Gas sensing performance of graphene-metal contact after thermal annealing

Abstract

The effect of thermal annealing on the graphene-nickel contact resistance and its gas sensing behavior is experimentally studied in this work. When the thermal annealing temperature (Ta) increases from 300 to 600 ℃, the graphene-nickel contact resistance is significantly reduced. The gas sensing performance of the contact resistance (RC) in a NH3 test is significantly improved after thermal annealing at higher temperature. The gas response increases about 3 times while the response time decreases nearly an order of magnitude. Raman analysis indicates an increase of defects in graphene on the contact area due to hydrogen etching at higher Ta. The defects introduced by thermal annealing serve as more adsorption sites in graphene and results in the improvement of the gas sensing performance. The resistance of the graphene channel and its gas sensing property are also affected by Ta. When Ta increases from 300 to 600 ℃, the response time of the channel resistance also decrease nearly an order of magnitude, but the sensitivity decrease to only one third. This work indicates the gas sensing performance of graphene-metal contact can be further improved significantly via thermal annealing. More importantly, an abnormal gas sensing behavior, namely a sharp increase followed by an exponential decrease of RC before purging, is observed when the device is measured in air with 80% relative humidity. This abnormal gas sensing behavior is attribute to the nonuniform NH3 molecule adsorption on graphene laying on metal and SiO2. It provides a new dimension for graphene gas sensor designing and optimization.