Simultaneous growth of MWCNTs at different temperatures in a variable gradient furnace

Multi-walled carbon nanotubes (MWCNTs) have been grown, simultaneously at different temperatures (600 degrees C, 700 degrees C, 725 degrees C, and 750 degrees C), by thermal chemical vapour deposition (CVD) of acetylene (C(2)H(2)) gas, in ammonia (NH(3)) atmosphere. The samples have been characterized morphologically by scanning electron microscopy (SEM) and a structurally by Raman spectroscopy. These analyses show that, when the temperature of substrate increases, the CNT average diameter and the density distribution decrease, and the CNTs are less defective. However there is a temperature limit (725 degrees C) for CNT growth. We have grown CNTs onto Si(3)N(4)/Si substrates with Pt electrodes, in order to realize the gas sensing devices. The CNTs grown at 725 degrees C, exhibit a fast response and a high sensitivity to NO(2) gas.