Vibrational and electronic structures of tin selenide nanowires confined inside carbon nanotubes

We study vibrational and electronic properties of tin selenide (SnSe) nanowires encapsulated in single walled carbon nanotubes (SWCNT) by combining experimental Raman spectroscopy and density functional theory (DFT) calculations at the Heyd-Scuseria-Ernzerhof (HSE) level. The theoretically investigated standalone SnSe nanowires are Sn4Se4 with square (2 x 2) atomic arrangement and Sn6Se6 with a repeating hexagonal Mo6S6-like structure. Raman data support the theoretical prediction that the square (2 x 2) nanowires possess specific modes at 151 and 185 cm(-1), whereas the hexagonal Sn6Se6 structure is characterized by a mode appearing at similar to 235 cm(-1). Calculations predict that the (2 x 2) nanowire has an electronic gap of 1.5 eV and the Sn6Se6 nanowire presents a semi-metallic character. Raman spectra of composite SnSe@SWCNT samples show that the radial breathing mode of the nanotubes is strongly suppressed indicating interaction between SWCNT and the encapsulated SnSe nanowire while the Fano asymmetry parameter of the G band is increased.