Se Matrix Research Articles

Wavelength dependence of the surface photogalvanic effect in CuSe film

We demonstrate the changing sign of the surface photogalvanic effect current in a film consisting of CuSe nanocrystallites in an amorphous Se matrix in a wide spectral range. The longitudinal and transverse photocurrents were measured as functions of polarization state of the excitation beam and its incidence angle in the spectral range of 355–1064 nm. It was found that the longitudinal photocurrent flows in opposite directions at 532 and 725 nm (825 and 1064 nm) for the p-polarized (s-polarized) excitation beam. The longitudinal photocurrent excited by p-polarized light is much higher than that excited by s-polarized light. Both for the elliptically and linearly polarized excitation, the transverse photocurrent changes the sign between 532 and 725 nm. Such a reversal of photocurrent flow is explained by the photoexcitation of light and heavy holes bands, which have different momentum distribution of excited carriers. The data obtained provide deeper understanding of surface photogalvanic effect in nanocomposites and are of interest for optoelectronics.

Emergency Treatment and Photoacoustic Assessment of Spinal Cord Injury Using Reversible Dual-Signal Transform-Based Selenium Antioxidant.

Spinal cord injury (SCI), following explosive oxidative stress, causes an abrupt and irreversible pathological deterioration of the central nervous system. Thus, preventing secondary injuries caused by reactive oxygen species (ROS), as well as monitoring and assessing the recovery from SCI are critical for the emergency treatment of SCI. Herein, an emergency treatment strategy is developed for SCI based on the selenium (Se) matrix antioxidant system to effectively inhibit oxidative stress-induced damage and simultaneously real-time evaluate the severity of SCI using a reversible dual-photoacoustic signal (680 and 750nm). Within the emergency treatment and photoacoustic severity assessment (ETPSA) strategy, the designed Se loaded boron dipyrromethene dye with a double hydroxyl group (Se@BDP-DOH) is simultaneously used as a sensitive reporter group and an excellent antioxidant for effectively eliminating explosive oxidative stress. Se@BDP-DOH is found to promote the recovery of both spinal cord tissue and locomotor function in mice with SCI. Furthermore, ETPSA strategy synergistically enhanced ROS consumption via the caveolin 1 (Cav 1)-related pathways, as confirmed upon treatment with Cav 1 siRNA. Therefore, the ETPSA strategy is a potential tool for improving emergency treatment and photoacoustic assessment of SCI.

Band Engineering of the Second Phase to Reach High Thermoelectric Performance in Cu2 Se-Based Composite Material.

Hitherto, Cu2 Se incorporated with a dispersed second phase shows extremely low thermal conductivity and excellent thermoelectric properties. However, the significant mismatch in electronic band structure between the second phases and the matrix often causes a deterioration of carrier mobility. In this work, based on density functional theory (DFT) calculations, the electronic band structure of the second phase is adjusted through doping S and Te. It is found that Cu2 Se0.88 S0.06 Te0.06 has a highly similar electronic band structure to the Cu2 Se matrix, which results in high carrier mobility and power factor in Cu2 Se-based composite materials. Additionally, the dispersed second-phase Cu2 Se0.88 S0.06 Te0.06 , dislocations, and nanograins are observed in the Cu2 Se/5 wt% Cu2 Se0.88 S0.06 Te0.06 product, which leads to a substantial reduction in the thermal conductivity. Finally, high figure of merit (zT) values of 2.04 (by Dulong-Petit heat capacity) and 2.34 (by Differential Scanning Calorimetry (DSC) measured heat capacity) are achieved at 850 K, which are about 65% higher than that of Cu2 Se in this work and comparable to the recently reported p-type Cu2 Se with outstanding performance.

Enhanced field-dependent conductivity and material properties of nano-AlN/micro-SiC/silicone elastomer hybrid composites for electric stress mitigation in high-voltage power modules

This paper reports an enhancement of the nonlinear conductivity, thermal and mechanical properties of micro-silicon carbide/silicone elastomer (m-SiC/SE) composites by adding nano-aluminum nitride (n-AlN) for power module encapsulation applications. The electrical properties (such as nonlinear conductivity characteristics and transient permittivity obtained from polarization current, and trap distributions obtained from thermally stimulated depolarization current) and material properties (including thermo-gravimetric analysis, coefficient of thermal expansion (CTE), and thermal conductivity, tensile strength, strain at break and Young’s modulus) of the pure SE, m-SiC/SE microcomposites, m-SiC/n-AlN/SE hybrid composites are investigated. The effect of the m-SiC fillers and n-AlN fillers on physicochemical properties of the SE matrix is analyzed by FT-IR spectroscopy and crosslinking degree. The measured nonlinear conductivity and transient permittivity are used for electric field simulation under DC stationary and square voltages. It is found that the addition of n-AlN fillers in the SE hybrid composite improves the nonlinear conductivity characteristics and mitigates the electric field under DC stationary and square voltages, compared to the SE microcomposite. Furthermore, the m-SiC/n-AlN/SE hybrid composite has a higher thermal degradation temperature, thermal conductivity, tensile strength, Young’s modulus, and crosslinking degree than the SE microcomposite, whereas their CTE and strain at break are lower. It is elucidated that the m-SiC/n-AlN/SE hybrid composite with enhanced nonlinear conductivity and material properties is a promising packaging material for high-voltage power modules.

