High-energy Band Research Articles

Synthesis of Zinc Oxide Nanoparticles by Hydrothermal Methods and Spectroscopic Investigation of Ultraviolet Radiation Protective Properties

Ultraviolet radiation causes damages to the human body, such as skin ageing, skin cancer, and allergies throughout the world. Applying zinc oxide nanoparticles (ZnO NPs) in sunscreen products (like cloths or textiles) to protect human skin by absorbing the ultraviolet radiations that emerged from the sun. The main aim of this study is to investigate both absorbance and transmittance characteristics of the untreated and treated cotton textiles. For ZnO NPs using hydrothermal methods, they were made from Zn(NO3)2·6H2O and NaOH at a constant annealing temperature of 300°C. Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis spectroscopy were used to analyze the produced ZnO NPs. From the FT-IR result, ZnO NPs were observed in the region of 400-600 cm-1. Wurtzite hexagonal structure of ZnO NPs with the average crystal size 32 ± 49 nm was observed from XRD results. Flowers in the shape of synthesized ZnO NPs were observed from SEM images. The UV-vis penetration peaks were identified at 264 nm and 376 nm, with energy band gaps of 4.68 and 3.536 eV, respectively. When compared to bulk ZnO, the energy band gap of ZnO NPs was blue-shifted due to the impact of quantum confinement. The peaks in UV-vis absorption were caused by an electronic transition from the valiancy to the conduction bands. The high energy band shows high absorbance of the synthesis sample in the case of 264 nm. The ZnO NPs were manufactured and applied to 100% of raw cotton to impart sunscreen action to both untreated and treated cotton fabrics. The performance of treatment has been evaluated utilizing UV-vis spectroscopy through quantifying ultraviolet protective factors (UPF) and percentage of transmitted (%T) radiations. The treated cotton textiles have 61.50% UPF while 2.65% ultraviolet radiations were transmitted. In other words, untreated cotton textiles have 1.63% UPF while 74.56% ultraviolet radiation was transmitted. Therefore, the treated cotton textiles have excellent protection categories when compared to untreated cotton textiles.

Dual-Emissive Tris-Heteroleptic Ruthenium Complexes: Tuning the DNA-Triggered Ratiometric Emission Response by Ancillary Ligands.

Three tris-heteroleptic mononuclear Ru(II) complexes with dual fluorescence and phosphorescence-[Ru(dpma)(bpy)(phen)]2+ (12+), [Ru(dpma)(bpy)(dppz)]2+ (22+), and [Ru(dpma)(phen)(dppz)]2+ (32+)-have been designed and used as ratiometric light-response probes for DNA, where dpma is di(pyrid-2-yl)(methyl)-amine, bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Single crystals of complex 2(PF6)2 have been obtained and studied by X-ray analysis. The interactions of these complexes with different DNAs are investigated by means of spectroscopic methods, viscosity measurements, and molecular modeling. In the presence of calf thymus DNA, complexes 2(PF6)2 and 3(PF6)2 show the emergence of a new lower-energy phosphorescence emission band; meanwhile, the higher-energy fluorescence emission band is essentially unchanged, functioning as an intrinsic internal reference. These two complexes exhibit stronger preference for calf thymus DNA over single-strand DNA (d(A)16 and d(C)16). In contrast, no binding interaction between 1(PF6)2 and calf thymus DNA is observed. The intrinsic binding constants (Kb) of 2(PF6)2 and 3(PF6)2 with calf thymus DNA are determined to be (1.4 ± 0.4) × 105 and (9.5 ± 0.15) × 104 M-1, respectively. In addition, these spectroscopic results are compared with those of the prototype complex [Ru(bpy)2(dppz)]2+ (42+), and density functional theory and time-dependent density functional theory calculations are employed to elucidate these experimental findings.

Sublattice Dependence and Gate Tunability of Midgap and Resonant States Induced by Native Dopants in Bernal-Stacked Bilayer Graphene.

The properties of semiconductors can be crucially impacted by midgap states induced by dopants, which can be native or intentionally incorporated in the crystal lattice. For Bernal-stacked bilayer graphene (BLG), which has a tunable band gap, the existence of midgap states induced by dopants or adatoms has been investigated theoretically and observed indirectly in electron transport experiments. Here, we characterize BLG midgap states in real space, with atomic-scale resolution with scanning tunneling microscopy and spectroscopy. We show that the midgap states in BLG-for which we demonstrate gate tunability-appear when the dopant is hosted on the nondimer sublattice sites. We further evidence the presence of narrow resonances at the onset of the high-energy bands (valence or conduction, depending on the dopant type) when the dopants lie on the dimer sublattice sites. Our results are supported by tight-binding calculations that agree remarkably well with the experimental findings.

