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

采用化学气相沉积法在有位置标记的电子显微镜网格上制备了氮化硼涂层的单壁碳纳米管。通过调整镀膜时间，控制了氮化硼壳层的数量。由于碳纳米管的原子薄性质，不同厚度的氮化硼涂层在光致发光激发光谱中观察到不同的激子能量漂移。观察到激子能量的蓝移和红移，认为红移是由氮化硼壳层的介电屏蔽引起的，蓝移是由非均匀涂层引入的应变引起的。尽管如此，更多的氮化硼壳层确实引起了较大的激子能量移动。用电子显微镜研究了氮化硼的实际壳层数与激子能量红移之间的关系。结果表明，用光致发光激发光谱测定的碳纳米管很难鉴定。为了简化鉴定过程，需要较低密度的碳纳米管。采用化学气相沉积技术，降低催化剂密度，缩短镀膜时间。

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.