Low-energy Shift Research Articles

A DFT study on catalytic cracking mechanism of tar by Ni or Fe doped CaO during biomass steam gasification

The presence of byproduct tar seriously reduces the efficiency and syngas quality in the biomass gasification process. The current understanding of CaO-catalyzed tar cracking mainly depends on experimental findings and conjecture about CaO properties. However, there is a significant lack of simulation studies that explore the conversion mechanism at the molecular level. In this work, the reaction mechanism of tar catalytic cracking on Ni or Fe doped CaO was studied using density functional theory simulation. The benzene, phenol and toluene were chosen as the tar model compounds to determine the influences of Ni and Fe on the adsorption characteristics of CaO surface. CaO doped with Ni and Fe increases its electron affinity and electron conductivity from 4.99 to 9.21/5.58 eV-1. It also enhances the interactions between the d-orbitals of Ni/Fe atoms and the p-orbitals of O atoms. The C-H activation of ·CH3 is the most kinetically and energetically feasible first step. The Ni-doped CaO and Fe-doped CaO decrease the energy barriers by 15.7 % and 21.7 %, respectively, compared with undoped CaO. Ni enhances the surface adsorption capacity for ·H radicals to form OH* at the O top site, whereas Fe promotes the stabilization of ·H radicals at the Ca-O vacancy. Through the enhancement of chemical adsorption capacity, improvement of electronic properties, introduction of electron reorganization and orbital hybridization, low-energy shift of energy levels, and generation of new energy states (from -0.85 to -1.64/-3.05 eV), the surfaces of Ni-doped CaO and Fe-doped CaO provide a favorable electronic environment for the tar catalytic cracking, which improves the reaction efficiency and selectivity.

Observation of energetic ion anisotropy using neutron diagnostics in the Large Helical Device

Energetic ion anisotropy was observed by tangential sightline compact neutron energy spectrometers (CNESs) in tangential neutral beam heated deuterium plasmas in Large Helical Device. Significant upper and lower energy shifts in D–D neutron energy from 2.45 MeV were measured according to the beam ion injection directions and CNES sightline using a conventional liquid scintillation detector with the unfolding technique and a novel Cs2LiYCl6:Ce with a 7Li-enrichment (CLYC7) scintillation detector without unfolding. The observed neutron energy spectrum was compared with that predicted by a numerical simulation based on orbit following models. Numerical simulation revealed that the Doppler shift in D–D neutron energy results from energetic ion anisotropy.

XPS and NEXAFS Characterization of Mg/Zn and Mn Codoped Bismuth Tantalate Pyrochlores

Two series of the bismuth tantalate pyrochlore samples, codoped with Mg,Mn and Zn,Mn, were synthesized via solid-phase reaction. It was established that the Bi2Mg(Zn)xMn1−xTa2O9.5−Δ (x = 0.3; 0.5; 0.7) samples contain the main phase of cubic pyrochlore (sp. gr. Fd-3m) and an admixture of triclinic BiTaO4 (sp. gr. P-1). In both sets, the amount of BiTaO4 is proportional to the amount of manganese doping, however, zinc-containing samples have a higher level of impurities than magnesium-containing ones. The unit cell parameter of the Zn,Mn codoped bismuth tantalate phase increases with an increasing content of zinc ions in the samples from 10.4895(5) (x = 0.3) to 10.5325(5) Å (x = 0.7). The unit cell parameter of Mg,Mn codoped bismuth tantalate pyrochlores increases uniformly with an increasing index x(Mg) from 10.4970(8) at x = 0.3 to 10.5248(8) Å at x = 0.7, according to the Vegard rule. The NEXAFS and XPS data showed that the ions were found to have oxidation states of Bi(+3), Ta(+5), Zn(+2) and Mg(+2). In the Ta 4f XPS spectrum of both series of samples, a low energy shift of the absorption band characteristic of tantalum ions with an effective charge of (+5-δ) was observed. The XPS spectra of Bi4f7/2 and Bi4f5/2 also show a shift of bands towards lower energies which is attributed to the presence of some low-charge ions of transition elements in the bismuth position. The NEXAFS spectroscopy data showed that manganese ions in both series of samples have predominantly 2+ and 3+ oxidation states. XPS data indicate that in zinc-containing preparations the proportion of oxidized manganese ions is higher than in magnesium-containing ones.

