In this study, they utilized medium power continuous wave CO2 laser to irradiate a sensitized mixture of Fe(CO)5 vapour and acetylene to heat the silicon substrate simultaneously on which CNTs were grown [52]. Similarly, Lackey et al. also demonstrated the use of LCVD for the synthesis of CNTs [53]. A novel continuous process registered by Khodadadi et al. involves catalytic chemical vapour deposition (CCVD) of methane on iron Inhibitors,research,lifescience,medical floating catalyst in situ deposited on MgO in fluidized bed reactor for the production of CNTs [54]. A major drawback associated with the CVD technique is that there

are high defect densities in the MWNT structures grown by this process due to the lack of sufficient thermal energy for annealing CNTs

because of relatively low growth temperature [55]. 2.3. Laser Ablation Method Inhibitors,research,lifescience,medical This method was developed by Smalley et al., in which direct laser beam was focused on transition-metal/graphite composite rods to produce SWCNTs [56]. In the laser ablation process, a pulsed laser is made to strike at a graphite target in a high temperature reactor (furnace) in the presence of inert gas such as helium which vaporizes the graphite target Inhibitors,research,lifescience,medical and forms a laser plume. The laser plume contains vaporized carbon and metallic nanoparticles that lead to the reassembling of carbon in the form of carbon nanotubes. The nanotubes develop on the cooler surfaces of the reactor, as the vaporized carbon condenses. Inhibitors,research,lifescience,medical Nanotubes produced by laser ablation have higher purity (up to about 90% pure) and their structure is better graphitized than those produced by the arc discharge method. The high cost of laser and small carbon deposit are the major limitations of this method. In addition to this, the Inhibitors,research,lifescience,medical method mainly favors the growth of SWCNTs and special reaction conditions are required to generate MWCNTs [57]. Several researchers reported different

modifications of the laser ablation method to improve the geometry and yield of SWCNTs (Figures 2(c) and 3(c)). In a study, Maser et al. used continuous wave 250W CO2 laser operating at 10.6μm wavelength to evaporate graphite/bimetal targets and produced high densities bundles of SWCNTs [58] while Yudasaka et al. showed an improved yield of SWCNTs by pulsed laser over a continuous one [59]. Zhang et al. studied the effect of laser frequency and laser Phosphatidylinositol diacylglycerol-lyase power (or temperature) on the diameter distribution of SWCNTs [60]. Scott et al. demonstrated the growth mechanism for SWCNTs in a laser ablation process. They suggested that in addition to the carbon MAPK inhibitor obtained from direct ablation of the target, other substances like carbon particle suspended in the reaction zone, C2 obtained from photodissociation of fullerenes, and other low molecular weight species may also serve as feedstock for nanotube growth [61]. Maser et al.