▎ 摘　　要

A physical route is proposed to obtain highly crystalline graphene sheets with minimal oxygen content similar to the precursor graphite. The functional graphene sheets obtained from graphite oxide by low temperature thermal exfoliation are annealed at high temperature (1900 degrees C) in a vacuum (10(-6) torr). The D band intensity in Raman spectroscopy is reduced significantly, while the G band intensity is recovered, similar to the level of precursor graphite. No appreciable oxygen content is observed from X-ray photoelectron spectroscopy and an electrical conductivity of similar to 56 500 S m(-1) is obtained, comparable to 100 900 S m(-1) of the precursor graphite.