The Effect of Precursor Concentration on the Particle Size, Crystal Size, and Optical Energy Gap of CexSn1-xO2 Nanofabrication.

In the present work, a thermal treatment technique is applied for the synthesis of CexSn1−xO2 nanoparticles. Using this method has developed understanding of how lower and higher precursor values affect the morphology, structure, and optical properties of CexSn1−xO2 nanoparticles. CexSn1−xO2 nanoparticle synthesis involves a reaction between cerium and tin sources, namely, cerium nitrate hexahydrate and tin (II) chloride dihydrate, respectively, and the capping agent, polyvinylpyrrolidone (PVP). The findings indicate that lower x values yield smaller particle size with a higher energy band gap, while higher x values yield a larger particle size with a smaller energy band gap. Thus, products with lower x values may be suitable for antibacterial activity applications as smaller particles can diffuse through the cell wall faster, while products with higher x values may be suitable for solar cell energy applications as more electrons can be generated at larger particle sizes. The synthesized samples were profiled via a number of methods, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). As revealed by the XRD pattern analysis, the CexSn1−xO2 nanoparticles formed after calcination reflect the cubic fluorite structure and cassiterite-type tetragonal structure of CexSn1−xO2 nanoparticles. Meanwhile, using FT-IR analysis, Ce-O and Sn-O were confirmed as the primary bonds of ready CexSn1−xO2 nanoparticle samples, whilst TEM analysis highlighted that the average particle size was in the range 6−21 nm as the precursor concentration (Ce(NO3)3·6H2O) increased from 0.00 to 1.00. Moreover, the diffuse UV-visible reflectance spectra used to determine the optical band gap based on the Kubelka–Munk equation showed that an increase in x value has caused a decrease in the energy band gap and vice versa.

Sonochemical synthesis of Fe-doped Cu3Se2 nanoparticles: Correlation of the strain and electrical properties for optoelectronics applications

This research presents the effect of different concentrations of iron (Fe) as dopants on the physical properties of the copper selenide (Cu3Se2) nanoparticle (NPs). The physical properties of the Cu3Se2 NPs were investigated using structural, morphological, and optical analysis. The results revealed that the Fe concentrations change the crystallite size (from ∼8 to 44 nm) and strain (from ∼0.0007 to 0.0030). Fe-doped Cu3Se2 NPs showed a higher optical energy band gap in comparison to the un-doped sample (1.80 eV). The films prepared by green binder (ethyl cellulose) indicated that the sample with minimum Fe concentration presents the highest carrier concentration (9.56e+18 cm−3) and lowest ideality factor (2.02) amounts. The electrical study shows space charge limited current (SCLC) mechanism in Fe-doped Cu3Se2 NPs that is not observed in un-doped sample. Using this mechanism, the highest carrier mobility (16.22 cm+2V−1s−1) obtained for sample with the lowest amount of Fe concentrations.

Ambipolar Channel p-TMD/n-Ga2 O3 Junction Field Effect Transistors and High Speed Photo-sensing in TMD Channel.

Highly crystalline 2D/3D-mixed p-transition metal dichalcogenide (TMD)/n-Ga2 O3 heterojunction devices are fabricated by mechanical exfoliation of each p- and n-type material. N-type β-Ga2 O3 and p-type TMD separately play as a channel for junction field effect transistors (JFETs) with each type of carriers as well as materials for a heterojunction PN diode. The work thus mainly focuses on such ambipolar channel transistors with two different types of channel in a single device architecture. For more extended applications, the transparency of high energy band gap β-Ga2 O3 (Eg ≈ 4.8eV) is taken advantage of, firstly to measure the electrical energy gap of p-TMDs receiving visible or near infrared (NIR) photons through the β-Ga2 O3 . Next, the p-TMD/n-Ga2 O3 JFETs are put to high speed photo-sensing which is achieved from the p-TMD channel under reverse bias voltages on n-Ga2 O3 . The photo-switching cutoff frequency appears to be ≈16 and 29kHz for visible red and NIR illuminations, respectively, on the basis of -3dB photoelectric power loss. Such a high switching speed of the JFET is attributed to the fast transport of photo-carriers in TMD channels. The 2D/3D-mixed ambipolar channel JFETs and their photo-sensing applications are regarded novel, promising, and practically easy to achieve.

