Defect Centers Research Articles

Effect and simulation of tensile stress on corrosion behavior of 7050 aluminum alloy in a simulated harsh marine environment

The corrosion behavior of the 7050 aluminum alloy was investigated in the presence of high concentrations of H+ and Cl- ions simulating the marine environment of high salinity and local acidification in tropical seas. The results highlight the significant influence of tensile stress on the corrosion rate of the aluminum alloy with higher stress levels resulting in faster corrosion. Under the influence of tensile stress, corrosion pits form on the alloy surface, and their depth increases with higher levels of applied stress. It is important to note that the presence of a corrosion defect leads to a pronounced stress concentration, resulting in a much faster rate of corrosion compared to other regions. However, when subjected to low tensile stress (≤174 MPa), the corrosion at the defect exhibits uniform characteristics similar to a uniform corrosion process. Moreover, the potential at the defect shifts positively with increasing stress level. Furthermore, stress has an effect on the diffusive behavior of the aluminum alloy, leading to a higher potential at the defect center compared to its surrounding region. Nevertheless, as the tensile stress is further increased, this behavior is disrupted and stress corrosion cracking becomes the dominant mode of corrosion.

A special issue preface: diamond for quantum applications.

This special issue discusses current progress in the utilization of defect centres in diamond as spin-photon interfaces for quantum applications. This issue is based on the discussions of the Theo Murphy meeting 'Diamond for quantum applications' which covered the recent progress of diamond growth and engineering for the creation and optimization of colour centres, toward the integration of diamond-based qubits in quantum systems. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Numerical investigation of the mechano-electro-chemical effect of X100 buried pipelines with pre-existing corrosion defects

This study investigates the corrosion kinetics and crack propagation in buried transmission pipelines made of high-strength low alloy steel API X100. Despite its cost-effectiveness and ability to withstand high operating conditions without increasing pipe wall thickness, the corrosion kinetics in near-neutral pH environments for this steel grade is not fully understood. To address this gap, two numerical models were developed. The first model, using COMSOL Multiphysics v5.6, showed higher electrolyte potential at the corrosion defect center due to stress-induced defect growth, increasing corrosion susceptibility. The second model, employing the XFEM approach, evaluated crack initiation, propagation, and von Mises stress distribution along the crack path. This research contributes to a better understanding of corrosion and crack behavior in corroded pipelines, aiding in their performance improvement in near-neutral pH soil environments.

Application of nonlinear regression in the analysis of relaxation photocurrent waveforms

This article discusses the performance of an algorithm for detection of defect centers in semiconductor materials. It is based on direct parameter approximation with nonlinear regression to determine the parameters of thermal emission rate in the photocurrent waveforms. The methodology of the proposed algorithm was presented and its application procedure was described and the results of its application can be seen in measured photocurrent waveforms of a silicon crystal examined with High-Resolution Photoinduced Transient Spectroscopy (HRPITS). The performance of the presented algorithm was verified using simulated photocurrent waveforms without and with noise at the level of 10 -2. This paper presents for the first time the application of the direct approximation method using modern regression and clustering algorithms for the study of defect centers in semiconductors.

Study of the centers responsible for the TL emission by EPR and PL analysis of Eu-doped CaSiO3 phosphors synthesized by the devitrification method

CaSiO3 doped at different ppm of Eu were synthesized by the devitrification method. Polycrystals exhibit a prominent high-temperature TL peak that increases in intensity and shifts toward higher temperatures with increasing amounts of dopant. TL emission spectrum of CaSiO3: Eu displays two very broad bands centered at 400 and 440 nm corresponding to the temperatures of 229.5 and 373.5 °C, respectively. PL measurements indicate the presence of Eu2+ and Eu3+ ions. EPR spectrum arises from two defect centers. One of the centers with principal g-values 2.016, 2.0091, and 2.0051 is attributed to O− ion and the center correlates with the TL peak at 236 °C. Center II with an isotropic g-value of 2.0018 is attributed to an F+ center and the center relates to the TL peak at 120 °C. Center III is also tentatively identified as the F+ center which is associated with the TL peak at 365 °C.

