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International audience; Self-ordering at crystal surfaces has been the subject of intense efforts during the last ten years, since it has been recognized as a promising way for growing uniform nanostructures with regular sizes and spacings in the 1-100 nm range. In this article we give an overview of the self-organized nanostructures growth on spontaneously nano-patterned templates. A great variety of surfaces exhibits a nano-scale order at thermal equilibrium, including adsorbate-induced reconstruction, surface dislocations networks, vicinal surfaces or more complex systems. Continuum models have been proposed where long-range elastic interactions are responsible for spontaneous periodic domain formation. Today the comparison between experiments such as Grazing Incidence X-Ray Diffraction experiments and calculations has lead to a great improvement of our fundamental understanding of the physics of self-ordering at crystal surfaces. Then, epitaxial growth on self-ordered surfaces leads to nanostructures organized growth. The present knowledge of modelization of such an heterogeneous growth using multi-scaled calculations is discussed. Such a high quality of both long-range and local ordered growth opens up the possibility of making measurements of physical proper-ties of such nanostructures by macroscopic integration techniques. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.

The role that occupied d bands play in the inelastic lifetime of bulk and surface states in Ag is investigated from the knowledge of the quasiparticle self-energy. In the case of bulk electrons, sp bands are taken to be free-electron-like. For surface states, the surface band structure of sp states is described with the use of a realistic one-dimensional Hamiltonian. The presence of occupied d states is considered in both cases by introducing a polarizable background. We obtain inelastic lifetimes of bulk electrons that are in good agreement with first-principles band-structure calculations. Our surface-state lifetime calculations indicate that the agreement with measured lifetimes of both crystal-induced and image-potential-induced surface states on Ag(100) and Ag(111) is considerably improved when the screening of d electrons is taken into account., We acknowledge partial support by the University of the Basque Country, the Basque Unibertsitate eta Ikerketa Saila, the Spanish Ministerio de Ciencia y Tecnologia, and the Max Planck Research Funds.

The morphological development of step edge patterns in the presence of meandering instability during step flow growth is studied by simulations and numerical integration of a continuum model. It is demonstrated that the kink Ehrlich-Schwoebel barrier responsible for the instability leads to an invariant shape of the step profiles. The step morphologies change with increasing coverage from a somewhat triangular shape to a more flat, invariant steady state form. The average pattern shape extracted from the simulations is shown to be in good agreement with that obtained from numerical integration of the continuum theory., Comment: 4 pages, 4 figures, RevTeX 3, submitted to Phys. Rev. B

Titelseite und Inhaltsverzeichnis 0\. Einleitung 5 1\. Allgemeiner Teil 7 1.2. Die (210)-Oberfläche 7 1.2. Allgemeines zur H-Adsorption 10 1.3. Dissoziation von Wasserstoff auf Metalloberflächen 13 1.4. Zur Bindung von Wasserstoffmolekülen an Metalloberflächen 23 1.5. Beispiele für molekularen Wasserstoff auf Metalloberflächen 30 2\. Experimenteller Teil 35 2.1. Augerelektronenspektroskopie (AES) 35 2.3. Beugung langsamer Elektronen (LEED) 37 2.3. Thermodesorptionsspektroskopie (TDS) 40 2.4. Änderung der Austrittsarbeit 44 2.5. Photoemissionsspektroskopie (UPS) 47 2.6. Schwingungsspektroskopie (HREELS) 53 2.7. Apparativer Aufbau 60 2.8. Substrate 63 2.9. Probenpräparation 65 Motivation 67 3\. Untersuchungen der reinen Wasserstoffsysteme H2/Pd(210) und H2/Ni(210) 69 3.1. Wechselwirkung von Wasserstoff mit einer Pd(210)-Oberfläche 69 3.2. Wechselwirkung von Wasserstoff mit einer Ni(210)-Oberfläche 86 4\. Zur konkurrierenden Adsorption von atomaren und molekularen Wasserstoff 101 5\. Untersuchungen zum Subsurface-Zustand 118 6\. Das H2/CO/Pd(210)-Koadsorptionssystem 130 6.1. Das reine CO/Pd(210)-System 131 6.2. Die H/CO Koadsorption auf der Pd(210)-Oberfläche 138 6.3. Diskussion 144 7\. Diskussion 150 8.1. Zusammenfassung 167 8.2. Summary 169 9\. Literatur 171, 8 In der vorliegenden Arbeit wurde die Wechselwirkung von Wasserstoff mit einer Pd(210)- und Ni(210)-Oberfläche mit Hilfe von Thermodesorptionsspektren (TDS), Messungen der Austrittsarbeitsänderung (DF), Photoemissionsspektren (UPS), Elektronenenergieverlustspektren (HREELS) und H2/D2-Isotopenaustausch- Messungen untersucht. Das H2-Adsorptionsverhalten stimmt für beide Oberflächen stark überein: Bei Temperaturen größer als 100K adsorbiert Wasserstoff spontan dissoziativ und bildet unter Erhöhung der Austrittsarbeit drei atomare Bindungszustände. Wird die Adsorptionstemperatur auf 50K reduziert, adsorbiert der Wasserstoff zusätzlich molekular in zwei Chemisorptionszustände. Dabei wird die Austrittsarbeit vermindert. Die molekulare Natur dieser Zustände wurde mit Hilfe von H2/D2-Austauschexperimenten, durch die Beobachtung einer H-H-Schwingungsbande im HREELS und der Detektion von s-H2/Pd- bzw. s*-H2/Pd- Bindungszuständen im UPS belegt. Neben den relativ hohen Desorptionstemperaturen weist auch die energetische Lage der Signale in den HREEL- und UP-Spektren eine chemisorptive Wechselwirkung nach. Die in den UP- Spektren beobachtete H2-induzierte Änderung der d-Bandstruktur kann mit einem Bindungsmodell entsprechend dem s-Hin/p-Rückbindungs-Synergismus nach Dewar- Chatt-Duncanson bzw. Blyholder erklärt werden. Die Beobachtung von chemisorbierten H2-Molekülen auf einer Übergangsoberfläche ist ungewöhnlich. Nach dem Harris-Andersson-Modell sollte auf Übergangsmetallen die Dissoziation spontan erfolgen, auf Edelmetallen hingegen inhibiert sein. Hier können bei Temperaturen kleiner als 10K molekular physisorbierter Wasserstoff stabilisiert werden. Das heißt, es besteht nur eine schwache Van-der-Waals-Wechselwirkung zwischen Molekül und Oberfläche. Das einzige weitere Beispiel von molekular chemisorbiertem Wasserstoff auf einer Übergangsmetalloberfläche ist das von A.-S. Mårtensson untersuchte H2/Ni(510)-System. Ist diese gestuften Ni(110)-Oberfläche mit atomarem Wasserstoff gesättigt, adsorbiert weiterer Wasserstoff molekular an den Stufen. Aus HREELS-Daten ergibt sich eine on top Adsorption. Wir machen ähnliche Beobachtungen: Während die atomare Adsorption auf der Pd(210)- bzw. Ni(210)-Oberfläche in hochkoordinierte Plätze erfolgt, adsorbiert das Molekül on top auf Substratatomen der ersten Lage. DF\- und TD- Experimente deuten darauf hin, daß zur Stabilisierung der molekularen Zustände eine partielle atomare Vorbelegung der Oberfläche notwendig ist. Mit Hilfe des in einer Kooperation mit einer Theoretischen Gruppe (A. Groß an der TU München) entwickelten Adsorptionsmodells wird den verschiedenen molekularen Desorptionssignalen derselbe Adsorptionsplatz bei unterschiedlicher atomarer Vorbedeckung zugeordnet. Der molekulare Adsorptionsplatz on top an den gering koordinierten Substratatomen der ersten Lage ist gleichzeitig der Dissoziationsplatz. Ändert sich aufgrund der benachbarten atomaren Adsorption von Wasserstoff die d-Bandstruktur und damit die Reaktivität dieser ausgezeichneten Substratatome, wird der dort gebildete molekulare Vorläufer- Zustand stabilisiert. Die in dieser Arbeit vorgestellten Systeme unterscheiden sich im Hinblick auf die Besetzung des Subsurface-Zustandes. Für die Pd(210)-Oberfläche wird eine Absorption von Wasserstoff in oberflächennahe Zwischengitterplätze beobachtet, für die H2/Ni(210)-Oberfläche nicht. Dabei ist mit Besetzung des Subsurface- Zustandes keine Änderung der Austrittsarbeit oder die Detektion eines Schwingungsverlustes im HREELS verbunden. In den TD-Spektren wird der Absorption ein schmales Niedertemperatur-Signal zugeordnet. Diese Beobachtung wird mit Hilfe des von Okuyama entwickelten Stamping-Modells diskutiert. Eine H-Absorption wurde bereits für andere offene Pd-Oberflächen ( (110) und (310) ) beobachtet und gilt als besondere Elementeigenschaft von Palladium. Im Unterschied zu den Pd(110)- und Pd(310)-Oberflächen ist zur Absorption in den Pd(210)-Kristall keine Rekonstruktion nötig. Dies und die Beobachtung der Abhängigkeit der Absorptionsgeschwindigkeit von der Probenpräparation ist Anlaß dafür die Existenz eines zur Absorption notwendigen