Victor Vega Mayoral, 11.01.2017 at 14:00, Seminar room F7

Photophysics of transition metal dichalcogenides obtained from liquid phase exfoliation

Victor Vega Mayoral
Trinity College Dublin, Dublin, Ireland


Two research lines are presented in this seminar. The first one is focused on exfoliating WS2 via liquid phase exfoliation and the use of some basic, commonly available and fast characterization techniques. Exfoliation in water/polymer dispersions has been studied. Poly(vynil alcohol) (PVA) is proposed as a model polymeric stabilizer. Effects of polymer concentration and centrifugation size- selection protocol on concentration, thickness and lateral size are reported. Extinction, Raman and photoluminescence spectroscopy were used for a fast and semiquantitative characterization supported by the more conventional TEM and AFM microscopy. The second research line focuses on a deeper characterization of the photoexcited states dynamics of few-layer MoS2 and WS2 where we have used spectrally-resolved femtosecond pump–probe spectroscopy. Photoexcited states dynamics in few-layer WS2 have beeen studied using femtosecond pump-probe spectroscopy. Using a cascade model I obtained an exciton dissociation lifetime of 1.3 ps. After excitons dissociation the geminated charges diffuse till they are trapped in defects such as grain boundaries or sulphur vacancies. There is a longer relaxation process that lasts hundreds of picoseconds assigned to charge recombination.