Using in situ synchrotron measurements of total reflection x-ray fluorescence, we find evidence of strontium surface segregation in (001)-oriented La0.7Sr0.3MnO3 thin films over a wide range of temperatures (25–900 °C) and oxygen partial pressures (pO2=0.15–150 Torr). The strontium surface concentration is observed to increase with decreasing pO2, suggesting that the surface oxygen vacancy concentration plays a significant role in controlling the degree of segregation. Interestingly, the enthalpy of segregation becomes less exothermic with increasing pO2, varying from −9.5 to −2.0 kJ/mol. In contrast, the La0.7Sr0.3MnO3 film thickness and epitaxial strain state have little impact on segregation behavior.

We report on the electron tunneling characteristics on La 0.7 Sr 0.3 MnO 3 ͑LSM͒ thin-film surfaces up to 580°C in 10 −3 mbar oxygen pressure, using scanning tunneling microscopy/spectroscopy ͑STM/STS͒. A thresholdlike drop in the tunneling current was observed at positive bias in STS, which is interpreted as a unique indicator for the activation polarization in cation-oxygen bonding on LSM cathodes. Sr-enrichment was found on the surface at high temperature using Auger electron spectroscopy, and was accompanied by a decrease in tunneling conductance in STS. This suggests that Sr-terminated surfaces are less active for electron transfer in oxygen reduction compared to Mn-terminated surfaces on LSM.

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A study of samarium powder‐catalyzed cross‐coupling reactions of aryl halides with terminal alkynes is described. The couplings performed in the polyethylene glycol PEG‐600 provided the corresponding coupling products in good yields. The first example of palladium‐free, copper‐free and amine‐free catalytic system for Sonogashira couplings is presented in the absence of ligand.

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Hybrid perovskites have attracted much attention as a promising photovoltaic material in the past few years. Typically, these hybrid perovskites such as methyl ammonium lead halides (MAPbX3) undergo dimensionality reduction from three-dimensional (3D) to zero-dimensional (0D), and finally to PbX2, upon continuous moisture exposure. Our current study shows that 0D-perovskite-related structures exhibit a reversible transformation from a transparent state to a colored 3D state upon exposure to humidity. Fluorescence imaging of individual microcrystals reveals that the structural phase transition could be visualized in the solid state, wherein the crystals transform into cubic crystals. The plausible reason for this transformation is proposed to be a dynamic dissolution and recrystallization of the excess methyl ammonium halide with varying humidity. The thermal and moisture stability are found to be greatly enhanced in the transformed 3D perovskite. Excellent device stability is also demonstrated when the devices are kept under moist (∼70% RH) conditions.

Mitigating photocorrosion in the light absorber material used for photoelectrochemical solar water splitting is a subject of major research. In this work, a systematic investigation is carried out on suppressing the photocorrosion in an electrodeposited Cu2O photocathode using stable protective layers. The photocathode protected with chemical vapor deposited graphene offers significant stability, till 600 s during light chopping chronoamperometry. However, the presence of a few microcracks in the graphene layer cannot offer complete protection, and causes a gradual decay in the photocurrent. The addition of an ultrathin layer (≈10 nm) of amorphous TiO2 on top of the graphene blocks the microcracks, thereby resulting in complete protection to the Cu2O absorber layer. The TiO2/graphene protected Cu2O photocathode generates ‐3 mA cm−2 photocurrent at 0.0 V versus reversible hydrogen electrode under 1 sun in 1 m Na2SO4 electrolyte (pH 7), which is twice that compared to the bare Cu2O electrode. The enhancement in photocurrent can be attributed to the ease of separating the photogenerated charge carriers due to the suitable band alignment and electron selective nature of the protective TiO2/graphene layers.