Abstract
Y-junction carbon nanocoils (Y-CNCs) were synthesized by thermal chemical vapor deposition using Ni catalyst prepared by spray-coating method. According to the emerging morphologies of Y-CNCs, several growth models were advanced to elucidate their formation mechanisms. Regarding the Y-CNCs without metal catalyst in the Y-junctions, fusing of contiguous CNCs and a tip-growth mechanism are considered to be responsible for their formation. However, as for the Y-CNCs with catalyst presence in the Y-junctions, the formation can be ascribed to nanoscale soldering/welding and bottom-growth mechanism. It is found that increasing spray-coating time for catalyst preparation generates agglomerated larger nanoparticles strongly adhering to the substrate, resulting in bottom-growth of CNCs and appearance of the metal catalyst in the Y-junctions. In the contrary case, CNCs catalyzed by isolated smaller nanoparticles develop Y-junctions with an absence of metal catalyst by virtue of weaker adhesion of catalyst with the substrate and tip-growth of CNCs.
Highlights
Morphologies of carbon nanomaterials are of great significance because their morphologies play key roles in determining their physical and chemical properties, as well as potential applications
Various mechanisms have been proposed to illustrate the formation of CNCs, and it is generally accepted that the distinct carbon extrusion rates on different catalyst facets, namely catalytic anisotropy, give rise to the helical morphology of CNCs21,22
To the best of our knowledge, no literature specific to the synthesis and formation mechanism of Y-junction CNCs (Y-CNCs) has been reported to date
Summary
It is the welding of the apex with a metal catalyst located on one CNC stem with the trunk of another that occurs, and the metal catalyst plays a key role in this case. Increasing spray-coating time leads to interconnected catalyst islands which have strong adhesion with the substrate, bringing about bottom-growth of CNCs and the presence of metal catalyst in the Y-junctions, whereas CNCs catalyzed by isolated smaller nanoparticles weakly adhering to the substrate follow a tip-growth mechanism, producing Y-CNCs which are free of metal catalyst in the junctions. Except for our proposed formation mechanisms, more specific growth mechanisms should be further investigated to understand the formation of Y-CNCs better
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