Decoupling the catalyst reduction and annealing for suppressing Ostwald ripening in carbon nanotube growth


Gul O. T.

Applied Physics A: Materials Science and Processing, vol.127, no.10, 2021 (Peer-Reviewed Journal) identifier identifier

  • Publication Type: Article / Article
  • Volume: 127 Issue: 10
  • Publication Date: 2021
  • Doi Number: 10.1007/s00339-021-04916-9
  • Journal Name: Applied Physics A: Materials Science and Processing
  • Journal Indexes: Science Citation Index Expanded, Scopus, Academic Search Premier, Aerospace Database, Chemical Abstracts Core, Chimica, Communication Abstracts, Compendex, INSPEC, Metadex
  • Keywords: Carbon nanotube, Chemical vapor deposition, Ostwald ripening, Catalyst reduction, Catalyst annealing, IN-SITU, NANOPARTICLES, SPECTROSCOPY, MORPHOLOGY, DIAMETER, H-2

Abstract

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.Abstract: The formation and morphological control of catalyst nanoparticles (CNPs) are crucial for reliable carbon nanotube (CNT) growth. Effects of catalyst reduction and annealing on CNP formation and coarsening are key parameters that need to be elucidated. Here, we decoupled catalyst reduction and high temperature annealing of catalysts in order to investigate their roles and respective effects on CNP formation, evolution and morphology which are critical for controlling diameter-, density- and length-dependent morphologies of CNTs. We found that catalyst reduction at low temperature was not sufficient to form CNPs and it needed to be followed by exposure of Fe catalyst to high temperature for annealing. High temperature without the catalyst reduction did not help forming CNPs. When the catalyst reduction and high temperature annealing were coupled, it induced CNP coarsening via Ostwald ripening causing bimodal and sparse CNP formation. A recipe, consisting of low temperature catalyst reduction and subsequent exposure to high temperature for annealing in an inert gas environment, mitigated Ostwald ripening and was favorable to form uniform and dense CNPs. Diameters and densities of resulting CNTs showed proportionality to CNP morphologies. In addition, height of vertically aligned CNT (VACNT) forests linearly decreased with increasing catalyst reduction temperature. Graphic abstract: [Figure not available: see fulltext.]