Erminald Bertel

The molecular structure of benzene on Rh(111)

Angle resolved ultraviolet photoemission spetroscopy (ARUPS) has been used to study the molecular structure and orientation of benzene on Rh(111). At room temperature, benzene adsorbs in a molecular state. The ARUPS are consistently interpreted in terms of a C6v symmetry of the adsorbate complex. This indicates that the benzene molecule is essentially undistorted at the surface and adsorbed in a planar geometry, i.e. with the aromatic ring plane parallel to the metal surface.

The surface properties of nanocrystalline diamond and nanoparticulate diamond powder and their suitability as cell growth support surfaces

Nanocrystalline diamond (NCD) films and nanoparticulate diamond powder (DP) are the two main representatives of diamond at the nanoscale. This study was designed to investigate the suitability of these biomaterials as cell growth supports and to determine surface characteristic properties best suited to cell attachment and proliferation. Surface topography, chemical termination and wetting properties of NCD- and DP-coated borosilicate glass substrates were correlated to attachment, proliferation and differentially regulated gene expression of human renal epithelial cells (HK-2 cell line) cultured on these surfaces. Hydrogen-terminated NCD (NCD-H) surfaces were shown to inhibit cell attachment, which indicates that the lack of functional polar groups prevents adherent cells from settling on a surface, whether nanostructured or not. In contrast to NCD-H, oxygen-terminated NCD (NCD-O) as well as DP surfaces demonstrated improved cell attachment, as compared to borosilicate glass, which is a commonly used material for cell growth supports. NCD-O not only revealed an increased cell attachment, but also a markedly increased proliferation rate. Finally, none of the investigated surface modifications appeared to cause adverse cellular reactions or markedly alter cellular phenotype.

Structure and orientation of benzene and pyridine on Ir(111): Evidence for molecular distortion of benzene

Angle-resolved UV photoemission (ARUPS) has been used in conjunction with electron stimulated desorption ion angular distribution (ESDIAD) to study the molecular structure and orientation of benzene and pyridine on Ir(111). ARUPS indicates C3v symmetry for the benzene adsorption complex, which is interpreted in terms of a trigonal distortion of the adsorbed molecules. For pyridine a distorted C2v symmetry is derived from ARUPS. This suggests that the pyridine molecules are adsorbed via the N atom in an upright standing geometry, with a small inclination of the ring plane with respect to the surface normal. ESDIAD specifies the tilt angle of the ring plane to ∼ 20° from the surface normal, and reveals azimuthal preference of the inclination.

Electronic Surface and Interface States on Metallic Systems

Surface states and surface dynamical phenomena, S.D. Kevan vibrations at surfaces and electronic excitations, M. Head-Gordon electronic structure and reconstruction of the Mo(001) surface, J.-W. Chung surface states and the geometric structure, the phonon dispersion and the chemical reactivity of beryllium surfaces, E.W. Plummer the interaction of adsorbates with surface states, E. Bertel low-dimensional electronic states on metal surfaces - quantum wells and quantum wires, F.J. Himpsel STM observation of surface states on Au(111), P. Avouris the role of surface-, interface-, and adlayer-states for the magnetism in ultrathin adlayers, S. Blugel magnetic surface states, M. Donath spin-polarized photoemission studies of interface and quantum well states in thin films, P.D. Johnson surface covalent-metallic transition in gallium and germanium, E. Tosatti. (Part Contents).

Surface science letterThe structure of benzene on Rh(111): Coadsorption with CO

The molecular structure of benzene coadsorbed with CO on Rh(111) has been investigated by angle resolved UV photoemission (ARUPS), LEED and thermal desorption spectroscopy. The symmetry of the benzene adsorption complex in a mixed benzene-CO (3×3) LEED structure has been determined to C6v by ARUPS. This indicates that the benzene molecules remain essentially undistorted in the CO coadsorbate layer, as it has been found for the pure benzene layer on Rh(111).

Reactive and non-reactive high rate sputter deposition of Tungsten carbide

Abstract Tungsten carbide coatings were deposited onto molybdenum and cemented carbide substrates using d.c. and r.f. magnetron sputtering. Tungsten targets were used in reactive (argon plus acetylene) atmospheres and tungsten carbide targets were used in non-reactive (argon) atmospheres. Substrates were r.f. biased with d.c. potentials of up to -1000 V. Sputtering from WC targets produced carbon-deficient mixed-phase structures with β-WC1-x as the main component. Reactive deposition led to highly disordered W-C films which X-ray studies showed to be almost amorphous. Fractograms revealed very fine-grained to fractured amorphous film structures in all deposition modes. Hardness values higher than 3000 HV 0.05 were reached using non-reactive d.c. sputtering.