Influence of thermal annealing on silicon negative ion implanted SiO2 thin films

SiO2 thin film of thickness 300 nm grown on p-type silicon substrate was implanted with 100 keV silicon negative ions with fluences varying from 5×1015 to 1×1017 ions cm−2. The implanted samples were annealed at the temperature of 500 °C under N2 ambient. Electron spin resonance (ESR), Fourier transform infrared (FTIR), Photoluminescence (PL), and glancing angle X-ray diffraction (GXRD) techniques have been used to investigate the implanted SiO2 thin film after thermal annealing. ESR studies revealed the absence of vacancy defects after thermal annealing. FTIR studies showed variations in the vibrational modes, attributed to the formation of new structures after annealing at 500 °C. PL studies showed the presence of a peak at 720 nm with an intensity higher than that observed for the unannealed SiO2 samples. This effect showed a decrease in the non-radiative defect centers with an increase in the radiative Si:SiO2 interface states after thermal annealing. The presence of an additional peak at 692 nm may be attributed to the radiative recombination centers associated with silicon nanoclusters formed after annealing at 500 °C. GXRD studies showed a decrease in the intensity of the spectra for the samples implanted with 1×1016 and 5×1016 ions cm−2 after thermal annealing at 500 °C. This result reveals the formation of new SiOx structures in SiO2 thin film.

Luminescent Properties of Composite Materials Based on Porous Glasses Activated by Silver and Lanthanum

Composite materials (CMs) based on matrices of high-silica nanoporous glasses activated by silver and lanthanum are synthesized. It is established that, depending on the composition, the CM samples exhibit luminescence in the UV, violet-blue, green, red, and infrared spectral ranges due to the presence of isolated Ag+-ions, Ag+–Ag+ paired centers, molecular clusters (MCs) and nanoparticles (NPs) of silver, and oxygen vacancies in La2O3, together with various silicon defect centers.

Systematic improvement of excitonic features in hydrothermally synthesized WS2 due to post-synthesis drying

WS2 nanostructures were produced by mechanically exfoliating bulk WS2 powders synthesized through a solution-based hydrothermal route using WCl6 and thioacetamide (TAA) as reactants. An unoptimized post-synthesis recipe, which constitutes the last step, is the major hindrance in achieving a reproducible and scalable production strategy of layered bulk WS2 crystals. We have reported a comprehensive study on the crystal, morphological, and luminescence properties of WS2 material which have undergone post-synthesis treatment i.e. dried at mild temperature with varied dwelling times. The as-synthesized WS2 material which used to be in distorted 1T metallic phase, due to ionic intercalation released from the organic reactants, was found to evolve crystallographically into a stable 2H semiconducting phase with increased drying temperature and dwelling time. An in-depth optical analysis of the WS2 nanostructures through PL and PLE spectroscopy revealed substantial improvement in the intensity of A and B excitonic features for the sample dried at 80 °C for 24 h, indicating a reduction in the non-radiative defect centers in the sample under the post-synthesis conditions. We believe an effective post-synthesis treatment is needed for semiconducting 2H-WS2 synthesis through the solution route to improve its crystal (i.e. structural) and optical properties for potential electronic applications.

Determination of lateral strain in InGaAsSb alloys and its effect on structural and optical properties

In_xGa_{1-x}As_ySb_{1-y} epilayers with a fixed In content of textit{x} = 0.145 were grown on GaSb(100) substrates using liquid-phase epitaxy (LPE). The lattice mismatch between the quaternary epilayers and substrates was analyzed for different As contents (textit{y}) by X-ray omega-2theta. Epilayers with As content between textit{y} = 0.120 and textit{y} = 0.124 exhibited a positive lattice mismatch, leading to compressive strain. These samples showed a high crystalline quality and flat surfaces, as confirmed by high-resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM). Quaternary alloys with As content between textit{y} = 0.133 and textit{y} = 0.141 displayed a negative lattice mismatch, resulting in tensile strain. Structural defects in these samples were evidenced by HR-XRD and on AFM micrographs. Raman measurements also revealed that lateral strain has a direct impact on the intensities of the LO-like, phonon–plasmon and disorder-activated longitudinal acoustic modes. For all In_xGa_{1-x}As_ySb_{1-y} films, photoluminescence (PL) spectra showed a bound exciton (BE) transition, with additional features observed in samples under tensile strain, indicating the involvement of native defect centers and donor–acceptor pairs. This study provides new insights into the effect of lateral strain on the crystalline and surface quality, and optical properties of quaternary alloys, relevant for novel optoelectronic applications.

