On the interplay between a novel iron and iron-carbide atomic layer deposition process, the carbon nanotube growth, and the metal–carbon nanotube coating properties on silica substrates

The fabrication of iron and iron carbide nanoparticles (NPs) for catalytic reactions such as the growth of carbon nanotubes (CNTs) compete with the challenge of covering a wide range of substrates with perfect control of the NP reactivity. We present in this work a novel atomic layer deposition (ALD) process to grow Fe/Fe3C thin films over silica flat substrates. The depositions were carried out exposing the surface through various number of ALD cycles, resulting in Fe-based films with thicknesses ranging from 4 nm to almost 40 nm. After a thermal treatment, the film dewetts into nanoparticles, where the efficiency to grow CNTs will depend on the average size distribution of the nanocatalyst. X-ray diffraction and x-ray photoelectron spectroscopy were used to track the elemental, phase, and shape (film to particles) transformation in order to identify the key features of the nanocatalyst, thereby controlling the CNT nucleation and growth. Thin film thickness of around 5 nm promotes the growth of a dense CNT forest. Furthermore, the metal–CNT films reveal optical properties that are totally tailored by the initial number of ALD cycles.