At present, there is a clear interest in developing redox materials with improved properties for high temperature thermochemical energy storage. Chemical modification of manganese oxides with cations ...such Li and Cu can produce, among other phases, LiMn2O4 and CuMn2O4 spinels, which are feasible candidates for heat storage due to their redox capacity. In this work, these materials were synthesized by Pechini method, and the characterization results confirmed the formation of the targeted phases with some minor contribution of Mn3O4. Thermogravimetrical redox tests in air established that both materials experience fully reversible redox transformations when the temperature is varied between 900 and 1000 °C. These assays showed the stability of both Cu and Li mixed oxides after five consecutive redox cycles and, in accordance, the XRD confirmed that the two samples retaining their spinel crystal structure after the treatment. However, in these conditions reduction temperatures are higher than 940 °C for both oxides and the enthalpies of these transformations are modest, with a maximum value of 36 kJ/kg for LiMn2O4. Alternatively, if the reduction is performed in argon and the oxidation in air, it is possible to increase the amount of oxygen exchanged in the gas-solids reactions and, accordingly, the heat storage capacity. Therefore, the heat recovered in the re-oxidation of CuMn2O4 at 700 °C was 144 kJ/kg (34 kJ/mol), while LiMn2O4 showed an enthalpy of 209 kJ/kg (37 kJ/mol). These changes in the composition of the atmosphere do not affect to the stability of the system and the conversion is maintained after five consecutive cycles. In all cases, the initial spinel phase is recovered after reoxidation, which takes place at remarkably fast rates. Analysis of the intermediate reduced materials reveals a significant complexity of the redox transformations, which imply the formation of LiMnO2 and CuMnO2, among other phases. Accordingly, considering the stability of these systems, as well as the relatively high enthalpies CuMn2O4 and LiMn2O4 appear to be promising materials for thermochemical energy storage.
•LiMn2O4 and CuMn2O4 materials are promising candidates for thermochemical heat storage.•These spinels showed excellent redox cyclability at high temperature and different atmospheres.•No degradation of the performance is observed in 5 cycles.•These spinels show relatively high enthalpies and fast reaction oxidation kinetics, specially LiMn2O4.
In this work, we demonstrate the effectiveness of nitrogen plasma treatment on the formation of low-resistive source/drain (S/D) in self-aligned (SA) oxide thin-film transistors (TFTs) using a ...high-mobility oxide semiconductor (OS), In-Ga-Zn-Sn-O (IGZTO). The nitrogen plasma treatment was more effective at reducing the sheet resistance (<inline-formula> <tex-math notation="LaTeX">{R} _{\mathrm{ sheet}} </tex-math></inline-formula>) of IGZTO films than the commonly used argon plasma treatment. Furthermore, <inline-formula> <tex-math notation="LaTeX">{R} _{\mathrm{ sheet}} </tex-math></inline-formula> for nitrogen-plasma-treated IGZTO films remained low, even when the RF power and radiation time during the plasma treatment were increased when the minimum <inline-formula> <tex-math notation="LaTeX">{R} _{\mathrm{ sheet}} </tex-math></inline-formula> was achieved. The same trends were also observed in OS films with different compositions, such as In-Ga-Zn-O and In-Sn-Zn-O. These results indicate that nitrogen plasma treatment is effective for achieving a reduction of <inline-formula> <tex-math notation="LaTeX">{R} _{\mathrm{ sheet}} </tex-math></inline-formula> for various OS films with a wide process window regarding plasma processing parameters. The advantages could be attributed to the smaller sputtering effect on the OS films due to the lower mass of nitrogen ions than argon ions, which was verified by X-ray reflectivity and X-ray photoelectron spectroscopy analyses. For further validation, SA IGZTO TFTs with a channel length (<inline-formula> <tex-math notation="LaTeX">{L} </tex-math></inline-formula>) of 3 to 100 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> were fabricated with nitrogen or argon plasma treatment. The width-normalized parasitic SD resistance (<inline-formula> <tex-math notation="LaTeX">R_{\mathrm{ SD}} {W} </tex-math></inline-formula>) with the nitrogen plasma treatment was determined to be 11.3 <inline-formula> <tex-math notation="LaTeX">\Omega \cdot </tex-math></inline-formula>cm, which was ca. 40% lower than that with the argon plasma treatment. This improvement in <inline-formula> <tex-math notation="LaTeX">R_{\mathrm{ SD}} {W} </tex-math></inline-formula> resulted in higher mobility (<inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>) in the nitrogen-plasma-treated SA IGZTO TFTs. A nitrogen-plasma-treated SA IGZTO TFT with <inline-formula> <tex-math notation="LaTeX">L=10\,\,\mu \text{m} </tex-math></inline-formula> exhibited a high <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> of 27.2 cm 2 /Vs.
