Band structure of MoS 2 , MoSe 2 , and α − MoTe 2 : Angle-resolved photoelectron spectroscopy and ab initio calculations

In this work the complete valence-band structure of the molybdenum dichalcogenides ${\mathrm{MoS}}_{2},$ ${\mathrm{MoSe}}_{2},$ and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{MoTe}}_{2}$ is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as ab initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component ${k}_{\ensuremath{\perp}}$ of the wave vector reveals a decreasing three-dimensional character from ${\mathrm{MoS}}_{2}$ to $\ensuremath{\alpha}\ensuremath{-}{\mathrm{MoTe}}_{2}$ which is attributed to an increasing interlayer distance in the three compounds. The effect of this ${k}_{\ensuremath{\perp}}$ dispersion on the determination of the exact dispersion of the individual states as a function of ${k}_{\ensuremath{\Vert}}$ is discussed. By performing ARPES in the CFS mode the ${k}_{\ensuremath{\Vert}}$ component for off-normal emission spectra can be determined. The corresponding ${k}_{\ensuremath{\perp}}$ value is obtained from the symmetry of the spectra along the $\ensuremath{\Gamma}A,$ $KH,$ and $\mathrm{ML}$ lines, respectively.