The variation of surface contact angles according to the diameter of carbon nanotubes

The shape of CNTs is affected by various growth parameters such as reaction time, temperature, working power, and pressure as well as the type of catalytic layer and synthesis method. In this work, the thickness of Ni catalyst layer was varied to control the diameter of synthesized CNT. Ni catalyst layer was prepared using a DC magnetron sputtering method and the layer thickness was varied from 40 nm to 100 nm with the increment of 20 nm. And CNTs were grown on Ni catalyst layer using the hot-filament plasma enhanced chemical vapor deposition (HF-PECVD) with ammonia (NH3) gas for pretreatment and acetylene (C2H2) gas for the synthesis. The shape of the resulting CNTs was analyzed using field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). The surface contact angle of well-aligned CNTs was correlated with the diameter of CNT. As determined by contact angle measurement, the surface of CNT forests became more hydrophilic as the diameter of CNT increased.