Enhanced thermoelectric properties of Cu2-xSe by coordinating carrier concentration to reduce thermal conductivity

Cu 2-x Se has been known as an ideal thermoelectric material for application in the middle-high temperature range due to the outstanding electric transmission conductivity and relatively low lattice thermal conductivity. However, its performance is significantly constrained by its high thermal conductivity and thermal stability issues, as well as its difficulty in element doping because of the influence of atomic size and atomic solid solubility. Here, we prominently reduced the thermal conductivity of Cu 2-x Se by addition different amounts of WS 2 to the Cu 2-x Se matrix, and successfully improved the power factor of the material because of the reduction of high Cu defects to coordinate the three mutually coupled parameters. The zT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K. Further, we found that the symmetry of the Cu 2-x Se crystal had not been destroyed undergoing the doping of WS 2 into its crystal lattice, and the doped sample showed good thermal stability when cycle test was carried out twice between 315 K and 823 K. Cu 2-x Se were prepared by colloidal synthesis, and it's thermal conductivity was reduced by doping with different amounts of WS 2 into the Cu 2-x Se matrix, and the power factor of the doping material was improved through the reduction of high Cu defects to coordinate the three mutually coupled parameters. The ZT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K. • The samples of WS 2 -doping Cu 2-x Se were prepared. • WS 2 -doping Cu 2-x Se had low thermal conductivity and high power factor through the reduction of high carrier concentration. • The zT value of the WS 2 -doping Cu 2-x Se sample was eventually enhanced by 56% compared with pristine Cu 2-x Se, and up to ca. 1 at 823 K.

Structural properties of CdSe nanocrystals in CdSe/Se multilayer

CdSe/Se multilayer thin films were prepared using sequential thermal evaporation technique by varying the thickness of selenium sublayers. Identifying the prominent peaks observed in the XRD spectra of the top layer CdSe which corresponds to the (100) plane with wurtzite structure, the average size of the crystallites was calculated for the CdSe nanocrystals. Experimentally measured band gaps are larger than bulk band gap of CdSe. This confirms the presence of spin-orbit splitting of energy levels. Size of the crystallites was then calculated with the theoretical prediction of the effective mass approximation model (i.e., Brus model). It resulted in that the diameters of crystallites were much smaller than the Bohr exciton diameter (11.2 nm) of CdSe. Thus, the structural and optical properties of CdSe/Se multilayer thin films reveal the effect of quantum confinement of CdSe crystallites in Se matrix for various sublayer thicknesses. Confinement effect is more pronounced while sublayer thickness of selenium increases.

Structural and optical properties of thermally evaporated and annealed Ge20Se76Sn4 thin films

Amorphous Ge20Se76Sn4 thin films of thickness ~150 nm were prepared, from bulk Ge20Se76Sn4, by thermal evaporation technique. The differential scanning calorimetry analysis of bulk Ge20Se76Sn4 exhibits one glass transition, one crystallization peak, and one melting point. The inclusion of Sn by substituting Se or Ge-atoms into the Ge–Se matrix has been studied using energy-dispersive spectral X-ray, and Fourier-transform infrared spectroscopy. The X-ray diffraction affirms that films annealed at annealing temperature (Ta) ≤ 553 K are amorphous; meanwhile, films annealed at Ta≥ 603 K are crystalline. It was found that the annealing process can be used to tune the linear and nonlinear optical parameters and constants. The decrease in the indirect optical bandgap energy (Eg) with an increase in Ta for Ta ≥ 603 K could be ascribed to the increase in the crystallinity and increasing the density of defects in the bandgap. The estimated Eg were correlated with the refractive index (n) using seven different approaches and the average value of n was increased as Ta increased. It is suggested that the structural, and optical characteristics of the thermally evaporated Ge20Se76Sn4 thin films can be tuned and engineered by the annealing process. Profound analysis of optical parameters for the Ge20Se76Sn4 thin films suggests the utilization of these glasses for numerous photonic applications.

