Investigating the Interaction of Encapsulated Sulfur and Phosphorus Chains with Carbon Nanotubes Using X-Ray Emission Spectroscopy

The K_α and K_β X-ray emission spectra of sulfur and phosphorus encapsulated within single-walled carbon nanotubes are measured using a laboratory X-ray spectrometer for the first time. The obtained spectra are compared with those of their bulk counterparts, namely, plastic sulfur and red phosphorus. Models of sulfur and phosphorus chains are constructed both in their free state and when encapsulated in nanotubes. Quantum chemical calculations are performed to analyze the distribution of the 3p electron density in the valence band. A strong correlation is observed between the positions of the theoretical bands and the shapes of the experimental K_β spectra. By comparing the spectra of free and encapsulated sulfur and phosphorus, we analyze their electronic interactions with the walls of carbon nanotubes. This analysis identifies specific features in the electronic structure of the models that contribute to the observed doping behavior in the nanotubes.