A methodology for the determination of the subsurface line direction of dislocations using scanning tunneling microscopy (STM) images is presented. The depth of the dislocation core is derived from an analysis of the displacement field measured by STM. The methodology is illustrated for dislocations at GaN(10 10) cleavage surfaces. It is found that the dislocation line bends toward the surface, changing from predominantly edge-type to more screw-type character, when approaching the intersection point. Simultaneously, the total displacement detectable at the surface increases due to a preferred relaxation towards the surface. V C 2015 AIP Publishing LLC.
Li and Na metals with high energy density are promising in application in rechargeable batteries but suffer from degradation in the ambient atmosphere. The phenomenon that in terms of kinetics, Li is stable but Na is unstable in dry air has not been fully understood. Here, we use in situ environmental transmission electron microscopy combined with theoretical simulations and reveal that the different stabilities in dry air for Li and Na are reflected by the formation of compact Li 2 O layers on Li metal, while porous and rough Na 2 O/Na 2 O 2 layers on Na metal are a consequence of the different thermodynamic and kinetics in O 2 . It is shown that a preformed carbonate layer can change the kinetics of Na toward an anticorrosive behavior. Our study provides a deeper understanding of the often-overlooked chemical reactions with environmental gases and enhances the electrochemical performance of Li and Na by controlling interfacial stability.
We present a grating model of two-dimensional (2D) rigorous coupled wave analysis (RCWA) to study top diffraction gratings on light-emitting diodes (LEDs). We compare the integrated-transmission of the non-grating, rectangular-grating, and triangular-grating cases for the same grating period of 6 µm, and show that the triangular grating has the best performance. For the triangular grating with 6-µm period, the LED achieves the highest light transmission at 6-µm grating bottom width and 2.9-µm grating depth. Compared with the non-grating case, the optimized light transmission improvement is about 74.6%. The simulation agrees with the experimental data of the thin polymer grating encapsulated flip-chip (FC) GaN-based LEDs for the light extraction improvement.
Solid-state batteries offering both high energy density and safety have aroused widespread interest as promising power sources for electric vehicles. However, the interfacial mechanical stability of inorganic electrolyte is inferior to that of organic electrolytes and the high stack pressure (several to hundreds of megapascals) is required to maintain the intimate contact with electrodes. Here we report a class of inorganic glass solid electrolytes with polymer-like viscoelasticity, which possess both advantages of inorganic and polymer electrolytes and can enable pressure-less Li- and Na-based solid-state batteries (< 0.1 MPa). These electrolytes are synthesized by simply replacing chlorine of tetrachloroaluminates with oxygen, demonstrating high ionic conductivity of ~1 mS cm-1 at 30℃ for both Li+ and Na+. They can also exhibit superior chemo-mechanical compatibility with 4.3 V cathodes without additional stack pressure. Moreover, the inorganic glass solid electrolytes are feasible for scale-up, not only enabling to be made into thin films through a rolling process owing to its polymer-like flexibility but also facilitating the complete infiltration of the electrode materials like a liquid battery due to the low melting temperature below 160℃. We believe that these viscoelastic inorganic solid electrolytes will inspire us to design new solid electrolytes and accelerate practical application of pressure-less solid-state batteries.
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