Synthesis of Oxygen Deficient TiO2 for Improved Photocatalytic Efficiency in Solar Radiation

The photocatalytic activities of TiO2 have been limited mainly to absorbing in the ultraviolet spectrum which accounts for only 5% of solar radiation. High energy band gap and electron recombination in TiO2 nanoparticles are responsible for its limitations as a photocatalyst. An oxygen deficient surface can be artificially created on the titanium oxide by zero valent nano iron through the donation of its excess electrons. A visible light active TiO2 nanoparticle was synthesized in the current investigation through simple chemical reduction using sodium boro-hydride. The physical and textural properties of the synthesized oxygen deficient TiO2 photocatalyst was measured using scanning/ transmission electron microscopy while FTIR, XRD and nitrogen sorption methods (BET) were employed for its further characterizations. Photochemical decoloration of orange II sodium dye solution in the presence of the synthesized TiO2 was measured using an UV spectrophotometer. The resulting oxygen deficient TiO2 has a lower energy band-gap, smaller pore sizes, and enhanced photo-catalytic properties. The decoloration (88%) of orange (II) sodium salt solution (pH 2) under simulated solar light was possible at 20 min. This study highlights the effect of surface oxygen defects, crystal size and energy band-gap on the photo-catalytical property of TiO2 nanoparticles as impacted by nano zero valent iron. It opens a new window in the exploitation of instability in the dopant ions for creation of a visible light active TiO2 photocatalyst.

Characterization of the UV-Visible absorption spectra of manganese(III) porphyrins with time-dependent density functional theory calculations

Abstract Mn(III) porphyrins display a unique UV–Vis spectrum: compared to the free-base and other metalloporphyrins, a strong red shift of the Soret-band and several extra bands can be observed in their spectra. To understand this behavior, we have recorded the UV–Vis spectra of differently substituted water-soluble Mn(III) porphyrins and conducted extensive theoretical investigations using time-dependent density functional theory. The calculated optical transitions, using the O3LYP functional, agree well with the measured absorption bands. According to the spectral interpretation, the Soret-band involves a mixture of L–L and ligand-to-metal charge transfer excitations, while the Q-bands and the higher-energy bands in the UV region correspond to pure LMCT as well as to ligand to metal-ligand mixed orbital excitations. The impact of the explicit and implicit water solvent on the spectral features is also discussed.

High impact of thiol capped ZnS nanocrystals on the degradation of single and binary aqueous solutions of industrial azo dyes under sunlight

Sulfur zinc (ZnS) nanocrystals were prepared using an aqueous colloidal route with thioglycolic acid (TGA) as a stabilizer. These ZnS-TGA nanocrystals were used as a low-cost and environmental friendly alternative for the photodegradation of methylene blue (MB) and methyl orange (MO) from aqueous solutions using sunlight irradiation. Structural and optical properties of nanocrystals were determined via X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopic, UV–Visible and photoluminescence spectroscopy. Results showed a blue shift of absorbance band and higher energy band gap values than bulk ZnS materials, which was in agreement with the quantum confinement effect. X-ray diffraction confirmed the formation of cubic phase of ZnS-TGA containing also a slight wurtzite phase. Calculated average size of ZnS nanocrystals by the Debye Scherrer relation was 3.5 nm. Characterization results showed the fixation of TGA on ZnS-NCs via sulphur and carboxylic functionalities on catalyst surface. Photoluminescence spectra obtained under excitation wavelength at 325 nm showed three emission bands (416, 441 and 484 nm), which were mainly related to band edge and defect-activated emissions. The photocatalytic activity of ZnS-TGA nanocrystals under sunlight irradiation to degrade tested MB and MO dyes and their mixture in aqueous solutions was evaluated. High dye degradation efficiency was achieved at a very short time (27 min) and this performance was attributed to the negative surface charge, surface area, surface defects and high dispersion of ZnS-TGA nanocrystals on the aquatic medium. Overall, this study demonstrates that these nanocrystals could be employed as low-cost nanocatalyst for the degradation of organic dyes in wastewater treatment.

