Intrinsic Structural Defects Research Articles

High‐resolution cathodoluminescence of calcites from the Cold Bokkeveld chondrite: New insights on carbonatation processes in CM parent bodies

AbstractCarbonates, as secondary minerals found in CM chondrites, have been widely employed for reconstructing the composition of the fluids from which they precipitated. They also offer valuable insights into the hydrothermal evolution of their parent bodies. In this study, we demonstrate that high‐resolution cathodoluminescence (HR‐CL) analyses of calcites derived from the brecciated Cold Bokkeveld CM2 chondrite can effectively reveal subtle compositional features and intricate zoning patterns. We have identified two distinct types of cathodoluminescence (CL) centers: a blue emission band (approximately 375–425 nm), associated with intrinsic structural defects, and a lower energy orange extrinsic emission (around 620 ± 10 nm), indicating the presence of Mn cations. These compositional variations enable discrimination between the calcite grain types previously designated as T1 and T2 in studies of CM chondrites. T1 calcites exhibit variable CL and peripheral Mn enrichments, consistently surrounded by a rim composed of Fe‐S‐rich serpentine–tochilinite assemblage. Conversely, T2 calcites display homogeneous CL and more abundant lattice defects. These polycrystalline aggregates of calcite grains, devoid of serpentine, contain Fe‐Ni sulfide inclusions and directly interface with the matrix. We propose that changes in the Mn content of calcite (indicated by the intensity of orange CL emission) are influenced by variations in redox potential (Eh) and pH of the fluid phase. This proposed hydrothermal evolution establishes a parallel between terrestrial serpentinization followed by carbonation processes and the aqueous alteration of CM chondrites, warranting further exploration and investigation of this intriguing similarity.

Intrinsic Grain Boundary Structure and Enhanced Defect States in Air-Sensitive Polycrystalline 1T'-WTe2 Monolayer.

Monolayer WTe2 has attracted significant attention for its unconventional superconductivity and topological edge states. However, its air sensitivity poses challenges for studying intrinsic defect structures. This study addresses this issue using a custom-built inert gas interconnected system, and investigate the intrinsic grain boundary (GB) structures of monolayer polycrystalline 1T' WTe2 grown by nucleation-controlled chemical vapor deposition (CVD) method. These findings reveal that GBs in this system are predominantly governed by W-Te rhombi with saturated coordination, resulting in three specific GB prototypes without dislocation cores. The GBs exhibit anisotropic orientations influenced by kinks formed from these fundamental units, which in turn affect the distribution of grains in various shapes within polycrystalline flakes. Scanning tunneling microscopy/spectroscopy (STM/S) analysis further reveals metallic states along the intrinsic 120° twin grain boundary (TGB), consistent with computed band structures. This systematic exploration of GBs in air-sensitive 1T' WTe2 monolayers provides valuable insights into emerging GB-related phenomena.

Growth and impact of intrinsic interlayers in high temperature vapor phase epitaxy of GaN

Structural quality of GaN layers grown on foreign substrates is usually improved by applying masks or interlayers, which interact with the crystal structure defects, mainly with threading dislocations, and consequently reduce their density. In this work, GaN interlayers with intrinsic defect structures were employed as barriers impeding the propagation of threading dislocations. The GaN samples were produced in a multistage deposition process by high-temperature vapor phase epitaxy (HTVPE). They consisted of GaN seed layers deposited on 15 × 15 mm2 (001)-oriented sapphire substrates, structured GaN interlayers and GaN top layers. The structuring of the interlayers was facilitated by changing the substrate temperature and the V/III ratio during the growth. The optical and scanning electron microscopies revealed that the structured interlayers contain pyramidal facets, vertical trenches and elongated voids. The results of X-ray diffraction and Raman spectroscopy have shown that these microstructure features are able to reduce the density of threading dislocations in the top layer and the tensile residual stress that develops in the top layer during the deposition process. These results demonstrate the potential of the intrinsic interlayer concept for the in-line defect and stress engineering in HTVPE GaN layer stacks.

