Low temperature growth of carbon nanotubes by microwave plasma stimulated by CO2 as weak oxidant and guided by shadow masking

Abstract

Operating at a moderate MW power of 600 W and employing optimized Fe nanoparticles as catalyst, growth optimization of multi-wall CNTs at a relatively low substrate temperature has been performed using tubular microwave plasma enhanced-CVD system. Moderately high energy density plasma facilitates formation of essential precursors for CNT growth. Two intriguing techniques have been integrated in the growth process. Specific shadow masking arrangement by specially designed stainless steel multiple mask assembly protects the growth surface from etching by direct plasma bombardment. CO2 has been used as an auxiliary gaseous component added to the (CH4 + H2) plasma. Instrumental presence of CO2 as a weak oxidant in the plasma accomplishes the removal of a-C coverage from the Fe catalyst nanoparticles via etching by atomic O and thereby, re-triggers their catalytic reactivity and ensures the persistent growth of CNTs. Altogether, a perpetual growth of multiwall CNTs has been realized through tip-growth process at the lowest substrate temperature (300 °C) reported so far in PECVD.