Wang, Yu

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  • Publication
    Early Stages on the Graphitization of Electrostatically Generated PAN Nanofibers
    (2002-08-26) Wang, Yu; Santiago-Aviles, Jorge J
    Carbon nanofibers were produced from polyacrylonitrile/N, N-Dimethyl Formamide (PAN/DMF) precursor solution using electrospinning and vacuum pyrolysis at temperatures from 773K to 1273K for 0.5,2, and 5 hours, respectively. Their conductance was measured. It was found that the conductivity increases sharply with the pyrolysis temperature, and increases considerably with pyrolysis temperatures of 873, 973 and 1073K, but varies, less obviously, with pyrolysis time at the higher pyrolysis temperatures of 1173 and 1273K.
  • Publication
    Electronic Transport Properties of Incipient Graphitic Domains Formation in PAN Derived Carbon Nanofibers
    (2004-03-01) Wang, Yu; Ramos, Idalia; Santiago-Aviles, Jorge J; Furlan, Rogerio
    The carbon nanofibers used in this work were derived from a polyacrylonitrile (PAN)/N, N-dimethyl formamide (DMF) precursor solution using electrospinning and vacuum pyrolysis techniques. Their conductivity, σ, was measured at temperatures between 1.9 and 300 K and transverse magnetic field between -9 and 9 T. Zero magnetic field conductivity σ(0,T) was found to increase monotonically with the temperature with a convex σ(0,T) versus T curve. Conductivity increases with the external transverse magnetic field, revealing a negative magnetoresistance at temperatures between 1.9 and 10 K, with a maximum magnetoresistance of - 75 % at 1.9 K and 9 T. The magnetic field dependence of the conductivity and the temperature dependence of the zero-field conductivity are best described using the two-dimensional weak localization effect.
  • Publication
    Large Negative Magnetoresistance and Strong Localization in Highly Disordered Electrospun Pregraphitic Carbon Nanofiber
    (2006-09-21) Wang, Yu; Santiago-Avilés, Jorge J
    A highly disordered pregraphitic carbon nanofiber with the product of its quasi-Fermi wave vector and mean free path close to 1 was fabricated using electrospinning technique. Strong localization made the conductivity vary with temperature as ln σ ∝ T−1/2 from 300 to 5 K, suggesting variable range hopping as the conductivity mechanism, and resulted in a large negative magnetoresistance from 300 K down to 1.9 K that can still be quantitatively described using weak localization and electron interaction models.