  We have synthesized single-layer graphene on Cu foils using chemical vapor
deposition method and transferred the graphene to the top of a Si/SiO2
substrate with a pair of prefabricated Ti/Au electrodes. A resistive
graphene-based gas sensor prepared in this way revealed n-type oxygen response
at room temperature and we have successfully fitted the data obtained with
varying oxygen levels using a two-site Langmuir model. P-type oxygen response
of our sensor was observed after the temperature was raised to 100 oC, with a
reversible transition to n-type behaviour when the temperature was lowered back
to room temperature. Such inversion of the gas response type with temperature
was interpreted as a result of interplay between the adsorbate-induced charge
transfer and charge carrier scattering. The transduction function was derived,
which relates the electrical response to surface coverage through both the
induced mobility and charge density changes.

Materials Science