1-keV emission from laser-plasma source based on an Xe/He double stream gas puff target.

Characterization of Xe emission in the spectral range between 1 and 1.5 keV is presented in the case when the laser-plasma is generated by nanosecond laser pulse irradiation of a double stream Xe/He gas-puff target. Gas target density was estimated using extreme ultraviolet (EUV) radiography. Emission spectral characteristics in the wavelength range from 0.8 to 5.2 nm were determined by using a flat field SXR spectrometer. Significant emission was recorded in two high-energy bands, the first one at wavelengths 0.8-1.6 nm (photon energy range 0.78-1.5 keV) and the second one at 1.6-2.5 nm (0.5-0.78 keV). Both plasma size and photon yield in each band were measured separately to individually assess radiation and source characteristics. Moreover, a proof-of-principle experiment for near-edge X-ray absorption fine structure spectroscopy of metallic sample near the L2,3 absorption edge was performed to show one of the applicability areas of such a compact source.

Long-term XMM–Newton view of magnetar CXOU J010043.1−721134: comprehensive spectral and temporal results

ABSTRACT We present an in-depth analysis and results of eleven XMM–Newton data sets, spanning 2000–2016, of the anomalous X-ray Pulsar CXOU J010043.1−721134 that has been classified as a magnetar. We find a spin period of 8.0275(1) s as of December 2016 and calculate the period derivative to be (1.76 ± 0.02) × 10−11 s s−1, which translate to a dipolar magnetic field strength of 3.8 × 1014 G and characteristic age of ∼7200 yr for the magnetar. It has a double-peaked pulse profile, with one broad and one narrow peak, in both soft (0.3–1.3 keV) and hard (1.3–8 keV) energy bands. The pulse fractions in the two energy bands are found to be consistent with constant values. These results are in agreement with previously published results for this source. Although two-component models produce acceptable fits to its energy spectra, single component models are much simpler and are able to explain the similarity of the pulse profiles in the low- and high-energy bands. We attempt fitting with four different single-component models and find that the best fit to the spectra is obtained by fitting a thermal Comptonization model with the photon index (Γ) between 2.0 and 2.7, and the electron temperature ( kTe) between 0.5 and 0.9 keV, for a seed blackbody photon distribution of 0.2 keV. Finally, we conclude by discussing our results briefly.

Understanding Sea Level Processes During Western Mediterranean Storm Gloria

In January 2020, the storm Gloria hit the Western Mediterranean Sea causing severe coastal damages, destruction of infrastructures, flooding and several casualties. This extreme event was characterized by strong Eastern winds, record-breaking waves heights and periods, and a storm surge that locally beat the record along Valencia’s coastline. This paper analyses the dynamic evolution of sea level during this storm. The study employs both the in situ data and the operational forecasts of the PORTUS early warning system. Tide gauge data are analyzed on the different temporal scales that contribute to total sea level: long-term and seasonal, tides and storm surges, and higher frequency oscillations. It was found that, due to the unusual long wave periods, infragravity waves were generated and dominate the high frequency energy band, contributing significantly to extreme sea level records. This is a relevant finding, since this kind of oscillations are usually associated with larger basins, where swell can develop and propagate. The impact of sea level rise is also analyzed and considered relevant. A multi-model ensemble storm surge forecasting system is employed to study the event. The system was able to correctly forecast the surge, and the measured data were always inside the confidence bands of the system. The differences of the results obtained by the available operational forecasting system integrated into the ensemble, including those from Copernicus Marine Service, are described. All the models provided useful forecasts during the event, but differences with measured data are described and connected with the known limitations in physics (for example, barotropic vs. baroclinic) and set-up of the models (model domain, lack of tides and different inverse barometer implementations at the open boundaries amongst others).

Novel sterically demanding Schiff base dyes: An insight from experimental and theoretical calculations

