Materials World Network: Novel Catalyst Systems for Carbon Nanotube (CNT) Synthesis and their Underlying Mechanisms

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This is a joint research program between the Massachusetts Institute of Technology (MIT) and the University of Cambridge in the United Kingdom. Chemical vapor deposition (CVD) techniques employing nanoparticulate catalysts have proven to be versatile and effective methods for synthesizing carbon nanostructures and, importantly, have enabled extensive investigation of these structures. Despite these successes, however, the mechanism(s) underlying the nucleation of graphitic layers and carbon nanotubes (CNTs) and their growth kinetics by CVD remain poorly understood. Without this understanding, practical integration of CNTs into complex devices and larger-scale materials remains exceedingly challenging, as synthesis and placement of CNTs needed for many applications are often not attainable or scalable. Important examples are the incorporation of CNTs into integrated circuits and into multi-scale hierarchical composites. Whereas most of the literature focuses on metallic catalysts and their interactions, the investigators in this project have recently demonstrated that an oxide, zirconia (ZrO2), can act as a nucleation and growth site for both single and multi-wall CNTs. This finding opens a unique opportunity to gain more insight into the self-organisation of carbon into graphitic nanostructures and promises new routes towards applications. This project explores mechanisms of graphene and CNT formation based on a broad range of identified oxide-based catalysts, and focus on new growth variables that are known in the oxide-catalysis community but have not been explored for graphene/CNT synthesis due to the focus on metal nanoparticles. An in-situ characterisation approach is applied, combining techniques such as in-situ x-ray photoelectron spectroscopy (XPS) and environmental transmission electron microscopy (ETEM) to resolve the size-dependent behavior of catalytically active oxides during the exposure to specific gaseous carbon precursors at elevated temperatures. The synthesis findings will feed directly back into application areas, such as electronics, hierarchical composites, photonics, and biology, where metal-contaminant free, reproducible, clean, deterministic growth of carbon nanostructures is of key importance. A key feature of the research is exchange of students between MIT and the University of Cambridge, including joint experimental investigations at locations in the U.S. and Europe.