Comparison of the electron energy loss spectrum of erbium metal with Er/O2 and Er/H2

Abstract Electron energy loss spectra of metallic erbium, Er under different exposures of oxygen at room temperature, and Er deposited in an atmosphere of H2 are presented in both N(E) and dN dE form for primary energies in the range 100–1000 eV. Resonant excitations associated with the 5p and 4d levels in Er show little environmental dependence, and are largely intraatomic in character. In contrast the main plasmon peak shifts to higher energy on exposure to oxygen or hydrogen, and the spectrum of one electron excitations at low energies alters with a decrease in metal losses around 3.5 eV accompanied by a build up of valence band transitions at 8–9 eV. There is no evidence of a stable chemisorption phase under oxygen exposure, but the results are consistent with rapid oxygen incorporation into subsurface layers and oxide formation.

Surface oxidation of cerium and lanthanum

Abstract The surface oxidation of Ce and La with oxygen and water vapour has been studied by electron energy loss spectroscopy (EELS), electron stimulated desorption (ESD) and work function measurements on polycrystalline film surfaces and on a Ce(001) single crystal surface. The changes in electronic structure during oxidation reaction have been successfully probed by ELS, and similar oxidation behaviour is deduced for Ce and La up to the sesquioxide stoichiometry. On Ce surfaces, a CeO 2 -like oxide phase is detected under heavy oxidation conditions; this phase is characterised by a sharp loss feature due to valence band → 4 f excitations. With water vapour, only trivalent sesquioxide phases are observed, in which the terminal groups are surface hydroxyl species. ESD time-of-flight experiments from the hydroxylated Ce(001) surface reveal H + as the dominant ion; on the well-ordered surface the H + ion yield as a function of H 2 O dose exhibits a maximum followed by a decrease, which is interpreted in terms of a cooperative effect within the surface OH layer.

Surface chemistry of cyanogen on Pt(111): Isotopic exchange and coadsorption with CO

Abstract The adsorption of C2N2 on Pt(111) has been studied by thermal desorption mass spectrometry using 12C214N2 and 13C215N2 under various adsorption conditions and by work function measurements. Thermal desorption spectra revealed three desorption peaks (α, β1, β2) in close agreement with results on other Pt single crystal surfaces. No isotopic exchange was observed in the α peak and it is attributed therefore to molecularly adsorbed C2N2. Isotopic exchange between coadsorbed 12C214N2 and 13C215N2 was found in the β peaks depending on the experimental conditions. Whereas the β2 state showed isotopic exchange irrespective of simultaneous or consecutive adsorption of 12C214N2 and 13C215N2, no isotopic exchange was detected after consecutive adsorption in the β1 state once preformed at the surface. These results are discussed in terms of dissociative adsorption of C2N2 yielding CN particles into the β2 state and of the association of CN units into a more complex adsorbate layer (β1) at higher adsorbate densities. An overall work function increase was observed during C2N2 adsorption yielding Δφ = 370 mV at saturation. An opposite surface dipole is suggested for the α and β states. Coadsorption of C2N2 and CO was followed by thermal desorption and work function measurements. Whereas the C2N2-saturated Pt(111) surface can accommodate a considerable amount of CO, CO preadsorption drastically reduces the subsequent C2N2 uptake. The results indicate no reaction and little interaction between C2N2 and CO in the mixed adlayer.

Visualization of Freezing Process in situ upon Cooling and Warming of Aqueous Solutions

The freezing of aqueous solutions and reciprocal distribution of ice and a freeze-concentrated solution (FCS) are poorly understood in spite of their importance in fields ranging from biotechnology and life sciences to geophysics and climate change. Using an optical cryo-miscroscope and differential scanning calorimetry, we demonstrate that upon cooling of citric acid and sucrose solutions a fast freezing process results in a continuous ice framework (IF) and two freeze-concentrated solution regions of different concentrations, FCS1 and FCS2. The FCS1 is maximally freeze-concentrated and interweaves with IF. The less concentrated FCS2 envelops the entire IF/FCS1. We find that upon further cooling, the FCS1 transforms to glass, whereas the slow freezing of FCS2 continues until it is terminated by a FCS2-glass transition. We observe the resumed slow freezing of FCS2 upon subsequent warming. The net thermal effect of the resumed freezing and a reverse glass-FCS1 transition produces the Ttr2-transition which before has only been observed upon warming of frozen hydrocarbon solutions and which nature has remained misunderstood for decades.