We analyzed reports for 59,073 contacts of 5,706 coronavirus disease (COVID-19) index patients reported in South Korea during January 20-March 27, 2020. Of 10,592 household contacts, 11.8% had ...COVID-19. Of 48,481 nonhousehold contacts, 1.9% had COVID-19. Use of personal protective measures and social distancing reduces the likelihood of transmission.
Yb2SiO5 (ytterbium monosilicate) top coatings and Si bond coat layer were deposited by air plasma spray method as a protection layer on SiC substrates for environmental barrier coatings (EBCs) ...application. The Yb2SiO5-coated specimens were subjected to isothermal heat treatment at 1400 °C on air for 0, 1, 10, and 50 h. The Yb2SiO5 phase of the top coat layer reacted with Si from the bonding layer and O2 from atmosphere formed to the Yb2Si2O7 phase upon heat treatment at 1400 °C. The oxygen penetrated into the cracks to form SiO2 phase of thermally grown oxide (TGO) in the bond coat and the interface of specimens during heat treatment. Horizontal cracks were also observed, due to a mismatch of the coefficient of thermal expansion (CTE) between the top coat and bond coat. The isothermal heat treatment improves the hardness and elastic modulus of Yb2SiO5 coatings; however, these properties in the Si bond coat were a little bit decreased.
In this study, the high-temperature corrosion behavior was evaluated for (La,Gd)2Zr2O7 (LGZ) used as a promising thermal barrier coatings (TBCs) material. (La,Gd)2Zr2O7 + YSZ multilayer prepared from ...atmospheric plasma spray (APS) were exposed to calcium-magnesium-alumino-silicate (CMAS) melt at 1300 °C for 2, 12, 48, and 100 h. Molten CMAS and (La,Gd)2Zr2O7 reacted to form reaction layer Ca2Gd8(SiO4)6O2 (apatite) at 1300 °C. The thickness of the reaction layer increased with increasing heat-treatment time. A correlation between the hardness and Young’s modulus relationship for the reaction layer of the coating was observed for the microstructure using nanoindentation. It was confirmed that the pores of the coating were reduced through the infiltration of molten CMAS in the initial stage of the corrosion reaction, and the hardness and Young’s modulus were increased due to densification. Fracture toughness increased with heat treatment time in both directions (in-plane and through-thickness). The fracture toughness in the in-plane direction is 0.19–0.23 MPa√m. On the other hand, the fracture resistance in the thickness direction was 0.87–1.26 MPa√m, which was higher than that in the in-plane direction. These results show that the crack propagates in the in-plane direction and causes TBC delamination.
Considering a strict global environmental regulation, fluorescent quantum dots (QDs) as key visible emitters in the next-generation display field should be compositionally non-Cd. When compared to ...green and red emitters obtainable from size-controlled InP QDs, development of non-Cd blue QDs remains stagnant. Herein, we explore the synthesis of non-Cd, ZnSe-based QDs with binary and ternary compositions toward blue photoluminescence (PL). First, the size increment of binary ZnSe QDs is attempted by a multiply repeated growth until blue PL is attained. Although this approach offers a relevant blue color, excessively large-sized ZnSe QDs inevitably entail a low PL quantum yield. As an alternative strategy to the above size enlargement, the alloying of high-band gap ZnSe with lower-band gap ZnTe in QD synthesis is carried out. These alloyed ternary ZnSeTe QDs after ZnS shelling exhibit a systematically tunable PL of 422–500 nm as a function of Te/Se ratio. Analogous to the state-of-the-art heterostructure of InP QDs with a double-shelling scheme, an inner shell of ZnSe is newly inserted with different thicknesses prior to an outer shell of ZnS, where the effects of the thickness of ZnSe inner shell on PL properties are examined. Double-shelled ZnSeTe/ZnSe/ZnS QDs with an optimal thickness of the ZnSe inner shell are then employed for all-solution-processed fabrication of a blue QD light-emitting diode (QLED). The present blue QLED as the first ZnSeTe QD-based device yields a peak luminance of 1195 cd/m2, a current efficiency of 2.4 cd/A, and an external quantum efficiency of 4.2%, corresponding to the record values reported from non-Cd blue devices.
