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Growth on nonpolar group III-nitride semiconductor surfaces has been suggested to be a remedy for avoiding detrimental polarization effects. However, the presence of intrinsic surface states within the fundamental bandgap at nonpolar surfaces leads to a Fermi-level pinning during growth, affecting the incorporation of dopants and impurities. This is further complicated by the use of ternary, e.g., Al x Ga 1 − x N layers in device structures. In order to quantify the Fermi-level pinning on ternary group III nitride nonpolar growth surface, the energy position of the group III-derived empty dangling bond surface state at nonpolar Al x Ga 1 − x N (10 1 ¯ 0) surfaces is determined as a function of the Al concentration using cross-sectional scanning tunneling microscopy and spectroscopy. The measurements show that the minimum energy of the empty dangling bond state shifts linearly toward midgap for increasing Al concentration with a slope of ≈ 5 meV/%. These experimental findings are supported by complementary density functional theory calculations. [ABSTRACT FROM AUTHOR]

Although lithium-sulfur (Li-S) batteries have an unparalleled specific capacity, the notorious shuttle effect, and slow reaction kinetics severely inhibit their development. Herein, a composite composed of ZnSe nanoparticles with a nitrogen-doped (N-doped) carbon shell uniformly dispersed in reduced graphene oxide (ZnSe/NC@rGO) is designed as a separator modifier for Li-S batteries. The underlying mechanism of the ZnSe/NC@rGO modified separator is confirmed by both systemic electrochemical characterization and density functional theory (DFT) calculations. Graphene as a highly conductive skeleton promotes electrical conductivity, while N-doping provides additional adsorption sites for the immobilization of lithium polysulfides (LiPSs). Moreover, the polar ZnSe has good chemical adsorption capabilities for LiPSs and could lower the decomposition energy barrier of Li 2 S, which effectively facilitates the catalytic conversion of polysulfides. In addition, the separator modifier is beneficial to the uniform deposition of lithium. Thus, the delicate catalyst can effectively suppress the shuttle effect and accelerate the redox reaction kinetics during the charging and discharging processes. When used as a separator modifier of Li-S batteries, ZnSe/NC@rGO delivers enhanced electrochemical performance, including a high capacity (1057 mAh g–1 at 0.2 C after 100 cycles) and excellent rate performance of 685 mAh g–1 at 3 C. The negligible capacity decay per cycle within 900 cycles at 1 C is as low as 0.043%. These findings not only provide a feasible method for boosting the electrochemical performance of Li-S batteries but also reveal that transition metal selenides have potential in energy storage as electrocatalysts. [ABSTRACT FROM AUTHOR]