ABSTRACT
Electrical characteristics of multi-walled carbon nanotubes (MWNTs) grown by chemical vapor deposition have been investigated as a function of the bias voltage, nanotubes length and temperature, in 2 and 4 terminal configurations. Nanotubes were deposited over metal electrodes using ac dielectrophoresis method. For better contacts between the nanotubes and electrodes, Ni and Pd films were deposited by an electroless deposition technique. Differential conductance was found to rise considerably with bias, and this effect was more pronounced for Ni. Using 2 and 4 terminal configurations, electrical resistance measurements for individual MWNTs were performed, and the results were interpreted using the model of nanotube as a resistive transmission line, where current at low bias flows mainly through the two outermost shells.
ABSTRACT
Bitumen is a complex mixture of hydrocarbons for which microstructural understanding is incomplete. In an effort to detail this microstructure, a asphalt cement sample (CAP 30/45) was analysed by thermal phase detection atomic force microscopy. Phase contrast and topography images showed that sample morphology is highly dependent on temperature. The 'bee structure' changed considerably at temperatures between 50 degrees C and 56 degrees C. A decrease of the oscillation amplitude was observed upon heating and the 'bees' completely disappeared at temperatures above 57 degrees C. When the temperature was decreased after melting at 170 degrees C, the 'bees' began to nucleate gradually at temperatures of 57 degrees C and its evolution with time was followed. Changes in morphology were compared to thermal analysis results and a model for the 'bee' structure was proposed.