In-situ Probing of Stack-Templated Growth of Ultrathin Cu2-xS Nanosheets

Celso de Mello Donega^a, Andrei Petukhov^a, Joost van der Lit^a, Robin Geitenbeek^a, Stijn Hinterding^a, Anne Berends^a, Jaco Geuchies^a, Freddy Rabouw^a, Ward van der Stam^a, Sylvain Prévost^b

^aEuropean Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, Grenoble, France

Materials for Sustainable Development Conference (MATSUS)
Proceedings of September Meeting 2016 (NFM16)

Berlin, Germany, 2016 September 5th - 13th

Organizers: Marin Alexe, Enrique Cánovas, Celso de Mello Donega, Ivan Infante, Thomas Kirchartz, Maksym Kovalenko, Federico Rosei, Lukas Schmidt-Mende, Laurens Siebbeles, Peter Strasser, Teodor K Todorov, Roel van de Krol and Ulrike Woggon

Poster, Ward van der Stam, 116
Publication date: 14th June 2016

Ultrathin 2D nanomaterials have attracted intense research efforts due to their extraordinary optoelectronic properties.^[1] However, the nucleation and growth mechanisms of 2D colloidal nanosheets are still under debate. For example, an oriented attachment pathway has been proposed for the preparation of PbS nanosheets,^[2] whereas other works show compelling evidence for a soft-templating mechanism, also resulting in PbS nanosheets.^[3] The formation of CdX (X= S, Se) nanosheets has been explained both by soft-template mechanisms,^[4] and by models based on monomer addition to (CdX)n magic-size cluster seeds, without the mediation of templating effects.^[5]

Here, we elucidate the formation mechanism of ultrathin 2D Cu_2–xS nanosheets with in-situ Small-Angle X-ray Scattering. While thermal decomposition of Cu-dodecanethiolates produces spheroidal Cu_2–xS nanocrystals, the addition of chloride to the reaction mixture results in 2 nm thick Cu_2–xS nanosheets with well-defined shape and size.^[6] We show that chloride stabilizes stacks of lamellar Cu-thiolate supramolecular complexes, so that they remain intact beyond the onset of Cu_2–xS nucleation at 230 °C, leading to 2D-constrained stack-templated nucleation and growth. The face-to-face stacking of the nanosheets reinforces the 2D-constraints imposed by the lamellar soft-template, since it prevents inter-nanosheet mass transport and nanosheet coalescence, thereby inhibiting growth in the thickness direction and allowing only for lateral growth. Furthermore, by fitting the lateral growth of the nanosheets to known models for monomer-, diffusion- and reaction-limited growth, we are able to distinguish between the different growth limiting cases and find that the lateral growth is mainly reaction-limited. Our results provide valuable insights into soft-templating formation mechanisms of ultrathin colloidal nanosheets, which may be exploited for other metal-sulfide compositions.

[1] Ithurria, S.; et al. Nat. Mater. 2011, 10, 936–941.
[2] Schliehe, C.; et al. Science 2010, 329, 550–553.
[3] Morrison, P. J.; Loomis, R. A.; Buhro, W. E. Chem. Mater. 2014, 26, 5012−5019.
[4] Son, J. S.; et al. Small 2012, 8, 2394-2402.
[5] Bouet, C.; et al. Chem. Mater. 2013, 25, 1262–1271.
[6] van der Stam, W. et al., Chem. Mater. 2015, 27, 283−291.

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