Maskless direct growth of carbon nanotube micropatterns on metallic substrates

Herein, we report on a simple process, which is suitable for producing carbon nanotube micropatterns on steel alloys without the use of catalyst deposition. The method is based on a pulsed laser beam induced surface microstructuring process, followed by a thermal chemical vapor deposition growth of carbon nanotubes that emerge exclusively from the surface areas of the alloys previously exposed to the laser pulses. As concluded from X-ray diffraction, electron microscopy, Raman and X-ray photoelectron spectroscopy analyses of pristine and laser treated surfaces, the area-selective growth is caused by a formation of a thin and nanostructured metal oxide layer during the laser treatment, which is then partially reduced during the subsequent nanotube growth steps. The partially reduced oxide nanoparticles provide catalytic sites for nanotube growth and are also believed to disable diffusion of catalytic metal atoms to the subsurface regions, giving rise to stable catalyst nanoparticle formation and nanotube growth in the chemical vapor deposition step. The proposed method is fast, scalable and has potential for use in multiple applications that require close metal to nanotube contacts with arbitrary microscopic pattern definition on two and three-dimensional surfaces such as those used in electromechanical contacts, electrochemical electrodes, field emitters, and thermal interfaces.