Systematic growth of carbon nanotubes on aluminum substrate for enhanced field emission performance

Abstract

For more than two decades, carbon nanotubes (CNTs) have shown great potential for a wide range of applications. Several methods are known to synthesize CNTs, though only a few of them are able to produce good quality and economically available CNTs. Chemical vapor deposition (CVD) is one of those methods that produce economically feasible and good quality CNTs onto specific substrates, even with nanopatterning. However, growing CNTs by CVD at temperatures below 700 °C remained a long-time challenge, as this meant keeping a host of low-melting materials out of bounds for direct CNT growth on them. In this work, CNTs have been synthesized directly onto a low-melting, conducting substrate, aluminum, by thermal CVD, at a temperature as low as 550 °C and up to as high as 650 °C (just below the melting point of aluminum). The diameters of the grown CNTs were observed to be influenced by process parameters, e.g., temperature and pressure. The effect of synthesis parameters on CNT diameters was verified by scanning electron microscopy and transmission electron microscopy. The quality of the CNTs was checked by Raman spectroscopy, selected area electron diffraction pattern of transmission electron microscopy, and XPS. It was observed that an increase in temperature and pressure had a significant effect on the diameters of the CNTs. Randomly entangled CNTs were measured to have an average diameter of 28 nm at 550 °C and one atmospheric (760 Torr) pressure, whereas it was observed to be 78 nm at a temperature of 650 °C and pressure of 0.01 Torr. The field emission response, i.e., the turn-on field (2.5 V/μm) and the maximum emission current density (2.17 mA/cm2) of the CNTs synthesized at the temperature of 550 °C and pressure of 1 atm (760 Torr) was found to be excellent.