Defects In Gap Research Articles

Temperature Dependent near Infrared Spectroscopy of Electron Irradiated Ceria Single Crystals.

The FTIR absorption bands of virgin and electron-irradiated CeO2 single crystals were measured from 20 K to 500 K between 4000 cm-1 and 12,000 cm-1 (~830 nm to 2500 nm). Three broad bands centered at about 6100 cm-1 (~0.75 eV), 7000 cm-1 (~0.87 eV), and 10,500 cm-1 (~1.3 eV) were recorded above 100 K for the 2.5 MeV electron energy. Two smaller bands at about 4300 cm-1 (~0.53 eV) and 5500 cm-1 (~0.68 eV) were also recorded below 100 K. Similar broad bands centered at about 4100 cm-1 (~0.52 eV), 6400 cm-1 (~0.79 eV), 7600 cm-1 (~0.94 eV), and 10,500 cm-1 (~1.3 eV) are also found for the 1.4 MeV electron energy above 300 K. The evolution of these absorption bands was followed as a function of temperature. The plots of band intensity ratios show a thermally activated process corresponding to the ionization of the deep electronic levels of point defects in the band gap of ceria of ~26,000 cm-1 (~3.2 eV). These five bands are assigned to the different charge states (0, -1, -2, -3, -4) of the Ce vacancies produced by elastic collisions above 1.0 MeV.

Characterization of Ce3+ and Eu3+ doped and co-doped ZnO nanoparticles for luminescence applications

This paper investigates the synthesis of Ce3+ and Eu3+ doped, as well as co-doped ZnO nanoparticles using the solution combustion route. The nanoparticles exhibit a hexagonal wurtzite structure of ZnO with crystallite sizes ranging from 19 to 22 nm. Structural parameters, including lattice constants, bond lengths, and bond angles, are evaluated. Morphological diversity is observed in field-emission scanning electron microscopy images. The diffuse reflectance spectroscopy results reveal an energy band gap of 3.20 eV for undoped ZnO nanoparticles. The energy band gap value slightly decreases for Eu-doped ZnO and certain (Ce, Eu) co-doped ZnO nanoparticles. Photoluminescence (PL) excitation peaks are attributed to energy levels of native defects in the ZnO band gap, along with f–d and f–f transitions of rare-earth ions (Ce3+, Eu3+). The PL emission spectra under different excitation wavelengths (350 nm, 394 nm, and 465 nm) display varied peak positions. ZnO co-doped with 0.96 mol% of Ce3+ and 0.92 mol% of Eu3+ emerges as a promising material for luminescence applications, exhibiting a significant increase in green emission intensity. Consequently, this study represents a novel contribution to the field of ZnO-based luminescent materials.

Bi-element gradient doped B/N-TiO2-x synthesized by one-step solvothermal method enhances the photocatalysis of Cr(VI)

Studying the influence of non-uniform distribution of bi-element doping on the surface structure and photocatalytic performance of TiO2 in interface photocatalytic processes can be an interesting research topic. Taking B/N bi-element doped TiO2 as an example, this article reports an extremely simple gradient doping method of TiO2 and its enhancement mechanism for high concentration wastewater treatment. The surface enrichment and doping of B caused by electrostatic and atomic radius factors changed the charge properties of the complex during the induction of in-situ reduction of Ti4+. The defects in gap N and Ti3+ lead to the formation of intermediate states, resulting in a narrowing of the band gap of the composite to 2.58 eV. The gradient doping of two atoms endows the optimal photocatalyst with a larger specific surface area (114 m2∙g), stronger photocurrent response (0.179 mA·cm−2), suitable Ti3+/Ov double defect structure, and surface positive charge properties. These characteristics improve the effective treatment of high-concentration pollutants by the preferred B2/N-TiO2-x [e.g., 0.0059 min−1 for 0.5 g·L-1 Cr(VI)] and sustainable treatment (removal efficiency > 90 % within 5 cycles). The synthesis strategy will provide a fast, simple, and safe method for the design and synthesis of new TiO2 based catalysts in the future.