We report extensive experimental and theoretical studies on structural and photophysical properties of two new bulky Schiff base dyes 1 and 2, obtained from the reaction of cyclohexylamine with the 5-bromosalicylaldehyde or 2-hydroxy-1-naphthaldehyde. The structure of 1 exhibits the enol-imine form in the solid state and is characterized by a typical intramolecular O–H⋯N hydrogen bond. Contrarily, the structure of 2 was found to be in the cis-keto-enamine tautomer, stabilized by an intramolecular N–H⋯O hydrogen bond. Favoured intermolecular H⋯H, H⋯C, H⋯O and H⋯Br contacts in the structure of 1 and H⋯H, H⋯C and H⋯O in the structure of 2 are responsible for the overall crystal packing of the dyes. The UV–vis spectra of 1 in cyclohexane, THF, CH2Cl2 and CH3CN exhibit bands in the UV region, indicating the enol-imine form, while in MeOH the UV–vis spectrum of 1 exhibits an additional band in the visible region at 410 nm, which corresponds to the cis-keto-enamine tautomer. The absorption spectra of 2 in the same solvents, except cyclohexane, also contain a band in the visible region up to about 450 nm. This band exhibits two maxima, which can be assigned to an equilibrium between the cis-keto-enamine and zwitterion forms, of which the latter one is structurally the same as the former isomer. The UV–vis spectrum of 2 in cyclohexane reveals only traces of the cis-keto-enamine. The dye 1 was found to be emissive exclusively in MeOH, while 2 is emissive in all the studied solvents, of which the most pronounced and the most negligible emission was found for MeOH and cyclohexane, respectively. An intense emission band in the spectrum of 1 at 468 nm arises from the emission of two conformers of the cis-keto-enamine* form. The solution of 2 in MeOH showed dual emission with the bands centered at 346 and about 450 nm, of which the latter one is a superposition of two single bands. The two low-energy emission bands arise from the emission of the cis-keto-enamine* and zwitterion* forms, while the high-energy emission band most likely corresponds to the naphthalene fragment. Finally, π-resonanse stabilization (RAHB) effect is found to be crucial for tuning the tautomerization mechanism through the alteration of intramolecular O–H⋯N hydrogen bond.

(Invited) High Performance Ternary Organic Solar Cells Based on Non-Fullerene Acceptors

Organic solar cells (OSCs) comprising of a photoactive layer of electron-donor and electron-acceptor have attracted great attention for decades due to their low-cost, large-area, solution-processed in flexible substrates, and indoor light energy harvester [1,2]. Their power conversion efficiencies (PCEs) have been boosted to over 18% via material design, device engineering, and theoretical studies [3]. One of the most promising methods to improve device performance is adding a third component into a binary system, resulting in a ternary blend. Ternary blends can form an even larger variety of morphologies, depending on the ratio and the interactions between the components. In a ternary blend, the third components not only provide a broadened light harvesting and optimizing the film morphology, but also facilitating exciton dissociation and charge transport. As a consequence, it is improving the device performance of OSCs, i.e., the fill factor (FF), short-circuit current density (Jsc), open-circuit voltage (Voc) and power conversion efficiency (PCE). On the other hand, the rapid progress of highly efficient NFAs materials has offered a new opportunity for studying ternary OSCs due to the great tunability of chemical structures, optical properties and electronic properties of NFAs, and their ability to phase separate into nanoscopic domains in blended thin films [4].In this study, we have been focusing first on the optimization of binary systems using fullerene and non-fullerene acceptors. We performed several strategies to improve the device performance and stability of these binary systems: engineering the electron transport layers, annealing treatment, using inkjet printing and spray pyrolysis deposition methods, and photoactive materials engineering. As a result, we achieved PCEs from ~3% using P3HT as donor polymer, ~10% PCE using PTB7-Th donor polymer up to more than 17% efficiency using PM6 donor polymer [5–10]. To the next level, we shift the direction of our work using ternary system through careful selection of the third component in donor-acceptor materials. However, blending three light-absorbing semiconductor materials is not a trivial work. A huge materials combination, their compatibility, relative-energies of their frontier orbitals and solubility need to be considered to achieve a successful high performance ternary bulk heterojunction OSCs.To date, we have been able to improve device performance by using new phthalocyanines derivatives as third components in binary PTB7-Th:PC70BM due to their high extinction coefficients, stability, and energy band gaps well-matched to the incident solar spectrum [11]. The proper choice of the central atom in pthalocyanine compound were studied to know their effect to the electrical parameters and absorption spectra of OSCs. Moreover, we also compare the effect of fullerene PC70BM and non-fullerene ITIC-M as third components in the bulk heterojunctions of PM6:Y7-based devices. Acknowledgements: This work was supported by the Ministerio de Ciencia, Innovación y Universidades (MICINN/FEDER) RTI2018-094040-B-I00, by the Agency for Management of University and Research Grants ref. 2017-SGR-1527 and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award References[1] L. Duan, A. Uddin, Adv. Sci. 2020, 1903259.[2] A. A. A. Torimtubun, J. G. Sánchez, J. Pallarès, L. F. Marsal, Sustain. Energy Fuels 2020, 4, 3378.[3] Q. Liu, Y. Jiang, K. Jin, J. Qin, J. Xu, W. Li, J. Xiong, J. Liu, Z. Xiao, K. Sun, S. Yang, X. Zhang, L. Ding, Sci. Bull. 2020, 65, 272.[4] L. Xiao, B. He, Q. Hu, L. Maserati, Y. Zhao, B. Yang, M. A. Kolaczkowski, et al., Joule 2018, 2, 2154.[5] J. G. Sanchez, A. A. A. Torimtubun, V. S. Balderrama, M. Estrada, J. Pallares, L. F. Marsal, IEEE J. Electron Devices Soc. 2020, 8, 421.[6] A. A. A. Torimtubun, J. G. Sanchez, J. Pallares, L. F. Marsal, in 2020 IEEE Lat. Am. Electron Devices Conf., IEEE, San Jose, Costa Rica, 2020, pp. 1–4.[7] J. G. Sánchez, V. S. Balderrama, S. I. Garduño, E. Osorio, A. Viterisi, M. Estrada, J. Ferré-Borrull, J. Pallarès, L. F. Marsal, RSC Adv. 2018, 8, 13094.[8] V. S. Balderrama, J. G. Sánchez, G. Lastra, W. Cambarau, S. Arias, J. Pallarès, E. Palomares, M. Estrada, L. F. Marsal, J. Mater. Chem. A 2018, 6, 22534.[9] V. S. Balderrama, M. Estrada, A. Cerdeira, B. S. Soto-Cruz, L. F. Marsal, J. Pallares, J. C. Nolasco, B. Iñiguez, E. Palomares, J. Albero, Microelectron. Reliab. 2011, 51, 597.[10] E. Osorio, J. G. Sánchez, L. N. Acquaroli, M. Pacio, J. Ferré-Borrull, J. Pallarès, L. F. Marsal, ACS Omega 2017, 2, 3091.[11] A. A. A. Torimtubun, J. Follana-Berná, Á. Sastre‐Santos, J. Pallarès, L. F. Marsal, to be Publ. 2020.

