Increase In Defect Concentration Research Articles

Theoretical study on local domain pinning effect due to defect dipole alignment

We have theoretically studied the domain pinning effect from the internal bias field generated by aligned dipolar defects. By ordering defect dipoles along the polarization direction, the experimentally observed ‘hard’ properties in ferroelectric materials, including shifted polarization–electric field (P–E) loops, biased strain-electric field (S–E) loops, suppressed piezoelectric and dielectric responses in sufficiently poled and aged ferroelectric system, can be well described by our model. As expected, the P–E loops and S–E loops become more asymmetric with the increase of defect concentration. The local domain evolution around dipolar defects under an electric field shows the physical process for the domain pinning effect, i.e. the difficulty of domain switching due to the presence of defect dipoles. Finally, the domain memory effect during heating/cooling cycle is simulated. Interestingly, domain configuration can be memorized when a ferroelectric system with dipolar defects goes through the ferro-para-ferro phase transition cycle, and the simulated time steps of domain recovery are strongly correlated with the defect dipole concentration. All theoretical results from our model are consistent with the experimental results. We can conclude that the local interaction between dipole defects and domains is the main mechanism of ferroelectric hardening.

Effect of cerium doped Baddeleyite on their antibacterial activity by co-precipitation method

The present work, antibacterial activity of pure and Ceria doped Baddeleyite (ZrO2) nanoparticles (Nps) were synthesized by Co-precipitation method using different bacterial strains (gram positive and gram negative). The obtained samples were characterized by using XRD; SEM and antibacterial study. XRD and SEM confirmed the crystalline nature and morphology of the as synthesized products. The antibacterial studies revealed that doped sample exhibits higher activity compared to pure sample, which can be attributed to an increase of defect concentration (oxygen vacancy) in the sample. In addition, the possible formation mechanism of pure and Ce-doped ZrO2 Nps have also been proposed.

Effect of Graphene Nanowall Size on the Interfacial Strength of Carbon Fiber Reinforced Composites.

Graphene nanowalls (GNWs) with different sizes (i.e., length and height) were grown directly on the surface of individual carbon fibers (CFs) using a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique. The size was controlled by varying the deposition time. The GNW-modified CFs were embedded into epoxy resin matrix to prepare a series of carbon-fiber-reinforced composites (CFRCs). The results indicated that GNWs were remarkably effective in improving the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the carbon-fiber-reinforced composites. The enhancement effect on the strength strongly depended on the size of GNWs. It increased with the increase in the GNWs’ size and reached the maximum upon the incorporation of GNWs that were grown for 45 min. Noticeable increases of 222.8% and 41.1% were observed in IFSS and ILSS, respectively. The enhancement mechanism was revealed by means of scanning electron microscope (SEM) fractography analysis. However, further increase of GNW size led to no more improvement in the shear strength. It could result from the increased defect concentration and wrinkle size in the GNWs, which deteriorated the strength.

X-Ray Diffraction Analysis of the Influence of the Absorbed γ-Irradiation Dose on Ti3Al Structural Characteristics

The influence of absorbed γ-quantum irradiation doses Dγ (60Co isotope) on the structural parameters of Ti3Al single-phase compounds is experimentally investigated. The structural characteristics are defined more accurately using X-ray diffractometry. On account of the results of structural studies, it is found that exposure to low γ-radiation doses (e.g., Dγ = 1 × 103 Gy) generates the nonequilibrium state of the Ti3Al structure. An increase in the absorbed dose (to Dγ = 1 × 105 Gy) stimulates the formation of a metastable radiation-induced state, which is identified by diffraction-reflection splitting, an increase in the crystal-lattice volume, and changes in the parameters of the fine structure (the coherent-scattering-region size decreases to 13 nm, and the defect concentration increases).

LiNaSO4 dispersed NaNO3 composite – A new solid electrolyte?

DC ionic conductivity of the composite formed between LiNaSO4 and dispersed Na ion conductor (NaNO3) was studied. The material was prepared by the ball milled technique. X-ray diffraction and differential scanning calorimetry studies confirmed the formation of composite between the host material and the dispersoid. The experimental data indicate that addition of NaNO3 significantly improves electrical conductivity of pure LiNaSO4 in the low temperature phase. A possible mechanism of conductivity enhancement in dispersed system is interpreted in terms of the formation of space charge layer between the host material and the dispersoid in which defect concentration increases.

