Low Defect Research Articles

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Anomalous X-ray pulse responses in MAPbBr3 single crystal-based detectors

Organic-inorganic perovskite single crystals (SCs) are considered promising semiconductors for high-sensitivity X-ray detectors because of their strong X-ray interaction, low-temperature processability, and excellent properties such as long diffusion length, low defect density, and long carrier lifetime. However, the specific pulse response of MAPbBr3 SC-based X-ray detectors frequently exhibits a tail and over/undershoots at several conditions, which degrades the X-ray image quality; however, no detailed analysis of these characteristics has been reported thus far. For high-resolution X-ray imaging, it is necessary to obtain an ideal pulse response that is free of tails and over/undershoots. In this study, we investigated the specific X-ray responses of solution-grown MAPbBr3 SC-based X-ray detectors under various externally applied voltages. Based on the study on charge carrier dynamics, we analyzed the origin of the tail and over/undershoots in X-ray pulse response shapes. We theoretically verified that the unideal pulse response in perovskite SC-based X-ray detectors is attributed to the defect states inherent in perovskite SCs.

Vacancy and Growth Modulation of Cobalt Hexacyanoferrate by Porous MXene for Zinc Ion Batteries

AbstractPrussian blue analogs (PBAs) featuring with 3D open framework are recognized as promising cathode candidates for Zinc‐ion batteries (ZIBs). However, challenges such as unsatisfactory active site utilization, low conductivity, and abundant structural vacancies have impeded fulfillment of their potential. In this work, a conductive in‐plane porous MXene is for the first time adopted as a multifunctional host material to enhance cobalt hexacyanoferrate (CoHCF) growth and crystallinity. Particularly, the uniform surface charges on MXene are identified to induce anisotropic and highly crystalline CoHCF, which are critical to alleviating the practical drawbacks associated with the PBAs family. Empowered by the targeted modification, the CoHCF nanotube/MXene composite realizes high surface area and low defectiveness, resulting in an impressive capacity of 197 mAh g−1 at 0.1 A g−1 and capacity retention of 95.3% over 3000 cycles at 2.0 A g−1. X‐ray spectroscopy and density functional theory (DFT) reveal that Co─C bonds in the heterostructure facilitate rapid electron/Zn‐ion transfer, enhancing Zn storage kinetics. To validate practical applicability, pouch cells incorporating Zn|CoHCF/MXene are further examined. This composition strategy, utilizing MXene as a multifunctional template, enhances the surface area, conductivity, and crystallinity of PBAs as cathodes for ZIBs, showcasing the significant potential for large‐scale energy storage applications.

Dielectric properties of hafnium oxide film prepared by HiPIMS at different O2/Ar ratios and their influences on TFT performance

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to higher crystallinity, higher density, and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased, thereby leading to lower crystallinity, lower density, and higher oxygen vacancy defect concentration of the film, therefore deteriorating the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric field (4.7 MV/cm), which should be attributed to the high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance, featuring a remarkably low subthreshold swing of 0.13 V/decade. It also exhibited fair stability against bending and gate bias stress.

Propeller vs. free fasciocutaneous flap in reconstruction of complex lower limb defects–A prospective study

BackgroundOf all body regions, lower extremity wounds have been and remain the greatest challenge. Free flaps have been accepted as a reasonable option to solve this dilemma, but they require the complexity of microsurgery. This study aimed to compare the postoperative and clinical outcomes of propeller flap and fasciocutaneous free flap in the reconstruction of complex lower limb defects. Materials and methodsThis randomized controlled trial was conducted from July 2021 to June 2023. Selected patients were randomized into two groups: the propeller flap group and fasciocutaneous free flap group. Demographic data, preoperative parameters, and postoperative parameter, including esthetic analysis, scar assessment, neurosensory analysis, psychosocial analysis, and lower extremity function, were estimated and statistically significant compared between the two study groups. ResultsRoad traffic accident (73.3%) was the most common etiology for lower limb defects in both groups. The foot and lower third of the leg were the most common site of defect, constituting 79.99%. The duration of surgery was significantly shorter in propeller flap as compared to fasciocutaneous free flaps. Flap size was smaller, with better neurosensory improvements in propeller flap group. Esthetic analysis, scar assessment, psychosocial analysis, and lower extremity functional analysis yielded similar results in both study groups. ConclusionPropeller flap has better outcomes compared to free flap in terms of smaller size of flap, shorter duration of surgery, and reduced length of hospital stay. Comparable results were obtained with respect to esthetic score, scar assessment score, psychosocial analysis, and neurosensory recovery and lower extremity functional score.