Identification of defect centers responsible for thermoluminescence emission in sol-gel synthesized calcium silicate phosphor

The thermoluminescence (TL) of calcium silicate phosphor (CSO) prepared by the sol-gel method and sintered at 1200 °C were investigated. From Tm-Tstop curve, TL emission spectrum and computer deconvolution using electron traps with discrete and continuous distributions, the glow curves were found to be composed of four TL peaks (117, 190, 250 and 275 °C) with a single emission band centered at 370 nm. Electron paramagnetic resonance (EPR) investigation has been carried out to identify the defect centers formed in the CSO phosphor by γ-irradiation and find the centers related to the TL process in the phosphor. At room temperature, three defect centers were observed. The first center, characterized by the principal g-values of 2.014, 2.011, and 2.0080 was assigned to an O− ion. The second center with g-values 2.015, 2.013, and 2.010 is also attributed to an O− ion and is associated with the TL peak at 280 °C. The third center, with an isotropic g-value of 2.0011 was identified as the F+ center (singly ionized oxygen vacancy) and relates to the TL peak at 280 °C.

Engineering intrinsic defects in CuO NWs through laser irradiation: Oxygen vs copper vacancies

Defect engineering in CuO nanomaterials has been extensively investigated because this technology can greatly improve the performance of CuO components in a variety of applications. While many previous studies have focused on the role of oxygen vacancies, (VO), in CuO, little attention has been paid to that of copper vacancy centers, (VCu), since the presence of these defects is often difficult to quantify. As a result, the specific roles played by these different vacancy centers on the measured properties of CuO have not been studied systematically. In this article, we show that the concentration of both VO and VCu centers can be engineered in CuO NWs through nanosecond (ns) laser irradiation. The identification of these vacancies was achieved through X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Absorption spectra and diffuse reflectance spectra of laser-processed samples show that increasing the concentration of VO centers enhances the optical absorption of CuO in the visible region. Data obtained from Mott-Schottky and Nyquist plots, together with measured I-V characteristics, show that laser-induced VCu centers can enhance the carrier concentration in CuO NWs. These data, in addition to O 1s XPS spectra on laser-processed and unprocessed samples as well as cyclic voltammetry, also indicate that laser irradiation can significantly enhance surface adsorption for applications in photo-electrochemistry and electrochemistry. To demonstrate the efficacy of this laser irradiation technique for potential electrochemistry applications, the role of laser-induced VCu and VO defect centers in CuO NWs on the non-enzymatic sensing of glucose has also been investigated. We find that the introduction of VO centers in CuO NWs enhances the current response for glucose sensing while the presence of VCu centers inhibits this response.

Enhancement of Er luminescence from bridge-type photonic crystal nanocavities with Er, O-co-doped GaAs

A bridge-type photonic crystal (PhC) nanocavity based on Er,O-codoped GaAs is employed to realize enhancement of Er luminescence. By adjusting the structural design and measurement temperature, the cavity mode's wavelength can be coupled to Er luminescence. The peak emission intensity from an Er-2O defect center was enhanced 7.3 times at 40 nW pump power and 77 K. The experimental Q-factor is estimated to be over 1.2 × 104, and the luminescence intensity shows superlinearity with excitation power, suggesting Er luminescence amplification. This result would pave the way towards the realization of highly efficient single-photon emitters based on rare-earth elements.

Effect of material properties on the laser-induced desorption of hydrogen from tungsten

One of the priority tasks for sustainable operations of future fusion devices is the systematic control of hydrogen isotope content in plasma-facing components. A remote non-damaging analysis of the gas content can be realised by applying laser-induced desorption (LID). LID is based on local heating of the studied surface, followed by the detection of desorbed particles. Interpretation of the LID measurements relies on the definition of effective desorption region from which particles are being released. This region strongly depends on the properties of a laser pulse, an analysed material, and defect centres containing hydrogen isotopes. To investigate the role of these properties on LID, a series of numerical simulation was conducted for the case of hydrogen release from a 10 μm tungsten layer, initiated under nanosecond, microsecond, and millisecond heat loads. The simulations were performed using a common reaction-diffusion model with sequentially varied tungsten thermal conductivity, detrapping energy of hydrogen from traps, concentration of hydrogen traps, and their initial filling ratio. Additionally, the Soret effect was considered in order to estimate its impact on the LID efficiency. Findings reveal that the peak surface temperature reached during heating can characterise the LID efficiency under a particular heat pulse. The LID efficiency dependence on the peak surface temperature weakly varies with material thermal properties, but can alter with the change of trap parameters. The detrapping energy of hydrogen from traps considerably influences the desorption efficiency, while concentration and the initial filling ratio of traps have a moderate effect. The Soret effect is shown to noticeably affect the LID efficiency per a laser pulse only at near-melting temperatures of tungsten. Finally, results demonstrate that the highest desorption efficiency from thick layers can be reached using laser pulses with millisecond duration regardless of surface effects, when the release under short-term pulses can be limited by them.

