Intercalation of Si between MoS(2) layers

We report a combined experimental and theoretical study of the growth of sub-monolayer amounts of silicon (Si) on molybdenum disulfide (MoS(2)). At room temperature and low deposition rates we have found compelling evidence that the deposited Si atoms intercalate between the MoS(2) layers. Our evidence relies on several experimental observations: (1) Upon the deposition of Si on pristine MoS(2) the morphology of the surface transforms from a smooth surface to a hill-and-valley surface. The lattice constant of the hill-and-valley structure amounts to 3.16 Å, which is exactly the lattice constant of pristine MoS(2). (2) The transitions from hills to valleys are not abrupt, as one would expect for epitaxial islands growing on-top of a substrate, but very gradual. (3) I(V) scanning tunneling spectroscopy spectra recorded at the hills and valleys reveal no noteworthy differences. (4) Spatial maps of dI/dz reveal that the surface exhibits a uniform work function and a lattice constant of 3.16 Å. (5) X-ray photo-electron spectroscopy measurements reveal that sputtering of the MoS(2)/Si substrate does not lead to a decrease, but an increase of the relative Si signal. Based on these experimental observations we have to conclude that deposited Si atoms do not reside on the MoS(2) surface, but rather intercalate between the MoS(2) layers. Our conclusion that Si intercalates upon the deposition on MoS(2) is at variance with the interpretation by Chiappe et al. (Adv. Mater. 2014, 26, 2096–2101) that silicon forms a highly strained epitaxial layer on MoS(2). Finally, density functional theory calculations indicate that silicene clusters encapsulated by MoS(2) are stable.