查看更多>>摘要：We report light-assisted iodine ion migration in CuI – a popular wide bandgap p-type semiconductor, which was synthesized via iodinating Cu film in iodine solution. In-depth crystallographic analysis was performed with the combination methods of X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), crystal modeling and diffraction simulation. The samples show strong diffraction peaks of γ-CuI, yet still exists β phase diffraction. Loop current-voltage (IV) test shows characteristics of resistive random access memory (RRAM), suggesting the existence of large amount of movable native defects, which forms the conductive filaments. UV irradiation was found to be effective to convert the RRAM device from low resistance state (LRS) to high resistance state (HRS), indicating potential application of novel memory device with electric read-in and optical erasure function. To study the properties of native defects, time-lapsed PL were employed, in which the near band edge defects luminescence, related to VCu, increased, whereas mid-band broad luminescence, related to VI, decreased, with the increase of irradiation time. UV irradiation induced defects evolution was also observed in X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). Finally, we propose the microscopic physical mechanism of defect migration in CuI with the assistance of UV irradiation. This work reveals the nature of point defects evolution in CuI under light irradiation and is expected to arise more discussions on defects formation, migration and light-defects interaction of CuI material.
查看更多>>摘要：This article reports on Cu2ZnSnSe4 (CZTSe) thin film preparation via a nonhydrazine, nonpyridine and environmentally friendly low-cost solution process method. CZTSe fabrication through a solution-based process has not yet been suitably demonstrated given the impediments to addressing the presence of selenium in solutions. In this study, we introduced a two-step CZTSe fabrication method that used monoethanolamine as the chelating agent/co-solvent and ethanol as the main solvent. Selenization was then conducted. In this process, we successfully avoided the use of hydrazine to synthesise CZTSe thin films. Material characterisations (e.g. UV–VIS–NIR, scanning electron microscopy, electron dispersive spectroscopy, X-ray diffractometry and Fourier transform infrared spectroscopy) confirmed the high quality of the deposited thin films. The deposited CZTSe thin film showed high crystallinity without carbon residues, indicating its potential application as a photovoltaic absorber. Hence, we investigated the photovoltaic parameters of the CZTSe-based solar cells on the basis of the deposited thin film's optoelectronic properties. We utilised Solar Cell Capacitance Simulator to examine the electrical effects of CZTSe solar cells and used three-dimensional finite-difference time-domain optical simulations to investigate the optics of the solar cells. We estimated that the realistic power conversion efficiency of the CZTSe solar cells could reach 18.5% with a short-circuit current density of 30 mA/cm2.
查看更多>>摘要：The goal of this study is to investigate the mechanical and elastic characteristics of the Mn15Si26 compound via experimental nanoindentation measurements and ab-initio calculations. The mechanical properties such as Young's modulus (E) and nanohardness are important inputs for improving the design and mechanical reliability of thermoelectric modules. The high-energy X-ray diffraction pattern of Mn15Si26 has been indexed with the Miller indices of a tetragonal crystalline structure whose cell parameters are the following: a = b = 5.535(3) ? and c = 65.552(4) ?. Nanoindentation measurements, with a Berkovich indenter tip have been performed on higher manganese silicide (HMS) compound mainly composed of Mn15Si26 grains. For the first time ever, it has been evidenced that both elastic modulus and nanohardness of the latter varied significantly depending on their crystallographic orientations provided by electron backscatter diffraction. Nanohardness and Young's modulus along the< 001 > orientations are higher than the< 100 > ones. The nanohardness value of Mn15Si26 ranges from 16 GPa to 20 GPa and the Young's modulus measured varies between 234 GPa and 300 GPa. The stiffness tensor (Sij = (Cij)?1) of Mn15Si26 has been deduced from these experimental measurements as well as calculated using Ab-initio calculations. The macroscopic elastic modulus (E, G, Β) and Poisson's coefficient have been examined and discussed and their 3D-representation has been plotted. The mechanical anisotropy hereby evidenced as the existence of anisotropy of the thermoelectric properties could be a significant factor for the mechanical reliability of thermoelectric modules which consisted of Mn15Si26 legs with a possible preferred crystallographic orientation induced during their fabrication.
