Silver surface preparation

Figure 19.2 Self-similarity analysis for nanotextured silver surfaces prepared in different ways. The root mean square roughness inferred from atomic force microscopy is plotted versus measurement area. The various surfaces are 100 nm thick evaporated silver films (solid squares, red line)-, 5.2 nm thick evaporated silver films (open circles, green line) nanoparticle films assembled from colloid attachment to self-assembled monolayers (solid circles, blue line) films from deliberate precipitation of silver colloid (solid up-triangles, black line) Tollens reaction films (open down-triangles, orange line). Lines with slopes H = 1.0 and H = l.S representing two-dimensional and 1.5 dimensional surfaces respectively are...

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. 

The first SERS spectra were recorded on a roughened silver surface prepared by the method of EC-oxidation/reduction cycles [23]. By application of an oxidation potential to the metal electrode, the electrode was oxidized to soluble ions or an insoluble surface complex a reduction potential will then reduce these species at the surface, forming surface nanostructures. As silver is one of the most extensively studied SERS substrate materials, it is reasonable to take this as an example to illustrate the oxidation/reduction cycles procedure in detail [88]. 

The experimental apparatus and the silver catalyst preparation and characterization procedure is described in detail elsewhere (10). The porous catalyst film had a superficial surface area of 2 cm2 and could adsorb approximately (2 +. 5) 10-b moles O2 as determined by oxygen chemisorption followed by titration with ethylene (10). The reactor had a volume of 30 cm3and over the range of flowrates used behaved as a well mixed reactor (10, 11). Further experimental details are given in references (10) and (11). 

The experimental procedures and x-ray photoemission results for the preparation of ultrathin (d = 1.1 nm) polyimide films on polycrystalline silver by co-condensation of PMDA and ODA are described elsewhere [5]. In that work our XPS results suggested that the polyimide chains bond to the silver surface via a carboxylate type bonding. This conclusion was derived from an analysis of the results obtained for the interaction of the monomers (PMDA and ODA) and of the resulting ultra-thin polyimide film. Due to the relatively larger thickness of the polyamic acid films as compared to the monomer adsorbate phases and the polyimide film, no conclusions were possible about the reaction of the polyamic acid with the silver substrate. 

One important chemical result from the ESCA studies involves the formation of surface carboxylates. Upon transfer of the monolayer to silver, the formation of a carboxylate could be detected by the production of a single peak in the oxygen Is line due to equivalent oxygens in the carboxylate structure. Since the oxygen spectrum of the monolayer yields near stoichiometric C-0/C==0 ratio of 1, the carboxylate is not detectable. Studies with monolayer films of cadmium arachidate indicated detectability of the carboxylate as a single carbon Is peak. The lack of the formation of this interfacial carboxylate indicates the strength (or weakness) of surface chemistry which occurs on this silver surface as prepared. 

Figure 8.11 Silver coatings prepared from PEG 400 (a) silver mirror on inside surface of flask, (b) SEM of silver particles after 3 h and (c) after 8 h, (d) cross-sectional SEM view of film on glass. [Reprinted with permission from Chem. Lett., 2007, 36, 782-783. Copyright 2007 The Chemical Society of Japan.]...

Stewart S, Fredericks PM (1999) Surface-enhanced Raman spectroscopy of amino acids adsorbed on an electrochemically prepared silver surface. Spectrochim Acta A Mol Biomol Spectrosc 55(7-8) 1641-1660... 

Smejkal P, Siskova K, Vlckova B, Pfleger J, Sloufova I, Slouf M, Mojzes P (2003) Characterization and surface-enhanced Raman spectral probing of silver hydrosols prepared by two-wavelength laser ablation and fragmentation. Spectrochim Acta A 59 2321-2329... 

Sun B, Jiang X, Dai S, Du Z (2009) Single-crystal silver nanowires preparation and Surface-enhanced Raman Scattering (SERS) property. Mater Lett 63 2570-2573... 

Taylor CE, Garvey SD, Pemberton JE (1996) Carbon contamination at silver surfaces surface preparation procedures evaluated by Raman spectroscopy and X-ray photoelectron spectroscopy. Anal Chem 68 2401... 

Rupeiez A, Lasema JJ (1994) Surface-enhanced Raman spectrometry on a silver substrate prepared by the nitric acid etching method. Anal Chim Acta 291 147-153... 

High enhancement of the copper localized surface plasmon absorbency was recorded at the two-layer planar system consisted of copper and silver nanoparticles prepared with successive vacuum evaporation. The result obtained may be caused by strong near-field coupling in the close-packed binary system. The effect may be used for the development of high-absorptive coatings and spectral selective nanoelements in the visible and near infrared spectral ranges. 

Electrochemical or chemical polishing, whatever is the rinsing procedure, leaves traces of chemicals at the surface (cyanide in the case of gold or silver, for instance). These polishing stages are followed either by annealing or by one of the final surface preparations (see Section IV.4). 

The importance of chloride ions for SERS was realized in the very first studies. In fact, Jeanmaire and Van Duyne have studied the dependence on chloride concentration and found that optimal signals were obtained for a halide/pyridine concentration ratio of about 2. This is dependent on the method of surface preparation. The role of chloride ions in the ORC, essentially in facilitating the formation of insoluble silver chloride in the oxidation stage, was already discussed in Section II.2(ii). 

It is senseless to specifically list here the studies done with silver they are referenced throughout this review. Work on gold and copper is also relatively abundant and full coverage of all pertinent references is not attempted here. To detect SERS from these metals, excitation in the red is required. A surface preparation, ORC for instance, is often needed, as described in Section II.2. 

Silver (111) slides can also be prepared by thermal evaporation of Ag onto cleaned Si or glass slides. However, as silver surfaces are readily oxidized in the ambient atmosphere, the slides must be transferred to the deposition solutions immediately, preferably in an inert atmosphere71. Auger electron spectroscopy showed that 2 h exposure of the freshly evaporated Ag slides to the ambient laboratory atmosphere doubles the oxygen content90. 

The processing and surface preparation of silver particles is critical to their performance as a filler. The first step in manufacturing silver flakes is to produce silver powder. Powdered silver may be produced by chemical precipitation, electrolytic precipitation, or melt atomization. Most commercially available silver powders are precipitated by reducing silver from a silver nitrate solution. Particle sizes of powdered silver range from submicron to 5 pm." Silver powders are selected based on size and... 

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