Biochemical mechanisms of the energy-protective action of blockers of slow high-threshold L-type calcium channels

This review discusses information about the structure and function of calcium channels in the plasma membrane and mitochondria of the heart, and pharmacological methods for modulating their conductance. Experimental data are presented that characterize the change in the energy metabolism of cardiomyocytes against the background of the transformation of the conductivity of L-type calcium channels of the cell membrane in a non-invasive model of vibration-mediated (56 sessions of total vertical vibration, with a frequency of 44 Hz and an amplitude of 0.5 mm) hypoxia.
 It was shown that in animals treated with calcium channel blocker adalat (nifedipine INN) against the background of vibration, the rate of endogenous respiration (Ve), measured by the polarographic method using a closed Clark electrode in native homogenate of rabbit myocardial tissue, remained at the level of intact animals and amounted to 16.3 4.3 ng-O atom/ min mg of protein, amytal sensitivity increased by 39% (p 0.05) compared to the group of vibrated animals, low-natality decreased by 40% (p 0.05). The dynamics of the rate of substrate respiration (Vac and Vglu + mal) in the group with adalat returned to that of intact animals, which indicated the restoration of the physiological predominance of the activity of theNADH CoQ-reductase complex in redox reactions. It was found that the blockade of transport of Ca2+ ions at the level of high-threshold (HVA) voltage-dependent ion channels of the L-type of the cell membrane, normalizing the activity of the I enzyme-substrate complex of the respiratory chain and regulatoryly restraining the hyperactivity of succinate dehydrogenase in zone II of the enzyme-substrate complex, has an energy-protective effect. Adalat prevented a low-energy shift and the development of bioenergetic hypoxia in the myocardial tissue of experimental animals.

Фотолиз сульфагуанидина в воде

The phototransformation of sulfaguanidine in water under ultraviolet (UV) radiation was studied experimentally and theoretically. Absorption, fluorescence and fluorescence excitation spectra of the studied substance before and after irradiation were obtained. Under the influence of KrCl excylamp radiation, stained photoproducts were formed. Quantum-chemical analysis of the orbital nature and localization of electronic transitions of complexes of photoproducts with water 1 : 3 reveals great similarity with the spectrum of the complex of the parent compound. The energy of electronic transitions of primary photoproducts decreases that is there is a low-energy shift of transitions S0→S1(ππ) and S0→S3(ππ) of the original molecule to long-wave region of spectrum (260-315 nm) and decrease of intensity of transition S0→S3(ππ) of sulfaguanidine coplex. In the process of irradiation under the action of KrCl excylamp, the transformation of sulfaguanidine, its primary photoproducts and their subsequent interaction with each other and the solvent occur, which leads to the appearance of a colored photoproduct absorbing at λmax = 560 nm.

Hydrogen Bond-Driven Order-Disorder Phase Transition in the Near-Room-Temperature Nonlinear Optical Switch [Ag(NH3)2]2SO4.

Herein, we report a near-room-temperature nonlinear optical (NLO) switch material, [Ag(NH3)2]2SO4, exhibiting switching performance with strong room-temperature second harmonic generation (SHG) intensity that outperforms the UV–vis spectral region industry standard KH2PO4 (1.4 times stronger). [Ag(NH3)2]2SO4 undergoes a reversible phase transition (Tc = 356 K) from the noncentrosymmetric room-temperature phase (P4̅21c, RTP) to a centrosymmetric high-temperature phase (I4/mmm, HTP) where both the SO42– anions and [Ag(NH3)2]+ cations are highly disordered. The weakening of hydrogen bond interactions in the HTP is also evidenced by the lower energy shift of the stretching vibration of the N–H···O bonds revealed by the in situ FT-IR spectra. Such weakening leads to an unusual negative thermal expansion along the c axis (−3%). In addition, both the atomic displacement parameters of the single-crystal diffraction data and the molecular dynamics-simulated mean squared displacements suggest the motions of the O and N atoms. Such a structural disorder not only hinders the phonon propagation and dramatically drops the thermal conductivity to 0.22 W m–1 K–1 at 361 K but also significantly weakens the optical anisotropy and SHG as verified by the DFT theoretical studies.

