  We investigate the thermal conductivity of suspended graphene as a function
of the density of defects, ND, introduced in a controllable way. Graphene
layers are synthesized using chemical vapor deposition, transferred onto a
transmission electron microscopy grid, and suspended over ~7.5-micrometer size
square holes. Defects are induced by irradiation of graphene with the
low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak
intensity ratio. As the defect density changes from 2.0x10^10 cm-2 to 1.8x10^11
cm-2 the thermal conductivity decreases from ~(1.8+/-0.2)x10^3 W/mK to
~(4.0+/-0.2)x10^2 W/mK near room temperature. At higher defect densities, the
thermal conductivity reveals an intriguing saturation behavior at a relatively
high value of ~400 W/mK. The thermal conductivity dependence on defect density
is analyzed using the Boltzmann transport equation and molecular dynamics
simulations. The results are important for understanding phonon - point defect
scattering in two-dimensional systems and for practical applications of
graphene in thermal management.
