Growth of CdS nanotubes and their strong optical microcavity effects.

Nanotubes are often formed by the folding of one-layer or multilayer compounds under microscopic catalytic growth conditions. Here, CdS nanotubes with tunable wall sizes and optical microcavities were prepared via a simple thermal evaporation co-deposition technique with Sn metal nanowire templating and ejection. Compared to core-shell Sn/CdS nanowires, which have poor microcavity quality, the hollow/CdS nanotubes have a higher quality factor (Q) that can reach approximately 400 in the spectral range of 550-800 nm when excited by a continuous-wave 405 nm laser. This high Q factor leads to low-threshold lasing and line-width narrowing due to the mode selection, which are important in many fields, including lasers, sensors, communications, and optical storage. A theoretical mode analysis of the hollow/CdS nanotubes with different thicknesses addressed their microcavity mode confinement and enhancements. This technique provides a new way to prepare semiconductor nanotubes for new photonic devices and photoelectric applications.