Electronic structure of intercalation compounds of molybdenum disulfide MMoS2 (M = Cu, Ag) studied by X-ray emission and X-ray photoelectron spectroscopies

Abstract

Electronic structures of intercalation compounds of molybdenum disulfide in which the MoS 2 layers alternate with layers formed by the metal atoms (Cu, Ag) were studied by X ray emission and photoelectron spectroscopies. The character of participation of these or other valence states of atoms in the construction of occupied and unoccupied energy bands of the substances studied was considered on the basis of the X ray spectra of various series.Key words: molybdenum disulfide, intercalation compounds, X ray emission spectroscopy, X ray photoelectron spectroscopy.Metal dichalcogenides МХ 2 (X = S, Se) are presently studied intensely as objects of fundamental research on the physical and chemical properties of low dimensional com pounds. 1 Transition metal dichalcogenides find practical use as materials for solid state current sources, lubricants with good antifriction properties, and components of com posite materials of heterophase systems of various distina tion. 2 Metal dichalcogenides are widely used as catalysts in petrochemical industry. 3 It has been found recently that multilayer polyhedral structures resembling carbon "on ions" and nanotubes can be obtained from transition metal dichalcogenides. 4 Molybdenum disulfide. Molybdenum disulfide (MoS 2 ) is the most frequently used object of investigation in the series of 4d transition metal dichalcogenides. The elec tronic structure of this compound is widely studied. 5-10 The band structure of molybdenum dichalcogenide is de termined by the interaction of 4d atomic orbitals (AOs) of molybdenum and 3s , 3p AOs of sulfur.The first X ray studies of the electronic structure of МоS 2 gave 11 the X ray emission spectra of Мо L β2,15 (N IV,V →L III ) and Mo L III absorption edge (transition 2p-4d, nd). The X ray emission spectra of Mo L β2,15 , Mo L β3 (M III →L I ), Mo L β4 (M II →L I ), Mo L β6 (N I →L III ), S L 2,3 (M I →L II,III ), and S K β1,3 (M II,III →K) in МоS 2 were studied. 12-14 The absorption spectra of Mo L III were studied more recently. 7, 15 The emission and absorption spectra were considered 11 in terms of the quasi atomic model, according to which selective lines that appear in X ray emission and absorp tion spectra characterize the participation of electrons in the quasi atomic hybrid states of molybdenum (d 4 sp hy bridization). The character of hybridization of the central metal atom is determined by the nearest environment of the molybdenum atom. The spectra obtained exhi bited considerable overlapping of the emission L β2,15 band and the band of the L III absorption edge of molybde num. The fluorescence Mo L β2,15 spectrum was not ob tained 11 because of the low intensity of the correspond ing line.In the next step of X ray spectral studies of МоS 2 , the emission Mo L β2,15 , Mo L γ1 , S L 2,3 , and S K β spectra were investigated 13,14 in molybdenite and the spectra were aligned on a common energy scale. The spectra were ob tained by the fluorescence method, which allowed the di rect interaction of the substance studied with the electron bea...