Three and four identical fermions near the unitary limit

This work analyzes the three and four equal-mass fermionic systems near and at the $s$- and $p$-wave unitary limits using hyperspherical methods. The unitary regime addressed here is where the two-body dimer energy is at zero energy. For fermionic systems near the $s$-wave unitary limit, the hyperradial potentials in the $N$-body continuum exhibit a universal long-range ${R}^{\ensuremath{-}3}$ behavior governed by the $s$-wave scattering length alone. The implications of this behavior on the low-energy phase shift are discussed. At the $p$-wave unitary limit, the four-body system is studied through a qualitative look at the structure of the hyperradial potentials at unitarity for the ${L}^{\ensuremath{\pi}}={0}^{+}$ symmetry. A quantitative analysis shows that there are tetramer states in the lowest hyperradial potentials for these systems. Correlations are made between these tetramers and the corresponding trimers in the two-body fragmentation channels. Universal properties related to the four-body recombination process $A+A+A+A\ensuremath{\leftrightarrow}{A}_{3}+A$ are discussed.

On lowest-lying 1/2− octet baryons * *Supported in part by National Nature Science Foundations of China (11975028, 10925522)

The recently proposed baryon is studied in a flavor scheme with K-matrix unitarization, by fitting to low-energy cross section and phase shift data. It is found that co-exists with low-lying poles in other channels, which have been extensively discussed in the literature, though they belong to different octets in the limit. Hence, the existence of is further verified.

Carbon Footprint Assessment of a Novel Bio-Based Composite for Building Insulation

This research explores the carbon removal of a novel bio-insulation composite, here called MycoBamboo, based on the combination of bamboo particles and mycelium as binder. First, an attributional life cycle assessment (LCA) was performed to define the carbon footprint of a European bamboo plantation and a bio-insulation composite, as well as its ability to remove CO2 along its lifecycle at a laboratory scale. Secondly, the Global Worming Potential (GWP) was estimated through a dynamic LCA with selected end-of-life and technical replacement scenarios. Finally, a building wall application was analyzed to measure the carbon saving potential of the MycoBamboo when compared with alternative insulation materials applied as an exterior thermal insulation composite system. The results demonstrate that despite the negative GWP values of the biogenic CO2, the final Net-GWP was positive. The technical replacement scenarios had an influence on the final Net-GWP values, and a longer storage period is preferred to more frequent insulation substitution. The type of energy source and the deactivation phase play important roles in the mitigation of climate change. Therefore, to make the MycoBamboo competitive as an insulation system at the industrial scale, it is fundamental to identify alternative low-energy deactivation modes and shift all energy-intensity activities during the production phase to renewable energy.

Study of the multiband exciton spectrum of ZnSe in the range of 477-490 nm

The photoluminescence spectra of CVD (chemical vapour deposition) ZnSe polycrystalline grown with a large excess of selenium and containing \O*Se-Cu+i\ complexes at stacking faults are studied. Absorbance was measured to complement these data. The features of the PL spectra in comparison with cathodoluminescence are considered. It is shown that PL bands identical to CL are observed as somewhat shorter wavelengths. For the studied crystals, a band model is presented according to the data obtained in this work. The low-energy shift of the PL spectra with decreasing excitation energy corresponds to a shift on the energy scale of the band model with a corresponding change in the type of radiative transitions. It is shown that identical photoluminescence bands are observed as somewhat shorter wavelengths than cathodoluminescence bands. For the crystals under study, a band model is presented according to the data obtained in the given decreasing work. The low-energy shift of the photoluminescence spectra upon the excitation energy corresponds to a shift along the energy scale of the band model with a corresponding change in the type of radiative transitions. Changes have been introduced that characterize the nature of the group of equidistant bands 477-490 nm, which are characteristic of ZnSe samples with an excess of oxygen and Se. The results can be useful for a more complete study of the structure of multiphonon exciton spectra of photo and cathodoluminescence of AIIBVI crystals. Keywords: band model, narrow-line multi-photon spectra, exciton radiation, stacking faults, isoelectronic oxygen impurity, carrying effective negative charge.