Defects in <i>h</i>-BN: computer simulation of size effects

The influence of size effects on the properties of a hexagonal boron nitride (h-BN) monolayer containing CBVN, NBVN, and OBOBVN defects has been studied by first principles methods. These defects are potentially capable of generating single photons in quantum optics and quantum information devices. Size effects here mean the dependence of the studied model properties on the simulated fragment size of the 2D structure under periodic boundary conditions. Physically, this means that the properties of a monolayer depend on the distance between defects. This dependence allows us to judge how strongly the defects interact with each other and whether they interact at all. For technical applications, the characteristics of the band structure (band gap, spectrum and density of electron states induced by the defect in the band gap) and the atomic structure of the defect (defect formation energy, geometry in the equilibrium configuration), which form this band pattern, are important. In this work, these properties are studied by using the density functional theory with the basis of atom-like functions (SIESTA package) and plane waves (VASP package). The results obtained using both packages are consistent with each other. It has been established that the defects can be considered non-interacting, when the distance between them is ten unit cell parameters.

High-Throughput Search for Triplet Point Defects with Narrow Emission Lines in 2D Materials.

We employ a first-principles computational workflow to screen for optically accessible, high-spin point defects in wide band gap, two-dimensional (2D) crystals. Starting from an initial set of 5388 point defects, comprising both native and extrinsic, single and double defects in ten previously synthesized 2D host materials, we identify 596 defects with a triplet ground state. For these defects, we calculate the defect formation energy, hyperfine (HF) coupling, and zero-field splitting (ZFS) tensors. For 39 triplet transitions exhibiting particularly low Huang-Rhys factors, we calculate the full photoluminescence (PL) spectrum. Our approach reveals many spin defects with narrow PL line shapes and emission frequencies covering a broad spectral range. Most of the defects are hosted in hexagonal BN (hBN), which we ascribe to its high stiffness, but some are also found in MgI2, MoS2, MgBr2 and CaI2. As specific examples, we propose the defects vSMoS0 and NiSMoS0 in MoS2 as interesting candidates with potential applications to magnetic field sensors and quantum information technology.

ASSESSMENT OF VOICE FUNCTION AND THE IMPACT OF VOICE DISORDERS ON THE QUALITY OF LIFE IN PATIENTS WITH LARYNX CANCER AFTER SURGICAL TREATMENT

Actuality: In Ukraine, according to the 2020 cancer registry, the incidence of laryngeal cancer is 5.2 per 100,000 population (the world standard rate is 3.3). The total number of cases of the disease in 2020 is 1845. Among them, 1763 persons are men, 82 - are women. [1] 39-42% of patients have tumor, which of the corresponds , and require organ-keeping surgical treatment.[2,3] Postoperative period accompanies voice disorders because of inflammatory changes in tissues of larynx and defect in the glottal gap. [4]

Structural, optical, and magnetic properties of V-doped ZnO nanoparticles and the onset of ferromagnetic order

Pure and vanadium (V) doped ZnO nanoparticles (NPs) were successfully synthesized via a modified sol-gel method. The wurtzite crystal structure of ZnO remained intact with the vanadium doping concentrations under the present synthesis environment as confirmed by an array of advanced analytical techniques; such as Rietveld refined X-ray diffraction (XRD) pattern, as well as bond valence sum (BVS) analysis. SEM and TEM techniques were used to examine the morphology of the samples. UV-Vis-NIR spectra showed an absorption band in the UV range with reduction in the band gap from 3.23 eV to 3.20 eV when V content increases. Photoluminescence (PL) shows that doping with V causes the creation of some defects in the band gap of ZnO. The energy position of the obtained PL emission introduces a blue shift when the measurement temperature increases. The M-T curve is successfully fitted using both three dimensional (3D) spin wave model and Curie-Weiss law which attests to the mixed state existence of ferromagnetic (FM) and paramagnetic (PM) phases. The electron paramagnetic resonance (EPR) analysis supports the XRD results and provides evidence of oxygen vacancies (VO). Magnetic interaction is quantitatively studied and explained by polaronic percolation of bound magnetic polarons (BMP) produced by VO defects.

