Substrate effect on the properties of functionalized multiwalled carbon nanotubes grown by e-beam evaporation for high performance H2O2 detection

Abstract

In the present study, the properties of functionalized multiwalled carbon nanotube thin films deposited on Ta and Al₂O₃ substrates were compared for better electrochemical sensing performance towards H₂O₂. We pioneer the fabrication of high quality carbon nanotubes by electron beam evaporation at a high vacuum of 10⁻⁶ mTorr. The fabricated films were further characterised using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Crystallographic properties revealed that the carbon nanotube (CNT) film grown on the Al₂O₃ substrate exhibits a preferentially oriented (002) peak with high intensity compared to that on Ta. CNTs fabricated on a Ta substrate show better morphology with tightly packed grains and decreased nanotube diameter than the film on sapphire. TEM images confirmed the well adherent and dense nature of the nanotubes on Ta. Electrochemical H₂O₂ sensors were constructed to demonstrate the sensing performance of CNT/Ta and CNT/sapphire electrodes. CV curves of the samples show high sensitivity for the MWCNT film grown on Ta due to the highly conductive acid resisting nature of the substrate, overcoming the obstacles to electrochemical H₂O₂ sensing. Compared with the CNT/sapphire electrode, the CNT/Ta electrode exhibited high electrocatalytic activity towards the oxidation of H₂O₂, as distinct nanotubes are electrochemically linked with the conductive Ta substrate_. The CNTs on Ta revealed a very low detection limit of 0.07 μm due to the nanoporous morphology of the film which supported better penetration of electrolytes into the electrode material. The synergetic electrocatalytic effect of the CNT/Ta electrode with excellent redox chemistry is promising for the development of highly sensitive biosensors.