Impurity Defects Research Articles

Modification of PEDOT: PSS to enhance device efficiency and stability of the Quasi-2D perovskite light-emitting diodes

Poly(3,4-ethylenedioxy thiophene): poly(styrene sulfonate) (PEDOT: PSS) is a hole transport layer (HTL) that is often employed in a diverse array of optoelectronic devices, such as perovskite solar cells and perovskite light-emitting diodes (PeLEDs). By simply doping lithium fluoride (LiF) into PEDOT: PSS, we demonstrate that the electrical characteristics of the HTL can be modified. Especially in quasi-2D perovskite LEDs, the crystallization process is regulated by LiF modification, leading to reduced phase impurity defects and improved carrier transport in the perovskite emission layer. Therefore, the luminance and efficiency of the quasi-2D PeLEDs are notably enhanced. The optimized PeLED with LiF modification exhibits a peak luminance of 21517 cd m −2 with 317% higher than the standard PeLED; and a high current efficiency of 39.8 cd A −1 with 237% higher than the standard PeLED. Moreover, the device stability is also improved with a nearly doubled half lifetime due to the reduced phase impurities. The work demonstrates a facile yet effective method for altering PEDOT: PSS hole transport layer, emphasizing the critical role of the underneath layer in the crystallization of quasi-2D perovskites. PEDOT: PSS with LiF modification can notably improve the device efficiency and stability of quasi-two-dimensional perovskite light-emitting diodes. • Electronic properties of the hole transport layer can be modified by lithium fluoride doping. • Reduced phase impurity defects and improved carrier transport. • Device stability is also improved with a nearly doubled half lifetime.

Single NV centers array preparation and static magnetic field detection.

To solve the problem of static magnetic field detection accuracy and consistency, we prepared an array of single NV centers for static magnetic field vector and gradient detection using the femtosecond laser direct writing method. The prepared single NV centers are characterized by fewer impurity defects and good stress uniformity, with an average spatial positioning error of only 0.2 µm. This array of single NV centers can achieve high accuracy magnetic field vector and gradient measurement with GBZ≈-0.047 µT/µm in the Z-axis. This result provides a new idea for large-range, high-precision magnetic field vector and gradient measurements.

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-Coated Aluminum/Water Interface Model for Corrosion Applications

The surfaces of most metals immersed in aqueous electrolytes have a several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the existence of both metal∣oxide and oxide∣liquid electrotlyte interfaces, and makes it challenging to correlate atomic length-scale structures with electrochemical properties such the potential-of-zero-charge (PZC). The PZC has been shown to be correlated the onset potential for pitting corrosion. In this work, we conduct large-scale Density Functional Theory and ab initio molecular dynamics to calculate the PZC of a Al(111)∣γ-Al2O3(110)∣ water double-interface model within the context of aluminum corrosion. By partitioning the multiple interfaces involved into binary components with additive contributions to the overall work function and voltage, we predict the PZC to be −1.53 V vs SHE for this model. We also calculate the orbital energy levels of defects like oxygen vacancies in the oxide, which are critical parameters in theories associated with pitting corrosion. We predict that the Fermi level at the PZC lies above the impurity defect levels of the oxygen vacancies, which are therefore uncharged at the PZC. From the PZC estimate, we predict the voltage needed to create oxygen vacancies with net postive charges within a flatband approximation.

Strain induced photonic topological insulator

Strain can be used to tune the electromagnetic properties of photonic crystals by altering their structural and mechanical properties. Nonetheless, photonic topological states associated with electromagnetic one-way edged modes induced by strain have never been observed in photonic crystals, and the connection between photonic topological states and strain remains unclear. Using COMSOL Multiphysics calculations, we demonstrated that strain can trigger photonic topological states with appropriate strain engineering. We also identified that these photonic topological states are insensitive to crystal defects (impurities, vacancies). Our results may promote future studies of novel applications in quantum computing and quantum simulations.