Modulating Intrinsic Defect Structure of Fibrous Hard Carbon for Super‐Fast and High‐Areal Sodium Energy Storage

AbstractCreating defects by heteroatom doping is commonly approved in respect of enhancing fast sodium‐ion storage of carbonaceous anodes ascribing to rich external defects, but the contribution of intrinsic carbon defects (e.g., vacancy) in improving rate‐capability has rarely been investigated. Here, a bio‐derived fibrous hard carbon with high‐reversible intrinsic defects is synthesized via metal‐assisted‐catalytic strategy. It is found that sp2‐hybridized carbon is united through catalytic‐tuning during thermal‐etching process along with the formation of low‐potential planar intrinsic carbon defects (vacancies and non‐hexagonal carbon rings) by sacrificing poor‐reversible carbon edges. Such integrated structures greatly improve the reversibility of defective sites and charge transfer kinetics, thus enhancing the slope sodium‐storage capacity of carbon below 1 V even at high current densities. Thus‐obtained fibrous carbon anodes enable boosted initial coulombic efficiency (≈90%) and ultrahigh‐rate capability in both half‐ (222.2 mAh g−1at 50 A g−1) and full‐cell (200 C, charged/discharged in ≈10 s). Interestingly, compared with meso‐/macroporous structures, such micropore‐dominated carbon fibers are more beneficial for fabricating high‐mass‐loading, crack‐free thick electrodes (>10 mg cm−2) with considerable areal‐capacity over 3.0 mAh cm−2. Paired with high‐loading Na3V2PO4 cathode (14.4 mg cm−2), full‐cell achieves admirable areal‐capacity over 1.4 mAh cm−2 and peak areal‐energy/power‐density of 3.2/74 mW cm−2.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

Low Temperature Synthesis of 2D p-Type α-In2Te3 with Fast and Broadband Photodetection.

2D compounds (A = Al, Ga, In, and B = S, Se, and Te) with intrinsic structural defects offer significant opportunities for high-performance and functional devices. However, obtaining 2D atomic-thin nanoplates with non-layered structure on SiO2/Si substrate at low temperatures is rare, which hinders the study of their properties and applications at atomic-thin thickness limits. In this study, the synthesis of ultrathin, non-layered α-In2Te3nanoplates is demonstrated using a BiOCl-assisted chemical vapor deposition method at a temperature below 350°C on SiO2/Si substrate. Comprehensive characterization results confirm the high-quality single crystal is the low-temperature cubic phase α-In2Te3 , possessing a noncentrosymmetric defected ZnS structure with good second harmonic generation. Moreover, α-In2Te3 is revealed to be a p-type semiconductor with a direct and narrow bandgap value of 0.76eV. The field effect transistor exhibits a high mobility of 18 cm2 V-1s-1,and the photodetector demonstrates stable photoswitching behavior within a broadband photoresponse from 405 to 1064nm, with a satisfactory response time of τrise = 1ms. Notably, the α-In2Te3 nanoplates exhibit good stability against ambient environments. Together, these findings establish α-In2Te3 nanoplates as promising candidates for next-generation high-performance photonics and electronics.

A Comprehensive Review on Defects-Induced Voltage Losses and Strategies toward Highly Efficient and Stable Perovskite Solar Cells

The power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has reached 26.1% in small-scale devices. However, defects at the bulk, surface, grain boundaries, and interfaces act as non-radiative recombination centers for photogenerated electron-hole pairs, limiting the open-circuit voltage and PCE below the Shockley–Queisser limit. These defect states also induce ion migration towards interfaces and contribute to intrinsic instability in PSCs, reducing the quasi-Fermi level splitting and causing anomalous hysteresis in the device. The influence of defects becomes more prominent in large-area devices, demonstrating much lower PCE than the lab-scale devices. Therefore, commercializing PSCs faces a big challenge in terms of rapid decline in working performance due to these intrinsic structural defects. This paper provides a comprehensive review of recent advances in understanding the nature and the classification of defects, their impact on voltage losses, device parameters, intrinsic stability, and defect quantification and characterization techniques. Novel defect passivation techniques such as compositional engineering, additive engineering, post-treatments, dimensionality engineering, and interlayer engineering are also reviewed, along with the improvements in PCE and stability based on these techniques for both small-area devices and large-area roll-to-roll coated devices.

Electronic properties of Fe impurities in SnS van der Waals crystals – Revealing high-mobility holes

Defect control is critical to achieve long carrier lifetimes in semiconductors. SnS is a promising thermoelectric and photovoltaic material, in which native defects play a detrimental role, particularly in photovoltaics. In this study, we investigated the Fe-doping of SnS and the interaction of Fe impurities with native defects in a series of single crystals of Sn1-xFexS up to concentrations of x = 0.05. Although the doped single crystals appear rather disordered, the hole mobility is very high (∼8500 cm2V-1s−1 at 30 K for Sn0.99Fe0.01S), suggesting that hole-mediated charge transport in this material is largely insensitive to extrinsic impurities. Charge transport analysis suggests that the incorporation of Fe atoms leads to the healing of the intrinsic defect structure and the exclusion of minority electrons from charge transport, allowing the observation of high hole mobility.

