Long-term instability and possible lead contamination are the two main issues limiting the widespread application of organic-inorganic lead halide perovskites. Here a facile and efficient solution-phase method is demonstrated to synthesize lead-free Cs2 SnX6 (X = Br, I) with a well-defined crystal structure, long-term stability, and high yield. Based on the systematic experimental data and first-principle simulation results, Cs2 SnX6 displays excellent stability against moisture, light, and high temperature, which can be ascribed to the unique vacancy-ordered defect-variant structure, stable chemical compositions with Sn4+ , as well as the lower formation enthalpy for Cs2 SnX6 . Additionally, photodetectors based on Cs2 SnI6 are also fabricated, which show excellent performance and stability. This study provides very useful insights into the development of lead-free double perovskites with high stability.
Abstract Surface plasmon induced hot‐carrier injection to semiconducting transition metal dichalcogenide (TMD) monolayers has been extensively studied. However, comprehensive understanding of the injection kinetics by fully considering the weak metal−TMD interaction and the TMDs’ exciton formation kinetics is missing. Here, a hot‐carrier injection pathway is elucidated by systematically investigating the interfacial interaction kinetics among different plasmonic metals and TMDs. The pathway highlights the exciton formation timescale as a threshold for interfacial carrier injection, before which plasmonic hot carriers and free electron−hole pairs are relaxed incoherently across the interface. The injected hot carriers will interact with excitons to form charged quasiparticles as trions, which have extended lifetime. The pathway reveals the fundamental mechanism of the plasmonic hot‐carrier−TMD interactions, opens the possibility of controllable manipulation of hot‐carrier injection process, and allows future research toward opto‐electrical guidance of trions in metal−TMD systems.
${(\mathrm{LaCo}{\mathrm{O}}_{3}/\mathrm{LaMn}{\mathrm{O}}_{3})}_{5}$ multilayers with fixed $\mathrm{LaMn}{\mathrm{O}}_{3}$ thickness and varying $\mathrm{LaCo}{\mathrm{O}}_{3}$ thickness grown on $\mathrm{SrTi}{\mathrm{O}}_{3}$ (001) substrates are studied by scanning transmission electron microscopy at the atomic scale. Utilizing peak pairs analysis on annular bright field images, the precise atomic positions and the degree of octahedral rotation are obtained. Our study shows that the $c$ axis of $\mathrm{LaMn}{\mathrm{O}}_{3}$ sandwiched by $\mathrm{LaCo}{\mathrm{O}}_{3}$ layers experiences a transition from the in-plane direction to the out-of-plane direction as the $\mathrm{LaCo}{\mathrm{O}}_{3}$ layer thickness increases, due to the oxygen octahedral coupling with $\mathrm{LaCo}{\mathrm{O}}_{3}$ layers. An abnormal suppression in saturation magnetization with increasing the thickness of the $\mathrm{LaCo}{\mathrm{O}}_{3}$ is observed and ascribed to the enhanced $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedral rotation. Our work provides a way to tune the magnetic properties of epitaxially grown thin films via interfacial octahedral engineering.
The IrO x electrodes fabricated by cyclic heating and quenching process show excellent comprehensive properties including wide E-pH range, near Nernst pH sensitivity, fast response rate, and long term stability etc. The IrO x electrodes are applied in the detection of surface pH changes during galvanic corrosion process of zinc/steel couple in 1 mm 3.5 wt.% NaCl electrolyte layer and 3.5 wt.% NaCl bulk solution, respectively. This detection is realized by integrating the self-fabricated IrO x pH sensor and self-assembled moving platform together. Before the application of the IrO x electrode, the appropriate way of scanning the surface of the zinc/steel galvanic couple is discussed. Comparing with the case in bulk solution, the zinc/steel couple corrodes faster in 1 mm electrolyte layer, the surface pH of which increases to a high value after corrosion begins for 20∼40 min, and the low pH region exists on the zinc surface and the region adjacent to border area of the steel surface, whereas the pH value of the steel surface away from the border area is relatively high. It is demonstrated that the IrO x electrode could detect the pH distribution effectively in surface region during metal corrosion, which could help the understanding of corrosion process under different situations.
