Water-Assisted Catalytic VACNT Growth Optimization for Speed and Height

Abstract

The super-growth approach for carbon nanotubes synthesis is frequently used to boost the growth rate, catalyst lifespan, and height of vertically aligned carbon nanotubes. The elimination of amorphous carbon from catalyst particles, commonly made of iron, by injecting water vapor into a chemical vapor deposition process can enhance the purity, alignment, and height of carbon nanotubes and prevent the partial oxidation of the metallic catalyst. We present the development of a modified growth-optimized water-assisted super-growth vertically aligned carbon nanotube process by optimizing the catalyst layer structure and water vapor concentration for a carbon nanotube growth process for 4” diameter Si wafers. A significant finding is that under optimized water-assisted growth conditions over 4 mm, highly uniform tall, vertically aligned carbon nanotube structures can be grown with a minimum top crust layer of about ~5–10 μm thickness. This was achieved with a catalyst film comprising a >400 mm thermal SiO2 layer on top of a 4” diameter Si wafer that was overcoated with an e-beam batch process run that first deposited a 20 nm SiO2 layer, a 10 nm Al2O3 layer, and a 1.1 nm Fe layer, in a 4-h growth process step.