Charge-stripe fluctuations in Nd4Ni3O8 as evidenced by optical spectroscopy

We present an investigation into the optical properties of Nd$_{4}$Ni$_{3}$O$_{8}$ at different temperatures from 300 down to 5~K over a broad frequency range. The optical conductivity at 5~K is decomposed into IR-active phonons, a far-infrared band $\alpha$, a mid-infrared band $\beta$, and a high-energy absorption edge. By comparing the measured optical conductivity to first-principles calculations and the optical response of other nickelates, we find that Nd$_{4}$Ni$_{3}$O$_{8}$ features evident charge-stripe fluctuations. The $\beta$ band is attributed to electronic transitions between the gapped Ni-$d_{x^2-y^2}$ bands due to fluctuating charge stripes, while the high-frequency absorption edge corresponds to the onset of transitions involving other high-energy bands. Furthermore, an analysis of the temperature-dependent optical spectral weight reveals a $T^{2}$ law, which is likely to originate from strong correlation effects.

Structural Optimization, Electronic Band Structure, Mechanical and Thermodynamics Properties of Fe3Al

We calculated the structural, electronic, mechanical and thermal properties of Fe3Al semiconducting using Quantum ESPRESSO, an open source first principles code based on density-functional theory, plane waves, and pseudopotentials. Structural parameter results (equilibrium lattice parameters, bulk modulus and its derivative pressure) have been reported. The underestimated band gap is obtained along with higher state density and energy bands around the fermi level. Mechanical properties of the rock-salt structure of Fe3Al, such as, shear modulus (G), Young’s modulus (E), and Poisson’s ratio () were investigated. The thermodynamic parameters are also present. The results are in good agreement with the available experimental and other theoretical results.

