Raman spectroscopy of intercalated and misfit layer nanotubes

We present Raman spectra of misfit layer $({\mathrm{PbS})}_1.14{\mathrm{NbS}}₂$ nanotubes and lead intercalated ${\mathrm{NbS}}₂$ nanotubes. They represent interesting model systems to investigate the nature of interlayer interaction in layered materials. A direct correlation to the Raman modes of the parent $2H\text{\ensuremath{-}}{\mathrm{NbS}}₂$ compound exists, but some modes are seen drastically upshifted in frequency in the misfit layer and intercalated compound while others remain almost unchanged. On the basis of the Raman spectroscopic investigations and with the help of supporting calculations we examine different interlayer bonding mechanisms and contribute to the discussion as to why these frequency shifts occur.