Multi-colour emission from ZnO[SO4]:Eu2+ nanophosphors: Effects of SO42- and Eu2+ doping concentration

Blue-emitting ZnO-SO4:Eu2+ powder phosphors were synthesized via solid state reaction method. Based on the X-ray diffraction (XRD) data, hexagonal wurtzite structures of ZnO were formed. Further structural elucidation via Raman spectroscopy showed a peak at 439 cm−1 associated with E2hgh optical mode that is a distinctive characteristic band of hexagonal wurtzite ZnO phase. The ZnO powders were composed of distorted spherical nanoparticles, which were agglomerated together as confirmed from scanning electron microscopy images. After incorporation of SO42- and Eu2+ into the ZnO lattices sites, the particle shapes became irregular. When excited at 351 nm with Xenon lamp, our samples emitted UV and blue-green visible light associated, respectively, with excitonic recombination and intrinsic structural lattice defects in ZnO. Both the photoluminescence (PL) peak intensity and positions of these emissions were influenced by SO42- and Eu2+ ions. The blue emission was dependent on the Eu2+ content with the largest intensity measured from the sample doped with 1.0 mol% of Eu2+ ions. Mechanisms of energy transfer and concentration quenching effect are discussed.

Research Progress on the Wear and Corrosion Resistant Plasma Electrolytic Oxidation Composite Coatings on Magnesium and Its Alloys

Plasma electrolytic oxidation (PEO), as a cost effective and environmentally friendly technology, has been applied on magnesium and its alloys to improve wear and corrosion resistance. Additionally, combining with particles addition in the electrolyte and/or various post-treatments could diminish the intrinsic structural defects of the PEO coatings and provide multifunctionalities, including wear resistance, corrosion resistance, self-lubrication, and self-healing. This paper reviews recent progress on PEO composite coatings prepared by in situ incorporation of functional particles and/or post-treatments on magnesium and its alloys. The focus is given to the microstructural and functional changes of the PEO coatings, particularly on the wear and corrosion behaviors.

Does photoinduced structural change by β-rhombohedral boron occur at room temperature?

β-rhombohedral boron (β-B) is an intriguing solid among the elements. The crystal structure of β-B is widely accepted as a complex structure based on the B12 clusters, and with a lot of intrinsic structural defects. In the last decade, β-B was proved to be the only elemental semiconductor that exhibits the self-compensation property accompanied by changing structural defects during atom doping. Moreover, it is reported that various physical properties of β-B change discontinuously around 550 K, which may originate from defect diffusion [S. Hoffmann and H. Werheit, Solid State Sciences 14, 1572 (2012)]. We previously reported that a volume expansion of about 1.5% takes place above this temperature (between 650 K and 850 K). On the other hand, this expanded structure is stable in dark conditions for more than 4.5 months. Light irradiation at room temperature reverses the volume back to the initial state, and a possible scenario will be discussed in this paper.

Development, characterization, and properties of LnSmZr2O7 (Ln = Dy, Ho, Yb) defect fluorite functional ceramics

LnSmZr2O7 (Ln = Dy, Ho, Yb) functional nanoceramics are prepared through a citrate-nitrate auto-combustion method. High-density pellets using the powder are obtained by sintering at 1530 °C for 2 h. The defect fluorite structure of the powder and sintered samples is established using XRD and Raman analysis. The morphology of the powder analyzed using Transmission Electron Microscopy revealed the nanocrystalline nature of the combustion powder. The microstructure of the sintered sample analyzed using Field emission Scanning Electron Microscopy showed increased grain growth with larger cationic substitution. LnSmZr2O7 (Ln = Dy, Ho, Yb) have an indirect-allowed optical wide band gap and exhibit photoluminescence due to intrinsic defect structure. LnSmZr2O7 (Ln = Dy, Ho, Yb) are pure oxide ion conductors in the temperature range from 400 °C to 900 °C, with conductivity values of 0.89 × 10−3 S/cm, 0.72 × 10−3 S/cm and 0.60 × 10−3 S/cm, respectively, at 900 °C.

