Experimental study of electron transport in mesoscopic carbon based nanostructures

Abstract

In this thesis we have studied experimentally electronic transport in mesoscopic hybrid polypyrrole-gold devices and single multiwalled carbon nanotube devices. A novel fabrication technique for mesoscopic conducting hybrid polymer-gold films has been developed. The hybrid polymer-gold films have been fabricated by electrochemical deposition of polypyrrole on a gold nanoisland layer. Temperature dependence of conductance show that the dominant transport mechanism in the polypyrrole-gold films is variable range hopping in the temperature range from 20 K to 300 K. At very low temperature strong nonlinearities in the field dependent conductance are observed. The field dependence follows a phenomenological model that is different from conventional field dependent transport theories probably due to the presence of gold islands embedded in polymer. Further, we have explored size and temperature dependences of basic electrical properties of intermediate sized multiwalled carbon nanotubes in a diameter range, 3 to 10 nm, which has not been systematically explored previously. In particular, we have observed in gate controlled conductance measurements, transport gaps which become more pronounced with decreasing temperature. Many transport features are found to scale with channel length and diameter of the nanotube devices. These include onstate and offstate resistances, on/off ratios, as well as periodicities of Coulombic oscillations. The kind of scaling behaviours observed are a manifestation of both diameter dependent intrinsic bandgaps and localization effects. However, some deviations from the scaling and complex transport gaps have also been observed which may be due to chiralities and possible interwall effects.