Calculations of adsorption of O2 and H2O on a carbon nanotube tip in field-emission conditions

In this paper, density-functional-theory calculations show that O2 and H2O behave differently when they are adsorbed on a single-walled carbon nanotube (SWNT) tip, especially if the tip carries a net negative charge as in the field-emission situation. H2O molecules can be adsorbed on both closed and open-ended SWNTs, and the extra negative charge strengthens the adsorption. O2 molecules can be adsorbed on a closed SWNT, but they are desorbed when an extra negative charge is present. Quite differently, O2 molecules are decomposed and chemisorbed on an open-ended zigzag SWNT, even if an extra negative charge exists. Furthermore, the adsorbed O2 and H2O molecules affect the potential distribution of the SWNT tip differently, leading to their different effects on the field-emission properties of SWNTs.