-doped ZnO. An analysis indicates that pressure-induced narrowing of the bandgap in Al-doped ZnO reduces the electron excitation energy, thereby optimizing the electrical properties of the samples. The Debye Callaway model is also used to fit the lattice thermal conductivity of the samples, thus enabling an in-depth analysis of the phonon scattering mechanisms. Our analysis suggests that graphene composites significantly enhance point defect scattering and Umklapp scattering, thus increasing the phonon relaxation time and effectively reducing the lattice thermal conductivity of the samples. The improvement in the figure of merit (zT) of ZnO is attributed to the simultaneous enhancement of its electrical properties under high pressure and the synergistic optimization of reducing the lattice thermal conductivity through doping and composites. In this work, we consider a fixed doping ratio of Al and a constant proportion of graphene composite, and analyze the microstructure and thermoelectric properties of 0.1C–ZnAl 0.04 O (C–ZnAlO) samples synthesized under pressures ranging from 1 to 5 GPa, with the aim of elucidating the influence of pressure and graphene composite on the electro-acoustic transport properties of ZnO. We find that the zT value for a sample synthesized at 5 GPa is increased to 0.27 at 973 K. [ABSTRACT FROM AUTHOR]

ZnO is a promising thermoelectric ceramic material, but the low electrical conductivity and high thermal conductivity restrict its satisfactory thermoelectric performance. Chemical doping is an effective way to improve the thermoelectric properties of ZnO. Due to the valence states and similar ionic radii of Fe3+ and Zn2+, Fe was selected as the effective dopant for ZnO. In this work, Fe-doped ZnO samples were prepared using hydrothermal synthesis and microwave sintering technology under oxygen-depleted conditions. The electrical conductivity of sintered Fe-doped ZnO was greatly improved owing to the energy band adjustment. The maximum power factor of 3108 μW/mK2 at 800 K was obtained from Zn 0.997 Fe 0.003 O, which is about 4.4 times greater than that of pure ZnO. Meanwhile, the small grain size (300–500 nm) and residual pores resulted from microwave rapid sintering in an oxygen-depleted environment, as well as the point defects caused by Fe3+ substituting for Zn2+, significantly reduced the thermal conductivity. Finally, the highest ZT value of 0.91 has been achieved in Zn 0.997 Fe 0.003 O at 800 K. [ABSTRACT FROM AUTHOR]