Correlation of the Microstructure and Electrical Transport Properties of Glassy Carbon Nanofibers

Open Access
Author:
Lentz, Christina Marie
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Md Amanul Haque, Thesis Advisor
Keywords:
  • nanoporous carbon
  • non-graphitizing carbon
  • glassy carbon
  • nanofibers
  • electrical transport
Abstract:
The objective of this research is to study the electrical property of disordered carbon nanowires as functions of (i) microstructure (controlled by varying the heat treatment temperature) and (ii) ambient temperature. The material studied is a disordered, nanoporous form of carbon, which is semiconducting in nature and is obtained from the pyrolysis of a polymeric precursor (polyfurfuryl alcohol). Unlike the other allotropes of carbon such as diamond, graphite, and fullerenes, disordered carbons lack crystalline order and therefore can exhibit a range of electronic properties, dependent on the degree of disorder, local microstructure, and temperature. The motivation for this research comes from the potential for engineering the electrical properties to desired specifications, which becomes possible only if we understand the structure-temperature-property correlations. We present experimental results connecting the changes in electrical transport of single disordered carbon nanofibers (diameter 150 – 250 nm), where the degree of disorder was controlled by varying the pyrolysis temperature from 600ºC to 2000ºC. Transmission electron and Raman microscopy, as well as dark DC electrical conductivity characterizations indicate strong microstructure dependence, which in turn can be controlled to a great extent simply by controlling the pyrolysis temperature. To study the role of ambient temperature, dark DC conductivity measurements were performed for nanowire surface temperature ranging from 90K to 450K. The charge transport behavior in the nanowires is observed to follow an activation-energy based conduction at high temperatures, transitioning to a hopping based mechanism below room temperature.