(Digital Presentation) Pinpointing the Potential-of-Zero-Charge in a Alumina-Coated Aluminum/Water Interface Model for Corrosion Applications

The surfaces of most metals immersed in electrolytes feature a several nanometer-thick oxide/hydroxide layer in aqueous electrolytes. This leads to the existence of both a metal/oxide and an oxide/liquid electrotlyte interface. The resulting complexity, and the uncertainty about the structure of and the charges on the surface films, make it challenging to predict from first principles the potential-of-zero-charge (PZC) which has been correlated to the pitting potential [1]. In this work, we use large-scale Density Functional Theory and ab initio molecular dynamics to calculate the PZC of a Al(111)|gamma-Al(2)O(3)|water model within the context of aluminum corrosion. By partitioning the multiple, complex interfaces involved into binary components with additive contributions to the overall work function and voltage, we calculate the PZC in liquid water for this model. Simultaneously, we calculate the orbital energy levels of defects like oxygen vacancies in gamma-Al(2)O(3), which are critical parameters in theories associated with pitting corrosion onset. Our predictions align the Fermi level at PZC with oxygen vacancy impurity defect levels, and estimate the voltage needed to generate charged oxygen vacancies in the flat band approximation. The similarities and differences in results and assumptions used between our model calculations and experiments will be discussed.[1] J.~O'M. Bockris and Y.~Kang, J. Solid Electrochem. 1:17 (1997).Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the document do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Figure 1

Interactions between Mg2+-doped kaolinite and coal: Insights from DFT calculation and flotation

In order to explore the micro-influence mechanism of clay surface/interface property differences on coal slime flotation based on impurity defects, the influence mechanism of Mg2+ doping on the microscopic interactions between particles of kaolinite and coal is preliminarily discussed by using DFT (density functional theory) and flotation. DFT results showed that different coal structural units adsorption on Mg(II)_K (Mg2+-doped kaolinite) surface mainly through electrostatic attraction, and the coal structural units can be stably adsorbed on Mg(II)_K surface in the case of competitive adsorption with H2O. When coal structural units and H2O competed for adsorption on Mg(II)_K surface, H2O promoted the adsorption of coal structural units on Mg(II)_K surface. Flotation results showed that with the increase of kaolinite mass percentage in mixed minerals, the clean coal yield significantly decreased, and the clean coal ash firstly decreased and then increased. The influence mechanism of Mg2+ doping on the interaction between kaolinite and coal was that Mg2+ doping significantly enhanced the interaction between Mg(II)_K surface and coal structural unit. The results revealed the complex interaction between fine particles in coal slime, paving the way for its efficient selective separation.

A first-principle study of the effect of Fe/Al impurity defects on the surface wettability of dolomite

A first-principle study of the effect of Fe/Al impurity defects on the surface wettability of dolomite

Room temperature ferromagnetism in Gd-doped AlN hierarchical microstructures: Experimental and theoretical insights

Diluted magnetic semiconductor materials have attracted extensive attention as candidate materials for a new generation of multifunctional spintronic devices. At present, doping is an effective method to adjust the physical properties of semiconductor materials. Here, the Gd doped AlN (AlN:Gd) hierarchical microstructures were synthesized from mixtures of Al and Gd2O3 powder and N2 working medium by improved arc discharge method. The samples were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, photoluminescence (PL) spectroscopy and vibrating sample magnetometer. The analysis results show that Gd ions are successfully doped into AlN hierarchical microstructures. The PL spectrum excited by 200 nm exhibits a sharp emission line at 318 nm corresponding to 6P7/2-8S7/2 transitions of the Gd3+ ion, and a broad emission band round at 395 nm, which is related to with Al vacancy and O impurity defects. The magnetization curves suggest AlN:Gd hierarchical microstructures process room-temperature ferromagnetic behavior. The latter first-principle calculations indicate that the main origin of the magnetism in AlN:Gd arise from Al vacancies rather than magnetic Gd dopants. Our results suggest that the AlN:Gd hierarchical microstructures are promising materials for spintronic applications.

