Question

Explain laser ablation method for production of CNT’s

Answer 1

1) CNT’s are prepared by dual pulse laser .
2) Quartz tube containing Argon and graphite mixed with ( Co + Ni ) in 1: 1 ratio is vapourised to 1200 ֯C , followed by heat treatment in a vacuum at 1000 to get C60 and other fullerenes .
3) The use of two successive laser pulses minimizes the amount of carbon deposited as soot .
4) The second laser pulse breaks up the larger particles ablated by the first one , and feeds them into the growing nanotube structure .
5) The material produced by this method appears as a mat of “ropes “, 10-20 nm in diameter and upto 100 μm or more in length .

6) Each rope is found to consist primariy of a bundle of single walled nanotubes ,aligned along a common axis .
7) By varying the temperature ,the catalyst composition ,and other process parameters ,the average nanotube diameter and size distribution can be varied .
8) Argon then sweeps C-atoms from high temperature zone to colder copper collector on which they condense into nanotubes .
The limitations of laser ablation method are :
1) Both methods involve evaporating he carbon source ,hence to increase production to the industrial level using these approaches is difficult .
2) Both methods produce CNT’s in highly tangled forms ,mixed with unwanted forms of carbon or metal species .
3) Hence ,CNT’s produced are difficult to purify ,manipulate and assemble for building nanotube device architectures for practical applications .