Height analysis of amorphous and crystalline ice structures on Cu(111) in scanning tunneling microscopy

Scanning tunneling microscopy imaging of amorphous and crystalline D2O ice on Cu(111) is discussed with respect to the apparent and the real heights of these structures above the metal surface. The apparent height increases linearly below the conduction band onset of amorphous ice and the first image state of crystalline ice, respectively. However, it largely underestimates the real height. For these voltages, histograms of the apparent height can be used to identify different layers. The dependence of the apparent height on voltage increases step-like up to the real height at the onsets of the first unoccupied electronic state. Apparent height spectroscopy is utilized to relate the apparent height to the real height of the different structures. The analysis reveals the layering during growth of porous amorphous ice between 0.1 and 1.4 BL and the dynamics of crystallization between 130 and 145 K.DF

Spatial variation of the surface state onset close to three types of surface steps on Ag(111) studied by scanning tunnelling spectroscopy

A regular step, a dislocation slip step and a step formed by the emergence of a split edge dislocation (SED) to the surface influence the local density of states close to the onset of the surface state as investigated by scanning tunnelling spectroscopy at low temperature.The onset of the surface state shifts close to the regular step and the dislocation slip step by approximately 15 meV towards the Fermi energy.Additional maxima above the onset are only observed if a second step leads to confinement.In both cases, the conductivity decreases close to the step.However, an increase in conductance above the surface state onset is observed close to the SED step.Furthermore, a variety of additional states are discernable.Thus, different types of steps lead to markedly different changes in the local electronic structure on surfaces.© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.DF

Long-range interaction of copper adatoms and copper dimers on Ag(111)

Formation and motion of copper adatoms and addimers on Ag( 1 1 1) are investigated with low-temperature scanning tunnelling microscopy between 6 and 25 K. Adatoms move between fcc and hcp sites with a strong preference for the fcc site. Adatom motion and dimer rotation change due to the presence of other adatoms or dimers. Furthermore, rotating dimers influence other rotating dimers. These changes are attributed to changes in the diffusion or rotation potential, which are mediated by the electrons in the two-dimensional surface state band

Light driven reactions of single physisorbed azobenzenes

We present a successful attempt of decoupling a dye molecule from a metallic surface via physisorption for enabling direct photoisomerization. Effective switching between the isomers is possible by exposure to UV light via the rotation pathway. © 2011 The Royal Society of Chemistry

Disorder induced local density of states oscillations on narrow Ag(111) terraces

The local density of states of Ag(111) has been probed in detail on disordered terraces of varying width by dI/dV-mapping with a scanning tunneling microscope at low temperatures. Apparent shifts of the bottom of the surface-state band edge from terrace induced confinement are observed. Disordered terraces show interesting contrast reversals in the dI/dV maps as a function of tip-sample voltage polarity with details that depend on the average width of the terrace and the particular edge profile. In contrast to perfect terraces with straight edges, standing wave patterns are observed parallel to the step edges, i.e. in the non-confined direction. Scattering calculations based on the Ag(111) surface states reproduce these spatial oscillations and all the qualitative features of the standing wave patterns, including the polarity-dependent contrast reversals.Comment: 19 pages, 12 figure

Femtosecond electron transfer dynamics across the D2_2O/Cs+^+/Cu(111) interface: The impact of hydrogen bonding

Hydrogen bonding is essential in electron transfer processes at water-electrode interfaces. We study the impact of the H-bonding of water as a solvent molecule on real-time electron transfer dynamics across a Cs+-Cu(111) ion-metal interface using femtosecond time-resolved two-photon photoelectron spectroscopy. We distinguish in the formed water-alkali aggregates two regimes below and above two water molecules per ion. Upon crossing the boundary of these regimes, the lifetime of the excess electron localized transiently at the Cs+ ion increases from 40 to 60 femtoseconds, which indicates a reduced alkali-metal interaction. Furthermore, the energy transferred to a dynamic structural rearrangement due to hydration is reduced from 0.3 to 0.2 eV concomitantly. These effects are a consequence of H-bonding and the beginning formation of a nanoscale water network. This finding is supported by real-space imaging of the solvatomers and vibrational frequency shifts of the OH stretch and bending modes calculated for these specific interfaces.Comment: 8 pages, 5 figure

Probing Oxide Reduction and Phase Transformations at the Au-TiO2 Interface by Vibrational Spectroscopy

By a combination of FT-NIR Raman spectroscopy, infrared spectroscopy of CO adsorption under ultrahigh vacuum conditions (UHV-IR) and Raman spectroscopy in the line scanning mode the formation of a reduced titania phase in a commercial Au/TiO2 catalyst and in freshly prepared Au/anatase catalysts was detected. The reduced phase, formed at the Au-TiO2 interface, can serve as nucleation point for the formation of stoichiometric rutile. TinO2n−1 Magnéli phases, structurally resembling the rutile phase, might be involved in this process. The formation of the reduced phase and the rutilization process is clearly linked to the presence of gold nanoparticles and it does not proceed under similar conditions with the pure titania sample. Phase transformations might be both thermally or light induced, however, the colloidal deposition synthesis of the Au/TiO2 catalysts is clearly ruled out as cause for the formation of the reduced phase