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Novel Chemoresistive CH4 Sensor with 10 ppm Sensitivity Based on Multi-Walled Carbon Nanotubes (MWCNTs) Functionalized with SnO2nanocrystals
Citation:
Humayun, M., R. Divan, Y. Liu, L. Gundel, P. Solomon, AND I. Paprotny. Novel Chemoresistive CH4 Sensor with 10 ppm Sensitivity Based on Multi-Walled Carbon Nanotubes (MWCNTs) Functionalized with SnO2nanocrystals. Journal of Vacuum Science & Technology A. AIP Publishing, Melville, NY, 34:01A131, (2016).
Impact/Purpose:
Semiconductive SnO2 is widely used in gas sensing metal oxide sensors1{5. However, the use of bare SnO2 as a gas sensor is limited by the requirement for continouous heating to initiate the surface chemisorption of O2; a pre-requisite for the SnO2 to react with the target gas species1{5. On the other hand, due to the excellent sur-
face area to volume ratio and extraordinary electronic property arising from its one dimensional nano-scale cylindrical shape, CNTs show remarkable modulation of
electrical properties, enabling the detection of low levels (about a ppm) gaseous species at room temperature6{9. However, the surface of bare CNTs is non-reactive to
many gas molecules, and in order to obtain selective gas sensing it is necessary to functionalize the surface of the CNTs, i.e, embedding it with active sites, by controlled deposition of functionalizing nano-materials8{12. Thus the nano-scale integration of SnO2 and CNTs opens a unique path to building sensitive (
Description:
Chemoresistive sensors based on multi-walled carbon nanotubes (MWCNTs)functionalized with SnO2 nanocrystals 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, andCNTs 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 e?ective atomic layer deposition (ALD) 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 electronmicroscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX), and Raman spectroscopy were implemented to study the morphology, elemental composition, and the crystal quality of SnO2 functionalized MWCNTs. High resolution TEM (HRTEM) images showed that the crystal quality of the functionalizing SnO2 NCs was of high quality with clear lattice fringes and the dimension almost 3 times smaller than shown thus far in literature. A lift-o? based photolithography technique comprising bi-layer 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 signicant reversible relative resistance change, is believed to be the direct result of the successful functionalization of the MWCNT surface by SnO2 NCs.