Group I–III–VI chalcogenides are emerging candidates for the synthesis of efficient quantum dot (QD) emitters, particularly since they are free from environmentally harmful substances such as Cd, Pb, ...and As. Among them, Cu–In–S (CIS) and Cu–In–Se1–x –S x (CISeS) are the most common compositions as visible and near-infrared (NIR) QD emitters, respectively. We herein explore efficient synthetic pathways to demonstrate extensively emission-tuned CIS QDs from visible to NIR with high photoluminescence quantum yields (PL QYs) of over 70%. To systematically tune PL, synthetic parameters of CIS core QDs are varied such as Cu/In molar ratio, core growth condition, Ag alloying, and In precursor change, whereas a highly reactive elemental sulfur is commonly adopted for core growth. Starting from visible CIS/ZnS QDs, whose emission is tuned in green (534 nm) to red (625 nm), depending on the Cu/In ratio, their emissions gradually shift in the PL peak to 744 nm by controlling the core growth condition to 806 nm by alloying with Ag and further to 868 nm by switching an In salt precursor from In acetate to In iodide. These NIR-emitting QDs, particularly those having PL peaks longer than 800 nm, possess excellent QYs of 81–91%, which are the record values among deep NIR-emitting I–III–VI QDs to date. To enhance the QD stability against environmental stimuli, Al doping into Zn shell is implemented on 868 nm emitting CIS/ZnS QDs, resulting in exceptional photostability under prolonged UV irradiation exposure. These highly luminescent, photostable NIR-emitting CIS/ZnS QDs will be attractive candidates for further application as fluorophores in luminescent solar concentrator and in vivo bioimaging.
In order to understand the erosion behavior of oxide ceramics during their exposure to fluorocarbon plasma, the thin films of AlF3, YF3, Al2O3, Y2O3 and SiO2 were deposited on silicon and then their ...surfaces were irradiated with Ar ions of different kinetic energies. When we measured the relative sputtering rates, fluoride was sputtered faster than oxide with strong dependency on its chemistry, while the sputtering rates of oxides were nearly identical. The fact that AlF3 was sputtered a few times faster than YF3 is consistent with previously observed faster etch rate in Al2O3 than in Y2O3 under fluorocarbon plasma. These results support that erosion of ceramics under fluorocarbon plasma occurs by a physical removal process of fluorinated surfaces which were simultaneously induced by their interaction with the fluorocarbon plasma. Based on these results, implications for plasma resistance of oxide ceramics and production of contamination particles in the silicon wafer processing chamber under fluorocarbon plasma will be discussed based on their thermal properties and a numerical simulation.
•Relative sputtering rates of fluoride and oxide of Al and Y were measured.•The sputtering rate of fluorides depended strongly on the chemistry, contrary to similar rates of oxides.•Oxide cearmics was confirmed to erode by a physical process under fluorine-based plasma.
Al–Si–Mg cast alloys can be imparted with a wide range of mechanical properties through heat treatment, thus meeting the required performance of various vehicle components. However, because of the ...characteristics of the high-pressure die casting process, the gas porosities in the casting can lead to blisters during the solution treatment of die-casting parts. Therefore, systematic studies on the solution temperature and solution time are required to prevent such blisters. In this study, the gas porosity and mechanical properties of T6 heat-treated specimens were evaluated under various solution treatment conditions. As the solution treatment temperature and time increased, the numbers and volume of individual gas porosity increased. On the other hand, there were little changes in the shrinkages upon heat treatment. As solution temperature and time increased, the area fraction of the eutectic Si particles and Mg2Si decreased slightly, whereas the area and sphericity of the eutectic Si and Mg2Si increased. As the solution treatment temperature and time increased, the ultimate tensile strength and yield strength increased, whereas the elongation tended to decrease. However, the maximum UTS and YS were obtained on treatment at 520 °C for 1.5 h.
