Cho, Seong-InKo, Jong BeomLee, Seung HeeKim, Junsung...
9页
查看更多>>摘要：Oxide thin-film transistors (TFTs) should be manufactured with high mobility and stability based on a selfaligned top-gate structure to drive high-end displays. In this study, the effect of oxygen plasma time over one cycle of plasma-enhanced atomic layer deposition (PEALD) SiO2 on the properties of top-gate oxide TFTs was investigated systemically. The subsurface reaction of oxygen plasma causes a difference in oxygen vacancy (Vo). In addition, hydrogen incorporation also differs according to plasma time. Considering Vo and hydrogen are donors, tendency of electric properties could be explained. These surface reactions and atomic incorporation also induce differences in the positive bias temperature stress (PBTS) stability. Based on oxygen plasma time of 2.0 s, a positive shift in threshold voltage (Vth) due to interfacial degradation was observed when the plasma was longer, while an abnormal negative shift due to H+ drift was observed when it was shorter. When the oxygen plasma time is 2.0 s, the TFT was free from the deterioration of the interface and SiO2. Based on this condition, a self-aligned TFT with superior performance including a high mobility of 31.1 cm2/V s, positive Vth and high stability of 0.016 V shifting during the PBTS was fabricated successfully. (c) 2021 Published by Elsevier B.V.
Rojas, David FunesLi, HaoyangOrhan, Okan K.Shao, Chenwei...
12页
查看更多>>摘要：We present a combined experimental and computational investigation of the mechanical properties of a CoCrFe0.75NiMo0.3Nb0.125 (composition in molar ratio) high-entropy alloy additively manufactured via cold spray. We find that the sprayed alloy exhibits extraordinary mechanical properties under compression, reaching yield stress of similar to 1745 MPa, ultimate stress of similar to 2622 MPa, and a maximum strain at failure of similar to 9%. These exceptional mechanical properties are the result of four independent hardening mechanisms. First, using ab initio simulations, we find that non-equiatomic compositions increase the enthalpy of mixing, promoting better solubility of solute Mo and Nb atoms while simultaneously preserving the electronegativity of the base alloy. The higher solubility results in solid-solution hardening and nanosized precipitate formation, promoting additional hardening. These effects are confirmed in the experimental characterization of the manufactured HEA, where nanosized precipitates of similar to 226 +/- 65 nm in size are identified. Additional hardening effects are associated with the manufacturing process, where the high velocity impacts of the microparticles promote dynamic recrystallization through dislocation emission and grain refinement. To understand the dynamic recrystallization of particles, high-velocity impact simulations using molecular dynamics are performed. We find that when particles reach a critical impact velocity (similar to 600-800 m. s(-1)), the dislocation density reaches a maximum, and grain refinement is maximized. The decaying wave pressures developed during the impact generate gradual refinement levels, leading to heterogeneous microstructures combining nano and micro grains, which was later confirmed experimentally using electron backscatter diffraction. These subtle atomic and microstructural features result in outstanding experimentally evaluated yield and ultimate stresses compared to other high-entropy alloys with similar compositions. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The effect of different retrogression and re-aging (RRA) treatment on the microstructure, strength and stress corrosion cracking (SCC) resistance of a high Zn content Al alloy was investigated. The peak microhardness values after retrogression and re-aging at 180 degrees C/30 min and 200 degrees C/10 min were 214 HV and 215 HV, respectively, which are higher than that after T6 and T7 aging. The retrogression re-aged samples have large numbers of eta ' precipitate (MgZn2), resulting in high mechanical properties of the alloy. The SCC resistance order of the alloys was found to be: T6 < RRA (120 degrees C/24 h + 180 degrees C/30 min + 120 degrees C/24 h) < RRA (120 degrees C/ 24 h + 200 degrees C/10 min + 120 degrees C/24 h) < T7, and the optimal retrogression re-aging process is 120 degrees C/ 24 h + 180 degrees C/30 min + quenching + 120 degrees C/24 h. The improvement in the stress corrosion cracking resistance of the retrogression re-aged samples can be attributed to the increased interspaces of grain boundary precipitates and uniform distribution of the elements (Cu and Mg) in the grain boundary precipitates. