The defect effect on hydrogen adsorption on single-walled carbon nanotubes ͑SWNTs͒ has been studied by using extensive molecular dynamics simulations and density functional theory ͑DFT͒ calculations. It indicates that the defects created on the exterior wall of the SWNTs by bombarding the tube wall with carbon atoms and C 2 dimers at a collision energy of 20 eV can enhance the hydrogen adsorption potential of the SWNTs substantially. The average adsorption energy for a H 2 molecule adsorbed on the exterior wall of a defected ͑10,10͒ SWNT is ϳ150 meV, while that for a H 2 molecule adsorbed on the exterior wall of a perfect ͑10,10͒ SWNT is ϳ104 meV. The H 2 sticking coefficient is very sensitive to temperature, and has a maximum value around 70 to 90 K. The electron density contours, the local density of states, and the electron transfers obtained from the DFT calculations clearly indicate that the H 2 molecules are all physisorbed on the SWNTs. At temperatures above 200 K, most of the H 2 molecules adsorbed on the perfect SWNT are soon desorbed, but the H 2 molecules can still remain on the defected SWNTs at 300 K. The detailed processes of H 2 molecules adsorbing on and desorbing from the ͑10,10͒ SWNTs are demonstrated.

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The effects of oxygen atoms in stabilizing zigzag single-walled silicon nanotubes (SWSiNTs) have been studied by using first-principles calculations within density functional theory. The incorporation of oxygen atoms in the form of silicon monoxides into the (8,0)SWSiNT are found to not only stabilize the SWSiNT but also tailor the electronic structures from semiconducting to metallic. These findings will promote the fabrication and the utilization of silicon suboxide nanotubes which may find potential applications in nanoscale electronics and optoelectronics.

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