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

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Angle-resolved photoelectron spectroscopy ͑ARPES͒ is commonly applied to map the shape of Fermi surfaces. Here we quantify the errors of simple criteria for extracting Fermi vectors by ARPES that are induced by strongly varying matrix elements. Sophisticated methods for determining the three-dimensional Fermi vector based on temperature and photon energy dependent photoemission are discussed with reference to data of the quasi-two-dimensional system 1T-TiTe 2 .

The electronic structure of semi-ir\flnite semiconductors with energy-optimized reconstructed surfaces is calculated self-consistently for the first time. Using local-density-functional formalism and scattering theory, the calculations yield the potential, charge density, surface band structure, and wave-vector-resolved layer densities of states with extreme spectral resolution. The results quantitatively explain recent surface spectroscopy data on occupied and empty states for Ge(001)(2x 1) andSi(001)(2xl).