Surface Structure of Single-Crystal MoS₂(0002) and Cs/MoS₂(0002) by X-ray Photoelectron Diffraction

Abstract

The surface structure of a clean MoS 2 (0002) and an in situ Cs surface-doped MoS 2 (0002) has been studied using high-resolution X-ray photoemission spectroscopy. The X-ray photoelectron diffraction (XPD) patterns of the Mo 3d 5/2 and S 2p core levels from a clean, well-ordered MoS 2 (0002) show forward focusing intensity maxima along the directions of nearest neighbors in MoS 2 in both the polar and azimuthal angle scans. The XPD patterns in the azimuthal angle scan exhibit a pronounced photoelectron intensity maximum at every 60°, reflecting the 6-fold rotational symmetry of the basal plane. In addition, because of the finite electron escape depth and the short-range order of the scattered photoelectrons, the azimuthal scans of both the Mo 3d 5/2 and the S 2p core levels further display the 3-fold rotational symmetry of the trigonal prismatic local structure, which MoS 2 (0002) possesses. The deposition of Cs onto the MoS 2 (0002) surface at room temperature did not introduce any significant changes either in the low-energy electron diffraction or in the XPD patterns, indicating the absence of Cs-induced surface relaxation, but a new photoemission was observed 1.6 eV above the valence band edge of MoS 2 , which corresponds to the Cs 6s photoelectron shared with the MoS 2 lattice. Thus Cs/MoS 2 represents an electron donor-acceptor (EDA) surface complex.

Optical and Transport Properties of Ni-MoS2

“…The three-dimensional crystal is formed by stacking the two-dimensional MoS2 sheets. Since there is the interaction of a weak van der Waals force providing a natural cleavage plane of the crystal between two adjacent MoS2 sheets [22], it would be easy to separate the samples into thin specimens with a smooth surface. The OM images of MoS2 and Ni-MoS2 are presented in Figure 2.…”

Core level spectroscopy of MoS2

“…shifts between detected components in the spectra. The intensity changes of the components as a function of the photon energy can be contributed by the photoelectron diffraction, since the effect has been reported to occur for MoS 2 single crystals [2,8].…”

“…It has been used, for instance, in catalysis to get rid of sulphur and nitrogen derivatives. The metal-sulphur bond strengths and the ability of MoS 2 to interact with metal atoms [8] or metal containing clusters [9] are studied because of their effect on the catalytic activity. An ion bombardment has been shown to be an effective tool to increase the reactivity of the MoS 2 basal planes [10][11][12][13].…”

“…An ion bombardment has been shown to be an effective tool to increase the reactivity of the MoS 2 basal planes [10][11][12][13]. In addition to the XPS [10,11,13] and UPS [14] studies of MoS 2 other methods like XPD [2,8], STM [1] and TEM [15,16] have been used to characterize this material. Various studies have focused on the band structure [17,18] or valence band and electronic structure of MoS 2 from both, theoretical and experimental point of view [2,14,[19][20][21][22].…”

Pressure induced anisotropy of electrical conductivity in polycrystalline molybdenum disulfide

“…Single-crystal electrical conductivity along the axis perpendicular and parallel to the layer plane shows a ratio σ σ ⊥ of about 10 3 [5]. However, in spite of the relatively high anisotropy of layered transition metal disulfide, the use of these kinds of materials to develop, for instance, new electronic and electrochemical devices is often discouraged by the difficulties in obtaining single-crystals [6,7].…”