Probing Oxygen Defects in Na0.5Bi0.5TiO3 Ferroelectric by Micro‐Raman Spectroscopy

Raman spectroscopy of Na0.5Bi0.5TiO3 ceramic is carried out at room temperature. In addition to well‐known Raman modes, two extra bands are also observed near 770 and 835 cm−1. Their presence is conjectured to the presence of oxygen defects in the crystal lattice. The intensity of these bands increases with an increase in oxygen defect concentration. It is proposed that Raman spectroscopy could be a useful tool for detecting the oxygen defects in Na0.5Bi0.5TiO3 based ferroelectrics.

The Effect of Low Energy Nitrogen Ion Implantation on Graphene Nanosheets

Herein, we report the effect 50 keV nitrogen ion implantation at varying fluence on the optical properties of graphene nanosheets (number of layers < 5). Initially, graphene nanosheets synthesized by the direct liquid exfoliation of graphite layers were deposited on a cleaned Si-substrate by drop cast method. These graphene nanosheets are implanted with 50 keV nitrogen-ion beam at six different fluences. Raman spectroscopic results show that the D, D′ and G peak get broadened up to the nitrogen ion fluence of 1 × 1015 ions/cm2, while 2D peak of graphene nanosheets disappeared for nitrogen-ions have fluence more than 1014 ions/cm2. However, further increase of fluence causes the indistinguishable superimposition of D, D′ and G peaks. Surface contact potential value analysis for ion implanted graphene nanosheets shows the increase in defect concentration from 1.15 × 1012 to 1.98 × 1014 defects/cm2 with increasing the nitrogen ion fluence, which resembles the Fermi level shift towards conduction band. XRD spectra confirmed that the crystallinity of graphene nanosheets was found to tamper with increasing fluence. These results revealed that the limit of nitrogen ion implantation resistant on the vibrational behaviors for graphene nanosheets was 1015 ions/cm2 that opens up the scope of application of graphene nanosheets in device fabrication for ion-active environment and space applications.

Immobile defects in ferroelastic walls: Wall nucleation at defect sites

Randomly distributed, static defects are enriched in ferroelastic domain walls. The relative concentration of defects in walls, Nd, follows a power law distribution as a function of the total defect concentration C: Nd∼Cα with α=0.4. The enrichment Nd/C ranges from ∼50 times when C = 10 ppm to ∼3 times when C = 1000 ppm. The resulting enrichment is due to nucleation at defect sites as observed in large scale MD simulations. The dynamics of domain nucleation and switching is dependent on the defect concentration. Their energy distribution follows the power law with exponents during yield between ε∼1.82 and 2.0 when the defect concentration increases. The power law exponent is ε≈2.7 in the plastic regime, independent of the defect concentration.

Structural, optical and magnetic properties of Pr doped CeO2 nanoparticles synthesized by citrate–nitrate auto combustion method

In the present work, pure and Pr doped CeO2 nanoparticles in the form of Ce1−xPrxO2 (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized by citrate–nitrate auto combustion method. The combustion derived products were annealed at 700 °C and characterized by X-ray diffraction (XRD) studies, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-diffuse reflectance spectroscopy (UV-DRS), Fourier transform-infrared spectroscopy (FT-IR), Fourier Transform-Raman Spectroscopy (FT-Raman), photoluminescence analysis (PL) and vibrating sample magnetometer (VSM) studies. XRD studies revealed that all the samples exhibited single phase cubic fluorite structure. SEM images displayed that pure and Pr doped CeO2 nanoparticles had irregular flaky shape with few agglomerations. TEM results show the proper formation of cubic fluorite structure of nanoparticles. UV-DRS spectroscopy results showed the red shifting in the absorption band edge with increased Pr concentration. The vibrational band assignment of pure and Pr doped CeO2 nanoparticles were analyzed by FT-IR spectroscopy. FT-Raman studies revealed increased defect concentration for the doped samples compared with pure CeO2. PL intensities of doped CeO2 nanoparticles decrease compared with pure CeO2 nanoparticles due to the evolution of non-radioactive oxygen vacancies in the structure. VSM results depicted the suppression of ferromagnetic behavior on Pr doping.

Study of Optical and Magnetic Properties of Graphene-Wrapped ZnO Nanoparticle Hybrids

In this work, we report a one-step method for the preparation of graphene-wrapped zinc oxide (ZnO) nanoparticle (NP) (ZnO@G) hybrids. These hybrids are characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, optical absorption measurements, photoluminescence (PL) emission spectroscopy, and M-H hysteresis measurements. All results reveal that the ZnO NPs are entirely covered with graphene sheets. In the PL spectra, the quenching of the band gap emission and the enhanced green emission serve as evidence of the electron transfer from the ZnO NPs to the graphene layer. The increase of the room-temperature magnetization of the hybrid, compared to pure ZnO NPs, is due to the increasing defect concentration. We suggest a band diagram model that accounts for these observations. We present the simple wet-chemical synthesis procedure to open a new way for the synthesis of NP-graphene hybrid systems having magnetic properties giving the large manifold potential application.