Structural analysis and properties of novel Terbium Samarium Zirconate functional ceramic

Synthesis and characterization of Terbium Samarium Zirconate (TbSmZr2O7) is reporting for the first time. XRD analysis along with Raman spectroscopy revealed that citrate-nitrate combustion synthesized TbSmZr2O7 powder and sintered sample crystallize in defect-fluorite structure with Fm3‾m space group. This composition lies at the pyrochlore-defect fluorite phase boundary. TEM analysis showed that the powder particles are in size range between 3 nm and 9 nm. FESEM image showed a well-sintered pellet surface with a grain size distribution between 0.1 μm and 2 μm. TbSmZr2O7 has an optical band gap of 1.66 eV and has an indirect allowed mechanism of optical transition. Due to intrinsic defect structure, TbSmZr2O7 exhibits photoluminescence with excitation bands at 270 nm and 313 nm and emission bands at 364 nm and 400 nm. Impedance spectroscopic analysis established that from 400 °C to 900 °C TbSmZr2O7 is a pure oxide ion conductor with a conductivity value of 1.9 × 10−3 S/cm at 900 °C.

Intrinsic point defects and the n -type dopability of Bi2MoO6 with higher photocatalytic performance: A hybrid functional study

Intrinsic point defects play a vital role in regulating the electronic structure and electron carrier concentration (${n}_{0}$) of ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$, which has been demonstrated as a promising photocatalyst. Unfortunately, the source of $n$-type conductivity for its intrinsic defects has proved challenging. Using first-principles hybrid density functional calculations, we investigate the formation energies and electronic structure of intrinsic point defects in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$. The self-consistent Fermi energies and equilibrium carrier and defect concentrations are calculated using the sc-fermi code based on thermodynamic simulation. It is found that the easy formation of the +2 charged O vacancy (${V}_{\mathrm{O}}^{2+}$) is responsible for its intrinsic $n$-type conductivity under Bi-rich/O-poor conditions, and thus, it can have a very high density (reaching up to ${10}^{19} \mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$), making it the dominant defect in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$. Under O-rich conditions, only adopting both ${\mathrm{D}}^{+}$ doping and quenching methods in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$ can reach a higher carrier density $(>{10}^{17}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3})$. Moreover, under the broad range of chemical potentials of $\ensuremath{-}2.50\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{Bi}}<0, \ensuremath{-}6.32\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{Mo}}<\ensuremath{-}1.48\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, and $\ensuremath{-}2.19\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{O}}<\ensuremath{-}0.65\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, after quenching from 700 to 300 K, ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$ can be effectively donor doped without significant compensation, and ${n}_{0}$ increases as $\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{O}}$ decreases or temperature increases. Our results can give a guide in selecting optimum growth and quenching conditions to achieve high $n$-type doping and suppress compensation.

Effect of low-dose-rate ionizing radiation on the complex dielectric permittivity of CdZnTe crystals

For the first time, the change in the real and imaginary parts of Cd1-xZnxTe crystals complex dielectric permittivity when exposed to ionizing radiation with a small exposure dose rate (about hundreds of μR/h) has been studied. Significant changes in the values of both parts of complex dielectric permittivity have been revealed. Regularities of specified changes have been established and explained taking into account a different radiation effect on free and bound charges. The basis of effect is the changes in the charge carrier localized states of point defect associates. Their appearance is due to a high concentration and a variety of intrinsic structural defects in the studied crystals as a consequence of the deviation of the crystal composition from the stoichiometric one.

Unveiling the Intrinsic Structure and Intragrain Defects of Organic-Inorganic Hybrid Perovskites by Ultralow Dose Transmission Electron Microscopy.

Transmission electron microscopy (TEM) is a powerful tool for unveiling the structural, compositional, and electronic properties of organic-inorganic hybrid perovskites (OIHPs) at the atomic to micrometer length scales. However, the structural and compositional instability of OIHPs under electron beam radiation results in misunderstandings of the microscopic structure-property-performance relationship in OIHP devices. Here, ultralow dose TEM is utilized to identify the mechanism of the electron-beam-induced changes in OHIPs and clarify the cumulative electron dose thresholds (critical dose) of different commercially interesting state-of-the-art OIHPs, including methylammonium lead iodide (MAPbI3 ), formamidinium lead iodide (FAPbI3 ), FA0.83 Cs0.17 PbI3 , FA0.15 Cs0.85 PbI3 , and MAPb0.5 Sn0.5 I3 . The critical dose is related to the composition of the OIHPs, with FA0.15 Cs0.85 PbI3 having the highest critical dose of ≈84 e Å-2 and FA0.83 Cs0.17 PbI3 having the lowest critical dose of ≈4.2 e Å-2 . The electron beam irradiation results in the formation of a superstructure with ordered I and FA vacancies along <110>c , as identified from the three major crystal axes in cubic FAPbI3 , <100>c , <110>c , and <111>c . The intragrain planar defects in FAPbI3 are stable, while an obvious modification is observed in FA0.83 Cs0.17 PbI3 under continuous electron beam exposure. This information can serve as a guide for ensuring a reliable understanding of the microstructure of OIHP optoelectronic devices by TEM.