Structural characterization of a square planar Ni(II) complex and its application as a catalyst for the transfer hydrogenation of ketones

A new 2-hydroxy-1-naphthaldehyde Schiff base derived nickel(II) complex (4) was synthesized and fully characterized. Analysis of the structure of 4 by single-crystal X-ray diffraction shows two chelating Schiff base ligands bound to nickel in a trans [O∧N(Ni2+)N∧O] fashion. Hence, in a molecule of 4, two ligands are four coordinate to a Ni(II) center through the imine nitrogen and naphthyloxyl oxygen atoms. This coordination mode resulted in a square planar complex that is stabilized in the solid-state by a network of intermolecular O-H···N hydrogen bonds between neighboring molecules. The 1H NMR data showed the loss of the hydroxyl (OH) proton signal and an upfield shift of the metal-bound imine (-NH) proton signal, while the IR data also showed a lower energy shift in the absorption frequency of the imine (C = N) bond due to back donation from the coordinated Ni(II) center. As a catalyst for the transfer hydrogenation of a range of ketones, 4 showed good catalytic activity at a very low concentration of 0.1 mol% with 2-propanol as the model substrate. The catalyst is also effective for various related ketone substrates bearing a range of steric and electronic regulating groups.

Scintillation yield and temperature dependence of radioluminescence of (Lu,Gd)3Al5O12:Ce garnet crystals

The scintillation characteristics of Lu3-xGdxAl5O12:Ce (x = 1, 1.25, 1.75, 2, and 2.25) garnet crystals were investigated. With increasing Gd content, the Ce3+ 5d1 → 4f luminescence band was red-shifted due to an increase in the crystal field splitting of the 5d levels. In addition, both the light yield value and contribution of fast scintillation component increased. We attribute this effect to the reduced electron trapping effects of shallow traps buried in the bottom of the conduction band, the lower-energy shift of which is due to the increasing Gd content. A decrease of scintillation yield at the lowest temperature region observed for all samples, showing large thermoluminescence peaks in the same temperature range, can be caused by the localization of electrons at shallow traps. Afterglow signals observed at 10 K for all samples after X-rays irradiation can be explained by quantum tunneling of electrons from nearby traps towards the holes captured at the Ce3+ recombination centers.

Ion-beam induced quasi-dynamic continual disorder in Bi-implanted Hongan silica glass

We have studied optical properties of glassy silicon dioxide (Hongan Silica Glass Store, China) irradiated with 30 keV bismuth ions. A broadening with a low-energy shift of absorption edge was found for the samples treated with 1 × 1016 – 3 × 1017 сm–2 ion fluences. The dose dependences of characteristic Urbach energy and width of the optical gap for direct interband transitions were determined and plotted. Based on the linear-type correlation between Urbach energy and optical gap width, the D/K ratio of deformation potential constants was established as well. The constancy of the D/K ratio for silicon dioxide at different fluences of bismuth ions indicates the proportionality between the values of the optical gap and band tails length, which are associated with the static atomic disorder of SiO2 host-matrix. An explanation of the obtained regularities was given using the quasi-dynamic (thermodynamic) approach. It was postulated that structural damage caused by ion-beam treatment determines Boltzmann entropy's magnitude as a combination of system various microstates. The functional dependence of σ-parameter (disordering effective cross-section) on the ion fluence has been established and proved experimentally.

