Huge Volume Expansion and Structural Transformation of Carbon Nanotube Aligned Arrays during Electrical Breakdown in Vacuum

TL;DR

This study reveals that electrical breakdown in vacuum causes massive volume expansion and structural transformation of aligned SWNT arrays, turning them into nanoparticle and amorphous carbon structures with increased resistance.

Contribution

It demonstrates the large-scale volume expansion and structural change of SWNT arrays during electrical breakdown, including detailed microscopy and spectroscopy analysis.

Findings

Volume expansion of ~400 times observed

Transformation from graphitic to amorphous carbon

Increase in electrical resistance after transformation

Abstract

We observed a huge volume expansion of aligned single walled carbon nanotube (SWNT) arrays accompanied by structural transformation during electrical breakdown in vacuum. The SWNT arrays were assembled between prefabricated Pd source and drain electrodes of 2 \mu m separation on Si/SiO_2 substrate via dielectrophoresis. At high electrical field, the SWNT arrays erupt into large mushroom-like structure. Systematic studies with controlled electrical bias show that above a certain field SWNTs swell and transform to nanoparticles and flower-like structures with small volume increase. Further increase in electrical bias and repeated sweeping results into amorphous carbon as determined from scanning and transmission electron microscopy (TEM). Cross sectional studies using focused ion beam and TEM show the height of 2-3 nm SWNT array increased to about 1 \mu m with a volume gain of ~ 400 times. The electron energy loss spectroscopy reveals that graphitic sp^2 networks of SWNTs are transformed predominantly to sp^3. The current-voltage measurements also show an increase in the resistance of the transformed structure.