Reduced phonon coupling via controlled defect levels in blue emitting CsPbBr3 nanoplatelets

Metal-halide perovskites (MHPs) are promising materials for light-emitting diodes (LEDs) because of their high color purity, wide gamut, and low-cost processing. However, blue-emitting MHP LEDs exhibit low external quantum efficiencies because they are more susceptible to defect states with a larger energy bandgap compared to their green and red counterparts. Current strategies for achieving blue-emitting MHP LEDs involve compositional engineering; however, the ion migration of mixed halides imposes significant challenges related to abundant trap states. Therefore, in this study, we systematically investigated the effects of short organic and inorganic ligands with characteristic molecular structures and adjacent moieties on the optoelectronic characteristics of low-dimensional CsPbBr3 nanoplatelets (NPLs) used as blue emitters in PeLEDs. Inorganic ligand (i.e., hydrazine monohydrobromide; HZBr) treatment achieved the most significant photoluminescence enhancement (∼10 fold) while preserving crystalline morphology and colloidal stability. Temperature-dependent photophysical properties reveal that HZBr treatment eliminates band tail states arising from lower defect levels in highly confined CsPbBr3 NPLs. Therefore, it suppresses defect trapping and electron–phonon coupling, thereby reducing thermal quenching properties. The HZBr-treated NPLs were integrated into blue perovskite LEDs and demonstrated a narrow emission peak at 471 nm.

Few-layer graphene production through graphite exfoliation in pressurized CO2 assisted by natural surfactant

Graphene research has captivated researchers worldwide, propelling innovation across diverse industries. Through the liquid-phase exfoliation methodology of graphite powder, we have demonstrated a rapid route for obtaining few-layer and multi-layer graphene using a natural surfactant, cardanol. Aqueous phase exfoliation of graphite in the presence of cardanol as a surfactant was conducted to obtain pre-exfoliated graphite suspensions. The influence of different ultrasonication times, 10, 20, and 30 min, and contact times with the surfactant, 1 and 60 min, on the stability and concentration of dispersed exfoliated graphite was evaluated. Results indicate that ultrasonication for 20 min resulted in improved stability and reduced graphene flake sizes, making it suitable for scalable graphene production. Subsequently, the most stable dispersions of exfoliated graphite were subjected to CO2-pressurized treatment. Promising results were obtained when employing cardanol at its critical micelle concentration. The graphene exhibited good structural quality, low defect density, and small stacking, with an average size of 15 nm, where 40 % of the stacked graphene was smaller than 5 nm. The findings provide valuable recommendations for the scalable production of graphene with multilayers and a few layers (FLG/MLG), using cardanol, a friendly surfactant, and a novel method of exfoliation utilizing supercritical CO2. This technology represents an innovative approach, with potential applications in supercapacitors, solar cells, biosensors, polymer composites, and advanced materials.

The effect of hydrogen-helium synergism on dislocation loops in RAFM steel at different temperatures by dual-beam ion irradiation

