Atomic force microscopy and transmission electron microscopy investigations of catalytic formed nanotubes in C60/C70+Ni layers

In this paper, atomic force microscopy (AFM) and transmission electron microscopy (TEM) results of the investigations of nanotubes formation in annealed C-60/C-70 + Ni layers are presented. The layers obtained by thermal evaporation of fullerenes and Ni compound on Mo substrate were annealed in vacuum at the pressure of 10(-5) Torr and at the temperature of 500 degrees C. The initial layers (before annealing process) contained 2-5 wt.% of Ni. This process led to formation of nanotubes and extraction of Ni from the layer to vacuum. The deposited layer did not posses any nanostructures what was confirmed by AFM and TEM. In result of the annealing process, the nanotubes were formed in the layer, The nanostructures formed in such manner were observed by TEM. The yield of the nanotubes formation process was estimated from AFM images of the layers. The length, shape and structure of nanotubes depended on Ni concentration in the initial layer. The length of nanotubes was within the range of 100-1200 nm and was longer for the nanotubes formed in layers with lower Ni contents. The shape of nanotubes was mostly cylindrical and they had multishell structure. The catalytic reaction of Ni with carbon structures in annealed C-60/C-70 + Ni layer is proposed as the mechanism forming nanotubes. (C) 1999 Elsevier Science B.V. All rights reserved.