Highly Consistent Atmospheric Pressure Synthesis of Carbon Nanotube Forests by Mitigation of Moisture Transients

Jinjing Li, Mostafa Bedewy, Alvin Orbaek White, Erik S. Polsen, Sameh Tawfick, A. John Hart

Research output: Contribution to journalArticle

Abstract

Consistent synthesis of carbon nanotubes (CNTs) using laboratory-scale methods is essential to the development of commercial applications, particularly with respect to the verification of recipes that achieve control of CNT diameter, chirality, alignment, and density. Here, we report that transients in the moisture level and carbon concentration during the chemical vapor deposition (CVD) process for vertically aligned CNT forests can contribute significantly to run-to-run variation of height and density. Then, we show that highly consistent CNT forest growth can be achieved by physically decoupling the catalyst annealing and hydrocarbon exposure steps, to allow the gas composition to stabilize between the steps. This decoupling is achieved using a magnetically actuated transfer arm to move the substrate rapidly into and out of the CVD reactor. Compared to a reference process where the sample resides in the furnace throughout the process, the decoupled method gives 21% greater CNT forest height, reduces the run-to-run variance of height by 76%, and results in forests with improved vertical alignment (Herman's orientation parameter of 0.68 compared to 0.50). Building on this foundation, we study the influence of the moisture level during the CNT growth step and find a 30% improvement in growth rate going from the baseline condition (<15 ppm) to 40 ppm. Interestingly, however, the increased moisture concentration does not improve the catalyst lifetime or the CNT forest density, warranting further study of the role of moisture on CNT nucleation versus growth.

Original languageEnglish (US)
Pages (from-to)11277-11287
Number of pages11
JournalJournal of Physical Chemistry C
Volume120
Issue number20
DOIs
StatePublished - May 26 2016

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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