Simultaneous Fe+H ion irradiation (denoted as Fe+H) and Fe+H ion irradiation with pre-implantation of He (denoted as He/Fe+H) were carried out on Chinese Low-Activation Martensitic (CLAM) steels at 350 ℃-550 ℃ to investigate the synergistic effect between H and He. The peak dose was 15 dpa, the He concentration in the observation area was 11 appm/dpa and the H concentration was 44 appm/dpa. The microstructure and hardening of the irradiated samples were evaluated by TEM and nanoindentation, respectively. Bubbles were not observed in irradiated CLAM steels at all temperatures, which implies that the promotion of bubbles by H may not be as strong as that by He and that H attenuates the promotion of bubbles by He. The hardening induced by He/Fe+H irradiation at 450 °C is about 1.6 times that of Fe+H irradiation, the synergistic effect of H and He is most significant at this temperature. Comparison with Fe+He irradiation and single Fe irradiation reveals that Fe+H irradiation at 350 °C induces lower interstitial defect damage than Fe+He irradiation, but the level of interstitial defects induced by the synergistic effect of both H and He with displacement damage is comparable at higher temperatures. The average size of dislocation loops induced by Fe+H irradiation is between that of single Fe irradiation and Fe+He irradiation, but the number density of dislocation loops induced by Fe+H irradiation is higher than that of Fe+He irradiation. The synergistic effect of He with displacement damage tends to promote the growth of dislocation loops, while the synergistic effect of H tends to promote the nucleation of dislocation loops.

Optimal cross-linking of MXene-based membranes for high rejection and low adsorption with long-term stability for water treatment

The unique layered structure and abundant 2D nanochannels of MXene membranes have demonstrated outstanding permeability, indicating their great potential in the field of water treatment. However, their unstable interlayer spacing and irregular layer structure have limited their ability to separate small molecular pollutants effectively. In this study, we successfully prepared composite MXene membranes with high rejection and low adsorption properties by exploiting the differences in the surface functional groups and chain lengths of dopamine (DA) and polyethylene glycol (PEG) through an optimal cross-linking approach. These composite membranes exhibited excellent stability in terms of interlayer spacing and mitigated the adverse effects of stacking defects. Compared to MXene membranes, the composite membranes achieved a 1.76-fold increase in dye rejection efficiency, reaching 98.7% at most, with an adsorption ratio of only 1.8%. Moreover, outstanding performances were also exhibited in pressure and concentration load tests. Furthermore, in the context of forward osmosis applications, the composite membranes demonstrated excellent Na+ rejection of 99.9%. More importantly, these membranes showed no performance deterioration throughout 50 filtration cycles, with only a slight increase in permeance of 19.3% over a 38-day testing period. Thus, this work presents a novel solution for fabricating MXene composite membranes with low swelling, minimal defects, and high stability, enhancing its potential in the field of water and wastewater treatment.

High-κ Wide-Gap Layered Dielectric for Two-Dimensional van der Waals Heterostructures.

van der Waals heterostructures of two-dimensional materials have unveiled frontiers in condensed matter physics, unlocking unexplored possibilities in electronic and photonic device applications. However, the investigation of wide-gap, high-κ layered dielectrics for devices based on van der Waals structures has been relatively limited. In this work, we demonstrate an easily reproducible synthesis method for the rare-earth oxyhalide LaOBr, and we exfoliate it as a 2D layered material with a measured static dielectric constant of 9 and a wide bandgap of 5.3 eV. Furthermore, our research demonstrates that LaOBr can be used as a high-κ dielectric in van der Waals field-effect transistors with high performance and low interface defect concentrations. Additionally, it proves to be an attractive choice for electrical gating in excitonic devices based on 2D materials. Our work demonstrates the versatile realization and functionality of 2D systems with wide-gap and high-κ van der Waals dielectric environments.

Influence of two collection frequency intervals on sperm quality of standard and miniature bull Terriers during short breeding periods: A clinical field study.

