Controlled Geometry Formation of the Carbon Coils by the Substrate Pretreatment

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Prior to the carbon coils deposition reaction, the supporting substrates were pretreated using various methods. Among the methods, the thermal etching pretreatment of Ni-SiO2 substrate with SF6 leads to the exclusive formation of the nanosized carbon coils. The diamond powders pretreatment of Si substrate gives rise to the dominant formation of the microsized carbon coils after 10 minutes reaction time. The geometry selectivity for the carbon coils in a specific pretreatment method was discussed in association with the peeled-off Ni layers by the thermal etching pretreatment with SF6 and the remained carbon particles on Si substrate by the diamond powders pretreatment. 1. Introduction Although the unique geometries of the carbon coils have been attracted as the promising potential materials in nano-/microelectronics or mechanics [1–4], the controlled geometry for as-grown carbon coils should be preferentially solved to practically apply them in diverse application fields [5, 6]. The metal catalyst was regarded as one of the indispensable factors for the formation of the carbon coils [7–11]. In addition, the characteristics of the used metal catalyst seem to affect the formation density and the geometry of the carbon coils via the vapor-liquid-solid growth mechanism of the carbon nanomaterials [9–13]. Meanwhile, the property of the supporting substrate may alternate the characteristics of the used metal catalyst, consequently affecting the formation density and the geometries of the as-grown carbon coils [13, 14]. Until now, Huang et al. reported that the formation of the carbon nanocoils would be critically affected by the morphology change of Si substrate which was induced by the HF solution corrosion [15]. They found the coils formation exclusively on the concavo-convex surface morphology of Si substrate with the straight carbon nanotubes on the flat Si surface, namely, on noncorroded Si surface. Veziri et al. demonstrated that the morphology of the carbon nanostructures grown by chemical vapor deposition (CVD) on the porous supports is strongly affected by the porosity of the supporting substrate [16]. Bai obtained a more or less controlled morphology of the carbon coils through the careful choice of alumina substrate pore size [17]. Despite many efforts to enhance the controlled geometry for the carbon coils, detailed reports regarding the effect of the substrate pretreatment on the formation of the