Browsing by Subject "Ionization potentials"

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    Accurate method for obtaining band gaps in conducting polymers using a DFT/hybrid approach
    (American Chemical Society, 1998) Salzner, U.; Pickup, P. G.; Poirier, R. A.; Lagowski, J. B.
    DFT calculations on a series of oligomers have been used to estimate band gaps, ionization potentials, electron affinities, and bandwidths for polyacetylene, polythiophene, polypyrrole, polythiazole, and a thiophene - thiazole copolymer. Using a slightly modified hybrid functional, we obtain band gaps within 0.1 eV of experimental solid-state values Calculated bond lengths and bond angles for the central ring of sexithiophene differ by less than 0.026 Å and 0.7° from those of the sexithiopnene crystal structure. IPs and EAs are overestimated by up to 0.77 eV compared to experimental bulk values. Extrapolated bandwidths agree reasonably well with bandwidths from band structure calculations.
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    Charge storage and release onto Au and Ag nanoparticles in aqueous medium as probed by optical spectroscopy
    (Cognizure, 2014) Tunc, I.; Sezen, H.; Guvenc, H. O.; Süzer, Şefik
    Gold and silver nanoparticles in aqueous solutions can store negative or positive charges when, respectively, NaBH4, KI are introduced into the same media. The charge storage can be followed by the spectral shifts in the corresponding surface plasmon resonance (SPR) bands of these nanoparticles. In a similar way, the kinetics of these two processes can be monitored by the same shifts. Accordingly, we show that although Au nanoparticles exhibit smaller spectral shifts upon both negative and positive charge storage, when compared with Ag nanoparticles, their kinetics are faster towards reduction (electron storage) and comparable towards oxidation. Hence, if not the spectral shifts, the kinetics of the electron storage process can be correlated to the larger electron affinity of Au nanoparticles, when compared with those of Ag. The similarity of the kinetics towards oxidation must also be related to the small difference between the ionization potentials of Au and Ag nanoparticles.