Effect of interface phonons on the functioning of quantum cascade detectors operating in the far infrared range

The spectral characteristics of a cascade of broadband quantum cascade detector, functioning in the far IR range, renormalized by the interaction with all modes of interface phonons are studied using the Green’s function method. Partial contributions into the magnitudes of shifts and decays of electron operating states due to their configurational interactions with all states of the cascade in the processes of emission and absorption of phonons are investigated. It is shown that interaction with interface phonons leads to low-energy shift and decay of operating states of the electron, with their magnitudes increasing at bigger temperature. It is shown that when the width of the potential barrier, which is located in the double-well active region, varies both the shifts and decays of high-energy operating states drastically increase.

(Invited) Quantum Multi-Body Interactions in Semiconducting WSe2 and C60-Graphene Hybrids for High-Performance Photodetectors

In this work we will discuss the use of halide-assisted low-pressure chemical vapour deposition (HA-LPCVD) with NaCl to help facilitate the growth of monolayer WSe2 at low growth temperatures of ~ 750oC, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. Moreover, we experimentally probed the quantum multi-body interactions in 1L WSe2 ascribed to excitons, trions and other localized states by analyzing the temperature-dependent photoluminescence spectra. A 1L WSe2 based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface state trap density of the Al/WSe2 junction was computed to be extremely low. Hybrids of two-dimensional (2D) graphene with fullerene (C60) molecules were also fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent. A low energy shift in the Fermi level EF ~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. We will discuss the strong photo-response of the C60-graphene hybrids reported here which we attribute to the doping enhancement arising in the graphene upon the adsorption of C60.

(Invited) Quantum Multi-Body Interactions in Semiconducting WSe2 and C60-Graphene Hybrids for High-Performance Photodetectors

In this work we will discuss the use of a halide-assisted low-pressure chemical vapor deposition (HA-LPCVD) with NaCl to help facilitate the growth of monolayer WSe2 at low growth temperatures of ~ 750oC, which is lower than the typical temperatures needed with conventional CVD for realizing monolayer (1L) WSe2. Moreover, we experimentally probed the quantum multi-body interactions in 1L WSe2 ascribed to excitons, trions and other localized states by analyzing the temperature-dependent photoluminescence spectra. A 1L WSe2 based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface state trap density (Dit) of the Al/WSe2 junction was computed to be extremely low. Hybrids of two-dimensional (2D) graphene with fullerene (C60) molecules were also fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent. A low energy shift in the Fermi level EF ~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. We will discuss the strong photo-response of the C60-graphene hybrids reported here which we attribute to the doping enhancement arising in the graphene upon the adsorption of C60.

Impact of defects on photoexcited carrier relaxation dynamics in GeSn thin films

We report the results of a study that was conducted to investigate the recombination paths of photoexcited charge carriers in GeSn thin films. The charge carrier lifetime was predicted as a function of temperature from a description of photoconductivity transients, assuming co-influence of Shockley–Read–Hall and radiative carrier recombination paths. We identify that dislocations are the source of a band of electronic states with the highest occupied state at E V + (85÷90) meV that acts as Shockley–Read–Hall centers determining the charge carrier lifetime. The photoluminescence (PL) and photoconductivity spectroscopy have been applied to distinguish between the contribution of both band-to-band and dislocation-related electron transitions. The PL band was found to demonstrate a low-energy shift of about 80 ± 20 meV relative to the edge of the photoconductivity spectra in the indirect bandgap GeSn films with dislocations. The role of a different nature deeper acceptor level at E V + (140 ÷ 160) meV in the recombination processes of the GeSn layers with better structural quality and the Sn content higher than 4% was discussed. This detailed understanding of the recombination processes is of critical importance for developing GeSn/Ge-based optoelectronic devices.

