15 research outputs found
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
Experimental and theoretical studies on the electronic properties of praseodymium chloride filled single walled carbon nanotubes
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
Experimental and Computational Insight into the Chemical Bonding and Electronic Structure of Clathrate Compounds in the Sn In As I System
The Chemistry of Imperfections in N Graphene
Many propositions have been already put forth for the practical use of N-graphene in various devices, such as batteries, sensors, ultracapacitors, and next generation electronics. However, the chemistry of nitrogen imperfections in this material still remains an enigma. Here we demonstrate a method to handle N-impurities in graphene, which allows efficient conversion of pyridinic N to graphitic N and therefore precise tuning of the charge carrier concentration. By applying photoemission spectroscopy and density functional calculations, we show that the electron doping effect of graphitic N is strongly suppressed by pyridinic N. As the latter is converted into the graphitic configuration, the efficiency of doping rises up to half of electron charge per N atom
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