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：To provide the process parameters for preparing semi-solid billets, the impacts of heating temperature on recrystallization of a hot-extruded 6A02 aluminum alloy in solid and semi-solid temperature ranges were studied. The static recrystallization (SRX) even occurred at semi-solid temperature due to the low deformation ratio in the starting hot-extruded sample. Almost all elongated grains were transformed into equiaxed grains at immediate 630 degrees C. But not all grains with equiaxed shape were pure recrystallized grains, and small static recrystallized grain even emerged inside them. Bulk insoluble second particles including Fe, Mn, and Si were distributed at the grain boundaries. With the increasing of heating temperature, Vickers hardness increased firstly, then decreased and increased finally. And it was relevant with external force direction. According to the electron backscatter diffraction (EBSD) analysis, the fraction of the recrystallized, sub-structured and deformed grains changed little at 540 degrees C, but varied greatly at 600 degrees C and 630 degrees C. The contents of <111> and <100> fiber deformed textures as well as {100} <001> Cube texture showed analogical variation tendencies. The dislocation densities decreased roughly with temperature both from grain based and kernel-based perspectives. Inhomogeneous deformation existed in an individual grain. Schmid factor had great relevance with external force direction and the gaps were narrowed by the equiaxed microstructure. In the isothermal deformation test, the liquid film was thickened and voids emerged in the shear-deformation region. (c) 2021 Published by Elsevier B.V.
查看更多>>摘要：In present study, the microstructure evolution and spheroidization behavior of (TiB+TiC+Y2O3)/alpha-Ti composite annealed at various temperatures and times were investigated. Results show that the volume fraction of alpha(p) is characteristic of S-type curve with the largest change rate in the range of 960-980 celcius. The mean length of alpha(p) lamellar is characteristic of Doseresp function, that is, the change rate decreases gradually as temperature increases. In the early stage of annealing, the spheroidization mechanism is associated with boundary splitting, which is controlled by the density of defects. When the heat treatment is prolonged, the spheroidization is completed by termination migration and Ostwald ripening. Owing to the heterogeneous geometrical orientation, crystallographic orientation, and (TiB+TiC+Y2O3), the spheroidization behavior is heterogeneous that is demonstrated by different spheroidization response of kinked and elongated alpha colonies. A positive spheroidization behavior is observed in particle-rich region, while a relatively negative spheroidization behavior is observed in particle lean region. The reinforcements hindered the dislocations movement and promoted spheroidization, thus, leading to the heterogeneous deformation and spheroidization. Furthermore, it could promote non-uniform nucleation to form remarkable random alpha(s) and alpha(p) texture, which gave a new inspiration to avoid "Macrozone". (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Ln(3+) (Ln=Eu, Tb, Eu/Tb) doping hexagonal BiPO4 nanorods were synthesized by a room-temperature co precipitation method using ethylene glycol as solvent. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), thermal gravimetric (TG), and photoluminescence spectroscopy (PL) were utilized to investigate the structure, morphology, surface chemistry, and fluorescence performance of the obtained phosphors, respectively. The results showed that hexagonal phase of BiPO4 formed at room temperature, which consisted almost entirely of nanorods with an average diameter of 70 nm and an average length of 292 nm. The chemical reactions mechanism was well elucidated. Under short-wavelength UV light excitation, the as-obtained BiPO4:Eu3+ and BiPO4:Tb3+ samples exhibited strong orange-red and green emissions, respectively. Moreover, the photoluminescence color could be tuned from red, orange, yellow, and green-yellow, to green by simply adjusting the relative doping concentrations of Tb3+ and Eu3+ ions. The room-temperature synthesis reported in the present study could be extended to prepare other rare-earth doped inorganic luminescent materials. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The thin films of (Ge2Sb2Te5)(100-x)Sm-x (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) (Sm-GST) phase change material have been investigated employing X-ray photoelectron spectroscopy (XPS) to examine the nature of chemical bonding in as-deposited thin films of Sm-GST. The composition of as-deposited thin films of Sm-GST has been also analyzed from the peak area ratios of XPS core-level spectra and the morphology of the thin film has been studied using field emission scanning electron microscopy (FESEM). The powder samples obtained from the as-deposited thin films have been utilized for the non-isothermal differential scanning calorimetry (DSC) measurements at the constant heating rate of 10 K/min. The values of glass transition temperature (T-g), onset crystallization (T-c), peak crystallization temperature (T-p) and melting temperature (T-m) obtained from DSC curves of Sm-GST thin films have been used for the evaluation of thermal stability parameters. The activation energy for crystallization (E-c) and avrami exponent (n) for fcc and hexagonal phase of Sm-GST thin films have been evaluated using Henderson's method and Matusita's method. The impact of Sm doping on the thermal stability, glass-forming ability and crystallization activation energy of as-deposited thin films have been examined and its possible influence on the memory device performance has been correlated. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Recently, developing an ideal electromagnetic wave (EM) absorption material, which can simultaneously possess the good abilities of EM energy dissipation, chemical stability and lightweight, has attracted significant attention. Herein, rational designed porous hollow carbon spheres have been prepared via a controllable chemical etching process and followed by a regulated sulfur doping process in the carbon frameworks. The content of sulfur doping can be exactly tuned by simplify adjusting the amount of thioacetamide during the reaction in which can effectively achieve the good balance between the impedance matching and dielectric loss. Benefiting from the porous hollow structure, good impedance matching condition and high dielectric loss, the as-prepared sulfur-doped porous hollow spheres (HCSs) could obtain an efficiency EM attenuation performance, with a maximum effective absorption bandwidth (f(E)) of 6.7 GHz at an absorbent thickness of 2.0 mm. When the matching thickness was only 1.65 mm, the minimum reflection loss (RL) value reached - 53 dB. Therefore, this work confirms that the sulfur-doped porous hollow carbon spheres are expected to be reliable microwave attenuation materials, which also opens up a potential strategy for design and synthesis of high-performance carbon-based materials with tunable EM properties. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Twinned crystal growth is studied in primary Al45Cr7 and Al13Fe4 intermetallic compounds (IMCs) to explore how different twin types and twin variants affect the growth morphology during solidification. In both IMCs, the number of twin variants increased as the cooling rate increased and, by similar to 5 K/s, both IMCs formed cyclic twins with combined icosahedral (Al45Cr7) or decagonal (Al13Fe4) pseudosymmetry. The growth morphology depended on which twin variants were present. When all twin domains shared a common direction that was a rod growth direction in single crystals, twinning did not prevent crystals from growing as rods. This was the case for both IMCs at slow cooling rate and Al13Fe4 at all cooling rates. Cyclic twinning of Al13Fe4 generated many re-entrant corners but resulted in only a modest reduction in rod aspect ratio. In contrast, when twin domains in Al45Cr7 had common directions along multiple pseudo-i(2) axes, crystal growth transitioned from rod-like to a near-equiaxed morphology. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The ferromagnetic damping and relaxation mechanisms of Ni80Fe20 (NiFe) films sputtered on rippled Al2O3 substrates were investigated by in-plane angular dependence ferromagnetic resonance (FMR) measurements where these rippled Al2O3 substrates were prepared by thermal annealing. The linewidth of intrinsic contribution due to Gilbert damping mechanism and linewidth of extrinsic contribution related to two-magnon scattering (TMS) and inhomogeneous broadening of films were identified by filtering different magnetic relaxation mechanisms of films. The results show that the magnitude of ferromagnetic damping of films deposited on rippled Al2O3 substrates can be manipulated by modifying the ripple morphology of substrates and it is strongly dependent on the angle between the direction of the ripple and the external field. The non-Gilbert-type damping for these films is an adjustable, anisotropic contribution to the overall relaxation. The two-magnon scattering and inhomogeneous broadening act as non-Gilbert damping mechanism in magnetization relaxation and they dominate the variation of total linewidth. This work revealed the tunable magnetization relaxation in films deposited on rippled Al2O3 substrates with different surface morphology formed by annealing and it would be helpful for utilizing these rippled substrates to design magnetization relaxation characteristics of spintronic and magnonic devices. (C) 2021 Elsevier B.V. All rights reserved.
NSTL
Elsevier