Influence of Disordered Regions on the Optoelectronic Properties of Heterostructures with Ge/Si Nanoislands Irradiated with Fast Neutrons

It is shown that the concentration оf disordered regions (radiation-induced defect clusters) formed during the irradiation of semiconductors by neutrons with a fluence of 1013–1015 cm–2 is just an order of magnitude less than the bulk concentration of Ge/Si nanoislands in modern multilayer heterostructures with their planar arrays. The elastic strain of the crystal lattice around the disordered regions is several times less than that around the Ge/Si nanoislands, which determine their optoelectronic properties. The irradiation of modern heterostructures with arrays of Ge/Si nanoislands by neutrons with a fluence of 1015 cm–2 means that up to 40% of nanoislands fall within the space charge area of many disordered regions. It is concluded that degradation of the optoelectronic properties of heterostructures with Ge/Si nanoislands irradiated with neutrons is mostly due to the influence of the energy levels of radiation-induced defects in the band gap and electric field of disordered regions on the charge carrier kinetics near nanoislands.

Antibacterial activity of In-doped ZnO nanoparticles

Undoped and In-doped zinc oxide (ZnO) nanoparticles have been synthetized by sol gel technique. The In doping concentration was ranged from 0 to 5 at.%. The prepared nanoparticles structural and morphological properties have been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The photoluminescence (PL) spectroscopy was used to determine the electronic defects in the samples band gap. The antibacterial activities of the synthetized nanoparticles have been tested against Gram negative and positive bacteria’s referring to the inhibition zone radius measurement. The obtained results indicated that In dopant improves its antibacterial activity. The antibacterial activity improvement with In doping effect is attributed to the enhancement of electronic defects including vacancy defect Vzn and interstitial defect Zni with In doping. These defects behave as electrons and holes source necessary for reactive oxygen species (ROS) responsible for bacteria’s destruction. We noticed that the prepared ZnO nanoparticles exhibit a low antioxidant activity, this is attributed to the bonded hydrogen charge transfer crystal screening.

Improved ultraviolet sensing, photo-stabilized visible transmission, and electrical conductance in Zn1−xGax/2Fex/2O

Abstract

Synthesis, structural, opticaland magnetic properties of Gd co-doped ZnO:V nanoparticles

In this work, we investigate structural, optical and magnetic properties of Zn0·96V0·04O (ZnV4), Zn0·92V0.04Gd0.04O (ZnV4Gd4) and Zn0·88V0.04Gd0.08O (ZnV4Gd8) nanoparticles synthesized by sol–gel. In our protocol, the water has been slowly released following an esterification reaction, then, this solution was dried under supercritical conditions of ethyl alcohol and heat treatment in air at 500 °C for 2 h. The structural properties showed that the obtained samples have a wurtzite structure with a crystallite size around 25 nm and a secondary phase has been detected, attributed to a vanadium complex. By increasing the doping concentration of Gd, the band gap energy decreased. Photoluminescence (PL) shows that doping with Gd causes the creation of some defects in the band gap of ZnO. Magnetic measurements at room temperature showed a ferromagnetic behavior after doping.

Thermal annealing and dopant dependence of nonlinear absorption characteristics in ZnO Nanoparticle/PMMA films

Cr and Sb doped ZnO/PMMA nanocomposite films were investigated to understand the effect of doping and annealing on linear and nonlinear optical properties. ZnO, ZnO:Cr and ZnO:Sb nanoparticles were synthesized by hydrothermal method. The structural results showed that the incorporation Cr and Sb dopant to the ZnO crystal lattice led to decreasing of the crystallite sizes from 30.3 nm to 24.4 nm due to the increasing of the number of defect states inside the energy band gap. The crystallite size of the synthesis nanoparticles increased with annealing due to the decreasing defects in the band gap. The band gap energies were estimated to be 5.240 eV, 5.260 eV, 5.246, 5.253 eV and 5.280 eV for undoped, Cr and Sb doped ZnO/PMMA nanocomposite films, respectively. After annealing, the band gap energies decreased to 2.505 eV, 2.510 eV, 2.610 eV, 2.755 eV and 2.597 eV values due to the increasing of the crystallite sizes of the nanoparticles, respectively. The transmittances of the films varied with Cr and Sb doping and annealing process. The open aperture Z-scan technique was used to measure the nonlinear absorption properties of investigated films at ns regime. The nonlinear absorption coefficient values were found to be 4.95 × 105 cm/GW, 7.21 × 105 cm/GW, 1.69 × 106 cm/GW, 8.18 × 105 cm/GW and 2.09 × 106 cm/GW for ZnO/PMMA, ZnO:Cr/PMMA and ZnO:Sb/PMMA nanocomposite films, respectively. The saturation intensity thresholds increased with doping from 5.15 GW/cm2 to 10.40 GW/cm2. After annealing, the nonlinear absorption coefficient values were found to be 2.14 × 105 cm/GW, 2.99 × 105 cm/GW, 4.85 × 105 cm/GW, 3.43 × 105 cm/GW and 6.91 × 105 cm/GW for ZnO/PMMA, ZnO:Cr/PMMA and ZnO:Sb/PMMA, respectively.