Electronic Transport and Ferroelectric Switching in Ion‐Bombarded, Defect‐Engineered BiFeO3 Thin Films

AbstractDespite continued interest in the multiferroic BiFeO3 for a diverse range of applications, use of this material is limited by its poor electrical leakage. This work demonstrates some of the most resistive BiFeO3 thin films reported to date via defect engineering achieved via high‐energy ion bombardment. High leakage in as‐grown BiFeO3 thin films is shown to be due to the presence of moderately shallow isolated trap states, which form during growth. Ion bombardment is shown to be an effective way to reduce this free carrier transport (by up to ≈4 orders of magnitude) by trapping the charge carriers in bombardment‐induced, deep‐lying defect complexes and clusters. The ion bombardment is also found to give rise to an increased resistance to switching as a result of an increase in defect concentration. This study demonstrates a systematic ion‐dose‐dependent increase in the coercivity, extension of the defect‐related creep regime, increase in the pinning activation energy, decrease in the switching speed, and broadening of the field distribution of switching. Ultimately, the use of such defect‐engineering routes to control materials will require identification of an optimum range of ion dosage to achieve maximum enhancement in resistivity with minimum impact on ferroelectric switching.

Admittance spectroscopy of InGaAsN based solar cells

Single-junction InGaNAs solar cells were grown by MBE with active layers based on a GaAsN/InAs superlattice. Dependence of defect formation on thickness of InGaNAs was explored in the study. Thickness increase from 900 nm to 1200 nm leads to defect formation with two activation energies of 0.20 eV and 0.50 eV but the value of quantum efficiency stays almost the same. Further thickness increase up to 1600 nm leads to the increase of defect concentration in the InGaNAs active layer. These defects are non-radiative recombination centres because a significant decrease of solar cell quantum efficiency was observed. The existence of a critical thickness for defect-free growth of InGaNAs based on GaAsN/InAs superlattice is proposed.

Room Temperature Growth of Epitaxial Titanium Nitride Films by Pulsed Laser Deposition

Reducing the thermal budget of epitaxial thin film growth has been one of the biggest challenges for the electronics industry. In this report, the room-temperature epitaxial growth of titanium nitride (TiN) thin films (∼75 nm) on (0001) Al2O3 substrates is demonstrated using a pulsed laser deposition technique. In TiN thin films, the epitaxial relationship is established by X-ray diffraction for (111)TiN//(0001) Al2O3 and TiN // Al2O3 which corresponds to a 30° rotation of titanium and nitrogen atoms with respect to the hexagon arrangement of aluminum atoms. An increase in the defect concentration is shown in the room-temperature thin film growth as compared to the ones grown at elevated temperature. A shift and broadening of the diffraction peaks is observed in the thin films as compared to the bulk value, indicating a higher residual tensile strain with decreasing growth temperature and an increase in defect concentration at room temperature. The increased defect concentration observed at...

Robust odd-parity superconductivity in the doped topological insulator NbxBi2Se3

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator ${\mathrm{Nb}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ ($x=0.25$) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature ${T}_{c}$ decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth $\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}(T)$ follows a power law $[\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}(T)\ensuremath{\sim}{T}^{2}]$ indicating the presence of symmetry-protected point nodes. Our results are consistent with the proposed robust nematic ${E}_{u}$ pairing state in this material.

Thermodynamics of vacancies and clusters in high-entropy alloys

By means of thermodynamic analyses, we provide the intriguing evidence that the equilibrium vacancy concentrations and their clusters in high entropy alloys (HEAs) are substantially larger than those in pure metals and simple binary alloys. The increased defect concentrations strongly change the thermodynamic and kinetic properties of the HEAs. With these findings, we predict a strong recombination tendency of vacancies and interstitials after excitation from radiation bombardments, and the results are favorably compatible with very recent experiments on the superior radiation resistance of HEAs. The thermodynamics of vacancies and clusters in HEAs will be of great interest to the design of advanced materials involving many thermodynamic and kinetic properties such as thermal conductivity, diffusivity, precipitation, creep, and irradiation damage.

