Dajo Boden^a, Mahesh K. Prabhu^a, Marcel J. Rost^b, Jörg Meyer^a and Irene M.N. Groot^a
aLeiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
^bLeiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

Since the discovery of graphene, the interest in atomically-thin 2-dimensional (2D) materials with unique mechanical and electronic properties has skyrocketed. One important class of 2D materials involves transition metal dichalcogenides (TMDCs), consisting of a transition metal sandwiched between two layers of chalcogenides (S, Se, Te). TMDCs often exhibit a unique electronic structure interesting for both catalysis and semi-conductor industries.1
TMDCs containing cobalt were previously overlooked, as bulk CoS₂ is not layered like MoS₂ or graphite. DFT-investigations of freestanding 2D TMDCs reported 2D CoS₂ as not stable.2 Nevertheless, our STM results indicate the presence of 2D CoS₂ on Au(111), which can only be supported by  DFT if the gold surface is also included explicitly in the DFT calculations. In H2S-rich gas atmosphere, a reconstructed 2D CoS_2-x sheet forms beyond the thiol desorption temperature. After cooling down it undergoes further sulfidation and becomes 2D CoS₂ sheet. With DFT, we show the CoS₂ sheet is metallic and has a structure similar to TiS₂ and ReS₂.3 Based on these results, CoS₂ can be added  to  the  list of  TMDCs  available  for  development  of  new materials with novel electronic and mechanical properties.

Acknowledgements

The authors would like to thank NWO for computer time on the Cartesius facility (grant number: 17216).

References

1. M. Chhowalla, H. S. Shin, G  Eda, L.-J. Li, K. P Loh,  H. Zhang, Nat. Chem. 2013, 5 (4), 263–275.
2. C. Ataca, H. Ȿahin, S. Ciraci, J. Phys. Chem. C 2012, 116, 8983-8999.
3. F. Güller, C. Helman, A.M. Llois,  Physica B 2012, 407, 3188-3191.