For traditional semiconducting materials, band gap is a unique characteristic which limits the material's applications and device's performance. The capability of on-chip adjusting semiconducting material's band gap is extremely important in manufacturing electronic devices. As a one-dimensional nano material with excellent electrical properties, carbon nanotube (CNT) has a band gap determined by the circumferential quantum confinement, which depends on the tube diameter. Hence for a multi-walled carbon nanotube (MWCNT), the band gap can be on-chip adjusted by electrically removing its outer carbon shells.

a real-time control method for controlling the MWCNT band gap adjusting process. A state space model was developed based on the quantum model for electron transport inside a nanotube. The rapid change of the system state, which represents the occurrence of electrical breakdown, can be observed using robust fault detection technique for breakdown process control. Experimental results show that the breakdown control system can effectively convert metallic MWCNTs to semiconducting MWCNTs and further adjust the band gap, which is especially important for optical detection to reduce the dark current and enhance the photo current.

Dr Ganesh, I understand your point, but I would like to have the value (probably the range of Eg) of the band gap of MWCNTs. 

 Band structure of one-dimensional CNTs depends  upon their different structures. Defects level ,dopants ratio and functionalization may be play an important role in Eg value. In general, electronic spectrum for MWCNT shows an intensive absorption peak at UV region(~260 nm) which means that the  Eg  value is more than 2  .This absorption band is due to π –π* transition. However, you can use diffuse reflectance  spectroscopy (DRS) to measure energy band gap of your semiconductive MWCNTs.

I thing the band gap of MWCNTs ranged from 2.9 to 3.7eV depending on the radial deformation

If the diameter of the NT in [nm], the optical band gap of about (2.7-3) eV.

Band gap of CNTs depends on dopant, chirality, synthesis method and ....

so, I want to suggest DRS analysis.

Good luck

So for every synthesızed MWCNTs we should measure band gap usıng DRS analysıs?

Yes, you can be using the SE technique, it is a perfect tool for this measurement.