Effects of ions and atomic hydrogen in plasma-assisted growth of single-walled carbon nanotubes

Abstract

The growth of single-walled carbon nanotubes (SWCNTs) in plasma-enhanced chemical vapor deposition (PECVD) is studied using a surface diffusion model. It is shown that at low substrate temperatures (⩽1000K), the atomic hydrogen and ion fluxes from the plasma can strongly affect nanotube growth. The ion-induced hydrocarbon dissociation can be the main process that supplies carbon atoms for SWCNT growth and is responsible for the frequently reported higher (compared to thermal chemical vapor deposition) nanotube growth rates in plasma-based processes. On the other hand, excessive deposition of plasma ions and atomic hydrogen can reduce the diffusion length of the carbon-bearing species and their residence time on the nanotube lateral surfaces. This reduction can adversely affect the nanotube growth rates. The results here are in good agreement with the available experimental data and can be used for optimizing SWCNT growth in PECVD.

Plasma‐Assisted Approaches in Inorganic Nanostructure Fabrication

“…The substrate-surface-dominated growth in PECVD and the plasma-treatment process are similar in many ways except for the source of growth precursors. Some important plasma effects such as etching and sputtering, ion bombardment, and catalyst-mediated growth appear in both substratesurface-dominated PECVD [47,49,50,61,79,83,[211][212][213][214] and plasma treatment. [202][203][204][205][207][208][209][210]225] The growth flux from the plasma may add some complications.…”

“…[78,80,87,89] Simulation suggested that ion-induced dissociation by plasma allowed the growth at lower temperature. [61] Another unexpected advantage of plasma-assisted growth of SWCNTs is the preferential formation of the semiconducting type of SWCNT, which is highly desirable for CNT-based nanodevice fabrication, [84,86,91] although the detailed mechanism is still under investigation. Post-plasma treatment also allowed the transition from metal type to semiconductor type, which was tentatively attributed to the bandgap structure change caused by H bonding to carbon atoms.…”

“…Simulations based on a surface-diffusion model showed that the amorphous carbon can be completely removed by etching with a reasonable H flux. [61] Compared to H 2 , NH 3 is a more efficient atomic hydrogen source. [38] Diagnosed by in situ optical emission spectroscopy (OES) and MS, the plasma chemistry and related CNT growth behavior in hydrogen carbon/ammonia plasma is studied.…”

“…Charged particles can also influence the plasma chemistry through many other channels such as electron-impact dissociation, recombination, ion-induced dissociation, etc. [61,[100][101][102][103] The excited neutrals including atoms, radicals, and molecules at excited electronic states consist of the majority of growth species in many materials systems. [69,85,[104][105][106] New chemistry can be introduced by these excited species, leading to chemical reactions at lower temperature or even thermodynamically forbidden conditions.…”

Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas

“…A surface diffusion model for SWCNT growth was used to obtain the conditions under which a plasma environment can improve the SWCNT growth. 37 Moreover, the growth parameters depend on the catalyst surface temperature, as well as on the ion and etching gas fluxes onto the catalyst nanoparticles. 38 During the initial stage of the nanotube formation on the catalyst nanoparticle patterns, 39 the degree of ionization of the carbon flux strongly affects the kinetics of nanotube and nanocone nucleation.…”