The valence band photoelectron spectra of liquid water (H2O and D2O) are studied in the photon energy range from hν = 60 to 120 eV. The experiments use a 6 μm diameter liquid-jet free vacuum surface at the MBI undulator beamline of the synchrotron radiation facility BESSY. Photoelectron emission from all four valence molecular orbitals (MOs) is observed. In comparison to those of the gas phase, the peaks are significantly broadened and shifted to lower binding energies by about 1.5 eV. This is attributed primarily to the electronic polarization of the solvent molecules around an ionized water molecule. Energy shifts, peak broadening, and relative peak intensities for the four MOs differ because of their specific participation in the hydrogen bonding in liquid water. Relative photoionization cross sections for MOs were measured for hν = 60, 80, and 100 eV. The main difference for liquid water, as compared to the gas phase, is the relative intensity decrease of the 1b 2 and 3a 1 orbitals, reflecting changes of the MOs due to H-bonding.

The valence band photoemission of aqueous alkali-metal halide solutions is studied for photon energies from 90 to 110 eV. A 6 μm diameter liquid microjet provides a free vacuum surface, allowing water molecules to evaporate without collisions, and hence enables the direct detection of photoelectrons originating from the liquid. The experiments were performed at the MBI undulator beamline of the synchrotron radiation facility BESSY. Here, we focus on the determination of electron binding energies of solvated anions and cations. The effect of different countercations (Li+, Na+, K+, and Cs+), and salt concentrations is systematically investigated. Electron binding energies of the solvated ions are found to differ considerably from those in the gas phase; contrary to intuition, the energies do not depend on the salt concentration. Measured binding energies can be surprisingly well explained within a simple dielectric cavity model. For a NaI aqueous solution, negative surface excess is inferred from the evolution of the ion photoemission signal as a function of the salt concentration.

Benzene adsorption on a single-domain Si(001)-(2×1) surface has been studied by thermal desorption spectroscopy (TPD) and angle-resolved photoelectron spectroscopy (ARUPS) using linearly polarized synchrotron radiation. Angle-resolved photoemission spectra for the saturated benzene layer exhibit well-defined polarization and azimuthal dependencies compatible with a flat-lying benzene molecule with local C2v symmetry. Based on these results two structure models are proposed. First-principles density functional cluster calculations have been performed for each of these structures. Total energy minimization and a detailed comparison of the experimental ARUPS spectra with the one-particle spectra of the model clusters leads to a 1,4-cyclohexadienelike adsorption complex with a flat-lying benzene molecule which is di-σ bonded to the two dangling bonds of a single Si–Si surface dimer. Especially, one of the unoccupied 1e2u (π*) orbitals of the free benzene molecule shifts down (by about 3 eV) and evolves into the highest occupied molecular orbital (HOMO) of the chemisorbed molecule.

The discovery of quasicrystals--crystalline structures that show order while lacking periodicity--forced a paradigm shift in crystallography. Initially limited to intermetallic systems, the observation of quasicrystalline structures has recently expanded to include 'soft' quasicrystals in the fields of colloidal and supermolecular chemistry. Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli-Gähler tiling having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously. Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy.