eV Line Research Articles

Luminescence properties of dislocations in α-Ga2O3

Abstract Dislocations in epitaxial lateral overgrown α-Ga2O3 are investigated using hyperspectral cathodoluminescence spectroscopy. The dislocations are associated with a reduction of self-trapped hole-related luminescence (ca. 3.6 eV line) which can be ascribed to their actions as non-radiative recombination sites for free electrons, to a reduction in free electron density due to Fermi level pinning or to electron trapping at donor states. An increase in the intensity of the ca. 2.8 eV and 3.2 eV lines are observed at the dislocations, suggesting an increase in donor–acceptor pair transitions and providing strong evidence that point defects segregate at dislocations.

Fröhlich resonance splitting in hybrid GaN nanowire-Ag nanoparticle structures

Plasmonic nanoparticles (NPs) have attracted significant attention due to their unique optical properties and broad optoelectronic and photonic applications. We investigate modifications of emission in hybrid structures formed by 60 nm silver NPs and GaN planar nanowires (NWs). Bare GaN NWs exhibit photoluminescence (PL) spectra dominated by broad bands peaking at ∼3.44 eV and ∼3.33 eV, attributed to basal plane stacking faults. In hybrids, two new narrow PL lines appear at 3.36 and 3.31 eV, resulting in PL enhancement at these energies. While the 3.36 eV line in hybrid structures can be explained using the Fröhlich resonance approximation based on the electric dipole concept, the appearance of two features at 3.36 and 3.31 eV indicates the splitting of resonance lines. This phenomenon is explained in framework of theoretical model based on the interaction of the dipole with its charge image, taking into account the quadrupole moment of the silver sphere and the quadrupole field of the charge image. A good agreement is obtained between the calculated Fröhlich resonance frequencies and the experimental PL lines in hybrid structures.

Rice tonoplast intrinsic protein member OsTIP1;2 confers tolerance to arsenite stress

The International Agency for Research on Cancer categorizes arsenic (As) as a group I carcinogen. Arsenic exposure significantly reduces growth, development, metabolism, and crop yield. Tonoplast intrinsic proteins (TIPs) belong to the major intrinsic protein (MIP) superfamily and transport various substrates, including metals/metalloids. Our study aimed to characterize rice OsTIP1;2 in As[III] stress response. The gene expression analysis showed that the OsTIP1;2 expression was enhanced in roots on exposure to As[III] treatment. The heterologous expression of OsTIP1;2 in S. cerevisiae mutant lacking YCF1 (ycf1∆) complemented the As[III] transport function of the YCF1 transporter but not for boron (B) and arsenate As[V], indicating its substrate selective nature. The ycf1∆ mutant expressing OsTIP1;2 accumulated more As than the wild type (W303–1A) and ycf1∆ mutant strain carrying the pYES2.1 vector. OsTIP1;2 activity was partially inhibited in the presence of the aquaporin (AQP) inhibitors. The subcellular localization studies confirmed that OsTIP1;2 is localized to the tonoplast. The transient overexpression of OsTIP1;2 in Nicotiana benthamiana leaves resulted in increased activities of enzymatic and non-enzymatic antioxidants, suggesting a potential role in mitigating oxidative stress induced by As[III]. The transgenic N. tabacum overexpressing OsTIP1;2 displayed an As[III]-tolerant phenotype, with increased fresh weight and root length than the wild-type (WT) and empty vector (EV line). The As translocation factor (TF) for WT and EV was around 0.8, while that of OE lines was around 0.4. Moreover, the OE line bioconcentration factor (BCF) was more than 1. Notably, the reduced TF and increased BCF in the OE line imply the potential of OsTIP1;2 for phytostabilization.

Increasing the immunogenic and protective activity of the vaccine strain Yersinia pestis EV line NIIEG using synthetic immunomodulators

Introduction. One of the main tasks of specific plague prevention remains the development of vaccines and their application schemes aimed at improving the effectiveness of vaccination through the use of adjuvants and immunomodulators.
 The purpose of the study were comparative evaluation of the effect of drugs from the group of synthetic immunomodulators on the immunogenic and protective properties of the Yersinia pestis EV line NIIEG vaccine strain in model animal experiments.
 Materials and methods. White mice and guinea pigs were immunized with the vaccine strain Y. pestis EV line NIIEG. The animals of the experimental groups were injected with oligopeptides O1 (Threonyl-glutamyl-lysyl-lysyl-arginyl-arginyl-glutamyl-threonyl-valyl-glutamyl-arginyl-glutamyl-lysyl-glutamate), O2 (Glutamyl-cysteinyl-glycine disodium) and O3 (Arginyl-alpha-aspartyl-lysyl-valyl-tyrosyl-arginine) one hour before vaccination or three times before infection. On days 3, 14 and 21, antibody and cytokine products were studied. Animals were infected with the test strain Y. pestis 231(708) at a dose of 400 LD50.
 Results. It was found that a single administration of immunomodulators 1 hour before vaccination did not change the susceptibility of animals to the plague microbe: ImD50 = 5860 (O1); 5860 (O2); 6454 (O3) and 6876 (control) CFU for white mice and 446 (O1), 551 (O2), 446 (O3) and 578 (control) CFU for guinea pigs. Three-time administration of drugs to vaccinated animals led to a decrease in the ImD50 Y. pestis EV line NIIEG indicators in the group with O1 by 2.2 times (mice) and 1.8 times (guinea pigs), with O2 and O3 by 1.2 times, regardless of the biomodel compared with the control. The stimulating effect of O1 and O3 on the production of antibodies to F1 of the plague microbe and cytokines interferon-gamma, interleukin-10 has been established.
 Conclusion. The stimulating potential of synthetic immunomodulators on the immune system of biomodels immunized by Y. pestis EV line NIIEG has been demonstrated, which determines the prospects of research to improve the schemes of prophylactic vaccination against plague.

Analysis of the Features of the Genomic Organization of Plague Microbe Strains Suitable for the Creation of a New Attenuated Vaccine

Relevance. To date, the specific prevention of plague remains the most effective measure to prevent to prevent the deterioration of the epidemiological situation for this especially dangerous infection in the territory of the Russian Federation. The development of new vaccine preparations created on the basis of avirulent strains of Yersinia pestis with specific genetic defects, can play a crucial importance in the issues of plague immunoprophylaxis.Aim. Determination and comparative analysis of the genomic organization of avirulent strains Y. pestis I-1, Y. pestis I-3536 and vaccine strain Y. pestis EV line NIIEG.Materials and methods. The features of the genetic structure of three Y. pestis strains were studied using plasmid screening and whole genome sequencing.Results and discussion. It was found that the Y. pestis I-1 and Y. pestis I-3536 strains, like Y. pestis EV, lack the chromosomal pgm region. Analysis the genome sequence of Y. pestis I-1 showed that this strain is devoid of the plasmid pMT1, while its individual genes were found in the chromosome structure and the unique 340 kb plasmid. It was revealed that the Y. pestis strain I-3536 lost the plasmid pCD1, however, fragments homologous to this plasmid were found in the structure of its genome.Conclusion. The data obtained allow us to recommend Y. pestis I-1 and Y. pestis I-3536 as the basis for the development of a modern live attenuated plague vaccine.

Sharp luminescence system in titanium dioxide with zero-phonon transition at 1.573 eV

In this paper, we discuss near-IR steady-state and time-resolved low-temperature (5 K) luminescence of crystalline titanium dioxide (TiO2) powders with different particle sizes. Upon optical excitation with quantum energy close to 3.1 eV, the near-IR luminescence of all the powders reveals a very similar characteristic spectrum, which includes a narrow 1.573 eV line, a set of wider peaks in 1.565–1.545 eV range, and a broad band at ∼1.42 eV. The spectrum remains unchanged when using different excitation quanta, thus indicating that all components are governed by the same luminescence system. It is also confirmed by identic two-exponential luminescence decays with characteristic decay times 70 μs and 400 μs observed for all parts of the spectrum. The properties of the luminescent system are not sensitive to the crystallite size reduction to 10 nm, and its intensity sharply increases after annealing converting the anatase phase into rutile. A comparison of the spectrum with TiO2 phonon density of states indicates that 1.573 eV peak is a zero-phonon transition, and 1.545–1.565 eV structure is due to interaction with bulk phonons of rutile phase. The band at 1.42 eV seems to be due to non-adiabatic electron-phonon coupling. The data obtained clearly indicates that the luminescent system is governed by inner shells of transition elements located in rutile lattice. This transition element can be vanadium as it follows from ICP-MS data and theoretical modeling. The detected luminescent system provides a convenient optical marker of TiO2, including nanoform, and thus can be useful for some applications related to medicine, biology, as well as the food industry.

Enhancement of the Yersinia pestis EV NIIEG Vaccine Srain Immunogenic and Protective Activity under Cultivation with Azoxymer Bromide (Polyoxidonium)

Background. The live-attenuated vaccine based on the Yersinia pestis strain EV line NIIEG is still used in Russia, providing protective efficacy against plague. Nevertheless, there is an urgent need for developing new ways to increase the immunogenicity of the Y. pestis EV NIIEG vaccine strain. In this study, the ability of direct action of immunoadjuvant azoximer bromide (polyoxidonium, PO) on the immunobiological properties of vaccine strain Y. pestis EV NIIEG during cultivation on a dense nutrient medium was evaluated.Materials & Methods. Y.pestis EV NIIEG, cultivated at 28 °С for 48 h on LB agar, Miller pH 7.2 ± 0.1 (Sigma-Aldrich, USA) with the addition of PO and without. MALDI-TOF mass-spectrometry was deployed for the obtainment of mass-spectra of ribosomal proteins from Y. pestis EV NIIEG cells on the MicroflexTM LT mass spectrometer (Bruker Daltonics, Germany). Protective efficacy was evaluated under subcutaneously challenge guinea pigs and mice BALB's with 400 LD50 doses of the Y. pestis 231, Y. pestis P-13268 Vietnam (MLD=5 CFU). Antibody titers to F1 in serum were determined using an ELISA.Results. The addition of the therapeutic concentration of PO in the cultivation medium induced a significant increase in the immunogenicity of Y. pestis EV NIIEG that resulted in enhancement of serum antibody levels against Y. pestis F1 antigen and several times the growth of protective efficacy in the bubonic plague model on two types of experimental animals. ImD50 of the vaccine strain Y. pestis EV NIIEG, cultivated with PO, was significantly (p < 0,05) lower in comparison to ImD50 for Y. pestis EV NIIEG in standard cultivation conditions. One year of storage at a temperature of 4 °С did not alter the protective properties of the vaccine strain Y. pestis EV NIIEG, cultivated with PO.Conclusions. Morphological studies confirmed the absence of influence PO introduction into the cultivation environment on the safety of the vaccine strain. MALDI-TOF MS profile of the Y. pestis EV NIIEG, cultivated with PO, had peaks characteristic features. The mass peak at m/z 3,061 was significantly down-regulated and new mass peaks at m/z 2,759, m/z 3,533 were determined. These changes are accompanied by the increase of Y. pestis EV NIIEG immunogenicity.

Yersinia pestis Antigen F1 but Not LcrV Induced Humoral and Cellular Immune Responses in Humans Immunized with Live Plague Vaccine-Comparison of Immunoinformatic and Immunological Approaches.

The recent progress in immunoinformatics provided the basis for an accelerated development of target-specific peptide vaccines as an alternative to the traditional vaccine concept. However, there is still limited information on whether the in silico predicted immunoreactive epitopes correspond to those obtained from the actual experiments. Here, humoral and cellular immune responses to two major Yersinia pestis protective antigens, F1 and LcrV, were studied in human donors immunized with the live plague vaccine (LPV) based on the attenuated Y. pestis strain EV line NIIEG. The F1 antigen provided modest specific cellular (mixed T helper 1 (Th1)/Th2 type) and humoral immune responses in vaccinees irrespective of the amount of annual vaccinations and duration of the post-vaccination period. The probing of the F1 overlapping peptide library with the F1-positive sera revealed the presence of seven linear B cell epitopes, which were all also predicted by in silico assay. The immunoinformatics study evaluated their antigenicity, toxicity, and allergenic properties. The epitope TSQDGNNH was mostly recognized by the sera from recently vaccinated donors rather than antibodies from those immunized decades ago, suggesting the usefulness of this peptide for differentiation between recent and long-term vaccinations. The in silico analysis predicted nine linear LcrV-specific B-cell epitopes; however, weak antibody and cellular immune responses prevented their experimental evaluation, indicating that LcrV is a poor marker of successful vaccination. No specific Th17 immune response to either F1 or LcrV was detected, and there were no detectable serum levels of F1-specific immunoglobulin A (IgA) in vaccinees. Overall, the general approach validated in the LPV model could be valuable for the rational design of vaccines against other neglected and novel emerging infections with high pandemic potency.

Positive temperature dynamics of near-band-edge photoluminescence in Nb-doped SrTiO3

The positive temperature dynamics in the near-band-edge (NBE) photoluminescence (PL) of Nb-doped SrTiO3 single crystal have been investigated in the temperature range of 10 K–120 K. Intensity of the NBE PL emission with a peak at 3.21 eV has shown increase with increasing temperature. This NBE PL consists of two emission lines with peaks at 3.208 and 3.167 eV. The thermal dynamic in the intensity of the 3.21 eV emission was mainly defined by the temperature behavior of the 3.208 eV transition. The increase in the intensity of the 3.208 eV line with increasing temperature was associated with an increase in the number of electrons thermally excited from the surface. Additionally, a critical point in intensity of the PL at 3.21 eV can be caused by the phase transition, which occurs in Nb-doped SrTiO3 at 115 K.

Very low energy peak shifts in EDS spectra

The response function of energy-dispersive X-ray spectrometers (EDS) has been a topic for investigation as long as EDS has been used. This work systematically investigates soft X-ray peaks with energies below 150 eV in regard to the detector energy calibration linearity. It was found that Si-L (92 eV) and Al-L (73 eV) lines are not shifted in energy position in comparison to higher energy K-lines of boron, carbon and nitrogen. The reason is simply the silicon detector material has a large absorption jump at 99 eV (Si-L2/Si-L3), which causes much higher detection depths of photons with energies below 99 eV. There is also less shift than assumed with older approaches in the energy region 100 to 149 eV (Si-L1). It is also expected that Li-K radiation will not be affected by an energy shift due to detector artefacts. The authors propose a modified shift-correction which corrects this detector artefact and linearizes the energy calibration of measured EDS spectrum below 600 eV. This energy shift effect of the measured X-ray lines is in principle with any silicon-based X-ray detector. But the shift value depends also on the front contact layer design and quality. The novelty with changed correction is that no shift is applied for X-ray peaks below 99 eV. Older applied correction procedures were found to produce a line energy misplacement in spectrum for this energy region.

The Analysis of Factors Influencing Immunologic Reactivity in People Vaccinated with a Live Plague Vaccine

Introduction: An increase in epizootic activity has been registered in a number of plague foci in the Russian Federation over the past few years. As part of securing sanitary and epidemiologic wellbeing of the population living in the natural foci of the disease, a mass immunization with a live plague vaccine based of the Yersinia pestis EV line NIIEG vaccine strain was carried out. Objectives: The purpose of the study was to assess the influence of a complex of factors including age, gender, health status, the number of previous vaccinations against plague, blood groups, and HLA gene polymorphism on the state of the cellular and humoral immune response in people vaccinated with the live plague vaccine. Materials and methods: The analysis of venous blood of 347 volunteers included determination of the concentration of specific antibodies to the capsular antigen (F1) of plague microbe, spontaneous and induced production of marker cytokines (IFN-γ, TNF-α, and IL-4) by ELISA, and genes of the main histocompatibility complex (HLA) class II by real-time PCR. We also analyzed medical documentation (Form 025/u) and the results of a questionnaire-based survey of the vaccinated people. Results and discussion: We established the influence of various factors, including genetic ones, on marker indicators of the humoral and cellular immune response in persons vaccinated with the live plague vaccine. We also characterized the relationship between the level of specific antibodies to plague microbe F1 production and some cytokines and the age and the number of previous vaccinations in our volunteers. The most common gene variants of the main histocompatibility complex of class II (HLA-DQA1, HLA-DQB1 and HLA-DRB1) in the cohort were identified and possible relationships between the production of IFN-γ, TNF-α, IL-4 and allelic polymorphism of HLA class II genes were determined. Conclusions: Immunologic reactivity in people vaccinated with the live plague vaccine is mainly determined by age, the number of previous vaccinations against this infection, and individual characteristics of HLA gene polymorphism.

Demonstration of Fine-Pitch High-Resolution X-ray Transition-Edge Sensor Microcalorimeters Optimized for Energies below 1 keV

In this paper, we report on X-ray transition-edge sensor (TES) microcalorimeters optimized to have the best possible energy resolution for a limited energy range for the incoming X-rays, such as an energy resolution of 0.3 eV full width half maximum (FWHM) for energies up to $$\approx 0.8\,{\mathrm{keV}}$$ as is desirable for one of the Lynx X-ray Microcalorimeter subarrays. The test array we have fabricated has $$60\times 60$$ sensors on a pitch of $$50\,\upmu {\mathrm{m}}$$, and has $$46\times 46\,\upmu {\mathrm{m}}^2$$ absorbers that are one micrometer thick. We have measured a spectral energy resolution of the same device using 3 eV photons delivered through an optical fiber. For the one-photon 3 eV line, we have obtained an energy resolution of 0.25 eV FWHM, which is consistent with the estimated performance based on the signal size and noise. Further measurements will determine how the energy resolution degrades with energy. Based upon measurements of the TES transition characteristics, it appears that this level of energy resolution should be achievable up to 0.5 keV, and the performance will then gradually degrade to the measured energy resolution of around 2.3 eV at 1.5 keV. In this paper, we describe the full design and characterization of this detector, and discuss the performance limits of pixels designs like this.

INFLUENCE OF POLYOXIDONIUM, Poly(I:C), DALARGIN ON THE PROTECTIVE EFFICACY OF YERSINIA PESTIS VACCINE STRAIN EV LINE NIIEG IN EXPERIMENTAL PLAGUE

In this study, the use of immunoadjuvants polyoxidonium (azoximer bromide), Poly (I:C) as a synthetic analog of double-stranded RNA (TLR3 ligand), and synthetic analog of leu-enkephalin dalargin (DA) was experimentally investigated for their potential to minimize ImD50 Yersinia pestis vaccine strain EV line NIIEG co-administrated via invasive (subcutaneous) and noninvasive (intranasal) routes in lethal bubonic and pneumonic models of plague followed by challenge with virulent Y. pestis strains of the main and non-main subspecies from various natural plague foci. The data showed that in all cases immunoadjuvants significantly increased protective efficacy of Y. pestis vaccine strain EV line NIIEG co-administrated to BALB/c inbreed mice in case of lethal challenge with virulent Y. pestis strains in spite of varying magnitude of humoral immune response. Y. pestis vaccine strain EV line NIIEG formulated with polyoxidonium provided more effective protection against lethal challenge with wild-type high virulent strain Y. pestis in pneumonic model of plague. Polyoxidonium introduced into vaccine formula resulted in four-fold rise in total survival in animals with pneumonic plaque. Feasibility of using immunoadjuvants for regimen of specific and urgent plaque prevention is justified.

A Sparkler in the Fireworks Galaxy: Discovery of an Ultraluminous X-Ray Transient with a Strong Oxygen Line in NGC 6946

Abstract We discovered and studied an ultraluminous X-ray source (CXOU J203451.1+601043) that appeared in the spiral galaxy NGC 6946 at some point between 2008 February and 2012 May and has remained at luminosities ≈2–4 × 1039 erg s−1 in all observations since then. Our spectral modeling shows that the source is generally soft but with spectral variability from epoch to epoch. Using standard empirical categories of the ultraluminous regimes, we found that CXOU J203451.1+601043 was consistent with a broadened disk state in 2012 but was in a transitional state approaching the supersoft regime in 2016, with substantial down-scattering of the hard photons (similar, for example, to the ultraluminous X-ray source in NGC 55). It has since hardened again in 2018–2019 without any significant luminosity change. The most outstanding property of CXOU J203451.1+601043 is a strong emission line at an energy of of (0.66 ± 0.01) keV, with an equivalent width of ≈100 eV and de-absorbed line luminosity of ≈2 × 1038 erg s−1, seen when the continuum spectrum was softest. We identify the line as O viii Lyα (rest-frame energy of 0.654 keV); we interpret it as a strong indicator of a massive outflow. Our finding supports the connection between two independent observational signatures of the wind in super-Eddington sources: a lower temperature of the Comptonized component and the presence of emission lines in the soft X-ray band. We speculate that the donor star is oxygen-rich: a CO or O–Ne–Mg white dwarf in an ultracompact binary. If that is the case, the transient behavior of CXOU J203451.1+601043 raises intriguing theoretical questions.

Unusual properties of the RY3 center in GaN

The investigation and identification of point defects in GaN is crucial for improving the reliability of light-emitting and high-power electronic devices. The RY3 defect with a characteristic emission band at about 1.8 eV is often observed in photoluminescence (PL) spectra of $n$-type GaN grown by hydride vapor phase epitaxy, and it exhibits unusual properties. Its emission band consists of two components: a fast (10-ns lifetime) RL3 with a maximum at 1.8 eV and a slow (100--300 \ensuremath{\mu}s lifetime) YL3 with a maximum at 2.1 eV and zero-phonon line at 2.36 eV. In steady-state PL measurements, the YL3 component emerges with increasing temperature from 90 to 180 K, concurrently with a decrease in the RL3 intensity. The activation energy of both processes is about 0.06 eV. In time-resolved PL, the YL3 intensity abruptly rises when the RL3 intensity begins to saturate. These and other phenomena can be explained using a model of an acceptor with two excited states. A delocalized, effective-mass state at about 0.2 eV above the valence band captures photogenerated holes. These holes transition to the ground state, which produces the RL3 component with a lifetime of \ensuremath{\sim}10 ns. Alternatively, they may nonradiatively transition over a 0.06 eV-high barrier to a localized excited state with a level at 1.13 eV above the valence band. Recombination of free electrons or electrons at shallow donors with the holes at this localized excited state is responsible for the YL3 component. The relative intensities of the RL3 and YL3 components are dictated by the probabilities of holes at the shallow excited state to transition to the ground or to the localized excited states. Transition metals and complex defects are considered as the main candidates for the RY3 center.

Comments on the fractal energy spectrum of honeycomb lattice with defects

We study the fractality of the energy spectrum of honeycomb lattice with various defects or impurities under a perpendicular magnetic field. Using a tight-binding Hamiltonian including interactions with the nearest neighbors, we investigate its energy spectrum for different choices of point defects or impurities. First, we fix a unit cell consisting of 8 lattice points and survey the energy eigenvalues in the presence of up to 2 point defects. Then it turns out that the existence of the fractal energy structure, called Hofstadter’s butterfly, highly depends on the choice of defect pairs. Next, we extend the size of a unit cell which contains a single point defect in the unit cell consisting of 18 and 32 lattice points to lower the density of the defects. In this case, the robust gapless point exists on the E = 0 eV line without depending on the size of unit cells. And we find this gapless point always exists at the center of the butterfly shape. This butterfly shape also exists for the case of no defect lattice which has the fractality.

Reflectance and fast polarization dynamics of a GaN/Si nanowire ensemble

Optical phenomena in an ensemble of high-quality GaN nanowires (NWs) grown on a Si substrate have been studied by reflectance and time-resolved luminescence. Such NWs form a structure that acts as a virtual layer that specifically reflects and polarizes light and can be characterized by an effective refractive index. In fact we have found that the NW ensembles of high NW density (high filling fraction) behave rather like a layer of effective medium described by the Maxwell Garnett approximation. Moreover, light extinction and strong depolarization are observed that we assign to scattering and interference of light inside the NW ensemble. The wavelength range of high extinction and depolarization correlates well with transverse localization wavelength estimated for such an ensemble of NWs, so we suppose that these effects are due to Anderson localization of light.We also report results of time-resolved measurements of polarization of individual emission centers including free and bound excitons (D0XA, 3.47 eV), inversion domain boundaries (IDB, 3.45 eV) and stacking faults (SF, 3.42 eV). The emission of the D0XA and SF lines is polarized perpendicular to GaN c-axis while the 3.45 eV line is polarized along the c-axis which supports a hypothesis that this line is emitted from IDBs. Time-dependent depolarization of luminescence is observed during the first 0.1 ns after excitation and is interpreted as the result of interaction of the emission centers with hot particles existing for a short time after excitation.

Temperature Dependence of Low‐Energy Electron Beam Irradiation Effect on Optical Properties of MQW InGaN/GaN Structures

The low‐energy electron beam irradiation (LEEBI) effect at 80 K on the optical properties of InGaN/GaN multiple quantum well structures has been studied. It is shown that the new emission band formed under LEEBI is related to quantum wells. At 80 K the total intensity of new and initial emission bands does not change under LEEBI. The intensity of the 3.3 eV line is shown to increase due to LEEBI. The results obtained are explained assuming a modification of properties of small local regions, which strongly localize the excess carriers.

Confirmation of Incorporation of Cu and Se Ions in Applied p- and n-Type-Doped Sb2S3 by Photoemission Spectroscopy

The effect of incorporating copper (Cu) and selenium (Se) ions into stibnite (Sb2S3) lattice was investigated using x-ray photoelectron spectroscopy (XPS). The incorporation of Cu and Se ions was verified by comparing the XPS spectra of the undoped (amorphous Sb2S3), doped (p and n-doped) and pure Se and Cu-acetate powders. The main photoelectron Cu 2p1/2 (951.8 eV) and Cu 2p3/2 (932.1 eV) lines derived from the Cu-doped and Cu-acetate powder samples were clearly observed, whereas in the undoped sample, none of the characteristic lines of Cu were detected. The Se Auger line (138.6 eV), the only line of Se which does not coincide with the lines of Sb and S, was successfully detected in an Se-doped XPS sample and the spectrum of pure Se, while Se in the undoped sample was not found. Further, the XPS measurements revealed the relative amounts of Cu and Se in antimony sulfide, as well as the oxidation state of copper incorporated into the matrix.

Buckminsterfullerene hybridized zinc oxide tetrapods: defects and charge transfer induced optical and electrical response.

Buckminster fullerene (C60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses the successful fabrication of C60 decorated ZnO tetrapod materials and their detailed structure-property relationships including device sensing applications. The electron microscopy investigations indicate that a quite dense surface coverage of ZnO tetrapods with C60 clusters is achieved. The spectroscopy studies confirmed the identification of the C60 vibrational modes and the C60 induced changes in the absorption and luminescence properties of the ZnO tetrapods. An increased C60 concentration on ZnO results in steeper ZnO bandgap absorption followed by well-defined free exciton and 3.31 eV line emissions. As expected, higher amounts of C60 increase the intensity of C60-related visible absorption bands. Pumping the samples with photons with an energy corresponding to these absorption band maxima leads to additional emission from ZnO showing an effective charge transfer phenomenon from C60 to the ZnO host. The density of states model obtained from DFT studies for pure and C60 coated ZnO surfaces confirms the experimental observations. The fabricated C60-ZnO hybrid tetrapod based micro- and nanodevices showed interesting ethanol gas sensing characteristics.