The Effect of Spin Center Parameters on the Photoactivity of Nanocrystalline Titanium Dioxide in the Visible Spectral Range

Nanocrystalline TiO2 samples, obtained by sol–gel and supercritical fluid (SCF) methods, have been studied by optical spectroscopy and electron spin resonance. It is established that the main type of spin centers in SCF samples are Ti3+/oxygen vacancy centers and conduction electrons. Radicals ($${{{\text{N}}}^{ \bullet }}$$, $${\text{N}}{\kern 1pt} {\text{O}}{{{\kern 1pt} }^{ \bullet }}$$) and ($${{{\text{C}}}^{ \bullet }}$$) are found in the samples doped with nitrogen and carbon, respectively. The energy levels of defects in the band gap of the structures studied are determined. It is explained why samples with close values of nanocrystal sizes, specific surface area, and defect concentration have a significantly different photocatalytic activity in the visible spectral range. It is found that impurity centers with energy levels near the middle of the semiconductor band gap must be incorporated into TiO2 to obtain samples with the highest photocatalysis rate. New possibilities for developing energy-efficient (without UV irradiation) photocatalysts are discovered.

Photoluminescence study of interfacial charge transfer and photocatalytic activity in titanium dioxide/copper multilayer film

The 100-nm titanium dioxide (TiO2) thin film and its composites with copper (Cu) underlayers of various thicknesses, 4 nm–16 nm, were fabricated on glass substrates by a DC-magnetron sputtering technique. Optical properties of the pristine and the composite films revealed that increasing Cu underlayer thickness greatly increased their absorption in the entire visible region, leading to a decrease in the band gap energy. This should significantly enhance the solar-driven catalytic activity. However, it was found that the photocatalytic activity under the UV radiation determined from photo-degradation of methyl orange (MO) of thick Cu underlayer films exhibited the reduction in degradation rate. The photoluminescence indicated that Cu nanoparticles at TiO2/Cu interface layer not only generated shallow level defects in TiO2 band gap but also acted as recombination centers for photo-generated carriers. This phenomenon was the result of the presence of Cu surface roughness as well as the presence of large aggregates in thick Cu layers. Therefore, the life time and the number of free carriers transported to the TiO2 surface decreased causing the reduction in photodegradation activity of TiO2 composite films.

Influence of thin MOCVD-grown GaN layer on underlying AlN template

Abstract We have studied the direct growth of a GaN film on an AlN template/sapphire substrate by metalorganic chemical vapor deposition. It was found that the GaN layer causes marked deformation of the underlying AlN template at the initial growth. The intensity of x-ray diffraction from AlN drops by a factor of 5 and the full widths at half maximum of the rocking curves of the on- and off-axis planes are increased from 50 to 300 arcsec. With increasing GaN growth time, these values gradually recover, and the crystalline quality of the GaN film is improved. No alloy formation is observed at the interface between AlN and GaN. An AlN template on a sapphire substrate seems to act as a buffer layer, adjusting the lattice constant to improve the crystallinity of the direct grown GaN. Compared with a GaN film grown on a sapphire substrate, GaN grown directly on an AlN template forms a smoother surface with better crystalline quality in a shorter growth time, and at a lower temperature with fewer nonradiative defects in the band gap.

Luminescence induced by N[sbnd]O ion implantation into diamond

The incorporation of shallow n-type dopants in diamond is one of the major challenges for its electronic applications. n-Type behaviour in diamond has been observed for substitutional phosphorus and nitrogen, with activation energies of approximately 0.62 and 1.7 eV, respectively. Both nitrogen and phosphorus are deep lying substitutional impurity states in diamond. It has been theoretically found that the substitution of the NO molecule into the diamond lattice forms a stable defect in the band gap and, in the negatively charged state induces a shallow defect below the conduction band edge which may lead to n-type conductivity. In this study, low-temperature photoluminescence measurements using different excitation wavelengths were used to investigate the nature and behaviour of the defects induced by the implantation of NO ions into type IIa Chemical Vapor Deposition (CVD) diamond samples. Luminescence peaks were observed at 293.3, 297.3, 305.9, 309.8, 314.4 and 556.7 nm on the sample which was implanted by NO ions and annealed at 600 °C. The origin of these peaks is discussed and the mechanism of electronic transitions leading to emission of photoluminescence from these samples is proposed.

