Atomic Hydrogen-Driven Size Control of Catalytic Nanoparticles for Single-Walled Carbon Nanotube Growth

Abstract

The effects of an atomic hydrogen (H at ) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al 2 O 3 surface by H at pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of H at , compared to H 2 , is also discussed. It was also found that the quality of SWCNTs can be enhanced when H at is flowed with CH 4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by H at . Therefore it is essential to use H at in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. H at can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.

Tuning bimetallic catalysts for a selective growth of SWCNTs

“…First, thanks to an appropriate surface chemical functionalization of the support substrate, the catalyst density has been shown to be limited to one monolayer. [43] Second, using highly activated hydrogen induces surface defects on the substrate with hightrapping energy over the substrate [46]. These defects limit the surface diffusion of the catalyst metal atoms and increase the pinning effect of the forming NPs [43,46,47].…”

“…[43] Second, using highly activated hydrogen induces surface defects on the substrate with hightrapping energy over the substrate [46]. These defects limit the surface diffusion of the catalyst metal atoms and increase the pinning effect of the forming NPs [43,46,47].…”

Diameter controlled growth of SWCNTs using Ru as catalyst precursors coupled with atomic hydrogen treatment

“…Prior to SWCNTs growth, the substrates are heated at different temperatures (800 °C, 850 °C, 900 °C and 950 °C) and exposed for 5 min to a hotfilament activated (160 Wapproximately 2000 °C measured with an optical pyrometer) hydrogen flow (100 sccm at 90 mbar) in order to transform the Ru thin film into a random collection of Ru nanoclusters (dewetting operation). Atomic hydrogen tends to block surface diffusion by creating defects on the SiO 2 surface; those defects pin the nanoparticles and prevents their agglomeration [14]. After this annealing under atomic hydrogen, the substrate is brought to various temperatures and a gas mixture CH 4 :H 2 (1:5) is introduced into the reactor to grow SWCNTs for 15 min.…”

Toward full carbon interconnects: High conductivity of individual carbon nanotube to carbon nanotube regrowth junctions

“…The CVD temperature was thus set at 700 ° C to produce small MWNTs. 23 In this process, ferritin and FeO x NP deposited on a SiO 2 substrate yielded MWNT of similar diameters (5-20 nm). In CVD regrowth from the MWNT-catalyst conjugates, the catalyst particles often appeared at the tip of the secondary MWNT [Figs.…”