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Temperature is known to affect deformation mechanisms in metallic alloys. As temperature decreases, the stacking-fault energy in many face-centered cubic (fcc) alloys decreases, resulting in a change of deformation mode from dislocation slip to deformation twinning. Such an impact of temperature can be more complex in compositionally heterogeneous microstructures that exhibit, for example, local concentration fluctuation such as that in multi-principal element alloys. In this work, we compare the dislocation behavior and mechanical properties of a fcc Cr20Mn10Fe30Co30Ni10 high-entropy alloy at ambient and liquid-nitrogen temperatures. We find that a network of stacking faults is formed by uniformly extended dislocations at ambient temperatures with low stacking-fault energy, whereas at lower temperatures, uneven dissociation of dislocations becomes significant, which results in severe dislocation pile-ups together with their pronounced entanglement. Our findings indicate that as the stacking-fault energy decreases with decreasing temperature, the heterogeneity of the distribution of elements becomes more dominant in tuning the local variation of lattice resistance. As a result, the change in dislocation behavior at low temperatures strongly affects microstructural evolution and consequently leads to significantly more pronounced work hardening. [ABSTRACT FROM AUTHOR]

A CrCoNi medium entropy alloy thin film is fabricated using magnetron sputtering. It exhibits a unique hierarchical nanostructure, featuring (1) a high density of planar defects (mostly stacking faults plus a small number of twin boundaries), (2) a dual-phase configuration (a mix of face-centred-cubic and hexagonal-close-packed), and (3) vertically aligned, textured nanocolumns, each with a width of ∼100 nm. The hierarchical nanostructure in this study is original, especially for its dual phase combination, since the bulk CrCoNi medium entropy alloy generally presents a single phase face-centred-cubic structure. The CrCoNi film shows a hardness quadruple that of its face-centred-cubic structured counterpart. The formation and its role of the hierarchical nanostructure in producing such mechanical strength are discussed. [ABSTRACT FROM AUTHOR]

By fabricating a submicron-scale grating structure on a bendable polymer substrate, we demonstrate a flexible distributed-feedback colloidal quantum dot laser. This laser uses cadmium selenide/zinc sulfide core-shell nanostructures, operating in transverse electric polarized multiple-modes, and has a typical threshold pump fluence of ∼4 mJ/cm2. [ABSTRACT FROM AUTHOR]

Hexagonal ZnO nanodisks were grown on silicon-on-insulator substrates by vapor-transport method without catalysts. The resulting nanodisks possess ultrathin thickness (10–20 nm) and most of them present vertical orientation on the substrate surface. Under optical excitation, these ultrathin nanodisks exhibit ultraviolet lasing emission with the excitation threshold of 205 μJ/cm2 and emission lifetime of 2 ps at room temperature. The detailed lasing analysis indicates that whispering-gallery-mode lasing may occur in the ZnO nanodisks. [ABSTRACT FROM AUTHOR]

PbS quantum dots/multiwalled carbon nanotube (PbS/MWCNT) heterostructures were fabricated via a simple wet-chemical method. The structural and optical properties of as-prepared samples were characterized by transmission electron microscopy, x-ray diffraction, micro-Raman, and photoluminescence spectroscopies. It was found that the size, shape, and coverage density of the PbS quantum dots on the MWCNT can be controlled through varying synthesis conditions. Photoluminescence spectrum revealed that the emission of the PbS quantum dots was partially quenched when they were coupled to the MWCNT. This suggests that the photoinduced charge transfer may occur between the PbS and the MWCNT. [ABSTRACT FROM AUTHOR]

Organic nanowires have been synthesized by hydrothermal method. The functional groups in chemical structure of the organic nanowire have been characterized by Fourier-transform infrared spectrum. Optical properties of organic nanowires have been demonstrated by linear absorption, photoluminescence spectroscopy, and time-resolved photoluminescence spectroscopy. Two emission peaks at 3.91 and 3.3 eV have been revealed by fluorescence spectrum at room temperature. For the emission peak at 3.3 eV, a blueshift occurred when the temperature rises. Two time components have been observed in fluorescence dynamic process of the nanowire by time-resolved decay curve. [ABSTRACT FROM AUTHOR]