查看更多>>摘要：In this paper, zinc ferrite nanowires with an average length of 6.3 μm and an average diameter of 38 nm, bismuth vanadate nanoparticles, and zinc ferrite nanowires/bismuth vanadate composites were fabricated by AC pulse electrodepositing, co-precipitation, and hydrothermal methods, respectively. In order to study the samples, XRD analysis, FESEM, FTIR spectroscopy, EDS spectroscopy, UV-Vis spectroscopy, PL spectroscopy, and VSM were used. XRD patterns of the samples revealed that they did not contain any impurities and that zinc ferrite nanowires and bismuth vanadate nanoparticles had cubic spinel and monoclinic structures, respectively. The optical gap energy of all the samples was in the range of visible light. According to the magnetic hysteresis loops, the composites exhibited paramagnetic behavior. The intensity of the photoluminescence spectrum of the composites (especially those containing 20 wt% of zinc ferrite) was less than the intensity of the photoluminescence spectrum of bismuth vanadate and zinc ferrite. The weaker the intensity of the photoluminescence spectrum, the longer the separation of electron-hole pairs and this leads to an increase of photocatalytic activity. The photocatalytic activity of the composites for decomposing Congo red under visible light was improved as compared to zinc ferrite and bismuth vanadate and the highest degradation rate was related to nanocomposite containing 20 wt% zinc ferrite. These results were obtained because the probability of recombining photogenerated electrons and holes was reduced and there were nanowires in the composite samples, leading to an increase of the contact surface. According to the results of this study, zinc ferrite nanowires/bismuth vanadate nanocomposite with 20 wt% of zinc ferrite is a good choice for the degradation of organic matter under sunlight.
查看更多>>摘要：In this work, a novel p-n heterojunction polyimide aerogel/BiOBr (PI/BOB) photocatalyst was successfully synthesized by combining supercritical drying and in-situ precipitation method, to degrade organic pollutants in visible light. The synthesized PI/BOB photocatalysts exhibited excellent photocatalytic activity by establishing p-n heterojunction with improved charge separation and transfer performance. Moreover, the combination of BiOBr and PI can effectively reduce the hydrophobicity of PI and help to improve its application in water pollution treatment. After a comprehensive study of the microstructure and optical properties of PI/BiOBr heterojunction, it is found that the combination of PI and BiOBr nanosheets can expand the light absorption range, and the porous PI can greatly increase the specific surface area of PI/BiOBr heterojunctions. Furthermore, XPS results showed that the electron in PI transferred to BiOBr through the concentration differences, thus generating an internal electric field (IEF) between PI and BiOBr. Under the effect of IEF, photogenerated carriers can be separated between PI and BiOBr more efficiently, which can effectively improve the photocatalytic efficiency. Photocatalytic degradation experiments showed that PI/BOB has excellent photocatalytic degradation effect on RhB, and the degradation rate of 50 mg RhB was 99% in 60 min for 20 mg catalyst.
查看更多>>摘要：Metal-organic frameworks (MOFs) derived oxide semiconductors have drawn more and more attention in many fields due to their unique structural merits. Herein, hierarchical flower-like Mo-doped Co3O4 derived Co-MOF has been synthesized through a solvothermal method and following annealing process. The gas sensing measurements show that the sensing properties of Mo-doped Co3O4 sample are far superior than that of pure Co3O4. In particular, 1 at% Mo-doped Co3O4 sample exhibits high response values of 92–50 ppm TEA at 180 °C, which are about 46 times than that of pure Co3O4 sample. In addition, it shows short recovery time (33 s), excellent gas selectivity, good repeatability and long-term stability. The improved gas sensing performance can be ascribed to Mo doping and hierarchical flower-like microstructure.
查看更多>>摘要：First-principles calculations and Boltzmann transport theory are used to evaluate the electronic structure and thermoelectric properties of the high-temperature rhombohedral Ge2Sb2Te5 compound. In this work, we have investigated the phonon spectrum, band structure and density of states with K-H configuration, respectively. In the phonon spectrum, the acoustic and optical branches are coupled, and their combined effect significantly reduces the thermal lattice conductivity. The conduction band contributed by the Ge, Sb, and Te has the characteristics of more multiple valleys and degenerate features. When the electron-doping level is 4.3 × 1019 cm?3, a large number of conduction bands are activated, thereby enhancing the conductivity and seebeck coefficient. The layered Ge2Sb2Te5 has significant anisotropy, and its thermoelectric performance along the z-axis is excellent. The thermoelectric transport coefficients are calculated using Boltzmann transport theory combined with relaxation time approximation. For p type, the largest ZT value of 1.509 could be obtained with the carrier density of 1.3 × 1020 cm?3 at 900 K, while for n type, the considerable ZT value of 3.124 could be obtained with the carrier density of 4.5 × 1019 cm?3 at 700 K.