•Vacuum die casting of Al–Si–Mg alloy under solution treatment conditions.•Separation of gas porosities and shrinkage and their quantitative measurement.•Mechanical property comparison between T6 heat-treated and as-cast specimens.
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•Cation-substituted Y2O3 evaluated as a promising material for enhancing plasma resistivity in next-generation semiconductor processes.•Plasma dry etching carried out with inductively ...coupled plasma, utilizing a CF4/O2/Ar gas mixture.•Essential factors for the enhanced plasma resistivity of cation-substituted Y2O3 are associated with surface reactions during plasma etching, atomic bond strength, and occupied oxygen vacancy sites in the yttria crystal structure.•The etch rate of cation-substituted Y2O3 is found to be lower than that of conventional Y2O3.
Ceramic Y2O3 thin films are often used to coat the inner walls of etching equipment during semiconductor manufacturing to protect them from bombardment by high-energy plasma ions, which can degrade the equipment and cause semiconductor contamination. In this study, the effects of HfO2 addition to the Y2O3 thin film on the plasma resistance were investigated. Thin films were fabricated using electron beam-physical vapor deposition. The addition of HfO2 maintained the cubic Y2O3 crystalline structure while substantially improving the etch resistance during fluorine-based plasma etching. X-ray photoelectron spectroscopy analysis of the etched surface showed that HfO2 addition resulted in a lower F/(O + F) ratio, thus promoting the formation of more Y–O bonds that are more resistant to physical sputtering. Additionally, the analysis indicated that Hf4+ was more likely to be removed from the etched surface than Hfx+ (x < 4). This novel strategy is expected to aid in the development of improved plasma-resistant ceramic materials.
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•All-halide nanocrystals phosphors embedded in a UV-polymer matrix is proposed.•Alternating stacks of red/green halide layers are controlled for best white luminescence.•Adjusted ...prismatic patterns for the red halide layer strengthen the white luminescence.•A polymer-passivation method is very effective for strong optical stability up to 120 h.
Perovskite halide nanocrystals have been actively investigated for use in white-luminescence photonic devices. Herein, a remote phosphor-layered composite consisting of all-halide red and green nanocrystals embedded in an ultraviolet (UV)-cured matrix is proposed as a facile way to create competitive white luminescence. Alternating stacks of cast halide layers with controlled concentration and thickness yielded true white luminescence characteristics when the halide layers were combined with a bottom blue chip. Specifically, the adjusted prismatic pattern for the red halide layer was found to effectively strengthen the emission of white luminescence. In particular, a phosphor-stacked structure of green and red layers with a 9-μm-pitch prismatic pattern resulted in an enhanced luminous efficacy of ∼54.4 lm W−1, which is higher than those of a non-prismatic layer or a larger pitch pattern. Encapsulating both sides of the halide layers with polydimethylsiloxane (PDMS) maintained very effectively the luminescence of the halide layers over the exposure of 300 h.
Y2SiO5 coatings are deposited by a flame-spray technique as protection layer on SiC substrates to prevent oxidation and steam corrosion. In this research, Y2SiO5 coatings were isothermally heat ...treated at different temperatures and different exposure times in a laboratory environment. The thermal behaviors such as phase transformation, microstructural change and thermally grown oxide (TGO) formation have been examined by XRD, SEM, and EDS analysis. Different modes of TGO growth behavior were found at different temperatures. In addition, the mechanical properties were evaluated by a Martens hardness tester. The results show that the change of microstructure and composition is not too critical, but higher temperatures and longer heating times do lead to the formation of Y2SiO5 crystalline phases and a β-Y2O3 phase. Thus, the isothermal heat treatment improves the hardness and elastic modulus of Y2SiO5 coatings.
•Y2SiO5 coatings are deposited by flame-spray technique as protection layer on SiC.•Thermally grown oxide observed at the interface between the Y2SiO5 coating and Si bond coatings•Hardness and Young's modulus of Y2SiO5 coatings increased with increasing heat treatment time at 1180°C and 1480°C.
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