Anders Sandell

Overlayer structure from adsorbate and substrate core level binding energy shifts: CO, CCH3 and O on Pt(111)

Abstract By combining high resolution photoemission measurements of adsorption induced binding energy shifts of both adsorbate and substrate core levels the nature and distribution of adsorption sites in the CO/Pt(111) system can be determined. The existence of different surface shifted components demonstrates the local character of the surface core level shift. This is used to study the O/Pt(111) (2 × 2) and CCH3/Pt(111) “(2 × 2)” phases. The intensity relations of the different surface peaks suggest O/Pt(111) to be a true (2 × 2) phase, while the CCH3/Pt(111) “(2 × 2)” phase is proposed to consist of three equivalent (2 × 1) domains.

Electronic structure of a vapor-deposited metal-free phthalocyanine thin film

The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

Titanium dioxide thin-film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

Titanium dioxide thin film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation

Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation

Chemisorption of CO on Cu(100), Ag(110) and Au(110)

Abstract The adsorption of CO on Cu, Ag and Au is studied using core and valence photoemission, X-ray absorption and autoionization of core excited states. The purpose is to investigate the nature of the adsorption bond starting out from the well-established chemisorption system CO/Cu(100)-c(2 × 2), and from the results we suggest that CO forms chemisorbed phases also on Ag(110) and Au(110). The photoemission spectra show strong shake-up satellites both for the valence levels and the core levels. The separation to the satellite appearing closest to the main line is observed to follow the position of the substrate d-band relative to the Fermi level. The CO adsorption strength for the noble metals is deduced to decrease in the order Cu-Au-Ag. This is based on the widths of the XA resonances, which are related to the adsorbate-substrate interaction strength of the core excited states, and the relative shake-up intensities, which are expected to increase with a decreasing adsorption strength in the ground state. The same trends regarding the shake-up intensities are observed both for the valence and core levels.

Growth of ultrathin ZrO2 films on Si(100): Film-thickness-dependent band alignment

The band alignment of ultrathin ZrO2 films of different thickness formed on Si(100) have been monitored with synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy. The films were deposited sequentially by way of metal-organic chemical-vapor deposition in ultrahigh vacuum. A significant decrease in the conduction band offset is found for increasing film thickness. It is accompanied by a corresponding increase of the valence band offset. The variations originate in the formation of an interfacial layer characterized by a lower degree of Zr-O interaction than in bulk ZrO2 but with no clear evidence for partially occupied Zr4d dangling bonds.

Electronic structure of electrochemically Li-inserted TiO2 studied with synchrotron radiation electron spectroscopies

The electronic properties of TiO2 and electrochemically Li-inserted TiO2 have been studied using synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy (XAS) in conjunction with resonant photoelectron spectroscopy. Core level (Ti 2p) and valence level spectra show the presence of Ti3+ states in LixTiO2. The x values determined from core level peak intensities were found to be directly correlated to the inserted amount of Li+ determined electrochemically. The x-dependent width of the Ti 2p peaks is consistent with a two-phase regime at intermediate x values. Resonant photoelectron spectroscopy at the Ti 2p edge was performed for TiO2 and Li0.5TiO2 to delineate the Ti4+ and Ti3+ contributions to the XAS spectrum.

Core level spectroscopy of physisorbed molecules on graphite

Abstract Several recent applications of high-resolution core-level spectroscopies to the investigation of physisorbed molecules (N 2 and O 2 on graphite) are reviewed. The ordered arrangements of the adsorbed molecules allow the distinction between σ and π molecular states revealing for instance a complex nature of the so called σ-resonance region. The molecular Rydberg states are found to persist in the adsorbates. An orientational phase transition of O 2 on graphite has been investigated using polarization dependent XAS. This phase transition also gives rise to pronounced changes in the XPS line profile due to a position dependent screening response from the substrate. The Auger spectrum of N 2 on graphite shows features corresponding to the decay of ionic as well as neutral states making it possible to determine the charge transfer rate for the neutralization process. The new possibility of recording autoionization spectra with vibrational selection in both the excitation and decay steps are demonstrated for adsorbed N 2 .

Li insertion in thin film anatase TiO2: Identification of a two-phase regime with photoelectron spectroscopy

Li insertion in thin film anatase TiO2: Identification of a two-phase regime with photoelectron spectroscopy

Interface electronic states and molecular structure of a triarylamine based hole conductor on rutile TiO2(110).

The molecular and electronic surface structure of a triarylamine based hole-conductor (HC) molecule evaporated onto rutile TiO2(110) single crystal is investigated by means of synchrotron light based photoelectron spectroscopy and x-ray absorption spectroscopy in combination with calculations based on density functional theory. Different amounts of the HC molecule was evaporated spanning the monolayer to multilayer region. The molecular surface structure is investigated and the results indicate that no specific covalent chemical bonding is formed and that the plane formed by the different nitrogens in the HC molecules has a rather small angle versus the TiO2 substrate surface plane. Some molecular ordering also persists in the multilayer region. The experimental core level spectra, valence level spectra, and the N 1s x-ray absorption spectroscopy spectra are well modeled by calculations on an individual molecule. Interestingly, the formation of the TiO2HC interface results in significant binding energy shifts in core levels and valence levels shifting all peaks of a the HC material to the same extent. Smaller shifts were also observed in the substrate core level peaks. The shift is discussed in terms of nanoscale energy level bending and final state hole screening. With respect to electronic applications, specifically in a solid state dye-sensitized solar cell, it is argued that the observed energy level alignment at the TiO2HC interface can act as a hole trap.