Quasi-Dynamic Approach in Structural Disorder Analysis: An Ion-Beam-Irradiated Silica

Optical properties of glassy silicon dioxide irradiated with 30 keV rhenium ions were investigated. The blurring and low-energy shift of the sample absorption edge was established in 5 × 1015–5 × 1017 cm–2 range of ion fluences. Dose dependences of characteristic Urbach energy EU and optical gap width were obtained for direct interband transitions. The ratio of deformation potential constants D/K was determined on the basis of the linear correlation between EU and parameters. The constancy of D/K ratio at different ion fluences indicates proportionality between optical gap values and band tails caused by local displacements of atoms in SiO2 host matrix. An interpretation of established regularities was given in the framework of thermodynamic approach. The structural damages induced by ion irradiation as a set of various system microstates and relationship with Boltzmann entropy value were postulated. Thermodynamic temperature and ion fluence were considered as equivalent factors that determine a certain d...

Dramatic Enhancement of Optoelectronic Properties of Electrophoretically Deposited C60-Graphene Hybrids.

Fullerene (C60) and multilayer graphene hybrid devices were fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent, acetonitrile, mixed with toluene, which facilitates their deposition on the graphene membranes. Raman spectroscopy unveiled the unique vibrational fingerprints associated with the A2g mode of the C60 molecules at ∼1453 cm-1, while blue shifts of ∼6 and ∼17 cm-1 were also attributed to the G- and 2D-bands of the hybrids relative to bare graphene, suggestive of p-doped graphene. The intensity ratio of the G- and the 2D-bands I2D/IG (hybrid) dropped to ∼0.18 from ∼0.3 (bare graphene), and this reduction in I2D/IG is also a signature of hole-doped graphene, consistent with the relatively strong electron accepting nature of C60. The electronic conductance of the two-terminal hybrid devices increased relative to bare graphene at room temperature which was attributed to the increased carrier density, and temperature-dependent electronic transport measurements were also conducted from ambient down to ∼5.8 K. Additionally, a low energy shift in the Fermi level, EF ≈ 140 meV, was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with a wavelength λ ranging from ∼400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. The responsivity of the hybrids was measured to be ∼109 A/W at λ ≈ 400 nm and ∼298 K, while the detectivity and external quantum efficiency were also exceptional, ∼1015 jones and ∼109%, respectively, at ∼1 V and a light power density of ∼3 mW/cm2. The values are ∼10 times higher compared to other hybrid devices derived from graphene reported previously, such as quantum dot-graphene and few-layer MoS2-graphene heterostructures. The strong photoresponse of the C60-graphene hybrids reported here is attributed to the doping enhancement arising in graphene upon the adsorption of C60. This work demonstrates the exceptional potential of such hybrid nanocarbon-based structures for optoelectronics.

Band-edge emission, defects, morphology and structure of in-doped ZnO nanocrystal films

In-doped ZnO films grown by ultrasonic spray pyrolysis have been studied by means of the scanning electron microscopy (SEM), energy dispersive X ray spectroscopy (EDS) and X ray diffraction (XRD) methods. The photoluminescence (PL), transmittance and absorbance have been controlled as well. It was shown that the ZnO optical band gap demonstrates the blue high energy shift to 3.31 eV at 300 K and the PL intensity of near band edge (NBE) emission enlarges at In doping 0.5–2.5 at%. Simultaneously, the positions of XRD peaks and their intensities vary insignificantly owing to the difference in the In3+and Zn2+ ionic radii. Meanwhile, intensity decreasing the green PL band confirms the occupation of the zinc vacancies by In ions with the formation of substitutional InZn defects and ZnO crystal quality improving.At higher In contents the new PL band (3.034eV) appears in PL spectra and its peak shifts to lower energy with In content increasing. This PL band was attributed to the emission via the complex defects, formed by Ini interstitial atoms. Simultaneously, the PL intensity and ZnO film crystallinity falling down, the ZnO crystal lattice parameters increase and the ZnO optical band gap demonstrates the red low energy shift. To reveal a nature of the optical transition responsible for the new PL band, PL spectra have been studied in the temperature range 11–290 K. The dependence of the Ini complex defect formation versus In contents in ZnO NC films is analyzed and discussed. The optimal In concentration range to fabricate the ZnO films with high optical parameters has been estimated.