| Summary: | We employ dispersion-corrected density functional theory to study the adsorption of CH<sub>4</sub> molecule on a singly and doubly decorated (8,0) single wall carbon nanotube (CNT80) with palladium atom and oxygen molecule. The obtained optimized energies indicate that double decoration with palladium atom and oxygen molecules significantly enhances the adsorption of methane on the CNT80, while single decoration with oxygen molecules gives rise to a weak physical bonding for methane molecules. Moreover, we observe that methane adsorption decreases the bandgap and the distance of the Fermi level to the top of the valance band of the doubly decorated CNT80. The calculated charge density plots and energy band diagrams demonstrate a charge transfer from doubly decorated CNT80 to CH<sub>4</sub>. Regarding the p-type nature of the structure, our results support the increment of the conductance of the doubly decorated CNT80 after methane adsorption, in agreement with a real measurement in the ambient conditions. This observation underlines the importance of ambient oxygen in the real performance of CNT-based gas sensors.
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