COMPUTATIONAL STUDIES ON FORMATION AND PROPERTIES OF CARBON NANOTUBES

Tahir Cagin, Jianwei Che, Weiqiao Deng, Xin Xu, William A Goddard, III

Materials and Process Simulation Center, Beckman Institute, 139-74, California Institute of Technology, Pasadena, California, USA

Abstract

The peculiar chemistry of carbon results in diverse forms of structure: the 3-dimensional network of diamond and the 2- dimensional sheets of graphite have been known through the ages. The discovery of lower dimensional forms with unique mechanical and electronic properties has generated new possibilities in many areas of technology especially in nanotechnology. Recent emergence of some nanoscale device applications show how this potential is turning into a reality.

Over the years, we have been using ab initio quantum chemistry, density functional theory and molecular dynamics methods to study the structure and properties of carbon based materials for nanoscale applications. In this paper, first we will present a brief review of the methods and some earlier applications: a) Structural and mechanical properties of nanotubes; a) Tribological properties of carbon for NEMS applications; and c) Thermal transport properties of nanotubes and carbon based hetero-structures.

We will also present two new theoretical studies. In the first application, we investigate the relation between mechanical deformation and excess charge in order to understand how introducing and controlling the charge at various locations might modify the mechanical and acoustical properties of carbon nanotubes. We demonstrate that introducing excess charges into single wall carbon nanotubes can lead mechanical deformations that do mechanical work. The results suggest a wide range for practical applications, such as NEMS, acoustic sensors and nanoactuators. Over the past several years a large number of synthetic procedures for the production of Carbon nanotubes have been developed. Since the electronic properties of carbon nanotubes depend on structure the control of growth is essential. Theoretical studies of growth mechanisms may shed some light on how to control the growth. We will present a study on the transition metal catalyzed growth of single wall carbon nanotubes.

A sample charge density map of SWCNT (from DFT). Nickel catalyzed CNT growth, reaction pathways.

Keywords: Modeling, Carbon nanotubes, Nanotube Growth, Deformation, Charged Nanotubes.

Posting online: tahir@wag.caltech.edu http://www.wag.caltech.edu/home/tahir/

Tahir Cagin

California Institute of Technology

1200 E California Blvd., MS 139-74

Pasadena, CA 91125 USA

Fax: (626) 585-0518

Tel: (626) 395–2728