We have studied the adsorption of gas molecules (CO, NO, NO 2 , O 2 , N 2 , CO 2 , and NH 3 ) on graphene nanoribbons (GNRs) using first principles methods. The adsorption geometries, adsorption energies, charge transfer, and electronic band structures are obtained. We find that the electronic and transport properties of the GNR with armchair-shaped edges are sensitive to the adsorption of NH 3 and the system exhibits n-type semiconducting behavior after NH 3 adsorption.Other gas molecules have little effect on modifying the conductance of GNRs. Quantum transport calculations further indicate that NH 3 molecules can be detected out of these gas molecules by GNR based sensor.

Our calculations demonstrate that the intrinsic magnetism of boron nitride nanotubes (BNNTs) can be induced by their open ends, and the resulting magnetic moment is sensitive to the chirality of BNNTs. It is found that BNNTs, a pure sp-electron system, present a tremendous spin-splitting larger than 1 eV and that B-rich-ended and N-rich-ended BNNTs exhibit "conjugate", spin-polarized, deep-gap states. Tremendous spin-splitting effects combined with considerable local spin-polarizations at the open ends make BNNTs significant for applications of nanoscale spintronics such as spin-polarized electron emitters.

From ab initio calculations, a nanoelectronic switch is proposed based on telescoping double-walled carbon nanotubes (TDWCNTs), which can be conveniently turned on or off via the relative motion of tubes along the tube axis. It is found that the quantum conductance of switch periodically oscillates with the overlapping length of the two shells of the TDWCNT, which is mainly attributed to the variation of coupling effect between π electronic states of the two shells. The switching of TDWCNTs is determined by the distributions of delocalized frontier molecular orbitals of this system.

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