Experiments and Consideration about Surface Nonstoichiometry of Few-Layer MoS₂ Prepared by Chemical Vapor Deposition

Abstract

A detailed chemical and structural characterization of the 2H-MoS 2 prepared by chemical vapor-phase method is presented. The nanosized MoS 2 (five to eight layers and the lateral planes area from 17 to 55 nm) was confirmed by atomic force microscopy, X-ray powder diffraction, and Raman spectroscopy. Here the main attention was given to active edge sites and vacancy defects in the nanosized MoS 2 .To settle the problem, we pioneered the application of an effective combination of adequate techniques such as highresolution differential dissolution, X-ray photoelectron spectroscopy with different excitation energies, and IR spectroscopy coupled to thermal gravimetric analysis. The results indicate that the sulfur vacancies at the topmost surface layers are created by the incongruent MoS 2 evaporation in vacuum at a temperature above 1000 K and the active chemically undercoordinated Mo atoms on the (110) plane react with residual oxygen to produce the surface-oxidized layers reconstructed relative to the perfect MoS 2 lattice. The structure of the surface-oxidized layers on the MoS 2 particles is presented by Mo with a varying number of nearest neighboring oxygen atoms. The sulfate species are anchored to the active sites of the (013) planes. The thickness of the surface coating was found to vary as a function of the sintering temperature, and the conditions to control composition and thickness of the altered top layers are given.

Sulfophobic and Vacancy Design Enables Self‐Cleaning Electrodes for Efficient Desulfurization and Concurrent Hydrogen Evolution with Low Energy Consumption

“…The peak at 533.5 eV can be attributed to the adsorbed water molecules while the peak at 532.5 eV indicates the presence of sulfate or carboxylate, which is common in sulfides as previous reports indicate. [ 42,43 ]…”

Molybdenum Disulfide (MoS2) Coating on AISI 316 Stainless Steel by Thermo-Diffusion Method

“…The FT-IR spectrum of coating is shown in Fig. 12 [14][15][16]. Using the diffraction peaks (0 0 3) (2θ = 14.05°) and (1 0 1) (2θ = 32.80°) an average grain was calculated for each coating at different sulfurizing temperature.…”

Mixed Films Based on MgO for Secondary Electron Emission Application: General Trends and MOCVD Prospects

“…Since the active surface oxygen vacancies and less-coordinated morphological sites are best determined through their different solubility in the acidic solvents, differential dissolution (DD) [14][15][16]56] was carried out in the specially induced dynamic regime with progressively increasing concentration of solvent, i.e., its chemical potential µ, that provided sequentially transfer of the phases into solution (Figure 1a). The solvent went over a film with a constant velocity, dissolving the~5 Å/cm 2 layer, and each solvent portion was fed by peristaltic pumps with a frequency of 1 s to the analyzer detector, an inductively coupled plasma atomic emission spectrometer (ICP AES, model 262477-364A, Baird, Zoeterwoude, Holland).…”

“…Ultraviolet photoelectron spectroscopy, optics and reflection electron energy loss spectroscopy are also sensitive to the hydroxylation effect and cannot detect selectively individual types of the F defects in the presence of the impurity oxygen atoms [42,48,52,54]. In such a situation, preference was given to differential dissolution (DD) method which inherently performs at once the phase and chemical analyses of the simple and complex films as it was shown before in [14][15][16]55,56]. Combining DD data with those obtained by XRD, scanning electron microscopy (SEM) and measuring SEEC of the films, we were in the certainty to get the exhaustive structural, chemical and phase information and to explain what the phase component and in what manner contributes in enhancement of SEE properties.…”