A role for oxygen vacancies in quartz luminescence

The role that oxygen vacancies can play in the emission of quartz ultraviolet luminescence is investigated. Within a defect pair model approach we highlight the significance of aluminium, titanium and germanium point defects. By comparing known trace element estimates with estimates of the number of luminescent photons that are emitted globally from our bright quartz samples, we confirm that the available impurity defects outnumber the emitted photons by several orders of magnitude. Our conclusion is that another defect species must play a significant role in the observed luminescence sensitivity of quartz. By reviewing the literature on oxygen vacancies, we develop a hypothesis that the well-known oxygen vacancy E′1 centres act as a barrier to migration of holes along the quartz c-channel wall structure, preventing the emission of luminescence. We proceed to examine the processes via which E′1 centres migrate historically under ambient temperature conditions from their source location. By applying known potential barrier information, we contend that a thermally-assisted solar UV exposure mechanism can explain the migration process. In particular, we argue that during such migration the E′1 centres can be trapped at other centres which neutralise them, allowing free passage for subsequent holes en route to the luminescence centres. Such a mechanism predicts that bright luminescence should be observed from quartz extracted from hot sunny locations, compared with lower levels of luminescence in the case of quartz from cool overcast locations. This is consistent with known observations that quartz sensitivity increases with cumulative sunlight exposure.

Electromagnetic wave absorbing properties of In–Sn/rGO composites supported by impurity defect

With the fast development of E-communication technology, effective electromagnetic wave absorbing materials are highly needed to address the growing electromagnetic pollution. Herein, Indium doped tin microsphere/reduced graphene oxide (In–Sn/rGO) composites with rich impurity defects were synthesized via the sol-gel and hydrothermal method. The excellent microwave absorption of In–Sn/rGO composites can be attributed to the modifications of electronics status and Fermi energy level after In doping. This can significantly increase the carrier mobility between In–Sn microspheres and rGO sheets to strike a superior interfacial polarization loss. As a result, the maximum absorptivity can reach −51.16 dB at 8.73 GHz (thickness: 3.5 mm) with a lower filler loading of 10 wt%. Meanwhile, the synthesized In–Sn/rGO composites also exhibit an ultra-wide absorbing frequency range of 13.84 GHz (within the X band, Ku band, and most of the C band). This research provides a new idea for the synthesis of effective microwave absorbing material by introducing impurity defects.

Diagnosis of inhomogeneous one-dimensional discrete chains by photon scattering

Among the ways to reduce radiation doses (increasing the distance from the source to the person, reducing the time spent in radiation fields, reducing the radiation dose rate of the source) an important role is played by shielding the source of ionizing radiation.Currently, the use of screens is limited by the small selection of materials and the inconvenience of their use, which complicates their operation, installation and replacement, or disassembly.The propagation of a plane wave in a one-dimensional force chain with Hertzian contacts is analyzed in a linear approximation for cases with the presence of incorporated single and double impurities (defects). The algorithm of analytical solution of control equations and finding of reflection and transmission coefficients of incident radiation is determined. In terms of phase shifts, the frequency criterion of multi-modes of generation of transparent modes for inhomogeneous chains (with double impurities) similar to the Ramsauer-Townsend effect in the scattering of electrons by inert gas atoms is established. The obtained theoretical results are consistent with the data obtained from alternative sources. Possibilities of application of terahertz spectroscopy of radiation transmission for structural diagnostics and detection of in homogeneities, impurities and defects in discrete micro-mechanical (granular) systems are discussed. In particular, preliminary experimental data on scattering of terahertz radiation on samples of granular materials with different degrees of packing, from low to densely packed, which clearly indicate the dependence of the transmittance on the degree of packing and the formation of the corresponding band structure of spectra. The obtained results are also discussed in terms of applications to the creation of the element base of photonic circuitry in the sub millimeter range using decorated with impurities and structured low-dimensional discrete power circuits.

