Multiscale modeling approach to catalytic growth of carbon nanotubes

William Marsh Rice University, Houston TX

Investigators

Abstract

0731246 Yakobson, Boris Production and quality control of carbon nanotubes hinges on the tiny metal catalyst particles which serve as nano-reactors". They decompose the feedstock gas to dissolve the released carbon atoms, which then rapidly diffuse to feed the growth of a carbon stem, a nanotube. The robustness of this process, its yield and the particular physical type of the emerging tubule-its diameter and chiral symmetry-are all determined by the drama of atomic dynamics and chemical interactions within this few cubic nanometers. In spite of great technological importance and decade-long progress in nanotube synthesis and theoretical modeling, the fundamental understanding of the processes guiding nanotube nucleation and growth is lacking. Based on previous experience, we propose a systematic study to advance the science of nanotube growth. Among several important aspects, we focus mainly on the (i) structure and state of the catalyst particle and its interface with the nanotube edge, (ii) the mechanisms of catalyst poisoning and how it can be delayed or prevented, and (iii) the defect annealing in the course of tube growth; the latter will further be connected with finding possible mechanisms defining the chirality of the emerging tube and how it can possibly be controlled. The intellectual merit of the proposed research lies in advancing the understanding of the intimate atomic mechanisms of carbon nanotube growth. In particular, it should reveal the interatomic physico-chemical interactions inside and at the surface of the catalyst particle. We plan to connect three scales of study (ab initio, atomistic-classical MD, and continuum phenomenological model), which has additional merit from the multiscale modeling viewpoint. The main intellectual value of course will lie in revealing the catalyst poisoning mechanism and how to reduce it, the structure of catalyst particle-nanotube interface, and the exact mechanisms of atomic accretion of carbon and the annealing of the structural defects in the body of the growing tube, in order to maintain its perfection. Based on accumulated knowledge we hope to suggest possible paths to achieving controlled chirality (and diameter) specific growth of nanotubes-a holy grail of materials chemists and especially carbon nanotube researchers and technology users. Beyond carbon nanotubes, the effort should provide more general insights into catalytic growth of other nearly-one-dimensional structures. General features established for carbon tubules may apply to boron-nitride tubes, and yet broader class of nanowires (silicon, boron, and other important inorganic compositions). Elements of educational activities are seamlessly integrated in this three-year project. An undergraduate and a graduate student will interact closely with the PI and Co-PI (as well as with nearly a dozen of other students and postdocs presently in the PI's group). The cross-disciplinary nature of the project, involving elements of computational quantum chemistry, molecular dynamics, nanomechanics, and dislocation theory, encourages training of truly interdisciplinary scientists. Elements of the research will be eventually incorporated into the already-offered (by PI) course MSCI614 Principles of Nanoscale Materials". The graduate student will gain some teaching experience through offering (later in the project) a few lectures within the course, on the topics related to this project. Rice has been working very aggressively at increasing the participation of underrepresented groups through targeted recruiting efforts. In this case, within the project we anticipate to engage Rice undergraduates and students from Mexico (who have previously spent the summer in the PI's group). We will work closely with DOD Air Force Research Laboratory (Materials Directorate) specifically interested in novel CNT-based materials, and with DOE ORNL colleagues interested in carbon nanostructure synthetic routs and improvements.