Atomic layer deposition of titanium dioxide on multi-walled carbon nanotubes for ammonia gas sensing

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Authors

KAUSHIK Preeti ZAJICKOVA Lenka ELIÁŠ Marek MICHALICKA Jan HEGEMANN Dirk PYTLÍČEK Zdenek NEČAS David ZAJÍČKOVÁ Lenka

Year of publication 2019
Type Article in Periodical
Magazine / Source Surface & coatings technology
MU Faculty or unit

Faculty of Science

Citation
Web Full Text
Doi http://dx.doi.org/10.1016/j.surfcoat.2019.04.031
Keywords Carbon nanotubes; Chemiresistive sensor; Ammonia; Titanium dioxide; Atomic layer deposition; Carboxyl plasma polymer
Description 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 double layer showed higher response as compared to the pristine CNTs and those without the carboxyl PP film.
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