Accurately Regulating the Electronic Structure of Nix Sey @NC Core-Shell Nanohybrids through Controllable Selenization of a Ni-MOF for pH-Universal Hydrogen Evolution Reaction.

N-doped carbon-encapsulated transition metal selenides (TMSs) have garnered increasing attention as promising electrocatalysts for hydrogen evolution reaction (HER). Accurately regulating the electronic structure of these nanohybrids to reveal the underlying mechanism for enhanced HER performances is still challenging and thus requires deep excavation. Herein, a series of pomegranate-like Nix Sey @NC core-shell nanohybrids (including Ni0.85 Se @ NC, NiSe2 @NC, and NiSe@NC) through controllable selenization of a Ni-MOF precursor is reported. The component of the nanohybrids can be fine-tuned by tailoring the selenization temperature and feed ratio, through which the electronic structure can be synchronously regulated. Among these nanohybrids, the Ni0.85 Se @ NC exhibits the optimum pH-universal HER performance with overpotentials of 131, 135, and 183mV in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m PBS, respectively, at 10 mA cm-2 , which are attributed to the increased partial density of state at the Fermi level and effective van der Waals interactions between Ni0.85 Se and NC matrix explained by density functional theory calculations.

Optical Control of Hole Wavefunction in Type-II Magnetic Quantum Dot Structures

Unlike the extensively studied, spatially direct, quantum dots (QDs) with type-I band alignment where both electrons and holes are confined in the QD, in ZnTe QDs embedded in a (Zn,Mn)Se matrix onl...

Structural, linear and non-linear optical properties of annealed and irradiated Ag/Se heterostructure films for optoelectronic applications

The present work demonstrates the effect of annealing and laser irradiation on the linear, nonlinear optical properties as well as the structural properties of thermally deposited Ag/Se bilayer thin films. The Ag diffusion into the Se layer by thermal annealing (annealed at 90 °C) and laser irradiation (532 nm) brings the changes which have been investigated. The structure of the studied films has been studied by X-ray diffraction and the surface morphology by field emission scanning electron microscopy. The optical transmission data of the films was collected from UV–vis-NIR spectrophotometer in the wavelength range 500–1200 nm. The refractive index (n) and extinction coefficient (k) were observed to be increased with photo thermal treatment. The indirect allowed optical band gap decreases with Ag diffusion as the width of the localised states increased. The dispersion of refractive index was analysed in terms of single oscillator Wemple-Di Domenico model. The third order nonlinear susceptibility (χ(3)) and nonlinear refractive index (n2) were calculated from the linear parameters using semi-empirical relations. The changes in the optical parameters with annealing and laser irradiation were explained on the basis of defect states and density of localised states due to Ag diffusion into Se matrix. The Raman study reveals the vibrational bonding information in the films. The tuneable optical properties can be used in various optoelectronic applications.

Reversible Interaction of Sb with an Active Se Matrix Enhances the Cycle Stability of Electrodes for Lithium-Ion Batteries

Sb is a promising anode material for lithium-ion batteries, but it suffers from fast capacity fading. Previous works have shown that the combination of Sb with an active S or Se matrix improves the cycle stability of the electrodes, although there was no clear verification of the exact mechanism. In this study, we used ex situ X-ray diffraction, ex situ Raman spectroscopy, and in situ dilatometry to study the interactions of Sb with S and Se and to reveal the reasons for the superior cycle stability of Sb2Se3 electrodes. Our results show that the poor stability of Sb electrodes is due to the crystallization of Li3Sb, leading to the large volume change, high stress, and mechanical failure of the particles. Addition of S or Se into the matrix can inhibit the formation of crystalline Li3Sb, thus improving capacity retention. The stabilization effect is stronger for a Se matrix than for a S matrix because it enables the re-formation of Sb–Se bonds upon delithiation and prevents phase segregation. In addition, the Se matrix reduces the volume change of the electrode during the charge and discharge, preventing electrode cracking and resulting in good mechanical reversibility.

Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9 Se8 /rGO Hybrid Nanosheets.

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one-step oriented attachment growth, a facile synthesis of Co9 Se8 nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co9 Se8 /rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g-1 at a current density of 50 mA g-1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g-1 at a high current density of 5 A g-1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co9 Se8 /rGO and Co nanoparticles/Na2 Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co9 Se8 /rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.

