Quantum Size Effects of Agn Clusters on Carbon Nanotubes

The electronic structures of different Ag clusters adsorbed on metallic and semiconducting carbon nanotubes (CNTs) were studied using a first-principles DFT method. More precisely, we have considered Agn with n = 4, 13, 55, and 147 atoms to describe the quantum size effects associated to the Agn-CNT interfaces. Although we observed a sharp transition from a molecular to a bulky behavior from Ag4 to Ag55, the electronic structure properties of Ag55 and Ag147 were found to be very similar to the extended slab Ag(111) surface. In contact to the CNTs, Agn is chemisorbed when n = 4 and 13 whilst it is physisorbed for larger systems (n > 55) similarly to the Ag(111) slab surface. As a result, the adsorption energy of Agn to CNTs decreases from around 300 to 100 meV/atom when n changes from 4 to ∞. This variation with cluster size is consistent with the calculated fluctuation of electron charge from Agn to the CNTs that sharply decreases with the Ag cluster size. Following an adsorption of CO on different sites ...