Robust Synthesis and Continuous Manufacturing of Carbon Nanotube Forests and Graphene Films.

Abstract

Successful translation of the outstanding properties of carbon nanotubes (CNTs) and graphene to commercial applications requires highly consistent methods of synthesis, using scalable and cost-effective machines. This thesis presents robust process conditions and a series of process operations that will enable integrated roll-to-roll (R2R) CNT and graphene growth on flexible substrates.

First, a comprehensive study was undertaken to establish the sources of variation in laboratory CVD growth of CNT forests. Statistical analysis identified factors that contribute to variation in forest height and density including ambient humidity, sample position in the reactor, and barometric pressure. Implementation of system modifications and user procedures reduced the variation in height and density by 50% and 54% respectively.

With improved growth, two new methods for continuous deposition and patterning of catalyst nanoparticles for CNT forest growth were developed, enabling the diameter, density and pattern geometry to be tailored through the control of process parameters. Convective assembly of catalyst nanoparticles in solution enables growth of CNT forests with density 3-fold higher than using sputtered catalyst films with the same growth parameters. Additionally, laser printing of magnetic ink character recognition toner provides a large scale patterning method, with digital control of the pattern density and tunable CNT density via laser intensity.

A concentric tube CVD reactor was conceptualized, designed and built for R2R growth of CNT forests and graphene on flexible substrates helically fed through the annular gap. The design enables downstream injection of the hydrocarbon source, and gas consumption is reduced 90% compared to a standard tube furnace. Multi-wall CNT forests are grown continuously on metallic and ceramic fiber substrates at 33 mm/min. High quality, uniform bi- and multi-layer graphene is grown on Cu and Ni foils at 25 - 495 mm/min. A second machine for continuous forest growth and delamination was developed; and forest-substrate adhesion strength was controlled through CVD parameters.

Taken together, these methods enable uniform R2R processing of CNT forests and graphene with engineered properties. Last, it is projected that foreseeable improvements in CNT forest quality and density using these methods will result in electrical and thermal properties that exceed state-of-the-art bulk materials.