Intercalation of Si between MoS₂ layers

Abstract

We report a combined experimental and theoretical study of the growth of sub-monolayer amounts of silicon (Si) on molybdenum disulfide (MoS2). At room temperature and low deposition rates we have found compelling evidence that the deposited Si atoms intercalate between the MoS2 layers. Our evidence relies on several experimental observations: (1) Upon the deposition of Si on pristine MoS2 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 MoS2. (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 MoS2/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 MoS2 surface, but rather intercalate between the MoS2 layers. Our conclusion that Si intercalates upon the deposition on MoS2 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 MoS2. Finally, density functional theory calculations indicate that silicene clusters encapsulated by MoS2 are stable.

High graphene permeability for room temperature silicon deposition: The role of defects

“…Concerning the chemical nature of the intercalated silicon, several papers report the formation of metal silicides after silicon deposition and annealing on graphene supported on metallic substrates, 5,[16][17][18][19][20]24,25 while others describe the possible formation of silicene [12,[26][27][28].…”

Raman investigation of air-stable silicene nanosheets on an inert graphite surface

“…In Fig. 2(d [18] and by van Bremen et al [30] where Si has been deposited on a MoS2 inert substrate and STM images showed no lattice parameter enlargement occurring on silicene formation. While the former interpreted these data in terms of a squeezing of the silicene lattice producing a huge buckling, the latter suggested that a silicene layer intercalation occurred under the first atomic layer of MoS2.…”

Engineering Epitaxial Silicene on Functional Substrates for Nanotechnology

“…In agreement with the computational modelling of the electronic bands, so-grown silicene proves to be metallic in character as resulting from direct evidence of the local density of states [9]. Recently, this picture has been objected by figuring out silicon intercalation in between the upmost adjacent MoS 2 layers [27]. Intercalation of silicon atoms inside layered materials to form a self-organized silicene layer is an emerging topic of study in a number of combinations; however, many factors in the silicon growth processing as well as in the affinity of silicon with underlying substrate may affect the details or the emergence of the intercalation.…”