Tailoring of nanostructures: Al doped CuO synthesized by composite-hydroxide-mediated approach

Abstract Pure and aluminum doped CuO nanocrystalline material is prepared by composite-hydroxide mediated (CHM) approach. The structural analysis of these superstructures by X-ray diffraction indicates reduction in average crystallite size estimated as 43–36 nm. This is due to formation of point defects and oxygen vacancies produced by the placement of Al atoms in CuO lattice site. Incorporation of Al content in CuO host matrix is evident as the lattice parameter variation, increase in micro-strain and dislocation density. FTIR spectroscopy gives information about the purity of CuO nanostructure formation. Interesting rods, flowers, triangular shapes and rectangular shaped morphological peculiarities provide evidence of Al incorporation at CuO lattice sites. Thermal gravimetric analysis reveals the thermal stability of as synthesized product. Diffuse reflectance spectroscopy indicates blue shift in band gap energy from 1.36 to 1.96 eV. This blue shift can be attributed to the existence of defects in the band gap produced by successful incorporation of Al+3 into CuO.

Damage removal and gap filling in nucleotide excision repair.

The nucleotide excision repair (NER) system removes a variety of types of helix-distorting lesions from DNA through a dual incision mechanism, in which the damaged nucleotide bases are excised in the form of a small, excised, damage-containing single-stranded DNA oligonucleotide (sedDNA). Damage removal leaves a gap in the DNA template that must then be filled in by the action of a DNA polymerase and ligated to the downstream phosphodiester backbone in the DNA to complete the repair reaction. Defects in damage removal, sedDNA processing, or gap filling have the potential to be mutagenic and lethal to cells, and thus several human pathologies, including cancer and aging, are associated with defects in NER. This review summarizes our current understanding of NER with a focus on the enzymes that excise sedDNAs and restore the duplex DNA to its native state in human cells.

Low analytical totals in EPMA of hydrous silicate glass due to sub-surface charging: Obtaining accurate volatiles by difference

The major and minor element chemistry of silicate glass is commonly measured using electron probe micro-analysis (EPMA). The volatile content (H2O ± CO2) can, additionally, be quantified using “volatiles by difference” (VBD), but a review of literature data shows that this method consistently overestimates the volatile content. We propose that sub-surface charging during EPMA reduces analytical totals, consequently elevating VBD. Sub-surface charging produces an internal electric field due to trapped implanted electrons, resulting in fewer X-rays being generated and their depth of generation being shallower. The maximum electric field strength required to produce the observed overestimation of VBD is calculated to be ~10−1 V·nm−1. Crystals are often used as standards for glass analysis but, as amorphous materials have more defects in the band gap, glasses can trap more electrons resulting in greater amounts of sub-surface charging. As this is not included in matrix corrections, it causes errors for glass analyses, but not for crystal analyses. By calibrating VBD using hydrous glass standards, the effect of charging can be incorporated, and volatile contents can be determined to an accuracy of ±0.1 wt%, compared to overestimation by ~1 wt% using conventional VBD methods.

(Invited) Characterization of Phases and Defects in Compound Semiconductors

Defects in semiconductors can be difficult to characterize, especially in complex semiconductors such as the chalcogenides. This talk presents several different and relatively unusual methods for their study along with examples of results. The talk will focus on semiconductors used for photovoltaic applications but the talk should illustrate methods that would be of use with any semiconductor material. Specifically the talk will address the use of admittance spectroscopy, nuclear magnetic resonance (NMR), scanning microwave impedance microscopy (SMIM), scanning tunneling spectroscopy (STS) and others to study defects in CdTe, CuInSe2 (CIGS), and Cu2ZnSnS4 (CZTS), and related compounds. Examples of results include the identification of two defects in the energy gap of CIGS by admittance spectroscopy, band edge fluctuations in CIGS by STS and their impact on the ability to obtain atomic resolution images, organized point defect structures in CZTS by NMR, and grain and grain boundary behaviors in CdTe by SMIM. Other examples will be included as time permits.