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ZnO Functionalization of Surface Pre-treated Multi-walled Carbon Nanotubes for Methane Sensing
Citation:
Humayun, T., R. Divan, L. Stan, A. Gupta, D. Rosenmann, Y. Liu, L. Gundel, P. Solomon, AND I. Paprotny. ZnO Functionalization of Surface Pre-treated Multi-walled Carbon Nanotubes for Methane Sensing. 2015 Advanced Photon Source/Center for Nanoscsle Material Users Meeting, Argonne, IL, May 11 - 14, 2015.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA mission to protect human health and the environment. HEASD research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Description:
Bare carbon nanotubes (CNTs) cannot be used to sense most gases due to poor bonding between the chemically inert graphitic surface and the different compounds CNTs are exposed to. Consequently, for gas sensing applications, functionalization of CNTs with reactive compounds is required. By introducing surface pre-treatments prior to functionalization, the affinity of the functionalizing species is enhanced, enabling the fabrication of highly sensitive CNT chemiresistor-based sensors. Atomic layer deposition (ALD) allows precise, uniform and conformal deposition of oxide coatings on geometrically complex substrates such as Multi–Walled CNTs (MWCNTs) ; thus offering a suitable route for the functionalization of MWCNTs for gas sensing applications. Motivated by the energetically favorable electron transport in ZnO-MWCNT junctions , we have performed ALD of ZnO for functionalizing O2 plasma and UV-O3 treated MWCNTs. Diethylzinc ((C2H5)2Zn) was used as an ALD precursor. Deposition was performed at three different temperatures, 175, 200 and 225 0C, with an Arradiance Gemstar ALD tool. Transmission electron microscopy (TEM) images show uniform deposition of ZnO nanoparticle (NP) layers on the MWCNTs. At ALD temperatures of 175 0C and 200 0C, the average NP size was found to be 7.2 nm (standard deviation [SD], 1.18 nm) and 10.8 nm (SD 1.81 nm) respectively. The higher resolution TEM image illustrates the wurtzite structure of the ZnO-NP and its good crystalline quality. The interplanar spacing of 2.8Å, 2.68Å and 2.48Å correspond to <100>, <002> and <101> planes of ZnO . Raman spectroscopy also suggests good crystal quality of ZnO-NP. The chemiresistor sensors based on the ZnO-functionalized MWCNTs were used to detect ppm level concentrations of methane in ‘zero-air’ at room temperature
