Adsorption behavior and electronic properties of Pdn (n ≤ 10) clusters on silicon carbide nanotubes: a first-principles study

First-principles calculations have been carried out to investigate the adsorption of Pd-n (n <= 10) clusters on the single-walled (8, 0) and (5, 5) SiC nanotubes (SiCNTs). We find that the Pdn clusters can be stably adsorbed on the outer surfaces of both SiCNTs through an exothermic adsorption process. The adsorption energies of the Pd-n clusters on the (8, 0) SiCNT are generally larger than those of clusters on the (5, 5) SiCNT. The number of bonds between the Pd-n clusters and the SiCNTs increases with increasing cluster size. The Pd atoms adjacent to the SiCNTs adsorb preferentially on the bridge sites over an axial Si-C bond. The adsorption leads to elongation of the Pd-Pd bond lengths and structural reconstruction for the Pdn clusters. Moreover, the adsorbed Pdn clusters show two-layered structures at the cluster size n >= 4. We also find that the adsorbed Pd-n clusters induce some impurity states within the band gap of the pristine SiCNTs and the strong pd hybridization near the Fermi level, thereby reducing the band gap. The charge transfer from the SiCNTs to the Pd atoms that occurs is observed for all the systems considered. Due to the strong interactions between the Pd-n clusters and the SiCNTs, most adsorbed Pd-n clusters exhibit zero magnetic moment.