Electron transport mechanisms in polymer-carbon sphere composites
  A set of uniform carbon microspheres (CS) whose diameters have the order of $ 0.125 \mu m$ to $10 \mu m $ was prepared from aqueous sucrose solution by means of hydrothermal carbonization of sugar molecules. A pressed pellet was composed by mixing CSs with polyethylene oxide (PEO). Electrical characterization of the pellet was carried out showing Ohmic current-voltage characteristics and temperature-dependent conductivity in the range $ 80K < T < 300K.$ The conductivity reached a maximum value of $ 0.245 S/cm $ at $ 258K. $ The dependence of conductivity on temperature was theoretically analyzed to determine predominating mechanisms of electron transport. It was shown that thermally-induced electron tunneling between adjacent spheres may take on an important part in the electron transport through the CS/PEO composites. 
Cesar A. Nieves, Idalia Ramos, Nicholas J. Pinto, and Natalya A.   Zimbovskaya
cond-mat.mes-hall cond-mat.mtrl-sci