Ni0.85Se@MoSe2 Nanosheet Arrays as the Electrode for High-Performance Supercapacitors

In this study, we report novel Ni0.85Se@MoSe2 nanosheet arrays prepared by a facile one-step hydrothermal method through nickel (Ni) foam as Ni precursor and the framework of MoSe2. Owing to the unique interconnection and hierarchical porous nanosheet array architecture, the Ni0.85Se@MoSe2 nanosheet arrays exhibit a high specific capacitance of 774 F g-1 at the current density of 1 A g-1, which is almost 2 times higher than that (401 F g-1) of the Ni0.85Se matrix and about 7 times greater than that (113 F g-1) of the MoSe2 nanoparticles. Moreover, we report an asymmetric supercapacitor (ASC), which is fabricated by using the Ni0.85Se@MoSe2 nanosheet arrays as the positive electrode and the graphene nanosheets (GNS) as the negative electrode, with aqueous KOH as the electrolyte. The Ni0.85Se@MoSe2//GNS ASC possesses an output voltage of 1.6 V, an energy density of 25.5 Wh kg-1 at a power density of 420 W kg-1, and a cycling stability of 88% capacitance retention after 5000 cycles. These results indicate that the Ni0.85Se@MoSe2 nanosheet arrays are a good electrode for supercapacitors.

Enhanced thermoelectric performance of highly oriented polycrystalline SnSe based composites incorporated with SnTe nanoinclusions

Binary single crystal compound SnSe with high thermoelectric performance has drawn great attention to polycrystalline SnSe. Here, we synthesized highly oriented p-type polycrystalline composite samples f mol% SnTe/Ag0.005Sn0.995Se (f = 0, 0.5, 1 and 1.5) and present thermoelectric performance from 300 K to 900 K. High thermoelectric figure of merit (ZT) of the matrix Ag0.005Sn0.995Se should be attributed to highly oriented crystal grains along the (400) plane. Moreover, proper proportional (f = 0.5) incorporation of SnTe nanoinlusions into Ag0.005Sn0.995Se matrix enhances the power factor and reduces lattice thermal conductivity, which could be due to the contribution of enhanced phonon scattering resulting from abundant interfaces. Consequently, a largest ZT value of 1.6 ± 0.2 is achieved at 875 K for composite sample 0.5 mol% SnTe/Ag0.005Sn0.995Se. Furthermore, these polycrystalline composites have large values of ZT (>1) from 800 K to 900 K and good experimental repeatability, which suggests that it is a promising candidate for high temperature power generation.

Determination of selenium and cadmium dopants in nanocomposites based on zinc and indium oxides by high resolution continuous source electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry

An approach is proposed to the determination of selenium and cadmium dopants in new nanocomposites based on zinc and indium oxides. The approach is based on a combination of highly efficient high resolution continuous source electrothermal atomic absorption spectrometry (ETAAS) for the analysis of suspensions and inductively coupled plasma mass spectrometry for the analysis of solutions. A procedure is developed for the determination of Se and Cd dopants and matrix components based on Zn and In in nanocomposite solutions by inductively coupled plasma mass spectrometry. Stabilizing agents for the preparation of suspensions are studied for the ETAAS analysis of powders without their decomposition. The results of determination of CdSe dopants by high resolution ETAAS are validated by inductively coupled plasma mass spectrometry.

Selenium supplementation has beneficial and detrimental effects on immunity to influenza vaccine in older adults

SummaryBackground & aimsMortality resulting from influenza (flu) virus infections occurs primarily in the elderly through declining immunity. Studies in mice have suggested beneficial effects of selenium (Se) supplementation on immunity to flu but similar evidence is lacking in humans. A dietary intervention study was therefore designed to test the effects of Se-supplementation on a variety of parameters of anti-flu immunity in healthy subjects aged 50–64 years.MethodsA 12-week randomized, double-blinded, placebo-controlled clinical trial (ClinicalTrials.govNCT00279812) was undertaken in six groups of individuals with plasma Se levels <110 ng/mL. Four groups were given daily capsules of yeast enriched with 0 μg Se/day (SeY-0/d; n = 20), 50 μg Se/d (SeY-50/d; n = 18), 100 μg Se/d (SeY-100/d; n = 21) or 200 μg Se/d (SeY-200/d; n = 23). Two groups were given onion-containing meals with either <1 μg Se/d (SeO-0/d; n = 17) or 50 μg Se/d (SeO-50/d; n = 18). Flu vaccine was administrated at week 10 and immune parameters were assessed until week 12.ResultsPrimary study endpoints were changes in cellular and humoral immune responses. Supplementation with SeY and SeO affected different aspects of cellular immunity. SeY increased Tctx-ADCC cell counts in blood (214%, SeY-100/d) before flu vaccination and a dose-dependent increase in T cell proliferation (500%, SeY-50/100/200/d), IL-8 (169%, SeY-100/d) and IL-10 (317%, SeY-200/d) secretion after in vivo flu challenge. Positive effects were contrasted by lower granzyme B content of CD8 cells (55%, SeY-200/d). SeO (Se 50 μg/d) also enhanced T cell proliferation after vaccination (650%), IFN-γ (289%), and IL-8 secretion (139%), granzyme (209%) and perforin (190%) content of CD8 cells but inhibited TNF-α synthesis (42%). Onion on its own reduced the number of NKT cells in blood (38%). These effects were determined by comparison to group-specific baseline yeast or onion control groups. Mucosal flu-specific antibody responses were unaffected by Se-supplementation.ConclusionSe-supplementation in healthy human adults with marginal Se status resulted in both beneficial and detrimental effects on cellular immunity to flu that was affected by the form of Se, supplemental dose and delivery matrix. These observations call for a thorough evaluation of the risks and benefits associated with Se-supplementation.

Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots

We used continuous wave photoluminescence (cw-PL) and time resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe/(Zn,Mn)Se system the holes are confined in the non-magnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the (Zn,Mn)Te/ZnSe system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding non-magnetic ZnSe matrix. The magnetic polaron formation energies in both systems were measured from the temporal red-shift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe/(Zn,Mn)Se system the magnetic polaron shows conventional behavior with decreasing with increasing temperature T and increasing magnetic field B. In contrast, in the (Zn,Mn)Te/ZnSe system has unconventional dependence on temperature T and magnetic field B; is weakly dependent on T as well as on B. We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.

Effect of copper introduction into As2Se3 glass matrix on crystallization processes

Crystallization processes in glasses of the Cux(As2Se3)100−x system for x=0, 1, 5, 10 and 15at.% were analyzed by non-isothermal differential scanning calorimetry at different heating rates. Based on the obtained thermograms, the mechanism of incorporation of copper into amorphous As–Se matrix and changes in the structure of the investigated system were analyzed. It was shown that the crystallization process essentially depends on the composition. Depending on the glass composition and the applied heating rate, crystallization of three structural units occurred: As2Se3, CuAsSe2 and Cu2Se. Activation energies of the crystal growth of these structural units were determined. The parameters n and m, numerical factors which depend on the morphology of nucleation and growth, were determined. The analysis of the mechanism of crystallization has shown that the crystallization of As2Se3 is characterized by the value of the Avrami index n=4, which indicates that volume nucleation and three-dimensional growth with variable number of centers of nucleation is involved. Analogous, analysis of the crystallization of structural units Cu2Se and CuAsSe2 has shown that the Avrami index has a value of n=3 (m=3) that corresponds to the volume nucleation and three-dimensional growth, but the number of centers of nucleation does not change.

Relaxation processes in Se-rich chalcogenide glasses: Effect of characteristic structural entities

Structural relaxation processes were studied by means of differential scanning calorimetry for a number of compositions belonging to the Se-rich sides of Se–Te, Ge–Se and As–Se chalcogenide systems. Based on the results of fitting and non-fitting methods, the relaxation behavior of these selenide glasses is described in terms of the Tool–Narayanaswamy–Moynihan (TNM) equations. The goal of this paper is to introduce an advanced model describing the relationship between the macroscopic relaxation behavior and molecular structure of the glass. Special attention is paid to differences between the particular structural units and molecular arrangements characteristic for each system studied. The TNM parameters as well as their changes are discussed with respect to both the increasing content of dopant in the Se matrix within each chalcogenide system and different structural units employed in the respective systems. A unique novel conception is suggested, showing a connection between the values of TNM parameters and respective molecular structures and their changes during structural relaxation.

Quantum confinement of CdSe nanocrystals in CdSe/Se multilayer thin films

CdSe/Se multilayer thin films were prepared using sequential thermal evaporation technique by varying the thickness of selenium sublayers. Identifying the prominent peaks observed in the XRD spectra of the top layer CdSe which corresponds to the (100) plane with wurtzite structure, the average size of the crystallites was calculated for the CdSe nanocrystals. Experimentally measured band gaps are larger than bulk band gap of CdSe. This confirms the presence of spin-orbit splitting of energy levels. Size of the crystallites was then calculated with the theoretical prediction of the effective mass approximation model (i.e., Brus model). It resulted in that the diameters of crystallites were much smaller than the Bohr exciton diameter (11.2 nm) of CdSe. Thus the structural and optical properties of CdSe/Se multilayer thin films reveal the effect of quantum confinement of CdSe crystallites in Se matrix for various sublayer thicknesses. Confinement effect is more pronounced while sublayer thickness of selenium increases.