University of Wollongong Research Online Australian Institute for Innovative Materials - Papers Australian Institute for Innovative Materials 1-1-2015 Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas Z Marvi Sahand University of Technology S Xu Nanyang Technological University, Singapore G Foroutan Sahand University of Technology Kostya Ostrikov University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/aiimpapers Part of the Engineering Commons, and the Physical Sciences and Mathematics Commons Recommended Citation Marvi, Z; Xu, S; Foroutan, G; and Ostrikov, Kostya, "Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas" (2015). Australian Institute for Innovative Materials - Papers. 1376. https://ro.uow.edu.au/aiimpapers/1376 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas Abstract The growth kinetics of single-walled carbon nanotubes (SWCNTs) in a low-temperature, low-pressure reactive plasma is investigated using a multiscale numerical simulation, including the plasma sheath and surface diffusion modules. The plasma-related effects on the characteristics of SWCNT growth are studied. It is found that in the presence of reactive radicals in addition to energetic ions inside the plasma sheath area, the effective carbon flux, and the growth rate of SWCNT increase. It is shown that the concentration of atomic hydrogen and hydrocarbon radicals in the plasma plays an important role in the SWCNT growth. The effect of the effective carbon flux on the SWCNT growth rate is quantified. The dependence of the growth parameters on the substrate temperature is also investigated. The effects of the plasma sheath parameters on the growth parameters are different in low- and high-substrate temperature regimes. The optimum substrate temperature and applied DC bias are estimated to maximize the growth rate of the single-walled carbon nanotubes. Keywords growth, single, walled, carbon, nanotubes, low, temperature, contribution, plasmas, radicals, ions, catalyzed Disciplines Engineering | Physical Sciences and Mathematics Publication Details Marvi, Z., Xu, S., Foroutan, G. & Ostrikov, K. (2015). Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas. Physics of Plasmas, 22 013504-1-013504-10. This journal article is available at Research Online: https://ro.uow.edu.au/aiimpapers/1376 PHYSICS OF PLASMAS 22, 013504 (2015) Contribution of radicals and ions in catalyzed growth of single-walled carbon nanotubes from low-temperature plasmas Z. Marvi,1,2 S. Xu,2 G. Foroutan,1 and K. Ostrikov3 1Physics Department, Faculty of Science, Sahand University of Technology, 51335-1996 Tabriz, Iran 2Plasma Sources and Applications Center, NIE, and Institute of Advanced Studies, Nanyang Technological University, 637616 Singapore 3Institute for Future Environments and School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD 4000, Australia; Plasma Nanoscience Center Australia (PNCA), Manufacturing Flagship, CSIRO, P.O. Box 218, Lindfield, NSW 2070, Australia; Plasma Nanoscience, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Institute for Superconducting and Electronic Materials (ISEM), University of Wollongong, NSW 2522, Australia; and School of Physics and Advanced Materials, University of Technology Sydney, Sydney, NSW 2006, Australia (Received 17 September 2014; accepted 8 December 2014; published online 9 January 2015) The growth kinetics of single-walled carbon nanotubes (SWCNTs) in a low-temperature, low-pres- sure reactive plasma is investigated using a multiscale numerical simulation, including the plasma sheath and surface diffusion modules. The plasma-related effects on the characteristics of SWCNT growth are studied. It is found that in the presence of reactive radicals in addition to energetic ions inside the plasma sheath area, the effective carbon flux, and the growth rate of SWCNT increase. It is shown that the concentration of atomic hydrogen and hydrocarbon radicals in the plasma plays an important role in the SWCNT growth. The effect of the effective carbon flux on the SWCNT growth rate is quantified. The dependence of the growth parameters on the substrate temperature is also investigated. The effects of the plasma sheath parameters on the growth parameters are differ- ent in low- and high-substrate temperature regimes. The optimum substrate temperature and applied DC bias are estimated to maximize the growth rate of the single-walled carbon nanotubes. VC 2015 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4905522] I. INTRODUCTION CNT nucleation, and help controlling the SWCNT thick- ness.1,31–34 In the SWCNT growth, the catalyst particle is In the last decade, low-temperature reactive plasmas located at the base of the nanotube.15,35,36,39 In this case, each have attracted a considerable attention for the controlled syn- nucleated SWCNT grows on a metal catalyst particle so that thesis of vertically aligned carbon nanostructures, such as the pattern of the nanostructure array repeats the catalyst pat- single-walled carbon nanotubes (SWCNTs) and carbon 1–13 tern, which is usually pre-fabricated on the substrate surface. nanofibers (CNFs), which are potentially attractive for Apart from the common processes in the CVD growth many applications including nanoelectronics, field emission, (adsorption and desorption of radicals, thermal dissociation nanocomposites, energy storage, sensors, biomedical device, 14–24 of hydrocarbon radicals and evaporation of C atoms), there and several others. are additional plasma-specific reactions on the SWCNT sur- The significant recent interest in reactive plasmas for face including ion-induced dissociation of adsorbed hydro- materials processing is due to their numerous remarkable 25–29 carbon species, direct ion decomposition, and etching gas characteristics. Through the various plasma-chemical interaction with the adsorbed species, which are responsible reactions, occurring in the gas phase of the plasma, diverse for the SWCNT growth at low temperatures. Through this combinations of electrons, ions, and radicals are created. The processes, the carbon atoms are created on the SWCNT sur- ions accelerated by the plasma sheath electric field at the face and then diffuse to the nanotube and are finally incorpo- plasma-substrate interface accompanied with fluxes of highly rated into the growing SWCNT via the CNP. reactive radicals towards the substrate provide the required The plasma sheath plays a crucial role in the nanostruc- carbon-bearing species for the plasma-based synthesis of ture growth processes. Changes in the sheath properties due high-aspect-ratio carbon nanostructures. to variations in the plasma parameters can be used to effec- Plasma-enhanced chemical vapor deposition (PECVD) tively control the plasma-assisted growth of different nano- is one of the most versatile plasma-based methods for highly structures.26 The sheath thickness can be controlled by the selective synthesis of well-aligned carbon nanostructures. plasma parameters and directly affects the electric field Using the PECVD technique, in addition to vertical growth, strength. Consequently, it can be used to control the distribu- the CNTs can be grown at lower temperatures than in the tion and kinetic energy of charged species impinging onto neutral gas-based CVD process, due to the ion and radical- the SWCNT surface. In order to control the deposition pro- related reactions on the CNT surface.9,19,20,30 cess and optimize the SWCNT growth parameters, it is nec- Catalyst nanoparticles (CNP) play multiple roles in the essarily to determine a self-consistent set of the plasma growth of carbon nanostructures in PECVD. They serve as a sheath parameters, in particular, to incorporate into the growth pattern for SWCNT arrays, activate the surface for plasma sheath and the surface interaction models. 1070-664X/2015/22(1)/013504/10/$30.00 22, 013504-1 VC 2015 AIP Publishing LLC This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 130.130.37.84 On: Fri, 10 Apr 2015 01:53:40 013504-2 Marvi et al. Phys. Plasmas 22, 013504 (2015) In recent years, many experimental and numerical stud- ies were devoted to the carbon nanotube and nanofiber growth by PECVD. 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 sur- face 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 pat- terns,39 the degree of ionization of the carbon flux strongly affects the kinetics of nanotube and nanocone nucleation. A sheath model was developed to quantify the plasma-sheath- related effects on the CNF growth characteristics.40 A hybrid molecular dynamics/force-biased Monte Carlo simulations FIG. 1. Schematics of the geometry of the plasma sheath and charged and explained the growth mechanism and