Influence of the roughness of the barrier layer on the formation of nanoparticles of the catalyst for the growth of carbon nanotubes

Abstract

Usually, the synthesis of carbon nanotubes arrays for use in nanoelectronics is carried out on a two-layer catalyst. The lower layer is a barrier for the interaction of the upper catalyst layer with the substrate. When heated to the synthesis temperature, the upper layer 2–4 nm thick melts and catalyst nanoparticles are formed on the surface of the barrier layer. The novelty of the presented research is the search for a technology that provides a smaller spread in the size of catalyst nanoparticles and, accordingly, a higher quality vertical array of carbon nanotubes during subsequent synthesis. To this end, the paper compares two methods of forming a TiN barrier layer, electron beam evaporation (EBE) and atomic layer deposition (ALD), to obtain Ni catalyst nanoparticles with the smallest average diameter and narrow distribution dispersion. The layers obtained by EBE have a roughness 1.5 times higher than the layers deposited by ALD (Ra = 1 nm and Ra = 0.6 nm respectively). The roughness of the barrier layer affects the dispersion of the size distribution of nanoparticles. Thus, the average size of nanoparticles on the EBE layer is about 30 nm, and the distribution dispersion is 1.3 times larger compared to the ALD layer. Wetting of the surface of the TiN barrier layer for EBE samples is better than for ALD samples. The contact angle for the catalyst nanoparticle on the surface of the TiN layer is about 30° for EBE samples and approaches 80° for ALD samples. In this case, the surface relief is filled with metal, which corresponds to the Wenzel model. It is assumed that the higher surface roughness of the EBE samples is associated with a higher temperature of titanium nitride film formation compared to ALD. ALD deposition of TiN barrier layers is preferable for the formation of catalytic nanoparticles on their surface for the growth of carbon nanotubes.