Abstract Highly uniform dispersed bimetallic Pt 3 Zn alloy nanocrystals (NCs) with unique geometries are obtained via a facile one‐pot synthesis process by regulating different reductants. To investigate the morphology and composition of the prepared catalysts, the transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy are utilized. Electrochemical measurements reveal that the Pt 3 Zn NCs significantly exhibited larger electrochemically active surface areas and excellent catalytic activity towards electro‐oxidation of methanol and ethanol in comparison to the commercial Pt/C. The optimized Pt 3 Zn (AA) NCs exhibit excellent mass activities in both methanol oxidation reaction (1251.4 mA mg Pt −1 ) and ethanol oxidation reaction (975.7 mA mg Pt −1 ) in acidic media, which are respectively 4.28 times and 3.02 times higher than those of commercial Pt/C. Moreover, the Pt 3 Zn NCs show a higher stability and better resistance to the CO ads poisoning. The activity enhancements are attributed to electronic effects and a bifunctional mechanism.
The Al‐doped SiC powder was prepared by solid‐state reaction at 2000°C, using Al powder and SiC powder as the starting materials. The X‐ray diffraction patterns show that there is no impurity phase in the doped powder. The Raman spectra of doped SiC reveal that the intensities of all the characteristic peaks decrease, and both the 783 and 964 cm −1 peaks shift to a higher wavenumber. The electric permittivities of undoped and doped SiC samples were determined in the frequency range of 8.2–12.4 GHz. Results show that the real part ɛ′ and imaginary part ɛ″ of the complex permittivity of SiC powder are greatly improved through Al doping.
Highly uniform Pd–Zn nanocrystals were facilely fabricated with coexisting noble metals and ascorbic acid, which exhibited superior electrocatalytic activity for formic acid oxidation.
One has discussed the principle and method of designing the heterojunction structure of n - Si/Si 1-x Ge x HEMT from the lattice match and the energy band discontinuity points, analysed and calculated the HEMT reported by K. Ismail and obtained 2DEG (two Dimension Electron Gas) density n s essentially according with the experiment data. Final the design of the heterojunction of K. Ismail's HEMT is improved to get a higher 2DEG density n s .
The electronic structure and permittivity of Al-doped 3C-SiC are studied by using the first principles plane-wave pseudopotential method based on the density functional theory, and compared with those of undoped 3C-SiC. Results show that the Fermi energy level introduced into valence band and band gap is slightly widened through Al doping for 3C-SiC, and that the permittivity is greatly improved in a frequency range of 8.2-12.4 GHz. Al doped 3C-SiC powder absorber is prepared by combustion synthesis, and the permittivities of the samples are measured in the frequency range of 8.2-12.4 GHz by vector network analyzer, which validates the results of theoretical calculation. The mechanism of microwave loss is discussed.
ZnO powders were prepared via the solid‐state reaction at 800°C in air, nitrogen, and hydrogen atmospheres, respectively. Raman spectra show that the concentration of oxygen vacancies greatly increases when the sample is prepared in hydrogen atmosphere. The particle size distributions of the powders prepared in air and nitrogen atmospheres are better than that in hydrogen atmosphere. The dielectric parameters of the samples were determined in the frequency range of 8.2–12.4 GHz. Results show that the real part ɛ′ and imaginary part ɛ″ of complex permittivity of the sample prepared in hydrogen atmosphere reveal the greatest values in three samples. The loss mechanism of the samples was discussed.
Abstract 3D organic–inorganic and all‐inorganic lead halide perovskites have been intensively pursued for resistive switching memories in recent years. Unfortunately, instability and lead toxicity are two foremost challenges for their large‐scale commercial applications. Dimensional reduction and composition engineering are effective means to overcome these challenges. Herein, low‐dimensional inorganic lead‐free Cs 3 Bi 2 I 9 and CsBi 3 I 10 perovskite‐like films are exploited for resistive switching memory applications. Both devices demonstrate stable switching with ultrahigh on/off ratios (≈10 6 ), ultralow operation voltages (as low as 0.12 V), and self‐compliance characteristics. 0D Cs 3 Bi 2 I 9 ‐based device shows better retention time and larger reset voltage than the 2D CsBi 3 I 10 ‐based device. Multilevel resistive switching behavior is also observed by modulating the current compliance, contributing to the device tunability. The resistive switching mechanism is hinged on the formation and rupture of conductive filaments of halide vacancies in the perovskite films, which is correlated with the formation of AgI x layers at the electrode/perovskite interface. This study enriches the library of switching materials with all‐inorganic lead‐free halide perovskites and offers new insights on tuning the operation of solution‐processed memory devices.
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