查看更多>>摘要：In this study, we investigate the characteristics of barium-addition indium-zinc-tin-oxide (B–IZTO) channels fabricated by the co-sputtering of barium-tin-oxide and indium-zinc-tin-oxide (IZTO) targets for the operation of thin film transistors (TFTs) and light emitting transistors (LETs). The X-ray photoelectron spectroscopy (XPS) analysis verifies that increasing the BaSnO3 sputtering power significantly decreases the concentration of oxygen vacancy from 35.0% to 16.3%. In addition, increasing the Ba concentration in the B–IZTO films increases the average transmittance of the B–IZTO channel in the visible light region (400–800 nm) from 86.7% to 88.3%, and the electrical resistivity from 84.3 to 5408 Ω?cm, respectively. We find that the appropriate composition of Ba in the IZTO channels greatly improves the subthreshold swing (SS), the stability against the negative bias illumination stress (NBIS) of the B–IZTO channels-based TFTs. As the Ba content of the IZTO channel layer increases, SS decreases from 0.49 to 0.13 V/decade and the threshold voltage shift (ΔVTH) by NBIS reduces from ? 13.1 to ? 5.07 V, respectively. In the case of the B–IZTO-based LET with the highest Ba content, the device has the lowest light turn on voltage (VON) of 1.84 V, and shows the maximum brightness of 1.53 × 104 cd/m2. In this study, we confirm that the addition of Ba in the IZTO effectively suppresses the oxygen vacancies in the IZTO channel, resulting in the enhanced stability of the B–IZTO-based TFTs, and improves the performance of the B–IZTO-based LETs.
查看更多>>摘要：A low-cost Ti-2Fe-0.1B alloy with high performance was manufactured and hydrogenated in this study. The effect of 0.3 wt% hydrogen addition on microstructure evolution, compression deformation behavior at room and high temperature of Ti–2Fe–0.1B alloy has been investigated. Results indicated that lamellar αL structure along with martensite α′ are formed after hydrogenation compared with initial equiaxed grains, and the fraction of β phase increased from 4.95% to 30.1%. Obvious phase transformation αeq→αH+ βH, β→βH during hydrogenation and βH→α + δ, αH→α + δ during subsequent cooling occurred. The hydrogenated Ti-2Fe-0.1B alloy is characterized by hardening effect during compression deformation at room temperature along with the loss of ductility due to the solid solution strengthening by hydrogen atoms and presence of hydride δ. However, peak flow stress of hydrogenated Ti-2Fe-0.1B alloy decreased from 49 MPa to 29 MPa extremely during compression deformation at 973 K, which can be attributed to the high volume of β phase induced by hydrogenation, as well as the promotion of dynamic recovery and dynamic recrystallization.
查看更多>>摘要：Alloy AA6013 (Al-Mg-Si-based aluminum alloy) is of particular interest to the aerospace and automotive industries because of its attractive combinations of properties, however, accelerated grain growth at elevated temperatures limits its superplastic formability. The motivation for this study was to refine grain structure and control grain growth at elevated temperature in order to eliminate the lack of superplasticity in the alloy. For this reason, minor additions of Y, Sc, Zr were considered and their influence on the microstructural evolution, superplastic deformation behavior, and room temperature mechanical properties of a novel AA6013-type alloy was studied. A noticeable refinement of as-cast grain structure was observed due to the co-effect of Sc, Zr, Y additions. It was demonstrated that the Mg2Si phase and Y-bearing phases were formed during solidification of the studied alloys. The phases of silidification origin were fragmented during thermo-mechanical treatment led to the near uniform distribution of coarse particles of 0.5–0.8 μm size in the matrix. The coarse particles caused grain refinement during the superplastic deformation due to the particle stimulated nucleation (PSN) effect. In the alloy containing yttrium, during the decomposition of the aluminum-based solid solution supersaturated by Y, Zr, Sc, the following two precipitation mechanisms were involved: continuous precipitation resulting in the formation of nanoscale L12 phase dispersoids distributed homogeneously throughout the aluminum matrix and discontinuous precipitation that caused fan-shaped aggregations of the same phase near the high-angle grain boundaries. The nanoscale continuously-formed dispersoids retarded the recrystallization and dynamic grain growth during superplastic deformation due to Zenner pinning mechanism. Both PSN and Zenner pinning effects led to the grain refinement and achievement of superplasticity. The maximum elongation of 470% was observed under the test condition of T = 520 °C and ?.= 1 × 10?3 ? 5 × 10?2 s ?1. The room temperature tensile test revealed the following maximum characteristics of the sheet of the alloy with Y additions: yield strength of 330 MPa, ultimate tensile strength of 375 MPa, and elongation at fracture of 10%.
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