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The present study discovers the significant enhancement of critical current density by borohydride pinning in H-doped MgB2 bulks. Second-phase borohydrides are formed by synthesizing MgB2 bulks ex situ in an H2 atmosphere and in situ with H-trapped boron based on the concept of gas doping. Second phase Mg(BH4)2 appears in the samples ex situ sintered in an H2 atmosphere, leading to an enhancement of critical current density at magnetic fields over 3 T. Moreover, the in situ synthesized samples from H-trapped boron also exhibit a significantly enhanced critical current density of 1.8 × 104 A cm−2 at 20 K and 3 T, due to Mg(BH4)2 pinning centers that are embedded in the MgB2 grains. In contrast, the critical current density is only 9.6 × 103 A cm−2 at 20 K and 3 T in an un-doped MgB2 sample. [ABSTRACT FROM AUTHOR]

Developing highly active and durable electrocatalysts for acidic oxygen evolution reaction remains a great challenge due to the sluggish kinetics of the four-electron transfer reaction and severe catalyst dissolution. Here we report an electrochemical lithium intercalation method to improve both the activity and stability of RuO2 for acidic oxygen evolution reaction. The lithium intercalates into the lattice interstices of RuO2, donates electrons and distorts the local structure. Therefore, the Ru valence state is lowered with formation of stable Li-O-Ru local structure, and the Ru–O covalency is weakened, which suppresses the dissolution of Ru, resulting in greatly enhanced durability. Meanwhile, the inherent lattice strain results in the surface structural distortion of LixRuO2 and activates the dangling O atom near the Ru active site as a proton acceptor, which stabilizes the OOH* and dramatically enhances the activity. This work provides an effective strategy to develop highly efficient catalyst towards water splitting. While water splitting in acid offers higher operational performances than in alkaline conditions, there are few high-activity, acid-stable oxygen evolution electrocatalysts. Here, authors examine electrochemical Li intercalation to improve the activity and stability of RuO2 for acidic water oxidation. [ABSTRACT FROM AUTHOR]

P-type doping of ultrawide-bandgap semiconductors, which are the key materials for fabrication of next-generation high-performance optoelectronic and electronic devices, is extremely difficult to achieve. The lack of p-type Ga2O3 has become a great obstacle to fabricate a full Ga2O3-based p–n homojunction for high-performance device applications. We demonstrate that N-doped β-Ga2O3 achieved by a phase transition from GaN to β-Ga2O3 possesses low formation energy and transition level ε(0/−), thereby with good N dopant solubility and low activation energy of N acceptors (0.355 eV). The delocalization effect, enhancement of valence band dispersion, and thus the decrease of the hole effective mass are predicted for N-doped β-Ga2O3 due to the hybridization of O 2p with N 2p and Ga 4s orbitals. Activated hole concentrations of 6.1 × 1015 and 2.1 × 1016 cm−3 at a valence band maximum are predicted for β-Ga2O3:NO(III) obtained by the nonspin and spin-polarized calculations, respectively. The hole mobility is 1.3 cm2 V−1 s−1 for undoped β-Ga2O3 and remarkably increases to 8.8 and 5.5 cm2 V−1 s−1 for β-Ga2O3:NO(III) obtained by the non-spin and spin-polarized calculations, respectively. The origins for the unusual increase of hole mobility are attributed to the decrease of the hole effective mass, and reduction in acoustic deformation potential scattering and optical phonon scattering due to the weakening of electron–phonon coupling by N-induced phonon stiffening for β-Ga2O3:NO(III). The p-type conductivity of N-doped β-Ga2O3 is demonstrated theoretically and also experimentally with a Hall hole concentration of 3.19 × 1015 cm−3 and a Hall hole mobility of 23.1 cm2 V−1 s−1 for N-doped β-Ga2O3 films, and the p-type conductivity mechanisms are clarified. These studies will open a new horizon for other p-type wide bandgap oxide semiconductors. [ABSTRACT FROM AUTHOR]

In this paper, we extended the microbridge testing method to characterize the mechanical properties of symmetrical trilayer thin films. Theoretically, we analyzed the deformation of a trilayer microbridge sample with a deformable boundary condition and derived load-deflection formulas in closed-form. The slope of a load-deflection curve under small deformation gives the relationship between the bending stiffness and the residual force of a trilayer microbridge. Taking this relationship, we were able to assess simultaneously the Young's modulus of two kinds of materials composing the symmetrical trilayer film and the thickness-averaged residual stress of the film. Experimentally, we fabricated symmetrical trilayer microbridge samples of Si[O.sub.2]/[Si.sub.3][N.sub.4]/Si[O.sub.2] on 4-inch p-type (100) silicon wafers and conducted the microbridge tests with a load and displacement sensing nanoindenter system equipped with a microwedge indenter. The experimental results verified the proposed microbridge testing method. The thickness-averaged residual stress of the 1.1-[micro]m trilayer thin films was determined to be 8.8 MPa, while the Young's modulus of the 0.3-[micro]m silicon oxide layers and the Young's modulus of the 0.5-[micro]m silicon nitride layer were evaluated to be 31 GPa and 294 GPa, respectively. [1205] Index Terms--Mechanical properties, microelectromechanical systems (MEMS), microbridge test, nanoindentation.