Effects of NO$_2$ physisorption and chemisorption on the conduction of graphene nanoribbons*

Graphene nanoribbons have the potential of being used as the functional part of nanoelectronic gas sensors. This study focuses on the changes induced in the conduction of graphene nanoribbons upon adsorption of NO$_2$. Both chemisorption and physisorption situations, i.e., NO$_2$ adsorption with and without chemical bond formation, are studied. We use ab initio electronic structure calculations with MP2 correlation energy in order to optimize the structures of graphene nanoribbons, with hydrogen-terminated edges, in presence of NO$_2$. Subsequently, quantum conductance calculations are performed using Green's function implementation of the Landauer's approach. We explain different conductance modulation patterns in terms of charge transfer and dipole interactions. The results clarify some of the basic functionality issues of nanoelectronic-based gas sensors.