The quality of canine sperm can be influenced by many factors, such as breed, body weight, age, ejaculatory frequency, nutrition, and environment. In the UK, it is common practice for standard Bull Terriers (SBT) and miniature Bull Terriers (MBT) to require male donors during a short breeding period. The aim of this study was to evaluate the effect of semen collection frequency on ejaculate volume and nine sperm parameters in SBT and MBT males, considering age and body condition score (BCS). Ejaculates from six adult SBTs and four MBTs were collected 5 times at two consecutive intervals (Time Series [TS]1, 24 h vs. TS2, 48 h), 1 week apart. Ejaculate volume, concentration, total output, viability (live sperm), subjective total motility, vigor, and total morphological defects, including head, midpiece, and tail defects of sperm, were evaluated. A multivariable mixed linear model for repeated measures was used to analyze the effects of semen collection frequency, age, breed, and BCS on ejaculate volume and sperm parameters. Semen collection frequency, age, and, to a lesser extent, breed, and BCS significantly affected sperm parameters. Semen collection frequency affected all sperm parameters (p < 0.05) but not ejaculate volume (p > 0.05). Total sperm output, sperm vigor, total motility, and tail defects decreased (p < 0.05) at the end of TS1. However, sperm parameters remained relatively constant (p > 0.05) in TS2 between semen collection sessions. Overall, poorer sperm parameters were observed in older dogs (aged 5-8 years) than in younger dogs (aged 4 years). MBT produced less (p < 0.001) ejaculate volume (3.2 ± 0.2 mL vs. 4.3 ± 0.2 mL: Least Squares Mean ± Standard Error of Mean), lower total sperm output (221.8 ± 19.2 × 106 vs. 348.6 ± 19.2 × 106) and lower total morphological defects (25.0 ± 1.1% vs. 31.3 ± 0.9%), and a higher percentage of live sperm (77.0 ± 1.4% vs. 71.7 ± 1.1%) than SBT. In addition, a BCS of 4 positively influenced (p < 0.05) viability, vigor, and total sperm motility. Despite differences in age, breed, and BCS, better sperm parameter values were observed in all semen collection sessions. However, intensive semen collection (TS1) appears to be less effective in maintaining good sperm quality. For breeding or artificial insemination purposes, a 48-h interval between collection sessions is recommended for both breeds. The results of this study could be used to further optimize assisted reproductive technologies in both breeds.

Quality of Life After Lower Leg Reconstruction With the Latissimus Dorsi Free Flap in Pediatric Patients.

The latissimus dorsi free flap is a widely used reconstructive technique for complex lower leg defects in the pediatric population due to its reliability and anatomical features. However, the impact of this technique on the postoperative quality of life in children and adolescents, who require appropriate lower extremity function during their developmental period, remains to be analyzed. Patients who underwent microsurgical lower leg reconstruction using the latissimus dorsi flap were analyzed retrospectively. The quality of life of these patients was assessed prospectively using the Lower Extremity Functional Scale (LEFS) at a minimum of 18 months after surgical reconstruction. Sixteen pediatric patients who had severe lower extremity injuries and underwent latissimus dorsi free flap reconstruction met the inclusion criteria. The mean follow-up period was 33.9 months (22-64 months). Two patients experienced postoperative complications: one had partial flap necrosis and surgical site infection, while the other developed a surgical site infection. The LEFS scores ranged from 26 to 80, with a mean score of 64.6. Remarkably, 14 of 16 patients achieved LEFS scores consistent with at least the 10th percentile when compared with normative data. Patients with severe associated fractures presented with the lowest scores. Based on our findings, the latissimus dorsi flap is reaffirmed to be an excellent choice for lower leg reconstruction in the pediatric population. It effectively restores the quality of life in patients who have experienced moderate to severe lower extremity injuries.

Functional and esthetic reconstruction of composite lower lip defects with a motor-innervated chimeric facial artery buccinator myomucosal-submental island flap

ObjectiveThis study aimed to assess the functional and esthetic outcomes of a chimeric innervated buccinator myomucosal-submental island flap (BMM-SIF) for large composite lower lip reconstruction. MethodsThis retrospective study included five patients who underwent lower lip tumor resection and BMM-SIF reconstruction at the Hospital of Stomatology, Sun Yat-sen University, between August 2021 and February 2023. Lip function was evaluated using water leakage, cheek puffing tests, and superficial electromyography. Lip appearance was observed using photographs and evaluated through subjective interviews. Donor-site conditions, including facial symmetry and mouth opening, were monitored. ResultsAll the BMM-SIFs survived. Drooling was the main complication observed shortly after surgery. The water leakage test showed complete oral competence for liquid holding in the 7th month; however, moderate air leakage was present in two patients. Electromyography revealed myoelectric signals from the innervated buccinator at the recipient site. Facial expression and food intake were typically managed. The shape and projection of the vermilion were harmonious and satisfactory for each patient. Neither microstomia nor mouth opening limitation was observed, with an average inter-incisor distance of 37.25±4.4 mm. ConclusionChimeric motor-innervated BMM-SIF effectively reconstructed large full-thickness lower-lip defects with satisfactory functional and esthetic outcomes.

