Asymmetric electron hole distribution in single-layer graphene for use in hydrogen gas detection

We demonstrate a highly sensitive hydrogen gas sensor using single-layer graphene exfoliated from highly oriented pyrolytic graphite, which one side of it was covered by palladium. In this asymmetric graphene sensor, the electrons generated from reaction between palladium and hydrogen accumulate at the interface between palladium and graphene, and these accumulated electrons changed the carrier density of graphene beneath the palladium film from hole-dominated to neutralized graphene. This half-neutralized and half hole-dominant graphene showed asymmetrical I-V characteristics in a hydrogen atmosphere. Moreover, this device showed promising sensing performance in hydrogen gas including good sensitivity, a few second response time, and a few minute recovery time from 50 to 20,000 ppm hydrogen depending on the current direction. The fact that the response of the sensor satisfies Sievert's law, suggests that graphene with lithographically patterned palladium on one half can exhibit direction dependent asymmetrical electric current performance in a hydrogen atmosphere and also can act as a highly sensitive sensor for the quantitative detection of hydrogen molecules over broad concentration ranges.