**Acknowledgements**

gon (Ar) gas in order to eliminate air from the quartz tube and then heated to a reaction temper‐ ature. The precursor mixture was sprayed into the quartz tube, using Ar gas. The concentration of ferrocene in carbon precursor was ~25 mg/ml. The flow rate of Ar was 200 sccm/min. The experiments were conducted at 650 ºC with reaction time of 45 min was main‐ tained for each deposition. After deposition, the furnace was switched off and allowed to cool down to room temperature under Ar gas flow. A uniform black deposition on the silicon sub‐ strate was observed. Finely, the substrate containing aligned CNTs was removed from the quartz tube for characterization. The experiments were repeated several times to ensure the re‐

The morphology of carbon sample grown on silicon substrate using a mixture of Pine oil and ferrocene at 650 °C can be observed in Figure 6a. The image revel the formation of high abun‐ dance of carbon nanotubes which are forest like and vertically-aligned to the substrate surface. The growth of carbon nanotubes seems to be uniform and reaches up to a length of 10µm. Fig‐ ure 6b shows the SEM image of carbon sample grown on silicon substrate using a mixture of Methyl ester of *Jatropha curcas* oil and ferrocene at 650 °C. The dense, aligned but non-uniform growth of carbon nanotubes was observed. The length of carbon nanotubes grown was found to be varied from 12.5 to 7.5µm. Figure 6c illustrates the SEM image of the carbon naotubes grown at 650 °C using Methyl ester of *Pongamia pinnata* oil. A thick carbon nanotube with poor

**Figure 6.** Representative SEM images of as-grown vertically-aligned carbon nanotubes at 650 °C using Pine oil (a),

From the experimental results we suggest that the synthesis of aligned CNTs is very sensitive to the carbon precursors used. Ferrocene on thermal decomposition at high temperature forms Fe nano particles on the silicon substrate surface. During the chemical vapor deposition process, the carbon precursor is catalytically decomposed and the carbon fragments formed diffuse into the Fe catalyst. The Fe particles may thus easily become saturated or supersaturated with car‐ bon atoms, and the precipitation of the carbon from the surface of the Fe particle leads to the for‐ mation of dense carbon nanotubes [48]. The high surface density of the growing nanotubes serves as an additional advantage for the constituent nanotubes to be "uncoiled". The Vander waals forces between the tube keep them aligned. Thus, the Fe catalysts can effectively catalyze the growth of highly dense vertically aligned carbon nanotubes on silicon substrate. Further in‐

Methyl ester of *Jatropha carcus* oil (b) and Methyl ester of *Pongamia pinnata* oil (c).

producibility of the formation of vertically aligned carbon nanotubes.

250 Syntheses and Applications of Carbon Nanotubes and Their Composites

**2.3. Result and Discussion**

structure and alignment was observed.

The authors acknowledge the UGC New Delhi for financial support, the Institute for Environ‐ mental and Nanotechnology for technical support and IITM for access to Electron microscopes.