Electronic spectrum of Kekulé patterned graphene considering second neighbor-interactions

The effects of second-neighbor interactions in Kekulé-Y patterned graphene electronic properties are studied starting from a tight-binding Hamiltonian. Thereafter, a low-energy effective Hamiltonian is obtained by projecting the high energy bands at the Γ point into the subspace defined by the Kekulé wave vector. The spectrum of the low energy Hamiltonian is in excellent agreement with the one obtained from a numerical diagonalization of the full tight-binding Hamiltonian. The main effect of the second-neighbour interaction is that a set of bands gains an effective mass and a shift in energy, thus lifting the degeneracy of the conduction bands at the Dirac point. This band structure is akin to a ‘pseudo spin-one Dirac cone’, a result expected for honeycomb lattices with a distinction between one third of the atoms in one sublattice. Finally, we present a study of Kekulé patterned graphene nanoribbons. This shows that the previous effects are enhanced as the width decreases. Moreover, edge states become dispersive, as expected due to second neighbors interaction, but here the Kek-Y bond texture results in an hybridization of both edge states. The present study shows the importance of second neighbors in realistic models of Kekulé patterned graphene, specially at surfaces.

Wavelength-Resolved Photoluminescence and Cathodoluminescence Decay Times of LSO:Ce Scintillator CO-Doped with Lithium and Scandium

We study the luminescence decay times of Ce3+: Lu2SiO5 scintillator, co-doped with Sc3+ and Li+ ions, under the direct photoexcitation of Ce3+ ions at 337 nm and excitation by a pulsed electron beam with energies of 100 – 300 keV. The cathodoluminescence (CL) and photoluminescence (PL) decay times of studied sample are equal within the experimental error. Two emission bands are found: in the range of 370 – 480 nm (“high-energy band”) and 500 – 570 nm (“low-energy band”). The highenergy emission band has the decay times ∼40 ns. The low-energy emission band has the maximum decay time ∼60 ns at 545 nm. The observed results show that the transport stage of Li:Sc:Ce:Lu2SiO5 scintillation mechanism is not affected by a high negative space charge and high density of electronic excitations provided by the high-power electron beam.

Relativistic fluid modelling of gamma-ray binaries

Context. In the first paper of this series, we presented a numerical model for the non-thermal emission of gamma-ray binaries in a pulsar-wind-driven scenario. Aims. We apply this model to one of the best-observed gamma-ray binaries, the LS 5039 system. Methods. The model involves a joint simulation of the interaction between the pulsar wind and the stellar wind and the transport of electron pairs from the pulsar wind accelerated at the emerging shock structure. We compute the synchrotron and inverse Compton emission in a post-processing step while consistently accounting for relativistic beaming and γγ-absorption in the stellar radiation field. Results. The wind interaction leads to the formation of an extended, asymmetric wind collision region that develops strong shocks, turbulent mixing, and secondary shocks in the turbulent flow. Both the structure of the collision region and the resulting particle distributions show significant orbital variation. In addition to the acceleration of particles at the bow-like pulsar wind and the Coriolis shock, the model naturally accounts for the re-acceleration of particles at secondary shocks that contribute to the emission at very-high-energy (VHE) gamma-rays. The model successfully reproduces the main spectral features of LS 5039. While the predicted light curves in the high-energy and VHE gamma-ray band are in good agreement with observations, our model still does not reproduce the X-ray to low-energy gamma-ray modulation, which we attribute to the employed magnetic field model. Conclusions. We successfully model the main spectral features of the observed multi-band, non-thermal emission of LS 5039 and thus further substantiate a wind-driven interpretation of gamma ray binaries. Open issues relate to the synchrotron modulation, which might be addressed through a magnetohydrodynamic extension of our model.

Development of bio-degradable based polymer electrolytes for EDLC application

In this work, bio-degradable blended solid polymer electrolyte (BSPE) films made up of PVA:PS:(CH3COO)2Mg with different wt% ratios 50:50:00, 40:40:20, 35:35:30 and 30:30:40, prepared using solution casting technique at room temperature. The physical and chemical properties of the prepared BSPE films were done using XRD, FTIR, UV–vis spectroscopy, TGA and SEM techniques. The electrical properties were measured using impedance analyzer. The highest conductivity 6.28 × 10−4 S/cm and the highest energy band gap 3.52 eV observed for the BSPE film with ratio at room temperature was. The charge storage capability of the material was analysed using dielectric analysis. Cyclic voltammetry (CV) analysis of PVA:PS:(CH3COO)2Mg (35:35:30 wt%) BSPE film showed specific capacitance value as 2 F/g, energy density value as 8.68 W h kg-1 and power density value as 312 W kg-1 respectively.