Silver 111 surfaces

Examples of ordered organic monolayers are normal paraffins on platinum and silver (111) surfaces. If straight-chain saturated hydrocarbon molecules from propane (CsHg) to octane (CgHig) are deposited from the vapor phase onto Pt or Ag (111) between 100 and 200 K ordered monolayers are produced. As the temperature is decreased a thick crystalline film can condense. The paraffins adsorb with their chain axis parallel to the platinum substrate, and their surface unit cell increases smoothly with increasing chain length as shown in Fig. 15. 

The rough electrode near a non primitive electrolyte. This is a case relevant to computer simulations of realistic solvent models near a model of a metallic surface such as the silver( 111) surface, for which experiments have recently been reported [61]. Most models of water employed in the computer simulations consist of neutral molecules with embedded point charges. 

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

Tarazona A, Kreisig S, Koglin E and Schwuger M J 1997 Adsorption properties of two cationic surfactant classes on silver surfaces studied by means of SERS spectroscopy and ab initio calculations Prog. Colloid Polym. Sol. 103 181-92... 

The strong bond fonned between tire tliiol endgroups and gold and silver surfaces allows tire possibility of fonning molecules tliat have a wide variety of different functional groups at tire opposite end and tluis of coating a noble metal surface witli a variety of differently functionalized molecules and mixtures. 

Harder P, Grunze M, Dahint R, Whitesides G M and Laibinis P E 1998 Molecular conformation in oligo(ethylene glycol)-terminated self-assembled monolayers on gold and silver surfaces determines their ability to resist protein adsorption J. Rhys. Chem. B 102 426-36... 

Laser stimulation of a silver surface results in a reflected signal over a million times stronger than that of other metals. Called laser-enhanced Raman spectroscopy, this procedure is useful in catalysis. The large neutron cross section of silver (see Fig. 2), makes this element useful as a thermal neutron flux monitor for reactor surveillance programs (see Nuclearreactors). 

Intensity enhancement takes place on rough silver surfaces. Under such conditions, Raman scattering can be measured from monolayers of molecular substances adsorbed on the silver (pyridine was the original test case), a technique known as surface-enhanced Raman spectroscopy. More recendy it has been found that sur-fiice enhancement also occurs when a thin layer of silver is sputtered onto a solid sample and the Raman scattering is observed through the silver. 

Fig. 4.56. Schematic diagram of a SERS-active substrate and the measurement arrangement. Alumina nanoparticles are deposited on a glass surface and produce the required roughness. A thin silver layer is evaporated on to the nanoparticles and serves for the enhancement. Organic molecules adsorbed on the silver surface can be detected by irradiation with a laser and collecting the Raman scattered light.

Fig. 4.59. Raman spectrum of methyl mercaptan (a) and SERS spectrum of methyl mercaptide (b) formed by adsorption ofthe mercaptan on a silver surface. The surface reaction is proven by the disappearance ofthe S-H stretching and bending bands at 2575 cm" and 806 cm", respectively. The Raman shift ofthe C-S stretching band at approximately 700 cm" is reduced during adsorption by withdrawal of electron density from the C-S, because of bonding to the silver. The symmetric methyl stretching appears above 2900cm" [4.303].

There have been some investigations into adsorption on zeolites (1, 2), and Greenler and Slager (3) have outlined a method for obtaining the Raman spectrum of a thin solid film deposited on a reflecting silver surface. 

K.J. Maynard, and M. Moskovits, A surface enhanced Raman study of carbon dioxide coadsorption with oxygen and alkali metals on silver surfaces,/. Chem. Phys. 90(11), 6668-6679 (1989). 

The effect of complex formation on the solubility of a solid can be observed in the home. Silver dinnerware eventually becomes discolored by an unsightly black tarnish of Ag2 S, formed from the reaction of the silver surface with small amounts of H2 S present in the atmosphere. Silver sulfide is highly insoluble in water. Commercial silver polishes contain ligands that form strong soluble complexes with Ag ions. If a tarnished serving pan is rubbed with a polish, the black tarnish dissolves, returning the silver to its brilliant shine. 

Loudiana, M.A., Dickinson, J.T., Schmid, A. and Ashley, E.J. (1987) Electron enhanced sorption of fluorine by silver surfaces. Applied Surface Science, 28, 311-322. 

Consequently, during interaction of oxygen with freshly reduced silver surface the emission of atom oxygen takes place. 

Figure 4.18 (a) STM image (39 x 23 nm) 02 molecules at Ag(l 10) at 65 K, illustrating the hot precursor mechanism at a coverage of 0.02. The inset shows an atomic resolution image of the silver surface and the 02 molecules as dark holes. Also shown (b) is a ball model with oxygen molecules (black) and surface silver atoms (white) and second layer silver atoms (grey). (Reproduced from Ref. 32). 

Beck, L., S. Bosonnet, S. Reveillon, D. Eliot, and F. Pilon (2004), Silver surface enrichment of silver-copper alloys A limitation for the analysis of ancient silver coins by surface techniques, Nuclear Instrum. Meth. (B) 226(1-2), 153-162. 

Figure 3.2 STM images obtained with a CO-terminated tip, Vt = 70 mV and /t= 1 nA. (a) Isolated CO molecule, (b) two O atoms (adsorbed on the nearest fourfold hollow sites along the [1 1 0] direction), (c) CO and two O atoms separated by 6.1 A along the [0 0 1] direction, and (e) O-CO-O complex. Grid lines are drawn through the silver surface atoms. Scan area of (a-c) and (e) is 25 A x 25 A.

Figure 3.3 Reaction of a CO molecule released from a CO-terminated tip with an O atom adsorbed on the surface, (a) STM image, taken with a CO-terminated tip, of two O atoms separated by two lattice spacings (2 x 2.89 A) along the [11 0] direction. Grid lines are drawn through the silver surface atoms, (b) Tunneling current during a 1470 mV sample bias pulse with the CO-terminated tip over one of the two O atoms (denoted by Two current rises...

The fact that the CT model is not sufficient to account for all SERS effects is most clearly illustrated by the work of Murray and Allara (1982), who used well-defined polymer films as separators between suitable test molecules and a roughened silver surface. 

Free radicals were found to be generated on the catalyst surface in hydrocarbon oxidation in the absence of hydroperoxide. The activation of absorbed dioxygen was supposed to be the source of radicals [255], The catalytic action of the silver surface on cumene oxidation was supposed to be the result of activation of sorbed dioxygen [265]. 

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