Using Mott-Schottky Equation for Studing the Influence of Impurities in Niobium on the Properties of Anodic Niobium Films

The aim of this work analysis of additive influence in niobium on formation of defects in anodic layers Nb2O5. It was shown that occurrence in niobium of minor amount of metal admixtures, which generate in electric field cations with a charge equal to the charge of oxygen vacancies, causes an increase in defect concentration in anodic niobium pentoxide (ANP).

Impact of defects on exciton diffusion in organic light-emitting diodes

Abstract The impact of defect concentration and current density on the effective singlet exciton diffusion length in 4’-bis(carbazol-9-yl)biphenyl (CBP) is quantified by analyzing the electroluminescent characteristics of several sets of OLEDs. The defect concentration and effective diffusion length are determined through fitting of the defect and CBP emission bands in the electroluminescence spectra under constant current operation using an analytical model derived based on the competition between exciton diffusion and energy transfer to defects. Defect concentrations of 3 ± 1 × 10 18 cm −3 , 2 ± 1 × 10 18 cm −3 and 0.3 ± 0.7 × 10 18 cm −3 are calculated in three sets of OLEDs, in which the effective diffusion length decreases as the defect concentration increases. Modelling the dependence of the effective diffusion length on defect concentration a “defect free” diffusion length of 4.5 ± 0.3 nm is obtained for CBP singlet excitons in these devices operated under low current density. We also show that the driving voltage scales linearly with the defect concentration.

Surface and Interface Engineering of Tungsten Oxide for Highly-Efficient Catalysis

The catalytic performance strongly relies on the composition, structure, and property of the material used. Earth-abundant tungsten oxides family (WOx≤3) has received considerable attention in photocatalysis, electrochemistry and catalytic hydrogenation due to its highly tunable structure and unique physicochemical properties. Substantial efforts have been made by us to improve the photocatalytic activity of WOx≤3 by enhancing light harvesting, charge transfer and separation, including defect engineering, morphology control, and hetero-junction construction. Additionally, the semiconductor-to-metal transition of WOx≤3 has been found with the increase of defect concentration, suggesting H2 can be activated on them in a similar way of a metal catalyst. As a result, WO2.72 also can function as a versatile and efficient catalyst for the saturation of olefins and selective transform of nitroarenes to anilines.

Empirical Study of the Disparity in Radiation Tolerance of the Minority-Carrier Lifetime Between II–VI and III–V MWIR Detector Technologies for Space Applications

The degradation of the minority-carrier recombination lifetime of various III–V nBn and II–VI HgCdTe midwave-infrared space detector materials under stepwise 63-MeV proton irradiation up to fluence of 7.5 × 1011 cm−2 and above has been measured using time-resolved photoluminescence while samples were held at 120 K to limit thermal annealing. As expected, the recombination rate of each sample was found to increase with proton fluence at a nearly constant rate, implying a near-linear increase in defect concentration. The rate of change of the carrier recombination rate, herein called the minority-carrier lifetime damage factor, was then plotted as a function of the initial recombination rate for each sample. Juxtaposing the III–V and II–VI results revealed a distinct disparity, with the incumbent detector material HgCdTe being roughly an order of magnitude more radiation tolerant to displacement damage from proton irradiation than any of the nBn materials. The results for the latter also suggest some degree of interrelation between the damage factor and initial lifetime. The behavior of the lifetime of each material under annealing revealed that HgCdTe exhibited nearly 100% recovery at 295 K whereas III–V materials recovered to only about 50% under the same conditions.

Structural, morphological, photoluminescence and photocatalytic properties of Gd-doped ZnO films

Nanostructured Gd-doped ZnO films were deposited at 600°C using RF magnetron sputtering technique. The effects of Gd concentration varying from 0 to 2.0at.% on structure as well as morphology and subsequent changes in optical and photocatalytic properties were studied using X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), optical absorption spectra and photoluminescence (PL) spectroscopy. XRD and selected area diffraction results indicated that all Gd-doped ZnO films were of highly (002) preferred orientation and possessed the hexagonal wurtzite structure. SEM images revealed that ZnO nanowires/film structures were grown with a lower Gd content or pure ZnO, and the film crystalline sizes were decreased with Gd doping. XPS results confirmed that the Gd ion was +3 valence states. PL spectroscopy demonstrated an immense enhanced deep-level emission which attributes to the increase in defects concentration due to Gd doping. With a critical doping concentration of 1.6at.% Gd, the ratio of the deep-level emission and the near band edge emission increases by a factor of almost five as compared with pure ZnO. The photocatalytic activities of the films were evaluated by the degradation of methylene blue in aqueous solutions under UV light. The photocatalytic results indicated that the 0.7at.% Gd-doped ZnO nanowires/film structure performed the hightest photocatalytic activity.