Roughened silver electrodes

Silver fractal-iike structures on Ag electrode, monotone coloring 

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Ever since Albrecht and Creighton [85], and Jenmarie and van Duyne [86], observed that the Raman cross-section for pyridine absorbed on a roughened silver electrode was larger than that in solution by six orders of magnitude, surface enhanced Raman spectroscopy (SERS) has steadily gained ground in analytical instrumentation. The sensitivity of this technique... 

Zheng et al. [29] have compared surface properties of the assembled silver nanoparticle electrode/indium-tin oxide (AAgNP/ITO) and roughened silver electrode, using electrochemical... 

As was mentioned in the previous section, the nature of the substrate is extremely critical in obtaining the maximum enhancement. For visible Raman excitation, the noble metals, such as Ag and Au, and the alkali metals are the substrates of choice. For other regions, other substrates are more suitable (e.g., Ge or Pt in the IR region). Probably the most common substrates used for SERS are the colloidal suspensions of silver or gold particles ( 5-20nm in diameter), and electrochemically roughened silver electrodes. 

Figure 47. Difference diffractograms from roughened silver electrodes. (A) Potential modulation between — 0.35 and — 1.05 V (bulk Tl deposition). (B) Potential modulation between — 0.25 and — 0.70 V (underpotential deposition of two Tl monolayers). (C) Potential modulation between — 0.25 V and 0.40 V (double-layer region). (From Fleischmann, M., and Mao, B. W., J. Electroanal. Chem. 247, 297 (1988), with permission.)...

Electron transfer is also common at electrodes. An example of such a process is the laser irradiation at 406.7 nm of methylviologen (20) as a thin film on a roughened silver electrode at liquid nitrogen temperatures which results in its reduction by electron transfer to its radical cation (21). Again, electron transfer from the metal to the dication of 20 is considered to be a reasonable mechanism for the process63. Apparently, the radical... 

In 1977 two groups, Jeanmaire and Van Duyne and Albrecht and Creighton showed that the Raman cross section for pyridine adsorbed onto electrochemically roughened silver electrodes was enhanced 10 times ... 

Fig. 29. 406.7 nm-excited Raman spectra of hemin chloride (15 mAf) in aqueous base (bottom spectrum, a), and of a roughened silver electrode surface in contact with hemin chloride (0.15 mA/) in aqueous base and held at the indicated potentials versus SCE (b-e). Experimental conditions laser power, 30 mW, spectral slitwidth 5cm" , accumulation time 1 s, scan rate 1 cm /s (Sanchez and Spiro, Ref. 

Fig. 30. Cyclic voltammogram for a roughened silver electrode in aqueous (pH 10.5) hemin chloride (0.5 mA/) containing 0.1 M K.C1 as supporting electrolyte. Scan rate 100 mV/s (Sanchez and Spiro, Ref.

Instrumentation. Instmmentation in the reported investigations is similar to that employed in SERS [497]. A powerful laser system is employed. In a study of pyrazine and pyridine adsorbed on a roughened silver electrode, it was observed, that spectra measured with adsorbed centrosymmetric pyrazine showed additional bands that were not observed with SERS [497]. With the non-centrosymmetric pyridine, the SEHR spectra were very similar to the respective SER spectra no new bands were found. Surface enhanced hyper-Raman spectra were found to be more sensitive (than SERS) towards interaction between the adsorbate and the surface. This is illustrated in vibrational spectra of bis(4-pyridine)acetylene (BPA) adsorbed on a silver electrode [497]. 

In a study of phenazine adsorbed on a silver electrode that employed both SERS and SEHRS, the electroreduction product of phenazine and the reduction intermediates could be identified [499]. In a comparative study with SERRS and resonantly enhanced hyper-Raman spectroscopy SERHRS, several dyes adsorbed on a roughened silver electrode were investigated [500]. According to the results, the efficiency... 

Over the past decades, smface enhanced Raman scattering (SERS) has became a valuable spectroscopic technique as a powerful smface diagnostic tool. In 1974 Fleischmann, Hendra, and McQuillan performed the first measurement of a surface Raman spectrum from pyridine adsorbed on an electrochemically roughened silver electrode. It has been explained that some vibrational bands of pyridine are selectively enhanced a million times. This increases the sensitivity of... 

Fig. 1 The first SER spectra obtained from an electrochemically roughened silver electrode in 0.05 mol 1 pyridine and 0.1 mol 1 KCl, compared with normal Raman spectra of a liquid pyridine and b 0.05 mol 1 aqueous pyridine. The applied potentials are c 0.0 V d —0.2 V e —0.4 V f —0.6 V g —0.8 V h —1.0 V. (Reproduced with permission from Ref. [3]. Copyright 1974, Elsevier Esquoida, S.A.)...

It has been known for some time that the Raman scattering intensity of molecules is greatly enhanced when they are adsorbed onto the roughened surfaces of certain metals. For example, the Raman intensity of molecules adsorbed on elec-trochemically roughened silver electrodes [212] is enhanced by factors of up to 10. The magnitude of this enhancement is related to the roughness of the surface, that is to say, the state of division of the adsorbing surface. 

Fig. 10.21 - Spectra for pyridine adsorbed on a roughened silver electrode at the potentials shown. Spectra were acquired for 3 s as the potential was slowly scanned.

Fleischmann, M., Graves, PR., HiU, I.R. and Robinson, J. (1983) Simultaneous Raman spectroscopy and dUferential double layer capacitance measurement of pyridine adsorbed on roughened silver electrodes. Chemical Physics Letters, 98, 503. 

Fleischmann, M., Robinson, J. and Waser, R. (1981) An electrochemical study of the adsorption of pyridine and chloride ions on smooth and roughened silver electrodes. Journal of Electroanalytical Chemistry, 117, 257. 

The first in-situ X-ray diffraction (XRD) investigations of phase transitions of adsorbed monolayers and multilayers [6] and reconstmction of a metal surface [7,8] were also reported by Fleischmann and Mao. The phase transitions were reported for the underpotential deposition (upd) and overpotential deposition (opd) of thallium onto a roughened silver electrode surfaces (similar to those used in surface-enhanced Raman spectroscopy (SERS) using the reflection mode of collection), and for upd of lead onto gold and silver... 

Bazzaoui et al. [956] reported in situ Raman spectra of films prepared by electropolymerization of bithiophene from a solution of CH2CI2 on a platinum electrode and on a roughened silver electrode. In the case of the latter electrode, surface enhancement was assumed (an overall increase by a factor of 10 was stated). Unfortunately the spectra displayed in the report do not support this claim convincingly. With the platinum electrode, the difference between the spectra of the reduced and the oxidized forms is limited to different overall intensities (as already stated). This... 

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