The electronic structures of two-dimensional materials are strongly dependent on their thicknesses; for example, there is an indirect to direct band gap transition from multilayer to single-layer ...MoS2. A simple, efficient, and nondestructive way to control the thickness of MoS2 is highly desirable for the study of thickness-dependent properties as well as for applications. Here, we present layer-by-layer thinning of MoS2 nanosheets down to monolayer by using Ar+ plasma. Atomic force microscopy, high-resolution transmission electron microscopy, optical contrast, Raman, and photoluminescence spectra suggest that the top layer MoS2 is totally removed by plasma while the bottom layer remains almost unaffected. The evolution of Raman and photoluminescence spectra of MoS2 with thickness change is also investigated. Finally, we demonstrate that this method can be used to prepare two-dimensional heterostructures with periodical single-layer and bilayer MoS2. The plasma thinning of MoS2 is very reliable (with almost 100% success rate), can be easily scaled up, and is compatible with standard semiconductor process to generate heterostructures/patterns at nanometer scale, which may bring out interesting properties and new physics.
•First use of plasma alternative to solid material as an inert anode in aluminum electrolysis;•The anode product of electrolysis is oxygen;•Plasma anodes are available easily and without complicated ...operations;•Theoretically, the plasma anode is completely inert in the aluminum cell;
The aluminum industry is one of the major causes of CO2 emissions into the atmosphere, mainly caused by carbon anode consumption and the emission of perfluorocarbon gases. Carbon anodes are consumed by anodic reactions in the standard technology. The environmental constraints and the costs associated with the utilization of carbon anodes have, for many decades, led to the look for non-consumable anodes, called “inert anodes,” considered for years to be the future of aluminum production. However, the current research on inert anodes is limited to metal, ceramic, cermet, and gas anodes and remains impotent in solving the difficulties of anode consumption, CO2, and other greenhouse gas emissions. Here, we propose the utilization of argon plasma as an inert anode for aluminum electrolysis. The results from emission spectroscopy analysis and Density Functional Theory (DFT) calculations depict a production of positively charged argon ion (Ar+) at the anode region, which infuses into the electrolyte and reacts electrochemically with the oxy-fluoro aluminate complexes (Al2OF6)2-. For a current ≤ 0.4 A, the oxygen evolution occurs anodically from 2Al2OF62- + 4Ar+ → 4AlF3 + O2 + 4Ar, with no argon consumption. Furthermore, the aluminum is reduced cathodically, and the decomposition reaction is 2Al2O3 → 4Al + 3O2. This innovative approach enables carbon-free aluminum electrolysis, a large-scale reduction in greenhouse gas (GHG) emissions, which can be extended to similar electrolytic industries.
The Russian-American experiment SAGE began to measure the solar neutrino capture rate with a target of gallium metal in December 1989. Measurements have continued with only a few brief interruptions ...since that time. In this article we present the experimental improvements in SAGE since its last published data summary in December 2001. Assuming the solar neutrino production rate was constant during the period of data collection, combined analysis of 168 extractions through December 2007 gives a capture rate of solar neutrinos with energy more than 233 keV of 65.4{sub -3.0}{sup +3.1} (stat) {sub -2.8}{sup +2.6} (syst) SNU. The weighted average of the results of all three Ga solar neutrino experiments, SAGE, Gallex, and GNO, is now 66.1{+-}3.1 SNU, where statistical and systematic uncertainties have been combined in quadrature. During the recent period of data collection a new test of SAGE was made with a reactor-produced {sup 37}Ar neutrino source. The ratio of observed to calculated rates in this experiment, combined with the measured rates in the three prior {sup 51}Cr neutrino-source experiments with Ga, is 0.87{+-}0.05. A probable explanation for this low result is that the cross section for neutrino capture by the two lowest-lying excited states in {sup 71}Ge has been overestimated. If we assume these cross sections are zero, then the standard solar model including neutrino oscillations predicts a total capture rate in Ga in the range of 63 SNU to 66 SNU with an uncertainty of about 4%, in good agreement with experiment. We derive the current value of the neutrino flux produced in the Sun by the proton-proton fusion reaction to be {phi}{sub pp}{sup {center_dot}}=(6.0{+-}0.8)x10{sup 10}/(cm{sup 2} s), which agrees well with the pp flux predicted by the standard solar model. Finally, we make several tests and show that the data are consistent with the assumption that the solar neutrino production rate is constant in time.
