Computational Studies of Defects in Nanoscale Carbon Materials
Metals on Carbon Nanotubes
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The interface between metals and carbon nanotubes is of interest in a wide range of domains: metallic contacts for nanoelectronic applications, interfaces between metallic nanoparticles and carbon nanotubes for catalysis or gas sensing, etc.
One area of potential application for carbon nanotubes (CNTs) is in gas sensing. However pristine nanotubes typically show low sensitivity, which has been ascribed to lack of reactivity of the CNT surfaces. In order to overcome this, cold low-pressure RF plasma methods have been shown to efficiently activate the surface of CNTs through the introduction of surface defects, or active sites. The deposition and growth behaviour of metal nanoclusters on CNTs differs dramatically depending on whether the surface of the tube has been activated by such a plasma treatment. Metal cluster morphology is dictated by interactions between the deposited atoms and the CNT surface. Thus, fine control of the local defects (type: structural or chemical; density) can be used to tune the interfacial properties of the metal clusters, that will determine their size and shape, diffusion (or not) avoiding aggregation, coalescence and complete wetting.
Modern theoretical modelling provides an unprecedented tool for realistic simulations of complex and messy experimental systems such as these. In particular a detailed understanding of the atomic structure and behaviour of the plasma induced surface active sites is required, as well as the resultant interaction with metal atoms and nanoparticles. Using DFT (AIMPRO) and DFTB+ codes we examine both graphene and CNTs with a variety of oxygen and fluorine plasma induced defects, as well as their interaction with a variety of metal species, notably Au, Pd and Ti. We correlate our results with experimental HRTEM, XPS and X-ray and Ultraviolet photoemission spectroscopy results of both plasma- treated and non-treated CNTs. Modelling successfully provides a complete picture of surface binding, diffusion and aggregation properties for these metals, notably highlighting fundamental differences in their surface chemical and electronic behaviour.
 C. Bittencourt, G. Van Lier, X. Ke, I. Suarez-Martinez, A. Felten, J. Ghijsen, G. Van Tendeloo, C. P. Ewels, ChemPhysChem accepted (2009).
 I. Suarez-Martinez, C. Bittencourt, X. Ke, A. Felten, J. -J. Pireaux, J. Ghijsen, W. Drube, G. Van Tendeloo, C. P. Ewels, Carbon accepted (2009).