Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

The high-temperature oxidation of Ni-20%Cr alloys containing various oxide dispersions

The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y₂O₃, ThO₂, and A1₂O₃ as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y₂O₃-, ThO₂-, Al₂O₃-, and Ce0₂-containing alloys is very similar and that some anomalies in the behavior of the ThO₂-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al₂O₃-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al₂O₃ particles and behaved exactly like the Y₂O₃-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.This work has been supported by the Naval Air Systems Command under Contract No. N00019-72-C-0190.     

表面氧化层对TiMn1.25Cr0.25储氢合金活化性能的影响

通过TiMn1.25Cr0.25合金粉活化前在空气中暴露不同的时间,探讨了表面氧化层的形成对其活化性能的影响。活化测试结果表明：合金的活化难度随着合金在空气中暴露时间的延长而加大。俄歇电子能谱(AES)结果表明,在空气中暴露后的合金表面形成了一层大约6nm-10nm厚的表面氧化层,正是这层氧化层的形成加大了合金的活化难度。扫描电镜(SEM)结果表明合金的活化过程与合金的碎化有着密切的联系。     

Effect of theθ-α-Al2O3 transformation on the oxidation behavior ofβ-NiAl + Zr

Isothermal oxidation of NiAl + Zr has been performed over the temperature range of 800–1200°C and studied by TGA, XRD, and SEM. A discontinuous decrease in growth rate of two orders of magnitude was observed at 1000° C due to the formation of -Al₂O₃ from -Al₂O₃. This transformation also resulted in a dramatic change in the surface morphology of the scales, as a whisker topography was changed into a weblike network of oxide ridges and radial transformation cracks. It is believed that the ridges are evidence for a shortcircuit outward aluminum diffusion growth mechanism that has been documented in a number of¹⁸O tracer studies.     

Performance of positive and negative electrodes in amorphous manganese oxide supercapacitor

Using potassium permanganate and acetic manganese as the reactants, amorphous manganese oxide was prepared with mechanochemical method. XRD was used for microstructure characterization, while cyclic voltammetry and constant current charge-discharge were used for electrochemical performance testing. The positive electrode （PE） and negative electrode （NE） were investigated respectively in amorphous manganese oxide supercapacitor, aiming to find their different performances in charging-discharging. The results show that the crystalline structure is destroyed in both the PE and NE material during charge-discharge process. Thereinto, the NE suffers a bit more seriously. When cycling, the PE potential scope diminishes while the NE potential scope enlarges. The increased inner resistance makes the NE curves almost bended to be a right angle, but not the PE curves. The cell＇s equivalent series resistance （ESR） is more dependent on the NE, and the capacitance is mainly determined by the rapid descent of the NE potential range. The capacitances of the NE are highly rate-dependent, decreasing from 121.3 to 53.1 F/g, by 56.2%, over the range of 5-25 mV/s. However, the PE appears to be weakly dependent and its capacitance is only dropped by 22.1%.     

Proximity-Induced Fully Ferromagnetic Order with Eightfold Magnetic Anisotropy in Heavy Transition Metal Oxide CaRuO3

Ferromagnetic materials with a strong spin-orbit coupling (SOC) have attracted much attention in recent years because of their exotic properties and potential applications in energy-efficient spintronics. However, such materials are scarce in nature. Here, a proximity-induced paramagnetic to ferromagnetic transition for the heavy transition metal oxide CaRuO₃ in (001)-(LaMnO₃/CaRuO₃) superlattices is reported. Anomalous Hall effect is observed in the temperature range up to 180 K. Maximal anomalous Hall conductivity and anomalous Hall angle are as large as ∼15 Ω⁻¹ cm⁻¹ and ∼0.93%, respectively, by one to two orders of magnitude larger than those of the typical 3d ferromagnetic oxides such as La_0.67Sr_0.33MnO₃. Density functional theory calculations indicate the existence of avoid band crossings in the electronic band structure of the ferromagnetic CRO layer, which enhances Berry curvature thus strong anomalous Hall effects. Further evidences from polarized neutron reflectometry show that the CaRuO₃ layers are in a fully ferromagnetic state (∼0.8 μ_B/Ru), in sharp contrast to the proximity-induced canted antiferromagnetic state in 5d oxides SrIrO₃ and CaIrO₃ (∼0.1 μ_B/Ir). More than that, the magnetic anisotropy of the (001)-(LaMnO₃/CaRuO₃) superlattices is eightfold symmetric, showing potential applications in the technology of multistate data storage.     

