Photoemission spectroscopy

About: Photoemission spectroscopy is a research topic. Over the lifetime, 10821 publications have been published within this topic receiving 250888 citations. The topic is also known as: photoelectron spectroscopy & PES.

Electronic Structure of Catalytic Metal Clusters Studied by X-Ray Photoemission Spectroscopy.

Abstract: Pd and Pt clusters on carbon substrates have been studied by x-ray photoemission spectroscopy (XPS) Variations in valence- and core-level spectra with cluster size have been observed Single-atom centers appear to exist in the ${d}^{9}{s}^{1}$ configuration The $d$-electron count increases with cluster size, and in the case of Pt a correlation between $d$-orbital occupation and catalytic activity in electroless nickel deposition is observed

Surface intercalation of gold underneath a graphite monolayer on Ni(111) studied by angle-resolved photoemission and high-resolution electron-energy-loss spectroscopy

Abstract: Quasi-two-dimensional intercalationlike systems, synthesized by surface intercalation of gold atoms underneath a monolayer of graphite formed on Ni~111!, have been investigated by angle-resolved photoemission spectroscopy ~PES! and high-resolution electron-energy-loss spectroscopy ~HREELS! Modifications of both electronic structure and vibrational properties due to the presence of the intercalated Au monolayer between the graphite monolayer and Ni~111! are reported The surface intercalation of the gold atoms underneath the graphite monolayer leads to a ‘‘stiffening’’ of the graphite-derived phonon modes and to an energetic shift of the graphite-derived p, s electronic states in the valence band toward lower binding energies The observed changes of the PE and HREEL spectra are explained by the saturation of the active Ni(d) bonds by the intercalated gold atoms and by the weakening of the interaction between graphite monolayer and substrate, due to the blockage of the graphite C(p)-Ni(d) hybrid bonds

Intra- and intermolecular band dispersion in an organic crystal.

Abstract: The high crystallinity of many inorganic materials allows their band structures to be determined through angle-resolved photoemission spectroscopy (ARPES). Similar studies of conjugated organic molecules of interest in optoelectronics are often hampered by difficulties in growing well-ordered and well-oriented crystals or films. We have grown crystalline films of uniaxially oriented sexiphenyl molecules and obtained ARPES data. Supported by density-functional calculations, we show that, in the direction parallel to the principal molecular axis, a quasi-one-dimensional band structure of a system of well-defined finite size develops out of individual molecular orbitals. In contrast, perpendicular to the molecules, the band structure reflects the periodicity of the molecular crystal, and continuous bands with a large dispersion were observed.

Electronic structure of the organic semiconductor copper phthalocyanine and K-CuPc studied using photoemission spectroscopy

Abstract: The changes of the electronic structure of copper phthalocyanine (CuPc) caused by the intercalation with potassium are studied using core-level and ultraviolet photoemission spectroscopy. The analysis of the valence-band spectra allows the estimation of the energy gap relevant for transport, which is substantially larger than the energy gap obtained using optical methods, showing that solid CuPc has to be regarded as a correlated material. Furthermore, our experiments indicate that there is structural (polaronic) relaxation of the CuPc molecules upon charging and that the lowest unoccupied molecular orbital of CuPc is more concentrated in the central part of the phthalocyanine molecules.

Quantum confinement in Si and Ge nanostructures

Abstract: We apply perturbative effective mass theory as a broadly applicable theoretical model for quantum confinement (QC) in all Si and Genanostructures including quantum wells(QWs), wires (Q-wires), and dots(QDs). Within the limits of strong, medium, and weak QC, valence and conduction band edge energy levels (VBM and CBM) were calculated as a function of QD diameters, QW thicknesses, and Q-wire diameters. Crystalline and amorphous quantum systems were considered separately. Calculated band edge levels with strong, medium, and weak QC models were compared with experimental VBM and CBM reported from X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or photoluminescence(PL). Experimentally, the dimensions of the nanostructures were determined directly, by transmission electron microscopy(TEM), or indirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline materials are best described by a medium confinement model, while amorphous materials exhibit strong confinement regardless of the dimensionality of the system. Our results indicate that spatial delocalization of the hole in amorphous versus crystalline nanostructures is the important parameter determining the magnitude of the band gap expansion, or the strength of the quantum confinement. In addition, the effective masses of the electron and hole are discussed as a function of crystallinity and spatial confinement.