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Preeti Kaushik, Marek Eliáš, Jan Michalička, Dirk Hegemann, Zdeněk Pytlíček, David Nečas, Lenka Zajíčková

Atomic Layer Deposition of Titanium Dioxide on Multi-Walled Carbon Nanotubes for Ammonia Gas Sensing

Surface and Coatings Technology 370 (2019) 235-243

Carbon nanotube (CNTs)-metal oxide semiconductor (MOS) hybrid nanostructures can provide a new pathway for room temperature chemiresistive gas sensors due to combined properties of both the materials and the creation of heterojunctions between CNTs and MOS. Multi-walled carbon nanotubes (MWCNTs) were grown on Si substrates coated with SiO2 layer by catalytic chemical vapor deposition (CCVD) and coated by TiO2 films of different nominal thicknesses, 5, 10 and 20 nm, using atomic layer deposition (ALD). ALD is a self-limiting surface process providing highly uniform and conformal coatings if reactive sites exist on the surface. The CNT surface is quite inert and therefore, a modification of MWCNTs by carboxyl plasma polymer (PP) film was applied prior to ALD of TiO2. The carboxyl PPs improved film uniformity, even though the thinnest TiO2 film still formed an island-like structure. Raman spectroscopy revealed that coating by TiO2 or carboxyl PP increased structural disorder of sp2 carbon in the MWCNTs and the thinnest TiO2 coatings induced the lowest disorder. The thinnest coatings also resulted in the highest sensor response to NH3. Nevertheless, for all thicknesses the sensors coated with carboxyl PP/TiO2 doublelayer showed higher response as compared to the pristine CNTs and those without the carboxyl PP film.

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DOI: 10.1016/j.surfcoat.2019.04.031

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