Strukturensembles auf der nicht-rekonstruierten Pd(210)-Oberfläche zu diskutieren. Als solches wird der vierfachkoordinierte Muldenplatz und sein benachbarter dreifachkoordinierter (111)-Mikrofacettenplatz identifiziert. Daneben wurde auch die H/CO-Koadsorption auf der Pd(210)-Oberfläche untersucht. Wenn Wasserstoff präadsorbiert und anschließend CO dosiert wird, beobachten wir eine H/CO-Komplexbildung. Dies wird durch die Detektion eines sogenannten S-Signals im H2-TD-Spektrum und eines nH-O-Schwingungsverlustes im HREELS belegt. Im Gegensatz zu anderen Koadsorptionssystemen desorbiert der S-Wasserstoff nicht bei den niedrigeren Temperaturen des Desorptionsbereiches, sondern simultan mit dem Stabilsten der CO-Zustände. Dies deutet auf eine ungewöhnlich stabile Komplex-Bildung hin., 8 This work presents investigations of the interaction of hydrogen with a Pd(210) and Ni(210) surface using LEED (low energy electron diffraction), thermal desorption spectroscopy (TDS), work-function measurements (DF),vibrational loss measurements (HREELS), and isotope exchange experiments. The interaction of hydrogen with both surfaces is very similar. For temperatures above 100K, hydrogen chemisorbs spontaneously forming atoms in three binding states (b1, b2, b3). The atomic adsorption leads to a work function increase. If the temperature is reduced to 50K, hydrogen additionally chemisorbs into two molecular states (g1, g2). In contrast to the b-adsorption, the population of g-states induces a work-function decrease. The molecular nature of the g-states was confirmed by observation of the H-H vibration mode in HREELS, by the detection of the s-H2/Pd- and s*-H2/Pd- bonding in UPS, and by H2/D2-exchange experiments. The energy range of the HREELS- and UPS-signals and the relatively high desorption temperature in TD-spectra verify a real chemisorptive interaction between molecule and surface. We consider a side-on complex configuration which allows a s/s*-synergism equivalent to the Blyholder backbonding mechanism for CO chemisorption or the classical Dewar-Chatt-Duncanson model for the bonding situation in olefine or other organometallic complexes. A molecular chemisorption of H2 on a transition metal surface is unusual. In general, hydrogen adsorbs dissociatively. While on noble metals the dissociation is hindered by a sizable energy barrier, it occurs spontaneously on transition metal surfaces. If molecular adsorption states exist, they are usually very weakly bound in shallow physisorption wells; beyond, it requires surface temperatures below 20K to stabilize those states. At Ni(510), molecular chemisorption has been observed at surface temperatures up to 125K, presumably at the steps, but only after the surface was passivated with a dense atomic layer. We made similar observations, namely the coexistence of chemisorbed molecular and atomic hydrogen on the relatively open Pd(210) and Ni(210) surfaces although the surfaces were not fully passivated. While the atomic adsorption takes place in high coordinated sites, the molecule adsorbs on top. It is very difficult to identify experimentally the exact location and nature of the hydrogen adsorption states. In order to obtain this microscopic information, A. Groß et al. performed DFT calculations. The results suggest that the hydrogen molecule is first attracted to the top Pd atoms. At the clean Pd(210) surface, no stable molecular adsorption state should exist and the hydrogen molecule dissociates into the higher coordinated sites. Due to the presence of atomic hydrogen on the surface however, this behavior changed considerably. The presence of hydrogen atoms leads to a molecular adsorption state at the top site. That the top site`s reactivity is hardly influenced by the pre-adsorbed hydrogen atoms can be traced back to the induced change in the local density of states. In the case of Pd, we observed the absorption of hydrogen atoms which reside ?close to the surface?. Evidence for such a ?subsurface state? is a low- temperature thermal desorption feature which cannot be saturated, combined with a vanishing work function change and negligible vibrational loss contributions of the respective H state. We discuss our observations using the stamping model developed by Okuyama. The hydrogen absorption has already been observed on other open palladium surfaces and is considered as a specific feature of the element palladium. But in contrast to other open Pd surfaces, the Pd(210) surface need not to reconstruct for absorption. Futhermore, the absorption velocity depends on the preparation of the sample. Both observations give rise to the assumption that a certain ensemble of substrate atoms necessary for chemisorption exists on the non-reconstructed Pd(210) surface. We can identify this ensemble as the four-fold coordinated hollow site and the neighbouring three-fold coordinated site. In addition, we examined the H/CO-coadsorption on the Pd(210) surface. If the Pd crystal was first exposed to hydrogen and then to carbon monoxid, we observed the formation of H/CO-complexes. This observation was verified by the detection of a so-called S desorption signal in TDS and by a O-H vibrational loss in HREELS. In contrast to other coadsorption systems the S-hydrogen does not desorb in the low temperature area. Rather, hydrogen desorbs simultaneously with the strongly bound carbon monoxid, indicating an unusually stable complex.

