Physisorption to chemisorption transition of NO2 on graphene induced by the interplay of SiO2 substrate and van der Waals forces: A first principles study

The effect of SiO2 substrate and van der Waals interactions on the adsorption of NO2 molecule on graphene is studied using density functional theory. Contrary to physisorption on suspended graphene, both physisorption and chemisorption phenomena can be found, which are mainly caused by the covalent C-O bonds, the broken symmetry, and the local corrugations induced by SiO2. The electronic structures of the system are significantly influenced after NO2 adsorption, enhancing the detection of NO2. Interestingly, NO2 induces magnetization into graphene, and the spin polarization locates mainly on carbon atoms of graphene. The barrier of the transition from physisorption to chemisorption is about 0.05 eV, and this pseudo barrier can be overcome by van der Waals interactions. This work explains the experiments of graphene as gas sensors with high sensitivity, and supports new applications for electronic, spintronic devices. (C) 2012 Elsevier B.V. All rights reserved.