Sapphire irradiation by phosphorus as an approach to improve its optical properties

Abstract Ion beam-induced luminescence (IBIL) is a versatile technique used to elucidate the chemical bond’s nature and analyze the defects study and impurities present in the material. In this study, IBIL spectra of phosphorus-irradiated sapphire has been analyzed under 2 MeV proton beam as a function of ion dose ranging from 1 × 1014 to 10 × 1014 ions/cm2 at room temperature in the wavelength range of 200–1,000 nm. The IBIL spectrum shows three kinds of luminescence features. The bands centered at 419 nm as F center and 330 nm as F+ center are associated with oxygen vacancies. The third kind of luminescence feature located at 704 nm is related to chromium impurities present in the crystal. The luminescence spectrum of the phosphorus-irradiated sapphire has been correlated with the spectrum obtained from pristine sapphire. The finding indicates that the intensity of defects due to phosphorus irradiation is reduced. As the proton ion fluence increases, the F and F+ center luminescence intensity eventually varies; it turns out that in phosphorus-irradiated sapphire, single crystal defects were reduced and the optical quality was improved.

Oxygen vacancies – Cu doping junction control of δ-Bi2O3 nanosheets for enhanced photocatalytic nitrogen fixation

Cu-δ-Bi2O3 nanosheets with uniform thickness of approximately 2.7 nm and length about 200 nm for photocatalytic nitrogen fixation and photocatalytic oxidation is achieved by simple hydrothermal method. The 2D ultrathin structure is benefit to the formation of the surface oxygen vacancies, meanwhile the impurity defect is formed due to the substitutive Cu doping of δ-Bi2O3. The as-prepared 5% Cu-δ-Bi2O3 exhibits excellent NH4+ generation rate of 142.8 µmol h−1 g−1 without any sacrificial agent irradiated by visible light. The remarkable photocatalytic ability can be attributed to the ultrafast carriers transfer from the interior to the surface because of 2D ultrathin structure feature, the separation of electrons-holes and molecular chemisorption due to the formation of surface oxygen vacancies and impurity defect.

Structure, optical absorption and photochromic effect in Rb0.95Nb1.375Mo0.625O5.79

The compound with β-pyrochlore structure with rare for structure type symmetry (orthorhombic, Pnma) has been prepared recently. In polycrystalline sample Rb0.95Nb1.375Mo0.625O5.79 with beta-pyrochlore structure type prepared by solid-state reaction, the diffuse reflection and transmission spectra have been studied. The spectral dependence of the photochromic effect and the temperature dependence of its kinetics have been investigated. It was found that Rb0.95Nb1.375Mo0.625O5.79 is an indirect-gap semiconductor with band gap of 3 ​eV. A study of the transmission spectrum and a detailed investigation of the photochromic effect made it possible to determine some characteristics of the deep impurity defect level and make a conclusion about the energy ranges in which the Fermi level can be localized in a band gap.

Features of the electronic structure and photocatalytic properties under visible light irradiation for RbTe1.5W0.5O6 with β-pyrochlore structure

The compound RbTe1.5W0.5O6 with β-pyrochlore structure has been recently obtained as visible-light photocatalysts material, which is capable for dye decomposition. The refinement of electron structure has been performed based on transmittance and diffuse reflectance spectra. The ability for visible light absorbance is related to impurity defect absorbance band (∼2.5 eV) in the electron structure, despite the wide band gap (∼3.4 eV). The active radical species, led to methylene blue photooxidation, have been predicted using electronic structure and confirmed experimentally using radical's scavengers. The significant impact of electron-hole pair's recombination process on photocatalytic efficiency has been found out for powder with average size particle of 700 nm, and it has been improved by decreasing the particles size up to 300 nm. The apparent quantum efficiency has been calculated and compared for prepared samples with different particles size. Moreover, the oxidized products of methylene blue have been defined and the possible oxidation pathway has been proposed.

