Optical and Optoelectronic Studies of Boron Nitride Nanotube/Carbon Nanotube Coaxial Heterostructures

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Boron nitride coated single-walled carbon nanotubes were synthesized on location-tagged TEM grids by chemical vapor deposition. The number of boron nitride shells was controlled by adjusting the coating time. Due to the atomically thin nature of carbon nanotubes, boron nitride coating with different thickness yields different excitonic energy shifts observed by photoluminescence excitation spectroscopy. Both blueshift and redshift of the excitonic energy were observed, the redshift was considered to be caused by dielectric screening from the boron nitride shells and the blueshift was a result of the strain introduced by nonuniform coating. Nonetheless, more coating of boron nitride shells indeed gave rise to large excitonic energy shifts. Transmission electron microscopy was also performed to explore the relationship between the actual boron nitride shell number and the redshift of the excitonic energies. Identification of the carbon nanotubes that had been measured by photoluminescence excitation spectroscopy turned out to be difficult. A lower density of carbon nanotubes were necessary to ease the identification process. Chemical vapor deposition with lower density of catalysts and shorter coating time are in process.