▎ 摘　　要

Graphene nanosheets have been synthesized from commercial expandable graphite by heating in a microwave oven and dispersing in ethanol by ultrasonication. Scanning and transmission electron microscopy and electron energy-loss spectroscopy and atomic force microscope showed that the nanosheets were about 2 nm in thickness and 10 mu m in diameter. The field emission of the graphene sheets has been investigated. An emission current density of 1 mA/cm(2) has been achieved at an electric field of 3.7 V/mu m with a turn-on field of 1.7 V/mu m at 0.01 mA/cm(2). The annealing of the samples at 400 degrees C in vacuum greatly improved the field emission performance.