▎ 摘　　要

Graphene and ultrathin graphite flakes prepared by exfoliation were characterized by microfocus synchrotron infrared mapping ellipsometry. The dielectric function of graphene in a dry-air atmosphere is determined and compared to that of ultrathin graphite, bulk graphite, and gold. The imaginary part of graphene is revealed to be about an order of magnitude higher than that of graphite and comparable to that of gold. Comparing the conductivity to an optical model considering intraband transitions, we discuss the critical effects of environmental exposure, relevant for real-world applications. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624826]