Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Ultrathin 2D nanomaterials (nanosheets, NSs) have attracted intense research efforts due to their extraordinary optoelectronic properties.[1,2] To date, colloidal NSs of a variety of compositions have been prepared. We have developed 2 nm thin colloidal Cu2-xS NSs with tunable lateral dimensions (100 nm to 3 µm) and well defined size (hexagonal or triangular).[3] Cu2-xS is a direct p-type semiconductor and its bandgap (1.1 – 2.0 eV) and the excess hole density depend on the concentration of Cu vacancies (indicated by x), which make Cu2-xS a versatile material for efficiently tuning the dopant concentration.
Here, we study the charge carrier dynamics in ultrathin Cu2-xS NSs with Terahertz (THz) spectroscopy. Ultrafast spectroscopy techniques are particularly relevant to study optoelectronic properties in detail.[4] For example, the mobilities of free charge carriers can be probed, or exciton relaxation rates can be investigated. We study the dynamics of the intrinsic charge carriers (i.e., without optical pumping) and of the photogenerated charge carriers (i.e., with optical pumping) using a THz probe pulse. Furthermore, we show that the mobility of the excess carriers (holes) depends on the lateral dimensions of the NSs (ranging from 80 mS for the smallest NSs to 200 mS for the largest NSs). We find that the mobility increases upon photoexcitation, due to the creation of free electrons and holes. Finally, we show that the charge carrier dynamics can be best described with the Drude-Smith model for backscattering charges.
[1] Ithurria, S.; Tessier, M. D.; Mahler, B.; Lobo, R. P. S. M.; Dubertret, B.; Efros, Al. L. Nat. Mater. 2011, 10, 936–941.
[2] Schliehe, C.; Juarez, B. H.; Pelletier, M.; Jander, S.; Greshnykh, D.; Nagel, M.; Meyer, A.; Foerster, S.; Kornowski, A.; Klinke, C.; et al. Science 2010, 329, 550–553.
[3] van der Stam, W.; Akkerman, Q. A.; Ke, X.; van Huis, M. A.; Bals, S.; Donega, C. d. M. Chem. Mater. 2015, 27, 283−291.
[4] Aerts, M; Bielewicz, T.; Klinke, C.; Grozema, F. C.; Houtepen, A. J.; Schins, J. M.; Siebbeles, L. D. A. Nat. Commun. 2014, 5, 3789−3794.
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