In this paper, I present first-principle calculations which are performed by using combination of DFT and NEGF methods to investigate the adsorption of CO2 and NH3 molecules on straight and U-shaped GNRs junctions. The density of state, molecular orbital, adsorption energy, transmission spectrum, and current-voltage characteristics were analyzed. | VNU Journal of Science Mathematics Physics Vol. 36 No. 1 2020 46-53 Original Article Gas Sensors Based on U-shaped Graphene Nanoribbons A first-principles Study Nguyen Tien Cuong Faculty of Physics VNU University of Science Hanoi Vietnam Received 11 January 2020 Revised 19 February 2020 Accepted 26 February 2020 Abstract In this paper I present first-principle calculations which are performed by using combination of DFT and NEGF methods to investigate the adsorption of CO 2 and NH3 molecules on straight and U-shaped GNRs junctions. The density of state molecular orbital adsorption energy transmission spectrum and current-voltage characteristics were analyzed. It is found that the adsorption of CO2 and NH3 on straight GNRs at the dangling bond edges exhibit chemical interaction behavior with high adsorption energy. Besides for U-shaped ZGRNs without adsorption the states around Fermi level are quasi-bound states localized at the zigzag edges. The electrons at these localized states are almost confined and do not contribute on conductance. However for U-shaped GRNs with CO2 and NH3 adsorbed on DB armchair edge defects these states become delocalized on whole of the U-shaped junction. The current-voltage characteristics show that the sensitivity and selectivity of the U-shaped GNRs gas sensors are significantly improved in comparison with the pristine GNR ones. Keywords DFT NEGF U-shaped GRNs CO2 Adsorbed on Graphene NH3 Adsorbed on Graphene Graphene gas sensors. 1. Introduction It is well known that Graphene is attracting massive worldwide interest for nano-scale device applications since its successful fabrication in 2004 1 . Graphene offer great potential applications for gas sensors due to their high mobility and high surface area to volume ratio 2 . Sensing toxic gas molecules is very important in environmental pollution monitoring and medical applications 3 . The adsorptions of gas molecules on the infinite Graphene surface have been studied theoretically 4 . .