Shape design of cerium oxide nanoparticles for enhancement of enzyme mimetic activity in therapeutic applications

Cerium oxide nanoparticles (CONPs), widely used in catalytic applications owing to their robust redox reaction, are now being considered in therapeutic applications based on their enzyme mimetic properties such as catalase and super oxide dismutase (SOD) mimetic activities. In therapeutic applications, the emerging demand for CONPs with low cytotoxicity, high cost efficiency, and high enzyme mimetic capability necessitates the exploration of alternative synthesis and effective material design. This study presents a room temperature aqueous synthesis for low-cost production of shape-selective CONPs without potentially harmful organic substances, and additionally, investigates cell viability and catalase and SOD mimetic activities. This synthesis, at room temperature, produced CONPs with particular planes: {111}/{100} nanopolyhedra, {100} nano/submicron cubes, and {111}/{100} nanorods that grew in [110] longitudinal direction. Enzymatic activity assays indicated that nanopolyhedra with a high concentration of Ce⁴⁺ ions promoted catalase mimetic activity, while nanocubes and nanorods with high Ce³⁺ ion concentrations enhanced SOD mimetic activity. This is the first study indicating that shape and facet configuration design of CONPs, coupled with the retention of dominant, specific Ce valence states, potentiates enzyme mimetic activities. These findings may be utilized for CONP design aimed at enhancing enzyme mimetic activities in therapeutic applications.

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Memory effects of all‐solution‐processed oxide thin‐film transistors using ZnO nanoparticles

Abstract— Non‐volatile memory effects of an all‐solution‐processed oxide thin‐film transistor (TFT) with ZnO nanoparticles (NPs) as the charge‐trapping layer are reported. The device was fabricated by using a soluble MgInZnO active channel on a ZrHfO^x gate dielectric. ZnO NPs were used as the charge‐trapping site at the gate‐insulator—channel interface, and Al was used for source and drain electrodes. Transfer characteristics of the device showed a large clockwise hysteresis, which can be used to demonstrate its memory function due to electron trapping in the ZnO NP charge‐trapping layer. This memory effect has the potential to be utilized as a memory application on displays and disposable electronics.     

Effect of micro-electrode geometry on NO2 gas-sensing characteristics of one-dimensional tin dioxide nanostructure microsensors

Electrodes with micro-gaps are fabricated by using dc-sputtering and FIB techniques. SnO₂ nanowires are deposited on the micro-gap (1-30 μm) by suspension dropping method to fabricate a micro-gas sensor. The sensing ability of various SnO₂ micro-gap sensors is measured. A comparison between sensors reveals that the short-gap electrode has numerous advantages in terms of reliability, high sensitivity and detection of low concentrations of NO₂, while the large-gap electrode is relatively sensitive for high concentrations. Conductance measurements are carried out at different surface temperatures and NO₂ concentrations in order to investigate the effects that the gap size has on the overall sensor conductance. The results suggest that the interface between the electrode and sensitive layer has a very important role for the sensing mechanism of tin dioxide gas sensors.     

Structural and properties of nanocrystalline WO3/TiO2-based humidity sensors elements prepared by high energy activation

Nanocrystalline WO₃/TiO₂-based powders have been prepared by the high energy activation method with WO₃ concentration ranging from 1 to 10 mol%. The samples were thermal treated in a microwave oven at 600 °C for 20 min and their structural and micro-structural characteristics were evaluated by X-ray diffraction, Raman spectroscopy, EXAFS measurements at the Ti K-edge, and transmission electron microscopy. Nitrogen adsorption isotherms and H₂ Temperature Programmed Reduction were also carried out for physical characterization. The crystallite and particle mean sizes ranged from 30 to 40 nm and from 100 to 190 nm, respectively. Good sensor response was obtained for samples with at least 5 mol% WO₃ activated for at least 80 min. Ceramics heat-treated in microwave oven for 20 min have shown similar sensor response as those prepared in conventional oven for 120 min, which is highly cost effective. These results indicate that WO₃/TiO₂ ceramics can be used as a humidity sensor element.