We have performed density functional calculations of O chemisorbed on a Pt(111) surface, for various chemisorption sites and geometries.We determined the forces acting on the surrounding substrate atoms before these are allowed to relax. The forces in the surface plane are quite large when allowed by symmetry. We have subsequently allowed the substrate to fully relax, and found the energy of adsorption into various sites, and the related relaxation of the substrate.These results can be used to determine the relative stability ofvarious sites, diffusion paths, and other related quantities.

Adhesion of the bacterial strain Staphylococcus epidermidis 3399 to titanium-oxy-nitride (TiNOX (R)) substrata with different specific resistivities was studied in a parallel plate flow chamber, while simultaneously measuring the electric potential of the substrata. During adhesion, bacteria either donated or accepted electrons to the substrata depending on the specific resistivity of the substratum and bacteria that had donated electrons to the substratum adhered more strongly than bacteria that had accepted electrons from the substratum. These results demonstrate that electron transfer plays a role in bacterial adhesion to conducting surfaces, which has hitherto been neglected. (C) 2000 Elsevier Science B.V. All rights reserved.

We present first-principles calculations of electron-electron scattering rates of low-energy electrons in Au. Our full band-structure calculations indicate that a major contribution from occupied d states participating in the screening of electron-electron interactions yields lifetimes of electrons in Au with energies of 1.0–3.0eV above the Fermi level that are larger than those of electrons in a free-electron gas by a factor of ∼4.5. This prediction is in agreement with a recent experimental study of ultrafast electron dynamics in Au(111) films [J. Cao et al., Phys. Rev. B 58, 10 948 (1998)], where electron transport has been shown to play a minor role in the measured lifetimes of hot electrons in this material., We acknowledge partial support by the University of the Basque Country, the Basque Hezkuntza, Unibertistate eta Ikerketa Saila, and the Spanish Ministerio de Educacion y Cultura.

Strong dependence of the surface-enhanced infrared spectroscopy (SEIS) on the nature of the substrate and the surface roughness were demonstrated. Surface-enhanced vibrational spectroscopy involves the study of molecules adsorbed on surfaces that can enhance the absorption and emission of electromagnetic radiation. Self-assembled monolayers (SAM), alkanethiols on gold and silver surfaces, were prepared by dipping the silver-coated samples in 1 mM solutions of the thiols in absolute ethanol for 12 hours. SEIR spectroscopy was applied successfully to the study of monolayers adsorbed on metal surfaces in reflection absorption ATR as well as in transmission geometries. The surprisingly high enhancement was observed for the IR spectra for SAM grown on Ag/Al suggesting a simple method for the preparation of SEIR active substrates. The spectra were acquired using standard detection systems in a commercial analytical spectrometer without additional preparation.

