Use of plasma treatment to grow carbon nanotube forests on TiN substrate

Abstract

Hydrogen plasma pretreatment is used to enforce the growth of vertically-aligned carbon nanotube forests on TiN substrates. The evolution of the substrate, catalyst, and nanotubes are studied by in situ and ex-situ photoemission and X-ray diffraction in order to understand the growth mechanism. We find that TiN retains its crystallographic structure and its conductivity during plasma pretreatment and nanotube growth, which is confirmed by electrical measurements. Plasma pretreatment is found to favor the growth of nanotube forests by root growth, as it binds the catalyst nanoparticles more strongly to the substrate than thermal pretreatment. We find that plasma pretreatment time should be limited, otherwise poor or no growth is found.

Effect of Catalyst Pretreatment on Chirality-Selective Growth of Single-Walled Carbon Nanotubes

“…In Figure 6 we study samples that only underwent pretreatment (i.e., no hydrocarbon exposure) in NH 3 or vacuum. Our AFM analysis shows that under our processing conditions both NH 3 and vacuum pretreatments give similar distributions of nanoparticle sizes. This suggests that under our low pressure pretreatment conditions the particle size distribution is mainly determined by the annealing temperature.…”

“…59 While possible chirality dependent effects on growth rate 13−15 or etching effects 43 may also play a role during continued growth our data clearly shows that Figure 6. (a) AFM scans of samples that underwent pretreatment in NH 3 or vacuum (i.e., no hydrocarbon exposure but immediate cooling in vacuum after pretreatment), confirming nanoparticle formation during both NH 3 and vacuum pretreatment (particle density estimated to ∼1 × 10 10 particles/cm 2 ). Similar AFM scans of samples that underwent pretreatment in Ar (not shown) exhibit in comparison only very few nanoparticles, indicating that the strongly reduced nanotube yield from Ar pretreatment is due to incomplete nanoparticle formation.…”

“…Exposure of transition metal catalysts to nitrogen compounds can alter their subsequent carbon uptake characteristics during hydrocarbon exposure. 44 Cobalt is a known catalyst for decomposition of NH 3 . 52,53 At our CVD temperatures NH 3 is know to dissociatively adsorb onto Co, 54 thus reducing the Co-oxide that is initially present due to ambient air exposure of our films during fabrication.…”

“…It is well-known in heterogeneous catalysis 1 in general and in catalytic chemical vapor deposition (CVD) of carbon nanotubes 2,3 in particular that catalyst pretreatment conditions can strongly affect the properties of the products of the catalyzed reactions. Here, we use a model catalyst system for growth of single-walled carbon nanotubes (SWNTs) to study the influence of catalyst pretreatment on the chiral distribution of the grown SWNTs.…”

“…First, we pretreat in pure NH 3 or, for reference, vacuum or argon (Ar), which is then followed by exposure to an undiluted hydrocarbon species (C 2 H 2 or ethanol vapor). Multiwavelength Raman spectroscopy on the as-grown SWNTs reveals that for both hydrocarbon precursor gases the pretreatment in NH 3 consistently narrows the obtained diameter range and chiral distribution toward smaller diameter SWNTs.…”