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Surface morphological control of the metal-insulator transition behaviors of VO 2 epitaxial thin films is achieved by annealing substrates of (0001)-Al 2 O 3 single crystals. The well-defined terraces of the (0001)-Al 2 O 3 substrates are formed by annealing in air at 1200 °C. Correspondingly, the surface roughness dramatically decreases in the VO 2 epitaxial thin films on the annealed substrates, compared with that on the unannealed substrates. The order of magnitude of the resistivity change ratio (~ 10 2 ) of annealed samples across the metal-insulator transition (MIT) decreases by a factor of one, compared with that (~ 10 3 ) in unannealed samples. This result is ascribed to grain size effect in the VO 2 epitaxial thin films. Moreover, the MIT temperature is reduced in the annealed samples with various thickness, compared with the unannealed ones. A reduction of 14.4 K of the MIT temperature is observed in the thinnest VO 2 films on the annealed substrates, compared with the unannealed samples. This behavior results from a compressive strain along the V-V atom chains in the annealed samples, which modifies the orbital occupancy of the V 4+ ions. While increasing the film thickness, the MIT change ratio keeps on the order of magnitude 10 2 , and the MIT temperatures of the VO 2 films on the annealed substrates becomes closer and closer to those of the unannealed samples due to the weakened substrate effect. This work suggests a promising approach to decrease the MIT temperature and still maintain a moderate change ratio for the MIT, potentially enabling room-temperature electronic devices based on VO 2 thin films. [ABSTRACT FROM AUTHOR]

Tunable magnetic anisotropy can greatly facilitate the integration of perovskite oxides in emerging magnetic memory devices. Tailoring the metastable structures is a powerful and effective method to tune the magnetic anisotropy of perovskite oxides possessing a large spin–lattice correlation. Herein, we stabilized SrRuO 3 (SRO) at two metastable phases by tailoring the interfacial octahedral coupling between SRO and LaCoO 3 (LCO). Two metastable phases, distorted-rhombohedral and tetragonal structures, were stabilized in turn as the SRO thickness increased. Through the stabilization of these metastable phases, we realized a strongly lattice-dependent magnetic anisotropy and magnetic structure symmetry of SRO, employing its large spin–orbit coupling. Detailed octahedral rotation analysis demonstrated that when the SRO film was thin, the rotation phase mismatch between SRO and LCO played a decisive role in stabilizing the distorted-rhombohedral phase, while the competition between the rotation phase mismatch and tilt propagation relaxation induced the tetragonal phase when the SRO film was thick. These results demonstrate the feasibility of tailoring various structural symmetries and exotic functionalities through interface coupling. [ABSTRACT FROM AUTHOR]

The development of portable and wearable electronic devices continues to increase the demand for miniature energy storage units. Here, we fabricate the flexible micro-supercapacitors (MSCs) through direct heating pattern on graphene oxide film. The shape designable MSCs are based on planar reduced graphene oxide/graphene oxide (rGO/GO) structure, with rGO as electrode and GO as separator. The GO area heated by heating pen is reduced to rGO, and the area with no heating is still GO. The interdigitated MSC made at 400 °C delivers high area capacitance of 94.8 mF cm−2 at current density of 0.25 mA cm−2 within poly(vinyl alcohol) (PVA)/H 2 SO 4 gel electrolyte. It provides high energy density of 10.7 mWh cm−2 at power density of 112.6 mW cm−2. In addition, it also has excellent mechanical stability, with basically unchanged area capacitance from 0° to 180° bending angles. The MSCs with shapes of spiral, concentric circle and eight-trigrams are also fabricated via this method. The results indicate that heating pattern on GO films to build flexible MSC is a promising and low-cost new method to fabricate energy storage equipment for future electronic devices. Image 1 [ABSTRACT FROM AUTHOR]

• The local lattice distortion appears at 90 K. • The local lattice distortion at Cu site in CuO 2 plane occurs with the inhomogeneous charge density distribution at 90 K. • Electron-lattice interaction play a key role in superconductivity of Sr 2 CuO 3 + δ. In order to study the relationship between local lattice distortion and superconductivity, we performed temperature dependent x-ray absorption fine structure (XAFS) on Sr 2 CuO 3 + δ powder sample (single phase with T c = 48 K). The temperature dependent Debye-Waller factor of Cu-O pair appears an anomalous upturn at 90 K and becomes drop around the superconducting transition temperature of ∼50 K. It means that local lattice distortion appears at 90 K. Furthermore, the analysis of temperature dependent X ray Absorption Near Edge Structure (XANES) shows that the R factor, which denotes the inhomogeneous charge density distribution, shows a sharp drop at 90 K. According to previous reports on other doped 214 cuprates, the above experimental results reveal that the local lattice distortion at Cu site in CuO 2 plane occurs with the inhomogeneous charge density distribution at 90 K. It indicates that the inhomogeneous charge density distribution may be caused by the local lattice distortion at Cu site before superconductive order formation, implying that electron-lattice interaction play a key role in superconductivity of Sr 2 CuO 3 + δ. [ABSTRACT FROM AUTHOR]