Realizing room-temperature self-powered ethanol sensing of Au/ZnO nanowire arrays by coupling the piezotronics effect of ZnO and the catalysis of noble metal

Chemoresistive sensors based on multiwalled carbon nanotubes (MWCNTs) functionalized with SnO2 nanocrystals (NCs) have great potential for detecting trace gases at low concentrations (single ppm levels) at room temperature, because the SnO2 nanocrystals act as active sites for the chemisorption of gas molecules, and carbon nanotubes (CNTs) act as an excellent current carrying platform, allowing the adsorption of gas on SnO2 to modulate the resistance of the CNTs. However, uniform conjugation of SnO2 NCs with MWCNTs is challenging. An effective atomic layer deposition based approach to functionalize the surface of MWCNTs with SnO2 NCs, resulting in a novel CH4 sensor with 10 ppm sensitivity, is presented in this paper. Scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy, and Raman spectroscopy were implemented to study the morphology, elemental composition, and the crystal quality of SnO2 functionalized MWCNTs. High resolution TEM images showed that the crystal quality of the functionalizing SnO2 NCs was of high quality with clear lattice fringes and the dimension almost three times smaller than shown thus far in literature. A lift-off based photolithography technique comprising bilayer photoresists was optimized to fabricate SnO2 functionalized MWCNTs-based chemoresistor sensor, which at room temperature can reliably sense below 10 ppm of CH4 in air. Such low level gas sensitivity, with significant reversible relative resistance change, is believed to be the direct result of the successful functionalization of the MWCNT surface by SnO2 NCs.

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The authors present a comparative analysis of ultraviolet-O 3 (UVO) and O 2 plasma-based surface activation processes of multiwalled carbon nanotubes (MWCNTs), enabling highly effective functionalization with metal oxide nanocrystals (MONCs). Experimental results from transmission electron microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy show that by forming COOH (carboxyl), C-OH (hydroxyl), and C¼O (carbonyl) groups on the MWCNT surface that act as active nucleation sites, O 2 plasma and UVO-based dry pretreatment techniques greatly enhance the affinity between the MWCNT surface and the functionalizing MONCs. MONCs, such as ZnO and SnO 2 , deposited by the atomic layer deposition technique, were implemented as the functionalizing material following UVO and O 2 plasma activation of MWCNTs. A comparative study on the relative resistance changes of O 2 plasma and UVO activated MWCNT functionalized with MONC in the presence of 10 ppm methane (CH 4) in air is presented as well. V