Using ab initio spin density functional theory, an investigation was made of the energetics and kinetics of Ti clustering on both neutral and charged C60 surfaces. A comparison was made of the formation energy of sparsely dispersed zero-dimensional (0D), compact single-layered two-dimensional (2D), and clustered three-dimensional (3D) TiN configurations as a function of cluster size (N≤12) and a study was made of the transformation kinetics between them. It was found that 0D configuration was always less stable than that of 2D and 3D configurations and 0D to 2D transformation involves in a single Ti diffusion process with kinetic barrier of ≤0.7eV. On the other hand, there existed a critical cluster size (NC) of NC = 5, below which 2D layers were preferred to 3D clusters. Hole- or B-doping greatly enhance the Ti-fullerene interaction and lead to stronger dispersion of Ti atoms. Even so, for moderate charge doping (less than seven holes) the critical size of Ti atoms on neutral C60 surprisingly remains unchanged or only slightly increased to NC = 6 by B-doping. However, it was found that the formation of 3D clusters may be hindered by a high kinetic barrier related to the process of single Ti atoms climbing up a single Ti layer. This barrier was ∼1eV or even 1.47eV for B-doped C60 surfaces which was high enough to stabilize larger 2D structures (N ≥ NC) at low temperatures. These findings may prove to be instrumental in stabilizing transition metal coated nanostructures and especially homogeneously Ti-coated fullerenes, which were believed to be a very promising material for hydrogen storage.

Energetics and Kinetics of Ti Clustering on Neutral and Charged C60 Surfaces. Yang, S., Yoon, M., Wang, E., Zhang, Z.: Journal of Chemical Physics, 2008, 129[13], 134707