The role of surface and electronic structure features of the CsTeMoO6 β-pyrochlore compound during the photooxidation dyes process

The surface features of CsTeMoO6 with β-pyrochlore structure have been investigated during adsorption and photocatalytic oxidation of methylene dye under visible light irradiation. The apparent quantum yields are 5.12•10−6 and 3.57•10−6 molecules/photons for MB and MO conversion. The refinement of the CsTeMoO6 electronic structure has been carried out by both transmittance and reflectance spectroscopy. The impurity defect absorbance bands in the visible light region have been found out into the wide band gap. Superoxide radicals have been detected as the main active radical species for oxidation, whereas hydroxyl radicals are not formed because of specific holes reaction. Features of surface interactions with cationic and anionic dyes have been studied. The abnormal high absorption capacity of methylene blue by CsTeMoO6 has been obtained. Cs atoms play important role for cationic dye oxidation, while anionic dye predominantly adsorbs and decomposes on the Te/Mo-atom surface centers. The phase stability and composition of catalyst powder have been confirmed by X-ray powder diffraction analysis and X-ray microanalysis. The surface composition and features have been investigated using X-ray photoelectron spectroscopy.

Effect of Point Defects on Electronic Properties and Structure of Talc (001) Surface by First Principles

The surface structure and electronic properties of Mg vacancy defects on talc (001) and impurity defects with Fe, Mn, Ni, Al, and Ca replacing Mg atoms were calculated by using density functional theory. The calculation results show that the order of impurity substitution energy is Mn < Ni < Al < Ca < Fe. This indicates that Fe impurity defects are most easily formed in talc crystals. The covalent bonding between Si atoms and reactive oxygen atoms adjacent to impurity atoms is weakened and the ionic property is enhanced. The addition of Fe, Mn, and Ni atoms makes the surface of talc change from an insulator to a semiconductor and enhances its electrical conductivity. The analysis of electron state density shows that surface states composed of impurity atoms 4S orbital appear near the Fermi level.

Дефекты и перенос энергии в Sr-=SUB=-9-=/SUB=-Lu(PO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=-, легированном ионами Pr-=SUP=-3+-=/SUP=-

In this work luminescence properties of crystalline powders of Sr9Lu(PO4)7 doped with Pr3+ ions were studied upon excitation in UV range in temperature range 5-320 K. Photoluminescence spectra show intensive emission corresponding to radiative interconfigurational 5d→4f electronic transitions, weak narrow lines of intraconfigurational 4f→4f transitions as well as emission of two types of crystal lattice defects. Upon pulsed excitation, timing characteristics of emission related to the impurity center and defects were studied, as well as temperature dependence of emission yield. The processes of energy transfer between impurity center and defects are discussed.

Photoluminescence of sapphire irradiated by low-energy electrons and ions

Photoluminescence (PL) of sapphire single crystals as received and preirradiated by low energy Ar+ ions and electrons has been studied to reveal a relationship between sapphire charging under electron beam irradiation and radiation-induced defect formation. The photoluminescence spectra were obtained using a confocal microscope excitation wavelength of 445 nm as well as by a nonconfocal method with excitation at a wavelength of 355 nm. The lines observed in PL spectra for all samples are associated with both intrinsic and impurity defects. It has been established that preliminary ion irradiation leads to disordering of the near-surface region of the sample resulting in a significant increase in the photoluminescence intensity. Preliminary electron irradiation can lead to a change in the charge state of defects that initially exist in the crystal. Keywords: radiation-stimulated defects, sapphire photoluminescence, ion and electron irradiation.

Фотолюминисценция сапфира, облученного электронами и ионами низких энергий

Photoluminescence (PL) of sapphire single crystals as received and preirradiated by low energy Ar+ ions and electrons has been studied to reveal a relationship between sapphire charging under electron beam irradiation and radiation-induced defect formation. The photoluminescence spectra were obtained using a confocal microscope wavelength of 445 nm as well as by a nonconfocal method with excitation at a wavelength of 355 nm. The lines observed in PL spectra for all samples are associated with both intrinsic and impurity defects. It has been established that preliminary ion irradiation leads to disordering of the near-surface region of the sample resulting in a significant increase in the photoluminescence intensity. Preliminary electron irradiation can lead to a change in the charge state of defects that initially exist in the crystal.