Phonon lifetimes and scattering processes in carbon fiber systems

Carbon fibers show ultrahigh strength to weight ratio and are sought as a replacement for steel
in numerous industries. The basic morphology of carbon fiber is a collection of graphitic
regions, with a higher degree of graphitization correlated with a higher stiffness fiber. Currently
carbon fiber applications are limited by the inability to obtain high strength and high stiffness in
the same fiber, which is presumably due to the effect of defects in the carbon fiber matrix. Here
we present an overview of the microstructure and spectral features of carbon fiber obtained
from Raman and x-ray scattering spanning a broad range of carbon fiber mechanical properties.
The combined results show a direct correlation between estimated interdefect distance and
ultimate fiber strength and a reduction in overall phonon lifetime for defect-mediated modes
for high strength fibers. Efforts to understand phonon transport across defect boundaries in
large scale models of defected graphite analogues are underway and will be briefly discussed.