Growth of Carbon Nanocoils from K and Ag Cooperative Bicatalyst Assisted Thermal Decomposition of Acetylene

Growth of amorphous carbon nanocoil (CNC) from acetylene on Si substrates was achieved by using nanosized Ag and K as the catalysts. The deposition of CNC was carried out inside a hot-wall reactor at 723 K using H2 as the carrier gas. Based on the observed results, we propose a cooperative bimetal catalyst enhanced vapor−liquid−solid (VLS) growth mechanism to rationalize the CNC growth. In the reaction, the liquid phase metallic K dehydrogenated acetylene into the solid-state carbon, while the Ag nanoparticle assisted the extension of carbon one-dimensionally (1-D) via a tip-growth mechanism. Due to the adhesive force between the K liquid and the carbon, the 1-D solid curled along the C−K interface into the nanocoil shape. Some CNC samples were further heat-treated at 1423 K and showed very good field emission properties. They emitted electrons (10 μA/cm2) at a turn-on field Eto of 2.51 V/μm, while Jmax reached 17.71 mA/cm2 at 5.64 V/μm. The field enhancement factor β was calculated to be 2124, comparable to other carbon nanotube (CNT) and CNC based emitters. The CNC was also characterized by using the electrochemical behavior of K3[Fe(CN)6] via cyclic voltammetry (CV). The electrochemical surface area of a CNC electrode (geometric surface area 0.078 cm2) was calculated to be 0.143 cm2. These properties suggest that the CNC electrodes may have potential applications in field emission and electrochemical devices.