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Title: Electron paramagnetic resonance study of paramagnetic centers in carbon-fumed silica adsorbent

Fumed silica A-300 was carbonized by means of pyrolysis of CH{sub 2}Cl{sub 2}. The obtained initial SiO{sub 2}:C nanopowders of black color, with an average diameter of 14–16 nm and carbon (C) concentration 7 wt. %, subjected to the oxidation and passivation treatment were studied by electron paramagnetic resonance (EPR) in the temperature range 4–400 K. Two EPR signals of Lorentzian lineshape with nearly equal g-factors and different linewidth were observed in the initial, oxidized, and passivated SiO{sub 2}:C nanopowders. The two-component EPR spectrum was explained by the presence of C in two electronic states. The intensive narrow EPR signal, which has a temperature-dependent intensity, linewidth, and resonance field position, was attributed to the carbon-related defect with non-localized electron hopping between neighboring C-dangling bonds. The striking effect is that the temperature dependence of the EPR linewidth demonstrates the motional narrowing of the EPR signal at very low temperatures from 4 K to 20 K, which is not typically for nonmetallic materials and was explained by the quantum character of C layer conductivity in the SiO{sub 2}:C. The observed peaks in the temperature dependence of the conduction electron EPR signal integral intensity in the high-temperature range 200–440 K was explained by the presence of the C nanodotsmore » at the surface of SiO{sub 2} nanoparticles and the ejection of electrons from the confinement energy levels of C quantum dot when the temperature becomes comparable to the confinement energy.« less
Authors:
 [1] ;  [2] ; ; ; ;  [3] ;  [4]
  1. Institute of Physics AS CR, Prague 182 21 (Czech Republic)
  2. (Ukraine)
  3. V.E. Lashkaryov Institute of Semiconductor Physics, NASU, Kyiv 03028 (Ukraine)
  4. A.A. Chuiko Institute of Surface Chemistry, NASU, Kyiv 03164 (Ukraine)
Publication Date:
OSTI Identifier:
22273683
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 13; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ADSORBENTS; CARBON; COLOR; COMPARATIVE EVALUATIONS; CONCENTRATION RATIO; ELECTRIC CONDUCTIVITY; ELECTRON SPIN RESONANCE; ELECTRONS; ENERGY LEVELS; LANDE FACTOR; METHYLENE CHLORIDE; OXIDATION; PARAMAGNETISM; POWDERS; PYROLYSIS; QUANTUM DOTS; SILICA; TEMPERATURE DEPENDENCE