Optimizing the Structure and Optical Properties of Lanthanum Aluminate Perovskite through Nb5+ Doping.

This work involves the introduction of niobium oxide into lanthanum aluminate (LaAlO3) via a conventional solid-state reaction technique to yield LaAlO3:Nb (LaNbxAl1-xO3+δ) samples with Nb5+ doping levels ranging from 0.00 to 0.25 mol%. This study presents a comprehensive investigation of the effects of niobium doping on the phase evolution, defect control, and reflectance of LaNbxAl1-xO3+δ powder. Powder X-ray diffraction (XRD) analysis confirms the perovskite structure in all powders, and XRD and transmission electron microscopy (TEM) reveal successful doping of Nb5+ into LaNbxAl1-xO3+δ. The surface morphology was analyzed by scanning electron microscopy (SEM), and the results show that increasing the doping concentration of niobium leads to fewer microstructural defects. Oxygen vacancy defects in different compositions are analyzed at 300 K, and as the doping level increases, a clear trend of defect reduction is observed. Notably, LaNbxAl1-xO3+δ with 0.15 mol% Nb5+ exhibits excellent reflectance properties, with a maximum infrared reflectance of 99.7%. This study shows that LaNbxAl1-xO3+δ powder materials have wide application potential in the field of high reflectivity coating materials due to their extremely low microstructural defects and oxygen vacancy defects.

Single-crystal strategy towards enhanced carrier mobility of fluorescent molecules for high-efficiency blue OLEDs

The organic single crystal, due to its long-range ordered molecular arrangement, high quality, low defect state density, and excellent luminescent properties, plays an irreplaceable role in the field of optoelectronics and organic light-emitting diodes. By employing strategies for constructing organic single crystals, it is possible to significantly enhance the carrier mobility and stability of devices, leading to superior optoelectronic properties. In particular, in organic light-emitting diode (OLED) devices, the introduction of an organic single crystal luminescent layer can unlock the potential of luminescent materials, extend their operational lifetimes, and enable them to withstand higher current densities. Here, we have grown high fluorescence quantum yield (PLQY) blue-emitting 1,4-bis (2-methylstyryl) benzene (BMSB) molecules in single crystal form. The average mobility has been improved from non-existent in thin films to 0.188 cm2/(V·s) in crystal devices. Additionally, through the rational design of device structures and the enhancement of electrical properties, we have achieved a transition from non-functional thin film devices to stable blue-emitting crystal devices, achieving a current density of 853.60 mA/cm2.

Influence of growth temperature on the magnetization dynamics of sputtered CoFeB thin films on various substrates and their microwave device functionality

In the present investigation, sputtering growth of 100 nm thick Co40Fe40B20 (CoFeB) film has been investigated in a low temperature range from room temperature (RT) to 400 ℃ on silicon (Si), silicon dioxide (Si/SiO2), and sapphire (Al2O3) substrates. The film surface morphology, static and dynamic magnetization were measured as a function of growth temperature and substrate. The grown films were further tested as a potential material for microwave device functionality in terms of filter and phase shifter. Surface roughness was lowest for the film grown on Si/SiO2 substrate at 200 ℃ (0.39 nm) measured from atomic force microscopy. Static magnetic properties measured by tracing magnetic hysteresis loop suggest a soft magnetic behaviour with in-plane magnetic anisotropy. Film saturation magnetization increases with the increase in growth temperature up to 200 ℃ and then decreases from 200 ℃ to 400 ℃. This suggest that the sputtering growth from room temperature to 200 ℃ offer a moderate to low interfacial stress resulting in low defects density. Gilbert damping constant (αeff) of the thin film is obtained from the ferromagnetic resonance measurements in a broad band of microwave frequencies. Damping was lowest (5.4×10−3) in the film grown at 200 ℃ on the Si/SiO2 substrate which correlates with the roughness and magnetization data. A low value of αeff is desirable for a material to be used in energy efficient spintronics and magnonic applications. The CoFeB films were also utilized in prototype microwave band-stop filter and phase shifter device applications. The filter has been tested in the frequency range from 6GHz to 25GHz with an applied magnetic bias up to 4.0 kOe. The frequency tunability with respect to the applied magnetic bias measured to be around 3.64 GHz/kOe. The maximum attenuation of −4dB was observed for the film grown on Si/SiO2 substrate at 200 ℃. Whereas, phase shifter fabricated on Si/SiO2/CoFeB film grown at 200 ℃ shows a differential phase shift up to 75°/cm. These results indicates that the CoFeB film deposited at low growth temperature can be a potential material in spintronics and CMOS applications where low temperatures are required for device fabrications.

