Improvement in gas sensitivity of carbon nanotube to volatile organic compounds by covering zinc oxide nanowire

Abstract

Carbon nanotubes (CNTs) have been utilized in many gas sensor structures, individually or in hybrid form with other materials to enhance their gas sensing properties. CNT and CNT–ZnO nanowire structures were fabricated by plasma-enhanced chemical vapor deposition (PECVD) and hydrothermal growth methods to explore and compare their gas sensing properties. The morphologies of the fabricated samples were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. Gas sensing properties of fabricated samples were assessed at different atmospheric and thermal conditions. Results verified CNT–ZnO has two times higher response than the CNT sample toward volatile organic compounds vapor at room temperature. A longer lifetime and more stability are other advantages of the CNT–ZnO hybrid. Moreover, it is shown that increasing the length of ZnO nanowires exhibits a higher response to examined analytes. It was found that increasing the temperature causes different sensing regimes in CNT and CNT–ZnO samples. At all ranges of temperatures, the resistance of CNT samples increased in the presence of reducing gases while CNT–ZnO samples exhibited similar behavior only below ∼90 °C. At elevated temperatures, their resistances decreased in response to the same gases.