Elucidating the capacitive behavior of Gd-doped BNT-BKT-BT electrodes in All-in-One supercapacitor devices

Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-BaTiO3 (BNT-BKT-BT) ceramics having various amounts of Gd-ions were synthesized via the solid-state reaction method. The electrochemical performance analysis of the Gd-doped BNT-BKT-BT ceramics has shown that the doping amount considerably impacts the BNT-BKT-BT electrode’s electrochemical performance. The analysis of the defect centers was carried out using EPR spectroscopy. The samples showed paramagnetic defects in the EPR analysis. The 0.001 mol% Gd-doped BNT-BKT-BT showed a maximum signal intensity with partly resolved hyperfine lines, reaching the highest specific capacitance value of 612 Fg−1. The EPR results were compared with the prototype BaTiO3 perovskite ceramic and concluded that the BNT-BKT-BT system has an extremely large strain, which hinders determining the spin-Hamiltonian parameters such as crystal field and hyperfine due to inhomogeneous line broadenings.

TL, OSL, EPR, and defect centers in Tb-doped strontium silicate phosphor synthesized by a solid-state reaction method

Strong thermoluminescence (TL) was observed in Tb-doped strontium silicate phosphor prepared by the solid-state reaction method. Two glow peaks are observed at 100 and 190 °C. TL emission spectra indicate three recombination centers. The number of peaks and the kinetic parameters associated with the TL glow peaks of Tb-doped Sr2SiO4 phosphor after gamma irradiation were analyzed by Tm-Tstop and deconvolution methods. A study of defect centers induced by γ-irradiation and identification of defect centers responsible for the observed TL glow peaks has been carried out using the electron paramagnetic resonance (EPR) technique. The observed spectrum at room temperature is a superposition of at least three defect centers. Center I is characterized by an axially symmetric g-tensor with principal values g|| = 2.019, and g⊥ = 2.0013 and is ascribed to a O2− ion. Center II has a rhombic g-tensor with principal values 2.0072, 2.0024, and 1.995 and is assigned to an F+ center (singly ionized oxygen vacancy) and correlates with the 190 °C TL peak. The third center (center III) has an isotropic g-value of 1.991 and is identified as an F+ center.

Study of the effect of the substitution of Fe by Ti on the microstructure and the physical properties of the perovskite system La0.67Ca0.2Ba0.13Fe1-xTixO3 with x = 0 and 0.03 at low temperatures.

La0.67Ca0.2Ba0.13Fe1-xTixO3 samples (x = 0 and 0.03) were synthesized by the auto-combustion method. Analysis of XRD diffractograms revealed that these compounds crystallize in the cubic system with the space group Pm3̄m. The dielectric properties have been studied in the 102-106 frequency range and the 120-280 K temperature range. Analysis of AC conductivity shows that the conduction mechanisms are of polaronic origin and that they are co-dominated by the NSPT and OLPT models. The monotonic increase in conductivity with increasing temperature results from the reduction of defect centers and the increase in charge carrier mobility. Such variation is consistent with impedance variation at different frequencies and temperatures indicating semiconductor behavior. Nyquist diagrams are characterized by the appearance of semi-circular arcs. These spectra are modeled in terms of equivalent electrical circuits confirming the contribution of grains (Rg//CPEg) and grain boundaries (Rgb//CPEgb). The dielectric analysis showed an evolution of the dielectric constant in accordance with Koop's theory and the phenomenological model of Maxwell-Wagner. The low conductivity and the high values of the real permittivity at low frequency make our compounds potential candidates for energy storage and applications for electronic devices and microwaves.

Insights into the mechanism of electric field regulating hydrogen adsorption on Li-functionalized N-doped defective graphene: A first-principles perspective

The hydrogen storage properties of lithium functionalized graphene under external electric fields have been studied in this work employing density functional theory (DFT) calculations. Lithium modified nitrogen doped double-vacancy graphene (Li_NDVG) was constructed as hydrogen storage material. It is examined in terms of the system’s electronic properties, H2 adsorption energy, and stable configuration. The results demonstrate that Li atoms can be distributed on the substrate surface and incorporated into defect centers without producing metal clusters. In comparison to pristine graphene, the adsorption energy of H2 on Li_NDVG is four times higher. The Coulomb force between Li atom and H2 molecule grows as the positive electric field’s strength increases, and the adsorption distance shrinks. On the contrary, the H2 adsorption energy decreases as the negative electric field’s strength increases, and the adsorption distance expands. Furthermore, adsorption occurs spontaneously within the range of 0–300 K and 1–100 atm, and the promoting effect of a positive electric field on adsorption only occurs in the temperature range of 0–140 K. Hydrogen storage properties of functionalized graphene modified with lithium trimer and tetramer respond to the electric field in the same way as single atom. And the presence of clusters and positive electric field increases the bond length of the H2 molecule, causing a tendency for the H2 molecule to dissociate.

