Polycrystalline graphene ribbons as chemiresistors.

A IO N Graphene is a two-dimensional semimetal with zero band gap that exhibits excellent electrical, mechanical and thermal properties.[1,2] Transport through delocalized pi bonds allows charge carriers in graphene to achieve high mobility[3,4] for both electrons and holes, over ∼105 cm2/V·s for freely suspended graphene and >104 cm2/V·s for graphene on SiO2. Recent studies have suggested that graphene could also be an interesting chemiresistor material.[6–9] In addition, when functionalized with single-stranded DNA, graphene provides a route towards “sequence-dependent” chemical sensing.[10] Single molecule detection has also been reported[11] using Hall measurements with mechanically exfoliated monolayer graphene. However, prior to this study, the sensitivity of simpler sensing configurations such as two-terminal graphene chemiresistors to many analytes has been below that of chemiresistors based on carbon nanotubes (CNTs).[7–9] The objective of this work was to understand what limits the sensitivity of simple, two-terminal graphene chemiresistors, and to study this in the context of inexpensive devices easily manufactured by chemical vapor deposition (CVD). We focused on the idea that while graphene shares several similarities with CNTs, graphene is a two-dimensional conductor while CNTs are essentially one-dimensional conductors. Could this difference in dimensionality be responsible for the difference in sensing behavior? Further, at this point, the physical mechanisms of interaction between adsorbed species and graphene are not as well understood as in CNT sensors. For instance, we have recently shown that point defects in CNTs are key to the highly sensitive response towards target analytes.[12–14] While much of the research within the graphene community is geared towards