Engineering the Band Gap of Carbon Nanotubes

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. This paper discusses 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.