Regular nanoscopic ripple and dot patterns are fabricated on poly‐crystalline titanium samples by irradiation with 1.5 keV argon ions at normal incidence. The morphology of the nanostructures is ...investigated by scanning electron microscopy and scanning force microscopy. The ripple structures exhibit a saw‐tooth cross‐section profile. Electron backscatter diffraction experiments are performed to analyze the local grain structure. The study suggests a distinct correlation of the nanostructure morphology to the crystallographic orientation of the titanium surface.
Xenon provides neuroprotection in multiple animal models; however, little is known about the other noble gases. The aim of the current study was to compare xenon, argon, and helium neuroprotection in ...a neonatal asphyxia model in rats.
Randomized controlled trial.
Laboratory.
Seven-day-old postnatal Sprague-Dawley rats.
Seventy percent argon, helium, xenon, or nitrogen balanced with oxygen after hypoxic-ischemic brain injury.
Control animals undergoing moderate hypoxic-ischemia endured reduced neuronal survival at 7 days with impaired neurologic function at the juvenile age compared with naïve animals. Severe hypoxic-ischemic damage produced a large cerebral infarction in controls. After moderate hypoxic-ischemia, all three noble gases improved cell survival, brain structural integrity, and neurologic function on postnatal day 40 compared with nitrogen. Interestingly, argon improved cell survival to naïve levels, whereas xenon and helium did not. When tested against more severe hypoxic-ischemic injury only, argon and xenon reduced infarct volume. Furthermore, postinjury body weight in moderate insult was lower in the helium-treated group compared with the naïve, control, and other noble gas treatment groups, whereas in the severe injurious setting, it is lower in both control and helium-treated groups than other groups. In the nondirectly injured hemisphere, argon, helium, and xenon increased the expression of Bcl-2, whereas helium and xenon increased Bcl-xL. In addition, Bax expression was enhanced in the control and helium groups.
These studies indicate that argon and xenon provide neuroprotection against both moderate and severe hypoxia-ischemic brain injury likely through prosurvival proteins synthesis.
The nanoreactor approach first introduced by the group of Martı́nez Wang et al. Nat. Chem. 2014, 6, 1044–1048 has recently attracted much attention because of its ability to accelerate the discovery ...of reaction pathways. Here, we provide a comprehensive study of various simulation parameters and present an alternative implementation for the reactivity-enhancing spherical constraint function, as well as for the detection of reaction events. In this context, a fully automated postsimulation evaluation procedure based on RDKit and NetworkX analysis is introduced. The chemical and physical robustness of the procedure is examined by investigating the reactivity of selected homogeneous systems. The optimized procedure is applied at the GFN2-xTB level of theory to a system composed of HCN molecules and argon atoms, acting as a buffer, yielding prebiotically plausible primary and secondary precursors for the synthesis of RNA. Furthermore, the formose reaction network is explored leading to numerous sugar precursors. The discovered compounds reflect experimental findings; however, new synthetic routes and a large collection of exotic, highly reactive molecules are observed, highlighting the predictive power of the nanoreactor approach for unraveling the reactive manifold.
Coating/substrate interface and oxide layers present in Inconel 625 film may cause significant impacts on its corrosion behavior. However, layered structure of Inconel 625 coatings remains poorly ...understood due to its requirement of high spatial resolution. This study applies X-ray reflectometry (XRR) to probe the layered structure of magnetron-sputtered Inconel 625 film with atomic spatial resolution. Our results indicate that there exists a 2 nm thick Cr-rich Inconel sublayer underneath the principal film. On top of the principal film, it is found a 2 nm thick oxide layer mainly consisting of NiO. In addition, we detected ~2 Å contamination layer on the sapphire substrate, although argon ion sputter cleaning had been applied to the substrate prior to deposition. By comparing the coatings with different deposition time, we observed that the thickness of principal Inconel 625 layer grows linearly with deposition time, with all other layers remaining constant. Our findings provide insight into the layered structures of Inconel 625 coatings with atomic-scale spatial resolution, and provide directions for future efforts that aim to improve the corrosion resistance of Inconel 625 coatings.
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•Multi-layered structure of Inconel 625 film is revealed with atomic-scale spatial resolution.•2.3 nm thick Cr-rich Inconel sublayer is found underneath the principal Inconel film.•Oxide layer with thickness of 2 nm is dominated by NiO.•2 Å and 15 Å thick contaminations are identified on the substrate and on the film respectively.•Principal Inconel 625 layer grows linearly with deposition time.
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