Electromechanical Effects in Carbon Nanotubes

TL;DR

This study uses ab initio calculations to reveal diverse electromechanical behaviors in graphene and carbon nanotubes, including expansion upon electron injection and complex responses to hole injection, explained by a tight-binding model.

Contribution

It provides a comprehensive analysis of electromechanical effects in graphene and CNTs, highlighting behaviors dependent on doping type, nanotube diameter, and electronic properties, with a unified theoretical explanation.

Findings

Both nanotubes and graphene expand upon electron injection.

Hole injection causes non-monotonic lattice behavior in metallic nanotubes and graphene.

Semiconducting CNTs with small diameters always expand upon hole injection.

Abstract

We perform ab initio calculations of charged graphene and single-wall carbon nanotubes (CNTs). A wealth of electromechanical behaviors is obtained: (1) Both nanotubes and graphene expand upon electron injection. (2) Upon hole injection, metallic nanotubes and graphene display a non-monotonic behavior: Upon increasing hole densities, the lattice constant initially contracts, reaches a minimum, and then starts to expand. The hole densities at minimum lattice constants are 0.3 |e|/atom for graphene and between 0.1 and 0.3 |e|/atom for the metallic nanotubes studied. (3)Semiconducting CNTs with small diameters (d <~ 20 A) always expand upon hole injection; (4) Semiconducting CNTs with large diameters (d >~ 20 A) display a behavior intermediate between those of metallic and large-gap CNTs. (5) The strain versus extra charge displays a linear plus power-law behavior, with characteristic exponents for graphene, metallic, and semiconducting CNTs. All these features are physically understood within a simple tight-binding total-energy model.