Silver-oxide overlayer

As a furtlier example for tire meaning of ex situ investigations of emersed electrodes witli surface analytical teclmiques, results obtained for tire double layer on poly crystalline silver in alkaline solutions are presented in figure C2.10.3. This system is of scientific interest, since tliin silver oxide overlayers (tliickness up to about 5 nm) are fonned for sufficiently anodic potentials, which implies tliat tire adsorjDtion of anions, cations and water can be studied on tire clean metal as well as on an oxide covered surface [55, 56]. For tire latter situation, a changed... 

High reaction pressures are needed for many other systems as well in order to convert the surface into a uniquely reactive state such as has been found for ethylene epoxidation. The epoxidation reaction of ethylene catalyzed by silver shows a distinct pressure gap. Higher oxygen pressures are needed in order to convert the silver surface into a silver-oxide overlayer where weakly adsorbed oxygen atoms are formed, that selectively epoxidize ethylene ]. 

Fig. 13. Structures (left) and STM simulations (right) for oxide overlayers with different stoichiometry on Ag lll. The O coverage in each overlayer is given on the far left and the stoichiometry on the far right. Oxygen (silver) atoms appear as dark grey (light grey) balls. The black squares on the right depict the location of Ag adatoms responsible for the bright features in the STM simulations. The extra O atoms, which are in excess of those in the reference Agx gO oxide (top), are circled in black.

Oxygen on Silver and the Structure of the Oxide Overlayer and Reaction Conditions 235... 

DESORPTION OF OXYGEN ON SILVER AND THE STRUCTURE OF THE OXIDE OVERLAYER AND REACTION CONDITIONS... 

Figure 5(left) shows the Gibbs energy of adsorption as a function of temperature at a typical UHV pressure (10-12 atm.). This figure reveals several important pieces of information. First, the silver deficient Agj gO oxide is more stable than the stoichiometric Ag20 oxide. Since both oxide phases contain the same number of O atoms, their relative stability is independent of temperature and pressure, with the silver deficient Agt 80 oxide favored by 0.74 and 0.46 eV per (4 x 4) oxide unit cell with CASTEP and VASP, respectively. Thus, as mentioned earlier, there is a clear preference for non-stoichiometric Agx gO growth on Ag lll. The reason for this preference is that in the ideal Ag20 overlayer an additional Ag atom would have... 

For reasons clear from the introduction, enhancement of phosphorescence is a particularly attractive application of plasmonics to OLED technology. Since carriers are injected into an OLED from separate contracts, their spins are uncorrelated and spin statistics dictate preferential formation of triplet excited states. Since these are generally poor emitters at ambient temperature, metallic enhancement of the phosphorescent rate would be desirable. Moreover, triplet states are typically long-lived and prone to oxidation reactions so that reduction of the triplet lifetime could potentially improve stability of the phosphors. PtOEP is a model phosphor and its application to electroluminescence was pioneered by the groups of Forrest and Thomson (46-47). We have investigated plasmonic enhancement of the PtOEP phosphorescence on silver surfaces prepared using the Tollens reaction. Dilute PtOEP in a polymer binder was spin cast onto substrates with various densities of nanotextured silver and assumed to deposit conformally, the spin speed being used to control the approximate thickness of the overlayer. 

In dielectric layers, where a surface phonon mode may occur, or in ionic crystals, multiple scattering from the surface phonon mode can result in Poisson replicas of the no-loss peak. These modes are referred to as Fuchs- Kliewer modes they are a general feature of HREELS spectra of ionic and polar materials, and metal oxides. Ordered overlays on surfaces can also exhibit collective modes, but at submonolayer coverages the HREELS loss peaks are due almost exclusively to single oscillations of the fundamentals. Substrate (silver) phonon modes are shown at 10 meV (83 cm ) in Figure 7. 

Fig. 8.8 Overlay plot of stripping voltammetry for a glassy carbon electrode modified with silver (peak potential =+0.5 V) and nickel nanoparticles (peak potential =+1.8 V) with impact frequency of the nanoparticle mixture at a carbon microelectrode in 10 mM HCIO4/IOO mM NaC104. The onset potential of spikes at 0.3 V corresponds to the direct oxidation of silver nanoparticles whilst the later switch on potential (+1.4 V) is caused by the mixed nanoparticles. Reproduced by permission of The Royal Society of Chemistry...

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