Effect of the on/off Cycling Modulation Time Ratio of C2H2/SF6 Flows on the Formation of Geometrically Controlled Carbon Coils

Abstract

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Nickel catalyst layer deposition and then hydrogen plasma pretreatment were performed prior to the carbon coils deposition reaction. To obtain the geometrically controlled carbon coils, the cycling on/off modulation process for C2H2/SF6 flows was introduced during the initial reaction. According to the different reaction processes, the different cycling on/off ratio and the different cycling numbers for C2H2/SF6 flows were carried out. The characteristics (formation density, morphology, and geometry) of the deposited carbon coils on the substrate were investigated. Microsized coils as well as nanosized coils could be existed under the higher growing/etching time ratio (180/30 s) condition. On the other hand, the formation of nanosized coils could be mainly observed under the lower growing/etching time ratio (30/180 s) condition. With increasing the numbers of cycles, the diameters of carbon nanofilaments composed the coils decreased. The enhanced etching ability by the fluorine species was considered the main cause to control the geometry of carbon coils according to the growing/etching time ratio of the cycling on/off modulation process for C2H2/SF6 flows.