Nickel and Cobalt Nanorods and Nanowires using Carbon Nanotubes as Templates
       The area of carbon nanotubes has progressed rapidly in the last couple of years. A variety of the thermal and plasma chemical vapor deposition (CVD) techniques have been employed to grow the single walled as well as the multiwalled tubes. Prominently thermal CVD and MPCVD techniques have attracted the attention. As a result of these efforts the yield as well as the purity of the tubes is increasing. The length of the carbon nanotubes has been grown of the order of hundreds of microns and this has promised their applications in composites and new structures. The filling of the carbon nanotubes has been attempted with the single elements as well as the compounds and alloys.
       The application of the carbon nanotubes as templates had been proposed almost at the same time as the discovery of the nanotube itself. However, after initial experiments from various groups further studies have not been very forthcoming. It is perhaps due to the technical difficulties involved in separating, filling the tubes uniformly and experimenting with them that the experiments are lacking. Although the applications of nickel nanorods are established already in bio-technology (cell separation) and cobalt nanorods for magnetic applications, very few detailed studies on the growth of these nanorods or nanowires have been made. IIT Bombay researchers have been active in the area of carbon nanotubes. We have fabricated multiwalled carbon nanotubes using microwave plasma chemical vapor deposition with electroplated nickel layer as catalyst. The nanotubes prepared by our technique are of high aspect ratio (@ 100) and the diameter varies in the range 5-25 nm. In addition, we find that core of the nanotubes are filled with nickel and cobalt resulting in the nickel and cobalt nanorods. The filling of nickel and cobalt are single crystalline and allows us to calculate the chirality of the tubes as shown by us recently. In this project we propose to develop our technique further to grow the nanorods and nanowires of nickel and cobalt. The structure of these nanorods shows interesting trends and emphasize the role of surface tension and surface energy in the self assembly of the nanorods. In the proposed project we plan to study the growth behavior of these materials and develop our technique further to make one-dimensional nanostructures of nickel and cobalt.
       At IIT Bombay we have employed a new route for filling of the tubes. We start with a thick electroplated layer of nickel and cobalt. This layer is converted into nanoparticles of nickel or cobalt after the ammonia plasma treatment at 350 C insitu and the carbon nanotubes deposition is done in a microwave plasma chemical vapor deposition chamber. The deposition temperature of the nanotubes is 820 0C. As the deposition temperature is too close to the melting temperature of nickel and cobalt, the filling of the core of the tubes takes place with nickel and cobalt. We find that the nickel and the cobalt filling in the core of the nanotubes have perfect crystalline structure. The diameter of the nickel and cobalt inside the tube is a perfect crystal of a diameter of 5-10 nm. The length of the nanorods of nickel and cobalt is of the order of 1-2 microns leading to an aspect ratio close to 100.