  Graphene is an intriguing material with properties that are distinct from
those of other graphitic systems. The first samples of pristine graphene were
obtained by peeling off and epitaxial growth. Recently, the chemical reduction
of graphite oxide was used to produce covalently functionalized single-layer
graphene oxide. However, chemical approaches for the large-scale production of
highly conducting graphene sheets remain elusive. Here, we report that the
exfoliation-reintercalation-expansion of graphite can produce high-quality
single-layer graphene sheets stably suspended in organic solvents. The graphene
sheets exhibit high electrical conductance at room and cryogenic temperatures.
Large amounts of graphene sheets in organic solvents are made into large
transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer
manner. The chemically derived high quality graphene sheets could lead to
future scalable graphene devices.