pH detection of strict environments such as deep sea environment, extremely acid or alkaline environment etc. put forward high requirements for pH monitoring electrode. In this paper, the IrO x electrodes prepared by cyclic thermal oxidation and quenching process (CHQ) went through thermostatic posttreatment process, i.e., heat treatment at the temperature of 400 °C, 500 °C, 600 °C for 0.5 h with furnace cooling to room temperature further. Aiming at filtrating an optimal posttreatment process and improving the comprehensive properties of the IrO x electrodes, the E-pH relationship, potential-time dependence tests, and long-term stability tests were carried out. Further characterizations including surface morphologies, surface roughness, surface crystal qualities, and surface compositions were examined through advanced detection methods. The results indicate that the IrO x electrode went through thermostatic posttreatment at 400 °C has larger surface roughness and relatively smaller cracks, implying the increasement in active surface area for electrode reaction. Optimal percentage of Ir 4+ and Ir 3+ revealed by the X-ray photoelectron spectroscopy (XPS), better crystal quality shown by Raman spectroscopy, relief of tensile stress in the surface film demonstrated by (X-ray diffraction) XRD and Raman could account for the excellent performance of the posttreatment IrO x electrode.
B-site Os-doped quadruple perovskite oxides LaCu3Fe4–xOsxO12 (x = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCu3Fe4O12 experiences Cu–Fe intermetallic charge transfer that changes the Cu3+/Fe3+ charge combination to Cu2+/Fe3.75+ at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os6+ and mixed Os4.5+ valence states are determined by X-ray absorption spectroscopy for x = 1 and x = 2 compositions, respectively. The x = 1 sample crystallizes in an Fe/Os disordered structure with the Im3̅ space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to x = 2, the crystal symmetry changes to Pn3̅, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu2+(↑)Fe3+(↑)Os4.5+(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.
In article number 1901650, Jia Liang, Jun Lou, and co-workers synthesize lead-free double perovskite Cs2SnX6 (X = Br, I) with a well-defined vacancy-ordered defect-variant crystal structure via a facile hydrothermal method. The as-obtained perovskite displays excellent stability against moisture, light, and high-temperature.
Silver (Ag) nanostructures are active functional platforms for catalysts, optical sensors, and transparent conductive networks with outstanding performance but present poor stability depending on their chemical, mechanical, or thermal surroundings. Doping with other elements and passivation with a chemically inert coating of a Ag nanostructure are proven to be efficient in enhancing the stability, while both methods have drawbacks such as cost and sacrifice of the on-demand properties. Here, we present a self-passivated Ag–Al nanostructure with a precisely controlled coating thickness, taking advantage of the intrinsic high conductivity and chemical reducibility of aluminum at the same time, fabricated by oblique angle codeposition of Ag–Al nanostructures followed by postannealing under mild conditions. With the nanometer-thick coating confirmed by transmission electron microscope (TEM) observations, surface-enhanced Raman scattering (SERS) measurements were successfully utilized to further demonstrate the quality of the in situ grown aluminum oxide (Al2O3) layer, including the thickness, coating integrity, and chemical stability. In addition, a mechanically robust nanostructure as well as an ultrathin conductive electrode ∼10 nm in thickness was enabled by dilute doping of Al into the Ag matrix. Interestingly, a bipolar change in the Ag–Al/MoS2/Ag–Al device after annealing was achieved. Further observation revealed that the Al2O3 layer grew on top of the Ag–Al alloys. The methods we developed require dilute doping of Al into a Ag matrix and mild processing conditions, yet precise interface thickness control and pronounced property enhancement are achieved, all of which pave the way for the practical application of Ag nanostructures in optical sensors and integrated circuits.
Abstract Interface engineering is an effective and feasible method to regulate the magnetic anisotropy of films by altering interfacial states between different films. Using the technique of pulsed laser deposition, we prepared La 0.67 Sr 0.33 MnO 3 (LSMO) and La 0.67 Sr 0.33 MnO 3 /SrCoO 2.5 (LSMO/SCO) films on the (110)-oriented La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 substrates. By covering the SCO film above the LSMO film, we transformed the easy magnetization axis of LSMO from the [001] axis to the [1\(\stackrel{\text{-}}{\text{1}}\)0] axis in the film plane. Based on statistical analyses, we found that the corresponding Mn-Mn ionic distances are different in the two types of LSMO films, causing different distortions of Mn-O octahedron in the LSMO film. In addition, it also induces diverse electronic occupation states in Mn 3+ ions. The e g electron of Mn 3+ occupies 3 z 2 -r 2 and x 2 -y 2 orbitals in the LSMO and LSMO/SCO, respectively. We conclude that the electronic spin reorientation leads to the transformation of the easy magnetization axis in the LSMO films.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