Laser melting of rough metal surfaces, in particular in those containing parallel scratch lines of micron and submicron size, differs from melting of smooth planar surfaces. It is associated with the reach of the spectra of self-organized structures, which consist of vortex filaments as basic entities. Self-organized structures of vortex filaments on rough metal surfaces were generated by short laser pulses and studied by optical and scanning electron microscopy. Their formation starts with melting of the surface that generates a shear layer with radially oriented flow in the laser spot. Parallel scratch lines represent the flow perturbation which is spanwise, streamwise or oblique in different zones of the spot giving, rise to the self-organized flow structures. The flow structures are permanently frozen by ultra-fast cooling after laser pulse termination, thus enabling a posteriori analysis. Long vortex filaments organized into very complex structures ranging from parallel Kelvin-Helmholtz rollers, to 'helically paired' counter-rotating filaments, to the braided vortex filaments (which become broken by the shock wave at higher pulse energy), and finally to the 'hairpin' or the Omega-shaped vortices (as the channel structure between two scratch lines) have been observed. The spectrum of surface self-organized hydrodynamic structure was found to depend on laser parameters: the beam energy, beam wavelength, pulse duration and the beam profile (Gaussian or 'top hat' type). Motivation for these studies is twofold: first theoretical, directed to elucidating the conditions of the hydrodynamic self-organized structure formation, and, second, technological, directed to elucidating and eventually opening up new possibilities in laser surface alloying, cladding, etc., with respect to the dynamics of the mixing layer.

Observation of microorganisms adhering to metal surfaces is more difficult than of those adhering to glass or translucent polymers and usually requires special techniques as e.g. epifluorescent microscopy, scanning electron microscopy or removal of adhering microorganisms followed by plating. In this paper, the use of metallurgical microscopy to observe microorganisms adhering to metal surfaces is described. The method is simple, attachment of the vertical illumination set up required to an ordinary light microscope is relatively cheap, and no additional manipulations are necessary. The image quality is high and individual adhering microorganisms can be easily observed, even without employing additional image analysis techniques. As an example of the application of this technique, the influence of Ca2+ ions on the adhesion of three strains of dairy Streptococcus thermophilus to 316-L stainless steel was studied. Using a parallel plate flow chamber with a stainless steel bottom plate and a glass top plate, adhesion was measured in situ on the bottom plate under moderate flow (15 s(-1)) in an adhesion buffer with various amounts of CaCl2 added. Neither the initial deposition rates nor the numbers of organisms adhering after 200 min showed systematic variation with the amounts of CaCl2 added. However, for S. thermophilus G1 initial the deposition rates with 1 mM CaCl2 were much higher (2170 cm(-2) s(-1)) than was the case without CaCl2, or with 5 mM CaCl2 added (approximately 1300 cm(-2) s(-1)). For S. thermophilus B and N-12 the initial deposition rates were only slightly higher with 5 mM CaCl2 than without CaCl2 or without 1 mM CaCl2 added. Thus in order to study adhesion of thermophilic, dairy streptococci under different conditions, such as in a pasteurizer, calcium must be added as its presence can have a major effect.

The electron density of the (1×2)Pt(110) surface is determined by He reflectivity measurements and compared to the electron densities previously reported for (1×2)Au(110) and (1×2)Rh(110). With respect to the superposition of free atomic electron densities, significant charge depletion and enrichment are observed, respectively, on top of the surface atoms and in the threefold sites of the (111) microfacets.

Raman spectra from single DNA molecules in their natural aqueous environment are presented. A DNA molecule that is anchored between two optically trapped dielectric beads is suspended in a solution with nanosized silvercolloid particles. The nonspecific binding of the metal to the DNA enhances the Raman scattering that is excited by a near-infrared beam. A Raman spectrum is first recorded followed by a force-extension curve that verifies the presence of a single DNA molecule.

The effect of inelastic scattering processes on the angular distribution of positrons spontaneously emitted from metal surfaces is investigated. Angular and energy spectra are calculated for positrons suffering energy loss due to electron-hole excitation in emission from materials with low (aluminum) and high (tungsten) positron work functions.