The Role Played by Strain Fields, Dislocation Arrays, and Domain Boundaries During the Catalytic Synthesis of Carbon Nan
- PDF / 235,901 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 169 Views
0900-O01-01.1
The Role Played by Strain Fields, Dislocation Arrays, and Domain Boundaries in the Catalytic Synthesis of Carbon Nanotubes Ludovico M. Dell’Acqua-Bellavitis 1,3, *, Jake D. Ballard 2,3, Robert Vajtai 2,3, Pulickel M. Ajayan 2,3, Richard W. Siegel 2,3 1. Department of Engineering Science, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 U.S.A. 2. Department of Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York 121803590 U.S.A. 3. Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 U.S.A. ABSTRACT Ex-situ transmission electron microscopy (TEM) was performed on catalytically-grown multi-wall carbon nanotubes (MWCNTs), leading to the identification of two types of catalyst-nanotube wall interfaces – respectively characterized by a quasi-spherical, low aspect ratio particle closer to the nanotube root and by a tapered, high aspect ratio particle farther away from it. The nanotubes exhibit two distinct types of boundaries between crystalline domains with different orientations – twist and twin boundaries in correspondence with quasi-spherical particles and tilt boundaries in correspondence with the tapered particles. TEM evidence suggests that the domain boundaries maintain a rather steady position coupled to the catalytic particles, while carbon atoms diffuse along the nanotube axis away from the particles. From these considerations, it is possible to conclude that the relative movement of the carbon atoms with respect to the dislocation lines comprising the nanotube domain boundary located at the catalyst-wall interface is a significant mechanism for nanotube crystal growth mainly driven by surface diffusion. The results are interpreted in light of the concurrence of base- and tip- growth for the catalytic synthesis of nanotubes dominated by surface diffusion.
INTRODUCTION The traditional view on nanotube catalytic growth maintains two distinct possible scenarios on the direction of carbon precipitation in the catalytic particle – respectively called the base growth [1] and the tip growth model [2]. A previous study on the catalytic synthesis of MWCNTs led to the formulation of a concurrent base and tip growth model for successive catalyst particles [3, 4]. According to this model, each nanotube is formed by a succession of iterative catalytic steps that concurrently catalyse carbon in the upward (in the case of base growth) and in the downward (in the case of tip growth) directions. The focus of the present study lies in the analysis of the interface between catalytic particles and the graphitic layers at the nanotube wall using TEM, in an attempt to explore the validity of the model of concurrent base and tip growth within this critical interfacial region. Several studies have used transmission electron microscopy (TEM) to investigate the structure of carbon nanotubes (CNTs) grown catalytically by chemical vapour deposition (CVD) in an effort to relate to specific growth models [5-8] and to a general kinetic theory of n
Data Loading...
