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Strain engineering has been widely applied to tune the performance of oxide thin film based devices. To precisely regulate the strain state of the thin film, nevertheless, still remains a challenging task. Herein, we demonstrate that the uniaxial strain along the c-axis of epitaxial SrCoO2.5 (SCO) (001) thin film can be continuously controlled by low-energy helium (He) irradiation (5 keV), leading to noticeable enhancement in resistive switching (RS) performance. All the irradiated SCO thin films exhibit out-of-plane tensile strain due to the implanted He interstitials in the lattice, and the strain increases linearly from 0.447% to 2.785% as the ion fluence increases from 1 × 1014 to 1 × 1015 ion/cm2. Although all the irradiated SCO-based devices follow similar conductive filaments mechanism as the pristine device, the performance shows a volcano shape dependence on the irradiation fluence. The device subjected to irradiation of 1 × 1014 ion/cm2 shows the optimal performance with the highest ON/OFF ratio and good endurance. Such dependence of RS behavior on irradiation-induced uniaxial strain is attributed to the widely observed nonlinear dependence of oxygen migration on the elastic tensile strain. Our results provide an effective strategy to regulate the strain states and the correlating functionality of oxide thin films. [ABSTRACT FROM AUTHOR]

Restructuring is an important yet less understood phenomenon in the catalysis community. Recent studies have shown that a group of transition metal sulfide catalysts can completely or partially restructure during electrochemical reactions which then exhibit high activity even better than the best commercial standards. However, such restructuring processes and the final structures of the new catalysts are elusive, mainly due to the difficulty from the reaction-induced changes that cannot be captured by ex situ characterizations. To establish the true structure-property relationship in these in situ generated catalysts, we use multimodel operando characterizations including Raman spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity to investigate the restructuring of a representative catalyst, Co 9 S 8 , that shows better activity compared to the commercial standard RuO 2 during the oxygen evolution reaction (OER), a key half reaction in water-splitting for hydrogen generation. We find that Co 9 S 8 ultimately converts to oxide cluster (CoO x ) containing six oxygen coordinated Co octahedra as the basic unit which is the true catalytic center to promote high OER activity. The density functional theory calculations verify the in situ generated CoO x consisting of edge-sharing CoO 6 octahedral clusters as the actual active sites. Our results also provide insights to design other transition-metal-based materials as efficient electrocatalysts that experience a similar restructuring in OER., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Transition metal dichalcogenides (TMDs) have attracted much attention due to their promising optical, electronic, magnetic, and catalytic properties. Engineering the defects in TMDs represents an effective way to achieve novel functionalities and superior performance of TMDs devices. However, it remains a significant challenge to create defects in TMDs in a controllable manner or to correlate the nature of defects with their functionalities. In this work, taking single-layer MoS 2 as a model system, defects with controlled densities are generated by 500 keV Au irradiation with different ion fluences, and the generated defects are mostly S vacancies. We further show that the defects introduced by ion irradiation can significantly affect the properties of the single-layer MoS 2 , leading to considerable changes in its photoluminescence characteristics and electrocatalytic behavior. As the defect density increases, the characteristic photoluminescence peak of MoS 2 first blueshifts and then redshifts, which is likely due to the electron transfer from MoS 2 to the adsorbed O 2 at the defect sites. The generation of the defects can also strongly improve the hydrogen evolution reaction activity of MoS 2 , attributed to the modified adsorption of atomic hydrogen at the defects.