Non-equilibrium optical properties of MoSI nanowires

MoSI nanowires are the one-dimensional systems with the weakest known interaction with their neighbours. Therefore they are expected to show most clearly the effects of one-dimensionality. We studied equilibrium and non-equilibrium optical properties via optical reflectivity and absorbance as well as femtosecond pump-probe spectra of oriented Mo6S3I6 nanowire thin films. Absorption of light polarised parallel to the axis of orientation shows a series of resonances that are absent for perpendicular polarisation. The sharp Van Hove features expected from the highly one-dimensional character of the material are not observed, partly because of the large density of electron sub-bands and partly because of electron energy damping. The electronic relaxation from a non-equilibrium situation was studied via femtosecond pump-probe spectroscopy. By exciting into the second optical resonance we found a complex relaxation behaviour involving three distinct excited states and determined the lifetimes of the involved states.