|Carbon Nanotubes Grown by Chemical Vapour Deposition: A Catalyst Activation Study |
|Cecilia Mattevi, Rutgers MS&E/University of Padua|
12:10 PM, CCR 201
Carbon nanotubes (CNTs) are important constituents of future electronic devices such as interconnects. The main challenge to fully exploit CNTs for potential applications consists of achieving complete control over their synthesis, in particular for surface-bound chemical vapour deposition (CVD) [1,2]. Synthesis control means the ability to selectively obtain isolated CNTs as well as bundles, different types of CNTs (single wall/multi wall), different chiralities and orientations. These goals can be achieved through a complete understanding of the interaction of the catalyst with its environment (substrate and feed stock).
We have investigated the effects of the substrate-catalyst interaction on the growth and the chemical decomposition of the carbon precursor gas on the catalyst clusters and the consequent formation of carbon structures during the growth process itself. We have concentrated on studying the growth by surface bound CVD method using Fe and Ni as catalysts, which are the most commonly used catalysts, but their physical state (solid or liquid) and chemical state (metal, oxide or carbide) related to the used supporting oxide (Al2O3 and SiO2) is in dispute.
By monitoring the chemical state of the catalyst and the substrate at each intermediate state of the catalyst preparation in situ by X-Ray photoemission spectroscopy (XPS) and in parallel the morphology of the surface ex situ by atomic force microscopy (AFM), we have been able to identify how different catalyst-substrate interactions between Fe-Al2O3 and Fe-SiO2, determine the difference in density, direction and type of CNT obtained by using the same pretreatment and growth conditions. Studying the catalyst-hydrocarbon interaction in situ via both environmental TEM (ETEM) and XPS techniques has allowed us to make progress towards an atomistic model of CNT growth. By in situ time-resolved ETEM, we have found that structural selectivity is determined by the dynamic interplay between carbon network formation and catalyst crystalline particle deformation. Our in situ time-resolved XPS study shows the selective acetylene chemisorption on metallic Fe catalyst, which is rapidly followed by the formation of a carbon-rich phase (iron carbide), to finally the formation of a sp2 carbon network characteristic of graphite.
 Hofmann et al., Nano Lett. 7, 602 (2007) .
 Mattevi et al., J. Phys. Chem. C 112, 12207 (2008).
Bio-sketch - Cecilia Mattevi is currently a postdoctoral associate in the Materials Science and Engineering Department at Rutgers University under the supervision of Professor Manish Chhowalla. She received her Ph.D. in Materials Science from the University of Padua in Italy. The primary thrust of her research was related to the characterization of Single Walled Carbon Nanotubes during the various stages of the CVD process. Dr. Mattevi's research was carried out at the CNR-TASC National Laboratory and Elettra Synchrotron Facility in Trieste, Italy.
Host: Manish Chhowalla x5-5619