National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Award Achievements (Nuggets)
Notable Accomplishments from CBET Awards
How Do Carbon Nanotubes Grow?
Boris Yakobson    William Marsh Rice University
Feng Ding

Background:  How do carbon nanotubes grow?  The intimate mechanisms of carbon nanotube growth have provided scientists and engineers with a compelling puzzle for more than decade.  Lack of experiments permitting the direct "viewing" of atomic-scale events along with seemingly chaotic data from computer simulations, such molecular dynamics, have added to this complex problem.  Professor Boris Yakobson from Rice University and his research team have elucidated novel insight into nanotube growth by using mathematical models.
Nanotubes grow in a twisting pattern as they self-assemble with new atoms attaching to the end as the tube forms.  The growth of the nanotubes depends on their chiral symmetry, or helicity.  One could compare this growth to a roll of gift-wrapping paper that is being rolled up.  As the roll of gift-wrapping paper is formed into a tube, excess paper sometimes hangs off the end.  As they form, nanotubes appear rolled, or twisted, resulting with an odd angle with the ends "hanging off" where new atoms are attached.  This angle is called the nanotube's "chiral" angle.  The larger the chiral angle, the more loose thread-ends are available to accept arriving atoms and, hence, the faster the tube grows.

Results:  The research team's efforts resulted in finding a direct proportional relationship between a nanotube's chiral angle (the amount the nanotube is twisted) and how fast it grows.  These results lead to a deeper understanding of growth regularity and to direct quantitative predictions of growth rate, as being proportional to the chiral angle, in comparison to available experimental data.

Boris Yakobson 1
    Figure 1Field-emission microscopy demonstrates unambiguous rotation of a growing tube [Nano Letters 2009].
Image Credit:  Kerry Wang, Rice University

Boris Yakobson 2
    Figure 2The atomic wall-tapestry of nanotubes depends on their chiral symmetry or helicity [Proceedings of the National Academy of Sciences, 2009].
Image Credit:  M. Bankehsaz and B.I. Yakobson;  Rice University

This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
Primary Strategic Outcome Goal:        (1) Discovery:  The fact that chiral symmetry controls the nanotubes growth rate, discovered through theoretical analysis, has further triggered experiments leading to discovery (through field-emission microscopy in situ video) of the rotational motion on a catalyst-to prompts including Galileo's "And yet it does turn" in the title of research paper [2009, Nano Letters].
                                                                     (1) Discovery Category:
                                                                            - Computer & Information Science and Engineering
                                                                            - Engineering Research
                                                                            - Mathematical & Physical Sciences

Secondary Strategic Outcome Goals:  (2) Learning:  The work directly involved underrepresented group students.  Moreover, it appeals to high-school students and has presently motivated a video game-development.  Through publicity, it raised awareness of a broad population in science and nanotechnology.  The material has been used in the lectures for Lockheed Martin Corporation Engineers.
                                                                     (2) Learning Categories:
                                                                            - Graduate Education and Graduate Student Research
                                                                            - Public Understanding of Science and Lifelong Learning
                                                                            - Broadening Participation to Improve Workforce Development

In terms of Intellectual Merit, this work is notable in helping to solve a long-standing puzzle involving the regularities and mechanisms of self-assembly for a key nanostructure, the carbon nanotube.

In terms of Broader Impacts, this work is notable. Understanding how carbon nanotubes grow can impact a variety of electronic and material applications.  These results could impact nano-electronic devices, large scale integrated circuits, gas sensors due to nanotubes' semiconducting and metallic properties.  Also, since carbon nanotubes are strong and lightweight, they could be used in important applications involving space technology, vehicles, and the military.
Additionally, an underrepresented PhD student received training as a result of this research.

This research is Transformative and has assessed the controlled process of nanotube growth whereas in previous studies the method of growth was viewed as chaotic.  The research reveals a very regular, controlled behavior which sets several compelling goals for future verification and refinement.

This research represents Broadening Participation.  Involved in this research and in an upcoming publication is a Hispanic female-scientist PhD candidate, Morgana Ribas.

Existing or potential Societal Benefits of this research:  This research could possibly open the way to controlled growth of nanotubes of given chirality, which is the holy grail of nanotube-based devices, electronics, and nanotechnology.

Program Director:
George Antos
CBET Program Director - Catalysis and Biocatalysis
NSF Award Number:   0731246
Award Title:   Multiscale modeling approach to catalytic growth of carbon nanotubes
PI Name:
  Boris Yakobson
Feng Ding  (Co-Principal Investigator)
Institution Name:   William Marsh Rice University;  Houston, Texas
Program Element Code:   1401
NSF Investments:   National Nanotechnology Initiative (NNI)
CBET Nugget:

  FY 2009

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This Nugget was Updated on 13 August 2010.