First-Principles Electronic Structure Calculations of N$_{2}$H$_{4}$ Adsorbed on Single-Wall Carbon Nanotubes

Recent experiments conducted by Desai \textit{et al.} [1] reveal that single-wall carbon nanotube (SWCNT) networks exposed to N$_{2}$H$_{4}$ vapor at various pressures exhibit considerable drop in resistance with respect to the pristine sample. Experimental findings reveal: (i) n-type behavior for the adsorption of N$_{2}$H$_{4}$/SWCNT, and (ii) the binding of N$_{2}$H$_{4}$ on SWCNT as chemisorption. In the present work, we have performed first-principles electronic structure calculations [2] for the N$_{2}$H$_{4}$ adsorbed on the (14, 0) SWCNT, where several orientations for the N$_{2}$H$_{4}$ molecule were considered. Calculations for the combined system were performed using 3 unit cells with the DFT/GGA and ultra soft pseudo-potentials. Our calculations reveal: (i) the binding of N$_{2}$H$_{4}$ on SWCNT as physisorption, and (ii) the electronic structure of SWCNT to be practically unaltered by the adsorption of N$_{2}$H$_{4}$, suggesting that there will not be a dramatic drop in resistance for N$_{2}$H$_{4}$/SWCNT. This is in disagreement with the experimental findings. To further understand the experimental observations, we will discuss mechanisms that may alter the binding nature of N$_{2}$H$_{4}$ on SWCNT. [1] S. Desai, G. Sumanasekera, et al. (APS, March 2008). [2] G. Kresse and J. Furthmuller, Phys. Rev. B \textbf{54}, 11169 (1996).