Supramolecular phthalocyanine dimers based on the secondary dialkylammonium cation/dibenzo-24-crown-8 recognition motif

[formula: see text] New unsymmetrically substituted DB24C8-phthalocyanines, which are able to form complexes with suitable dialkylammonium cations, have been prepared. These complexes most probably have a pseudorotaxane geometry.     

Comment on recent theories of photoemission

A number of points in recent articles on the theory of photoemission are clarified.     

Geometric vs. electronic factor in surface electronic structure-H adsorption on Sc and Ti(0001)

By comparing outer layer local densities of H monolayers on Sc(0001) surfaces, we show that it is geometry and not electron number per atom that is the dominant influence on the surface electronic structure of these adsorption systems.     

Spatial variation of the electron mean free path near a surface

The electron plasmon-emission-mean-free-path in semi-infinite Jellium is evaluated as a function of position, and of electron emergence angle. The usual assumption that this free path is spatially non-varying inside the “metal” is found to be a reasonable approimation to reality by virtue of the fact that the surface plasmon emission probability increases where that of the bulk plasmon decreases (and vice-versa). The inverse mean free path, however, does not fall to zero for an appreciable distance (on the order of angstroms) outside the surface defined by the vanishing of the electron density.     

The angular dependence of plasmon loss features in XPS spectra from polycrystalline aluminum: Clean surfaces and effects of oxygen adsorption

The angular dependence of relative intensities of bulk- and surface-plasmon loss peaks associated with X-ray photoemission from the Al 2p core level has been measured for aluminum samples under ultrahigh vacuum conditions. At near-grazing electron exit angles, a sixfold increase in the single-surface-plasmon relative intensity is observed, while the single-bulk-plasmon relative intensity is decreased by ～20%. These experimental results are compared with theoretical calculations based on a dispersionless-plasmon jellium model and including both extrinsic and intrinsic plasmon creation. The presence of intrinsic creation is suggested and theoretical relative intensities are in good agreement with, although generally somewhat higher than, corresponding experimental values. For specimens with low coverages of oxygen (～0.15 monolayer), only surface-plasmon loss features are found to be associated with the O 1s core level, indicating near-surface adsorption.     

Interpretation of high-resolution images of the best-bound wetting layers on Pt(111)

Two interpretations have been proposed of dark triangles observed in scanning tunneling microscopy (STM) images of the best bound, √37×√37-R25.3°, and √39×√39-R16.1° periodic water monolayers on Pt(111). In one, a "Y"-shaped tetramer of water molecules is removed, leaving a vacancy island behind; the other assumes the Y is replaced by a hexagon of H(2)O molecules, amounting to a di-interstitial. Consistent only with the di-interstitial model are thermal desorption and CO coadsorption data, STM line scans, and total energies obtained from density functional theory calculations.     

Adsorbate band dispersions for C on Ru(0001)

We have studied carbon-induced two-dimensional energy bands on Ru(0001) using angleresolved photoelectron spectroscopy and have compared them with ab initio calculations. We find a nearly parabolic band (bottom at E_F ?9.8 eV at k_∥ = 0, effective mass ～ 1.5 m_e) which we assign to the C 2p_z valence states of a graphitic carbon overlayer. Compared to graphite, these states are bound more tightly by 2.3 eV.     

Surface states of Sc(0001) and Ti(0001)

Calculated electronic properties are compared for 11-layer Sc(0001) and Ti(0001) films. Prominent surface states are found whose locations conform to expectations based on the respective bulk band structures establishing a roughly rigid band picture of the surface bands. Surface core-level shift and work function results are qualitatively explained.     

Reactive wetting: H2O/Rh(111)

First-principles calculations imply that neither H2O bilayers nor half-dissociated, H2O+OH+H monolayers are thermodynamically stable on clean Rh(111). Thus, the experimental observation that Rh(111) supports a periodic 2D water adlayer needs an explanation. Chemistry involving common surface impurities, notably C atoms, may be the answer. Calculations show they provide favorable binding sites for H atoms detached from H2O. The resulting OH fragments can anchor a 2D water layer to the surface.