Factors affecting the growth of carbon nanofibers on titanium substrates and their electrical properties

The goal of this work is to investigate the growth mechanism of carbon nanofibers (CNFs) on titanium (Ti) substrates and the factors that affect the growth the CNFs. Ti substrates were chosen because they are a biocompatible material and the results of this work have potential application for electrochemical biosensors and/or supercapacitors. CNFs were synthesized via water-assisted chemical vapor deposition at 800 degrees C and at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C2H4) as the precursor gas, and argon (Ar) and hydrogen (H2) as the carrier gases. The introduction of an Al2O3 buffer layer and the thickness as well as the roughness of the Ti substrates was found to affect the morphology and distribution of the Fe nanoparticles, and thus the morphology of the CNFs. The sputtered buffer layer leads to fewer catalyst nanoparticles that diffuse into the underlying Ti layer which results in a more uniform and denser distribution of the Fe nanoparticles. Stronger catalyst-substrate interaction results in a larger and sparser distribution of the Fe nanoparticles. On the other hand, when the roughness of the substrate exceeds the thickness of the Fe catalyst layer, the nanoparticles tend to form into large sized particles. The longest and densest CNFs (10.7 microm in length) were grown on a Ti layer of 10 nm in thickness with the introduction of the buffer layer. The characterization of CNFs was carried out using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), atomic force microscopy (AFM), transmission electron microscopy (TEM). The electrical properties of the CNF films were investigated via the four-point probe method that showed an ohmic behavior. The sheet resistances of the CNF films on Ti substrates of different thickness were also reported.