Signatures of the Dichalcogenide–Gold Interaction in the Vibrational Spectra of MoS₂ and MoSe₂ on Au(111)

Abstract

Various atomic structures for the interface between Au(111) and monolayers of MoS 2 and MoSe 2 are investigated by means of first-principles calculations approximating van der Waals interactions by pairwise atomic interactions. Calculated bond lengths and interface energies are reported. The focus is on the calculation of vibrational spectra and their comparison to experimental data. The MoSe 2 monolayer, due to its almost perfect match with the Au(111) surface in the (√3 × √3) R30°s uperstructure, shows shifts of less than one wavenumber of the Raman-active A 1g and E 2g vibrational modes upon physisorption on Au(111). For MoS 2 , we find that two structural models, an almost unstrained superstructure with large periodicity and a strained layer with (√3 × √3) R30°supercell, may coexist, as evidenced by their almost identical formation energy. Considerable mode softening in the strained MoS 2 layer is observed in both the E 2g(1) mode as a consequence of strain and the A 1g mode due to spill-over of charge from the Au(111) surface into the conduction band minimum of strained MoS 2 . The latter observation helps us to rationalize the experimentally observed satellite peak of the A 1g Raman signal from MoS 2 /Au(111) and other layered sulfides while this feature is absent in MoSe 2 .

Tunable Encapsulation and Doping of Monolayer MoS2 by In Situ Probing of Excitonic Properties During Atomic Layer Deposition

“…For the case of the gold-capped alumina-coated MoS 2 , the stronger dielectric screening reduces the band gap as a consequence of band gap renormalization, resulting in an additional red shift of the exciton peak energies (Table S3, Supporting Information). [37] For the case of a 3 nm gold layer applied directly onto the surface of monolayer MoS 2 without AlO x present (Figure 5b, red line), we observed a softening of both Raman modes as a consequence of strain (4.1%) and charge transfer effects, [38] as well as a splitting of the A´1 mode, which has previously been attributed to the formation of gold islands on MoS 2 . [39] Indeed, the 3 nm thin gold coating forms a dense film of gold nanoparticles (Figure S9, Supporting Information) rather than a smooth and continuous layer.…”

“…For the case of a 3 nm gold layer applied directly onto the surface of monolayer MoS 2 without AlO x present (Figure 5b, red line), we observed a softening of both Raman modes as a consequence of strain (4.1%) and charge transfer effects, [ 38 ] as well as a splitting of the A´ 1 mode, which has previously been attributed to the formation of gold islands on MoS 2 . [ 39 ] Indeed, the 3 nm thin gold coating forms a dense film of gold nanoparticles (Figure S9, Supporting Information) rather than a smooth and continuous layer.…”

Evaluating strain and doping of Janus MoSSe from phonon mode shifts supported by ab initio DFT calculations

“…To take the van der Waals interactions into account, a correction to the conventional Kohn–Sham DFT energy and forces was applied in the form of the dDsC dispersion correction proposed by Becke and Johnson, 52 similar to previous work on vibrational modes in MoS 2 . 53 The electronic band structure was sampled on a 9 × 9 k -point grid in the 2D Brillouin zone. Electron doping was simulated by including a small amount of additional charge when calculating band occupations, such that the conduction band minima became occupied.…”

Structural and electronic properties of MoS2 and MoSe2 monolayers grown by chemical vapor deposition on Au(111)

“…48,49 Most probably, a weaker interaction of sulfur to Au(111) is insufficient to achieve the intercalation. Note that the interatomic distance of the MoSe 2 monolayer to Au(111) is higher than that of the MoS 2 , 50 which can also facilitate intercalation of the chalcogen atoms.…”