Molecular dynamics study of mosaic structure in the Ni-based single-crystal superalloy

The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of （011）{100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.

Ablation characteristics of mosaic structure ZrC-SiC coatings on low-density, porous C/C composites

Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.

Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.

Depth-dependent mosaic tilt and twist in GaN epilayer:An approximate evaluation

An approach based on depth-sensitive skew-angle x-ray diffraction （SAXRD） is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that （103） plane and （101） plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive （103）/（101） ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.

High-temperature annealing of(201)β-Ga_(2)O_(3) substrates for reducing structural defects after diamond sawing

A commercial epi-ready(201)β-Ga_(2)O_(3) wafer was investigated upon diamond sawing into pieces measuring 2.5×3 mm^(2).The defect structure and crystallinity in the cut samples has been studied by X-ray diffraction and a selective wet etching technique.The density of defects was estimated from the average value of etch pits calculated,including near-edge regions,and was obtained close to 109 cm^(-2).Blocks with lattice orientation deviated by angles of 1-3 arcmin,as well as non-stoichiometric fractions with a relative strain about(1.0-1.5)×10^(-4)in the[201]direction,were found.Crystal perfection was shown to decrease significantly towards the cutting lines of the samples.To reduce the number of structural defects and increase the crystal perfection of the samples via increasing defect motion mobility,the thermal annealing was employed.Polygonization and formation of a mosaic structure coupled with dislocation wall appearance upon 3 h of annealing at 1100℃ was observed.The fractions characterized by non-stoichiometry phases and the block deviation disappeared.The annealing for 11 h improved the homogeneity and perfection in the crystals.The average density of the etch pits dropped down significantly to 8×10^(6) cm^(-2).

RuCo alloy nanoparticles embedded within N-doped porous two-dimensional carbon nanosheets:a high-performance hydrogen evolution reaction catalyst

Developing cost-effective electrocatalysts with high activity and stability especially at high current density is of great significance for the large-scale commercial application of electrochemical water splitting to hydrogen production but still remains challenging.Herein,we report an effective confinement pyrolysis strategy to fabricate embedded ruthenium-cobalt nanoclusters supported on N-doped porous two-dimensional carbon nanosheets(RuCo@CN).Markedly,the embedded structure can effectively prevent the migration,agglomeration,and leaching of nanoparticles,thus endowing the RuCo@CN catalyst with high stability.To be exact,high stability with up to 650 h can be achieved at high current density(-500 and-1000 mA·cm^(-2)).Besides,the RuCo@CN catalysts also exhibit highly reactive with low overpotentials of only 11mV at-10 mA·cm^(-2).Density functional theory calculations reveal that the introduction of cobalt reduces the decomposition barrier of H_(2)O for RuCo@CN alloy,thus promoting hydrogen evolution reaction.

Sesquiterpenes from the leaves of Nicotiana tabacum and their anti-tobacco mosaic virus activity

In searching for more bioactive compounds, phytochemical investigations on the acetone extract of the leaves ofNicotiana tabacurn resulted in the isolation of two new sesquiterpenes, nicosesquiterpene A and B （1 and 2）, along with four known sesquiterpene derivatives （3-6）. Structural elucidation of I and 2 was performed by spectral methods, such as HRMS, IR, UV, 1D and 2D NMR spectroscopy. Compounds 1 and 2 are the first naturally occurring pterosin-type sesquiterpene bearing an isopropyl moiety. Compounds 1-6 were also evaluated for their anti-tobacco mosaic virus （anti-TMV） activity. The results showed that compounds 1 and 2 exhibited high anti-TMV activity with inhibition rates of 36.7% and 45.6%, respectively, which is higher than that of positive control. The other compounds also showed potential activity with inhibition rates in the range of 22.7%-29.2%.