Diamond MEMS: From Classical to Quantum

AbstractDiamond has numerous outstanding properties in mechanics, physics, chemistry, electronics, thermodynamics, and spintronics for either classic micro/nanoelectromechanical systems (MEMS/NEMS) devices or hybrid quantum MEMS/NEMS systems. The extremely high mechanical strength and the ultra‐wide bandgap energy enable the development of mechanically and thermally robust MEMS/NEMS sensors and switches, while the long coherence time of spin defects center enables the reading out through optical methods, precise quantum sensing, and quantum information processing. In this paper, the development of diamond‐based MEMS/NEMS from the viewpoints of classic devices to quantum systems are reviewed. The fabrication process and the classic applications of diamond MEMS/NEMS devices are first described, including those from micro‐crystalline, nano‐crystalline/ultranano‐crystalline, and single‐crystalline diamonds. Then, the physical properties of nitrogen‐vacancy defect center, as well as the application referred to the hybrid system composed of MEMS structures and nitrogen‐vacancy centers embedded, strain–spin interaction, and diamond‐based optomechanics are introduced. Finally, a conclusion and outlook are presented. It is expected that diamond MEMS/NEMS is not only an ideal platform for high‐performance and high‐reliability advanced classic MEMS devices but also for quantum sensing, information, and exploring the fundamentals of quantum mechanics.

Dual facet passivation of silver halometallate for eco-friendly silver bismuth sulfide near IR photodetector

Ternary chalcogenide silver bismuth sulfide nanocrystals (AgBiS2 NCs) have taken great strides in the past few years to emerge as one of the better eco-friendly alternatives to compete with the prevalent toxic semiconductor materials such as lead sulfide quantum dots (PbS QDs) in the near-infrared (NIR) region. Nevertheless, their implementation in photodetectors has been scarce due to high dark current and complicated solid-state ligand exchange fabrication steps involved, resulting in a lower overall detectivity. The performance is further deemed to be stunted due to the difficulty associated with the passivation of the charge-neutral (100) facet of larger AgBiS2 NCs efficiently. In this work, we aimed to develop a mixed ‘halometallate’ ligand approach, wherein we introduce silver bromide (AgBr) as an ancillary ligand to silver iodide (AgI), passivating both (100) and (111) facets of cubic AgBiS2 solids in a facile solution-phase ligand exchange step to obtain highly dispersible colloidal ink. Decreased bond length, bond angle (Br-Ag-Br), and ionic size of [AgBr2-] anion induces less compressive strain compared to [AgI2–], culminating in higher molecular stability on the AgBiS2 surface. This dual passivation reduces the dark current to 6.01 × 10-7 A cm−2 and a high specific detectivity of 1.8 × 1012 Jones at 800 nm is achieved, comparable to ubiquitous PbS QD devices. We also demonstrate diminished in-gap carrier density population, enhanced light detection, and ultrafast microsecond response at higher wavelengths operating under high bias (-1V) photoconductive mode. This study illustrates the role of optimum surface coverage in eliminating the deleterious non-radiative recombination defect centers by introducing additional ligands in solution-processed AgBiS2 NC and the viability of the mixed ligand approach for stable eco-friendly NIR photodetectors.

Defective Au nanoparticles manipulated by Au-MgxAl-LDH interplay for alkali-free oxidation of benzyl alcohol

Supported gold catalyst, especially in terms of nanosized particles with defective surface and low-coordinated structure, plays a vital role in the heterogeneous catalysis. However, such defective Au nanoparticles are hardly acquired when supporting on non-reducible metal oxides/hydroxides due to insufficient Au-support interaction. In this work, we found that the defective Au NPs could be fabricated via the strong interplay between Au and crystal lattices of layered double hydroxides-MgxAl-LDH. Experimental and theoretical evidences revealed that the formation of a preferential-oriented LDH(015) plane enabled the surface configuration for defective Au centers with the maximized number of step sites at Mg/Al ratio of 3.0–3.5. The optimized Au/Mg3.5Al-LDH catalyst shows a boosting catalytic activity for benzyl alcohol oxidation (TOF, 1008 h−1) at only 80 °C with the lowest activation energy in the absence of alkali. The work provides a new insight for manipulating the defective-enriched Au particles via the fine-tuning Au-LDH interplay for alkali-free selective oxidations.