In the search for gas sensors with enhanced performance low-dimensional nanomaterials such as carbon nanotubes are attracting increasing interest. Their huge surface to volume ratio greatly increases sensitivity. However, selectivity still remains an important issue to be addressed.

In the last few years our approach to enhance selectivity has consisted of using plasma treatments to control interfacial (structural and chemical) defects that rule the deposition and growth of metal nanoclusters deposited on carbon nanotube sidewalls. Metal cluster surfaces act as reactive sites for the adsorption of the target molecules, and a substantial polarisation and accumulation of charge in the region between the metal cluster and the nanotube may result. This charge transfer provides important information regarding the system’s electronic response. It affects the ionic component of the bonding, alters the position of the Fermi level and the band alignment (electron transport in the nanotube is affected).

In this lecture, cold plasma methods for cleaning, creating defects, functionalising and decorating with metal nanoclusters the surface of multiwall carbon nanotubes in a single step are reviewed. Details on the fabrication of gas sensors based on the resulting nanohybrid materials are given and the gas sensing properties towards traces of toxic gases such as NO2, CO, hydrocarbons and also humidity in air are shown. In order to better understand the observed gas sensing properties, a realistic description of the gas-nanohybrid material interaction (including electronic transport calculations) is provided based on density functional theory. While the presence of metal clusters favours the detection of some species (case of NO2), it is the presence of oxygenated defects caused by the plasma treatment what favours the detection of other species (case of CO).

Nano2Hybrids project (EC-STREP-033311).

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