Growth of vertically oriented films of carbon nanotubes by activated catalytic chemical vapor deposition on Fe–Co/TiN/Si(100) substrates

Abstract

In this paper, the growth of thin and dense films of vertically aligned carbon nanotubes (CNTs) on Fe–Co/TiN/Si(100) substrates is reported. Special attention is held to the preparation of the TiN buffer layers. This layer is deposited by pulse laser deposition at high temperature with a high texturation according to [TiN(100)//Si(100)]. Further ammonia heat treatment is performed at 623 K to control a Ti:N stoichiometry and remove oxygen impurity. Fe and Co as catalysts are subsequently deposited at high temperature (923 K) at the monolayer level with two ultrahigh vacuum evaporator cells. The growth of CNTs is performed by a direct-current plasma-enhanced and hot filaments-assisted catalytic chemical vapor deposition (dc HF CCVD) process. Highly dense films of CNTs, are obtained with only 0.5 nm Fe(Co) evaporated. Observations by transmission electron microscopy show that most of the CNTs display sizes in the 2.5–6 nm range, most of them with a double-wall (DW). This is in agreement with spectral features of the Raman radial breathing modes (RBM) in the 70–130 cm−1 range. Generally, these large-diameter DWCNTs display a high defect density with morphologies partially collapsed into flattened twisted shapes.