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The electronic structure of ZrSe2 was studied by high resolution angular resolved photoemission spectroscopy (ARPES) and by density functional theory (DFT). ARPES with distinct horizontal (P) and vertical (S)-polarized synchrotron radiation was performed on the sample kept at room temperature and 20 K to unravel the electronic structure especially at the Fermi energy (EF). The DFT calculations including spin-orbit coupling using the modified Becke-Johnson potential reveal the presence of three occupied valence bands at the Γ(A)-point and show that the minimum indirect bandgap is between the Γ- and L-points of the Brillouin zone (BZ) similar to the experimental results. While the DFT calculations give only a single conduction band at the L and M-points of the BZ, the ARPES data (20 K) show two bands with opposite dispersion at EF. The observation of two bands close to EF was already reported in the charge density wave phase of TiSe2. The underlying mechanism of our observations is possibly a folding of the valence band states of ZrSe2 from the Γ(A) to M(L)-point accompanied by an energy shift due to internal dipolar momenta. Furthermore, at the A-point, the experimental dispersion of the lower occupied valence band and the size of its energy separation to the middle occupied band are not in line with the DFT calculations. Possible reasons of such discrepancies are discussed. [ABSTRACT FROM AUTHOR]

The control of the graphene electronic structure is one of the most important problems in modern condensed matter physics. The graphene monolayer synthesized on the Re(0001) surface and then subjected to the intercalation of Pb atoms is studied by angle-resolved photoelectron spectroscopy and low-energy electron diffraction. The intercalation of Pb atoms under graphene takes place when the substrate is annealed above 500°C. As a result of the intercalation of Pb atoms, graphene becomes quasi-free-standing and a local band gap appears at the Dirac point. The band gap changes with the substrate temperature during the formation of the graphene/Pb/Re(0001) system. The band gap is 0.3 eV at an annealing temperature of 620°C and it increases up to 0.4 eV upon annealing at 830°C. Based on our data, we conclude that the band gap is mainly caused by the hybridization of the graphene π state with the rhenium 5d states located near the Dirac point of the graphene π state. [ABSTRACT FROM AUTHOR]

We investigate the N = 9 atoms wide armchair-type graphene nanoribbons (9-AGNRs) by performing a comprehensive spectroscopic and microscopic characterization of this novel material. In particular, we use X-ray photoelectron, near edge X-ray absorption fine structure, scanning tunneling, polarized Raman and angle-resolved photoemission (ARPES) spectroscopies. The ARPES measurements are aided by calculations of the photoemission matrix elements which yield the position in k space having the strongest photoemission cross section. Comparison with well-studied narrow N = 7 AGNRs shows that the effective electron mass in 9-AGNRs is reduced by two times and the valence band maximum is shifted to lower binding energy by ∼0.6 eV. In polarized Raman measurements of the aligned 9-AGNR, we reveal anisotropic signal depending upon the phonon symmetry. Our results indicate the 9-AGNRs are a novel 1D semiconductor with a high potential in nanoelectronic applications. [ABSTRACT FROM AUTHOR]

We present the results of a joint experimental and theoretical investigation concerning the effect of crystal packing on the electronic properties of the H2OEP molecule. Thin films, deposited in ultra high vacuum on metal surfaces, are investigated by combining valence band photoemission, inverse photoemission, and X-ray absorption spectroscopy. The spectra of the films are compared, when possible, with those measured in the gas phase. Once many-body effects are included in the calculations through the GW method, the electronic structure of H2OEP in the film and gas phase are accurately reproduced for both valence and conduction states. Upon going from an isolated molecule to the film phase, the electronic gap shrinks significantly and the lowest unoccupied molecular orbital (LUMO) and LUMO + 1 degeneracy is removed. The calculations show that the reduction of the transport gap in the film is entirely addressable to the enhancement of the electronic screening. [ABSTRACT FROM AUTHOR]

The electronic structure of ZrSe2 was studied by high resolution angular resolved photoemission spectroscopy (ARPES) and by density functional theory (DFT). ARPES with distinct horizontal (P) and vertical (S)-polarized synchrotron radiation was performed on the sample kept at room temperature and 20 K to unravel the electronic structure especially at the Fermi energy (EF). The DFT calculations including spin-orbit coupling using the modified Becke-Johnson potential reveal the presence of three occupied valence bands at the Γ(A)-point and show that the minimum indirect bandgap is between the Γ- and L-points of the Brillouin zone (BZ) similar to the experimental results. While the DFT calculations give only a single conduction band at the L and M-points of the BZ, the ARPES data (20 K) show two bands with opposite dispersion at EF. The observation of two bands close to EF was already reported in the charge density wave phase of TiSe2. The underlying mechanism of our observations is possibly a folding of the valence band states of ZrSe2 from the Γ(A) to M(L)-point accompanied by an energy shift due to internal dipolar momenta. Furthermore, at the A-point, the experimental dispersion of the lower occupied valence band and the size of its energy separation to the middle occupied band are not in line with the DFT calculations. Possible reasons of such discrepancies are discussed. [ABSTRACT FROM AUTHOR]