Direct nano-wiring carbon nanotube using growth barrier: A possible mechanism of selective lateral growth

In this work we report the direct nano-bridging of carbon nanotubes (CNT) between micro-sized islands using conventional photolithography technique necessary for the nanomachining and the molecular device applications compatible with the Si-based process. The most distinct feature in this work is to use a growth barrier of Nb metal or insulating layer on the top of the catalytic metal to prevent the growth of CNT from the vertical direction to the substrate. As a result, CNTs of either "straight line" or a perfect "Y shape" were selectively grown between lateral sides of the catalytic metals or pre-defined electrodes without any trace of vertical growth. The length of the CNTs was 500-1000 nm and the diameter thinner than about 20 nm. We suggest that magnetic and crystallographic characteristics due to the unique interaction between the Nb overlayer and ferromagnetic Ni catalysts and nano-granulation of Ni layer during the growth process are important for the lateral (i.e., parallel to the substrate) CNTs growth. These results clearly indicate that this method would be one of the most feasible fabrication techniques for the nanomachines or the electronic applications with a high integration level.