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• Making use of the surface modification via ion beam irradiation, we bring the "smaller is softer" into being in a typical covalently-bonded, hard and brittle material−amorphous Si. • This "smaller is softer" size effect is manifested as the deformation mode transition from the quasi-brittle failure to the homogeneous plastic flow as well as the reduction in the stress for initiating plastic flow with decreasing dimensions. • The transition size is about one order of magnitude larger than that reported previously (in metals). "Smaller is softer" is a reverse size dependence of strength, defying the "smaller is stronger" tenet. It usually results from surface-mediated displacive or diffusive deformation and is mainly found in some ultra-small-scale (below tens of nanometers) metallic materials. Here, making use of the surface modification via ion beam irradiation, we bring the "smaller is softer" into being in a covalently-bonded, hard, and brittle material-amorphous Si (a-Si) at a much larger size regime (< ∼500 nm). It is manifested as the transition from the quasi-brittle failure to the homogeneous plastic deformation as well as the decreasing yield stress with sample volume reduction at the submicron-scale regime. An analytical model of hard core/superplastic shell has been proposed to explain the artificially-controllable size-dependent softening. This surface engineering pathway via ion irradiation is not only of particular interest to tailor the strength and deformation behaviors in small-sized a-Si or other covalently-bonded amorphous solids but also of practical relevance to the utility of a-Si in microelectronics and microelectromechanical systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Hard and brittle materials usually exhibit a much lower strength when loaded in tension than in compression. However, this common-sense behaviour may not be intrinsic to these materials, but arises from their higher flaw sensitivity to tensile loading. Here, we demonstrate a reversed and unusually pronounced tension–compression asymmetry (tensile strength exceeds compressive strength by a large margin) in submicrometre-sized samples of isotropic amorphous silicon. The abnormal asymmetry in the yield strength and anelasticity originates from the reduction in shear modulus and the densification of the shear-activated configuration under compression, altering the magnitude of the activation energy barrier for elementary shear events in amorphous Si. In situ coupled electrical tests corroborate that compressive strains indeed cause increased atomic coordination (metallization) by transforming some local structures from sp3-bonded semiconducting motifs to more metallic-like sites, lending credence to the mechanism we propose. This finding opens up an unexplored regime of intrinsic tension–compression asymmetry in materials.

The native oxide thin scale on magnesium (Mg) surface appears continuous and crack-free, but cannot protect the Mg matrix from further oxidation, especially at elevated temperatures. This thermal oxidation process is witnessed in its entirety using a home-made in-situ heating device inside an environmental electron transmission microscope. We proposed, and verified with real-time experimental evidence, that transforming the native oxide scale into a thin continuous surface layer with high vacancy formation energy (low vacancy concentration), for example MgCO 3 , can effectively protect Mg from high-temperature oxidation and raise the threshold oxidation temperature by at least two hundred degrees. [ABSTRACT FROM AUTHOR]

In situ bending tests of amorphous Si nanowires (a-Si NWs) found different elastic behavior depending on whether they were straight or curved to begin with. The axially straight NWs exhibit pure elastic deformation; however, the axially curved NWs exhibit obvious anelastic behavior when they are bent in the direction of original curvature. On the basis of STEM-EELS analysis, we propose that the underlying mechanism for this anelastic behavior is a bond-switching assisted redistribution of the nonuniform density (structure) in the curved NWs under the inhomogeneous stress field. This mechanism was further supported by the fact that the originally straight a-Si NWs also display similar anelasticity with the as-grown curved NWs after focused ion beam irradiation that can cause nonuniform structure distribution. As compared to what has been reported in other 1D materials, the anelasticity of a-Si NWs can be tuned by modifying their morphology, controlling the loading direction, or irradiating them via ion beam. Our findings suggest that a-Si NWs could be a promising material in the nanoscale damping systems, especially the semiconductor nanodevices.

Chestnut-like SnO2and SnO2/C nanocomposites with hierarchical structures are synthesized by hydrothermally oxidizing Sn nanoparticles in glucose solution. Structural characterizations using SEM and TEM reveal that the SnO2nanoparticles are composed of numerous, randomly arranged SnO2nanosheets with hollow cores. Owing to the short electron and ion diffusion distances and transformation strain accommodation mechanism of this structure the new SnO2/C nanocomposites exhibit enhanced lithium ion storage properties with a capacity of ~930mAhg−1and capacity retention of about 96% after 100 cycles at 0.1C. An in situTEM study of the electrochemically driven lithiation/delithiation of SnO2/C nanocomposites reveals that their enhanced cycling stability is mainly facilitated by the limited volume expansion and excellent mechanical robustness of the hollow chestnuts.

Pearl fiber is evenly mixed with ultra-fine pearl particles spinning solution of cellulose fibers, made of a blend of functional spinning of regenerated cellulose fiber. This new fiber material not only preserves the beauty of pearls skin function, but also cellulose fiber material with moisture breathable, soft and comfortable, and other features. In this paper, on the basis of understanding of pearls on the fiber properties, being blended with cotton, for pearl yarn fiber blends high technology design. According to the design of spinning yarn spinning process of high principle requires, selecting process, determining the opening and cleaning, carding, combing, drawing, roving, spinning the reasonable parameters of procedures. At the same time, the problems in the spinning process and technical measures to be described. Include optimizing the process configuration, temperature and humidity control, choose the appropriate spinning equipment. For the development of high functional pearl textiles, clothing to meet consumer comfort, functionality needs make a help.