Enhanced Formation of Carbon Microcoils with Ni Catalysts of Different Sizes

Abstract

Carbon microcoils were synthesized using C2H2 as the source gas together with an initial SF6 flow for a short period as an incorporated additive gas in a thermal chemical vapor deposition (CVD) system. In different experiments, different injection sequences of gas flows were used. The injection sequences starting with C2H2 or SF6 flows were adopted for Ni catalysts of two different diameters: small (∼0.1 μm) and large (∼100 μm). In the case of the small-sized Ni catalyst, the formation of carbon microcoils could be efficiently achieved while using the injection sequence of SF6 → C2H2. In contrast, for the large-sized Ni catalyst, the injection of C2H2 prior to the injection of SF6 promoted the formation of carbon microcoils. Based on these results, we explain the role of the injection sequence with C2H2 flow or SF6 flow for Ni catalysts of different sizes to achieve the selective formation of carbon microcoils.