Mechanism of Transverse Charge Transfer in Thin Films of Hexagonal Boron Nitride

A mechanism of transverse charge transfer through hexagonal boron nitride (h-BN) in a MIS structure has been studied. Experimental data for charge transfer have been analyzed in terms of different models of charge transfer in insulators. It has been shown that charge transfer in h-BN is described by the model of phonon-assisted tunneling between neutral traps. The thermal and optical energies of phonon-coupled traps in h-BN have been determined. Based on charge transfer measurements, XPS spectra, and the ab initio electronic structure of intrinsic defects in h-BN it has been found that boron–nitrogen divacancies are most probably responsible for charge transfer in h-BN and transfer is provided by electrons.

Analysis of the electronic structure of β-SiO2 intrinsic defects based on Density Functional Theory

In order to characterize the effect of β-SiO2 intrinsic defects on the properties of the perfect structure, the electronic properties of the perfect β-SiO2 and its four typical intrinsic defects under the generalized gradient approximation (GGA) based on Density Functional Theory (DFT) were performed, and the defect formation energy, energy band, density of states (DOS) and differential charge density were calculated. The defect formation energy calculation results showed that interstitial defects were easier to form but less stable than vacancy defects. Meanwhile, the analysis of energy band and DOS indicated that the perfect and defective structures of β-SiO2 were indirect band gap insulators. Furthermore, the appearance of DOS at the Fermi level in the silicon interstitial structure and the energy band passing through the Fermi level indicated that the conductivity of the structure was improved. Moreover, the study of differential charge density illustrated charge transferred from silicon atoms to oxygen atoms, and Si-O covalent bonds with strong polarity were formed between silicon and oxygen atoms. Our studies could provide a theoretical basis for the study of the evolution of intrinsic defects and damages in ultra-precision machining such as ion beam figuring.

Defect study of phosphorous doped a-Si:H thin films using cathodoluminescence, IR and Raman spectroscopy

The phosphorous (P) doping induced defects and deviation in microstructural properties of a-Si:H films have been investigated by Infrared (IR), Raman and Cathodoluminescence (CL) spectroscopy. The analysis of local vibration mode of IR and Raman spectra points out the evolution of defects and cluster structure with a P-doping in a-Si:H films. Undoped a-Si: H films show no CL spectra while it emerges in P-doped films. Intensification in CL spectra with P-doping intimates that the crystallites and defects in films are the origin of CL spectra. CL peaks are emanated from intrinsic structural defects, interstitial cations and two-fold coordinated silicon in films. Peaks at 784 nm and 945 nm in CL spectra are originated from Si micro-crystals.

Insight into H2S production from CS2 hydrolysis for heavy metals treatment: In-situ FT-IR and DFT studies over crystalline phase-dependent ZrO2

H2S is an efficient vulcanizing reagent for heavy metals treatment in nonferrous smelting industries, yet these industries lack of H2S source is a well known problem. In this study, CS2 was hydrolyzed to a high concentration of H2S (>20 vol%) with different crystalline phase zirconium oxide catalysts. The metastable tetragonal ZrO2 (t-ZrO2) exhibited a sunk octahedron structure was successfully synthesized by calcination of MOF-808. Compared to monoclinic ZrO2 (m-ZrO2), it obtained excellent H2S production performance, which can reach near-perfect 100 % at 450 °C. Furthermore, experimental results shown that KOH modified t-ZrO2 could increase CS2 hydrolysis activity due to it is a base catalytic reaction. The in-situ FT-IR demonstrated that reaction sequences followed the order of CS2 → COS → H2S, in which CS2/H2O adsorption and CO2 desorption would influence the hydrolysis efficiency. t-ZrO2 obtained better CS2 adsorption, hydrophobicity, and CO2 desorption than m-ZrO2, which were attributed to intrinsic structure and abundant surface defects. Subsequently, DFT results profiled that cleave of the first CS bond in CS2 was rate-determining step with the activation energy about 63 kJ/mol over t-ZrO2.