Dept of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul 151-742, Korea.
Phys Chem Chem Phys. 2012 Oct 28;14(40):14041-8. doi: 10.1039/c2cp42566a. Epub 2012 Sep 19.
The formation of carbon nanotubes (CNTs) through precipitated carbons emerging from supersaturated metal catalysts is an established mechanism for their growth during the CVD process. Here, the CNT growth mode is determined by the interaction between the substrate and the catalyst nanoparticle, e.g., the tip-growth mode for the weak adhesion between them and the base-growth mode for the strong adhesion case. With microscopic evidence, this study reports another factor that governs the growth mode of CNTs on carbon-based substrates. Catalyst nanoparticles after only sputtering and annealing processes before the chemical vapor deposition (CVD) process are fully or partially wrapped with some graphitic layers, which are formed by carbons escaping from the carbon substrate. The formation of the wrapping graphitic layers is initiated by catalyst atoms diffusing into the carbon substrate during the catalyst sputtering process. The diffused catalyst atoms later coalesce into the nanoparticles, during which carbon atoms escape from the carbon substrate, forming the graphitic layers which wrap around the catalyst nanoparticles for energy minimization. Then, the carbon atoms generated from the catalytic reactions during the CVD process interact with the carbons in the graphitic layers wrapped around the catalyst nanoparticles, bringing about clear tip-growth of CNTs on carbon-based substrates and a stable interface (carbon-carbon bonding) between CNTs and carbon-based substrates.
通过过饱和金属催化剂中析出的碳形成碳纳米管（CNTs）是其在 CVD 过程中生长的一种既定机制。在这里，CNT 的生长模式取决于基底和催化剂纳米颗粒之间的相互作用，例如，它们之间弱附着力的尖端生长模式和强附着力情况下的基底生长模式。本研究通过微观证据报告了另一个控制 CNT 在碳基基底上生长模式的因素。在化学气相沉积（CVD）过程之前，经过溅射和退火处理后的催化剂纳米颗粒完全或部分被一些石墨层包裹，这些石墨层是由从碳基底逸出的碳形成的。包裹石墨层的形成是由催化剂原子在催化剂溅射过程中扩散到碳基底中引发的。随后，扩散的催化剂原子在纳米颗粒中聚合并融合，在此过程中，碳原子从碳基底逸出，形成包裹催化剂纳米颗粒的石墨层，以实现能量最小化。然后，CVD 过程中催化反应生成的碳原子与包裹在催化剂纳米颗粒周围的石墨层中的碳原子相互作用，导致 CNT 在碳基基底上的明显尖端生长以及 CNT 和碳基基底之间稳定的界面（碳-碳键合）。
