Can any one have a suggestion for the CNT growth by low pressure CVD?

Growing carbon nanotubes (CNTs) via low-pressure chemical vapour deposition (LPCVD) involves several critical factors affecting the final results. The catalyst, precursor gases, temperature, pressure, and deposition time are all crucial to the process. Here are some areas you might want to investigate:

Catalyst: The catalyst plays a key role in CNT growth. The type, size, and distribution of the catalyst particles can significantly impact the quality of the CNTs. If you're using iron (Fe) as a catalyst, ensure the catalyst particles are well-distributed and of the right size. Moreover, you might want to consider using a bi-metallic catalyst such as Fe-Mo, which has been reported to enhance the yield and quality of CNTs.

Temperature: The growth temperature is also critical. The optimal temperature for CNT growth can vary, but it's often in the range of 600-1000 °C for LPCVD. If your growth temperature is outside this range, you may not be able to grow CNTs effectively.

Gas Flow Rates: The flow rates of the precursor gases can also affect CNT growth. You'll want to ensure you provide enough of each gas, but not so much that they inhibit growth or cause unwanted side reactions.

Deposition Time: The duration of the CVD process can also influence the growth of CNTs. Depending on the other parameters, you might need to adjust the deposition time to achieve the best results.

Substrate: The catalyst and substrate interaction can significantly affect CNT growth. Ensure the catalyst layer has good adhesion to the substrate and that the Al2O3 layer isn't preventing interaction between the catalyst and the carbon source.

Pressure: Process pressure could also be a factor. You mentioned you're using LPCVD, which generally operates at pressures lower than atmospheric. Ensure your system maintains a consistent and appropriate pressure for your specific process.

Remember that CVD is a complex process, and even small changes in these parameters can greatly impact your results. It could be beneficial to experiment systematically with each of these factors to identify the conditions that work best for your specific setup.

Lastly, it's worth noting that CNT growth can be difficult to visualize directly, especially if the CNTs are not well-aligned or if the growth is sparse. You may want to use techniques like scanning electron microscopy (SEM) or transmission electron microscopy (TEM) to verify whether you're actually getting CNT growth or not.

This is a challenging process, and it might take some trial and error to optimize it, but with patience and systematic investigation, you should be able to make it work. Good luck with your research!

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