Cross-leg flaps: A nonmicrosurgical alternative treatment method in complex lower extremity trauma reconstruction.

This study aimed to present our experiences with cross-leg flap surgery, which demonstrates successful outcomes in lower limb soft tissue defects without the necessity of microsurgical intervention. The retrospective study included 26 patients (18 males, 8 females; mean age: 35.6±12.2 years; range, 18 to 65 years) between January 2015 and September 2019. A fasciocutaneous cross-leg flap was applied to the recipient extremity, and the extremities were immobilized by a tubular external fixator. Flap divisions were performed on the 21st postoperative day. At least two years of clinical outcomes were presented. Twenty-five flaps survived and recovered completely without any complication at the donor site, flaps, or the recipient area. In one diabetic patient, partial flap loss was encountered, which granulated with secondary healing. All patients demonstrated stable wound coverage, with none demanding additional soft tissue surgeries. All patients resumed normal ambulation and physical activity without any residual joint stiffness. Cross-leg flap method is an effective and respectable option for extremity salvage as a good alternative to free flaps for the management of traumatic complex lower limb defects. This method is simple, provides abundant blood supply to the wound, and does not require microsurgical experience or a good working recipient artery.

Full-thickness nasolabial facial artery flap: A modified surgical approach for reconstruction of lower lip defects.

Reconstruction of large lower lip defects remains challenging in terms of aesthetics, function and safety. The aim of this study is to explore a modified nasolabial flap to repair large lower lip defects. The full-thickness nasolabial facial artery flap was used for reconstruction of defects in lip squamous cell carcinoma (LSCC) patients after tumor ablation. The postoperative recovery of patients was obtained through clinical review and follow-up in the first and sixth month. There were four LSCC patients who received tumor ablation at the Beijing Stomatological Hospital of Capital Medical University from November 2022 to March 2023, were included in our study. All patients did not suffer from postoperative infection, orocutaneous fistula, flap necrosis, and flap loss. One patient had the trapdoor deformity. These patients achieved better lip closure function. One patient developed cervical lymph node metastasis 2 months after surgery. The modified nasolabial flap could achieve good outcomes in terms of aesthetics, function, and safety. It provided a supplementary strategy for the using of nasolabial flap in larger defects of lower lip.

Effects of beam oscillation on porosity and microstructure of laser welded TC11 titanium alloy

Oscillating beam was used for laser welding of TC11 titanium alloys. The porosity, microstructure, and mechanical properties of welds with different parameters were studied. It was found that increasing the oscillation frequency could effectively suppress porosity. When the oscillation amplitude was less than or equal to 1 mm, the laser power was about 3 kW, and the welding speed was less than 15 mm/s, porosity could be effectively suppressed. Both oscillation frequency and amplitude could increase the number of α′-phase. The oscillation frequency promoted the cross distribution of α′-phase and α″-phase in the columnar crystal. The oscillation amplitude promotes the uniform distribution of α′-phase in the columnar crystal. Increasing the oscillation frequency and the oscillation amplitude was beneficial to increase the tensile strength. In the case of low defect rates, the tensile strength of the weld could reach more than 90% of the base metal, and the maximum elongation was 7.5%.

Native point defects in HgCdTe infrared detector material: Identifying deep centers from first principles

We investigate the native point defects in the long-wavelength infrared (LWIR) detector material Hg0.75Cd0.25Te 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 (Eg) for Hg1−xCdxTe (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 VHg(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 VHg–TeHg defect complex introduces a deep acceptor level within the bandgap.