▎ 摘　　要

Extremely high gas sensing properties of p-type few layer graphene flakes exfoliated from highly oriented pyrolytic graphite have been demonstrated. The current response to ammonia adsorption is strongly dependent on film thickness and is higher than that for graphene by 1-8 orders of magnitude. A maximal response was found for sample thickness similar to 2 nm. The effect is attributed to the formation of multiple p-n-p junctions at the grain boundaries in the polycrystalline graphene flakes exposed to ammonia-containing ambient.