Impact of ordering on the reactivity of mixed crystals of topological insulators with anion substitution Bi2SeTe2 and Sb2SeTe2

Three dimensional topological insulators TIs are exotic materials with unique properties. Tetradymite type binary chalcogenides of bismuth and antimony, as well as their mixed crystals, belong to prototypical TIs. Potential device applications of these materials require in depth knowledge of their stability in the ambient atmosphere and other media maintained during their processing. Here we investigated the reactivity of mixed crystals with anion substitution, Bi2 Se1 xTex 3 and Sb2 Se1 xTex 3, towards molecular oxygen using both in situ and ex situ X ray photoelectron spectroscopy. The results indicate that, in contrast to cation substitution, partial substitution of tellurium by selenium atoms leads to anomalously high surface reactivity, which even exceeds that of the most reactive binary constituent. We attribute this effect to anion ordering that essentially modifies the bond geometry, especially the respective bond angles as modeled by DF

Features of structural-phase state of Pd-Ag nanoparticles supported on silica gel

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Acceptor doping of single-walled carbon nanotubes by encapsulation of zinc halogenides

To modify the electronic properties of single-walled carbon nanotubes (SWCNTs), ZnX2@SWCNT (X  =  Cl, Br, I) nanostructures were prepared by capillary filling of 1.4–1.6 nm single-walled carbon nanotubes (SWCNT) with zinc halogenide melts. The loading factor is estimated as 30% for ZnCl2 and approximately 60% for ZnBr2 and ZnI2. Well-ordered 1D crystals were observed by TEM only for ZnI2@SWCNT. We propose two possible atomic structures of the 1D crystals, (Zn4I7)n and less stable (Zn4I9)n. According to the optical absorption and photoemission data, there is a charge transfer from the nanotube to the filler for all ZnX2@SWCNT nanostructures. The results of the DFT PW-GGA modeling indicate that the acceptor properties correspond to (Zn4I9)n only

Single walled carbon nanotubes filled with nickel halogenides Atomic structure and doping effect

NiX2 SWCNT X Cl, Br nanostructures were prepared by capillary filling of single walled carbon nanotube channels with nickel halogenide melts with slow cooling down to room temperature for better crystallization. TheHRTEMdata indicated formation of well ordered 1D NiBr2 crystals, with the experimental atomic structure representing a fragment of the bulk structure. The lattice constant coincides with the corresponding distance in bulk lattice. The 1D crystal structure was modeled using DFT within the PW GGA approach. According to the Raman, X ray photoelectron, X ray and optical absorption spectroscopic data and the DFT results obtained within the rigid band model, nickel halogenides display acceptor behavior with the corresponding charge transfer from the single walled carbon nanotube walls to the NiX2 nanocrystal

Negligible Surface Reactivity of Topological Insulators Bi2Se3 and Bi2Te3 towards Oxygen and Water

The long term stability of functional properties of topological insulator materials is crucial for the operation of future topological insulator based devices. Water and oxygen have been reported to be the main sources of surface deterioration by chemical reactions. In the present work, we investigate the behavior of the topological surface states on Bi2X3 X Se, Te by valence band and core level photoemission in a wide range of water and oxygen pressures both in situ from 10 8 to 0.1 mbar and ex situ at 1 bar . We find that no chemical reactions occur in pure oxygen and in pure water. Water itself does not chemically react with both Bi2Se3 and Bi2Te3 surfaces and only leads to slight p doping. In dry air, the oxidation of the Bi2Te3 surface occurs on the time scale of months, in the case of Bi2Se3 surface of cleaved crystal, not even on the time scale of years. The presence of water, however, promotes the oxidation in air, and we suggest the underlying reactions supported by density functional calculations. All in all, the surface reactivity is found to be negligible, which allows expanding the acceptable ranges of conditions for preparation, handling and operation of future Bi2X3 based device

Reactivity of Carbon in Lithium Oxygen Battery Positive Electrodes

Unfortunately the practical applications of Li-O₂ batteries are impeded by poor rechargeability. Here we for the first time show that superoxide radicals generated at the cathode during discharge react with carbon that contain activated double bonds or aromatics to form epoxy groups and carbonates, which limits the rechargeability of Li-O2 cells. Carbon materials with a low amount of functional groups and defects demonstrate better stability thus keeping the carbon will-o’-the-wisp lit for lithium-air batteries