Formation and Growth of Tarnish on Evaporated Silver Films

Bennett, H. E.; Peck, R. L.; Burge, D. K.; Bennett, Jean M.

doi:10.1063/1.1658187

Cited by 154 publications

(117 citation statements)

References 28 publications

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“…In order to transfer and expose the desired metal surface after evaporation, the sample is glued with the vacuum silver side (fiber optic grade epoxy, EpoTek 377, EpoTek) to another cleaned piece of Si wafer, and the epoxy cured at 150°C for 30 min. To minimize the effect of surface oxidation [65], samples are then stripped to expose the Ag film but only shortly before the measurement.…”

Section: Methodsmentioning

confidence: 99%

Optical dielectric function of silver

et al. 2015

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The dielectric function of silver is a fundamental quantity related to its electronic structure and describes its optical properties. However, results published over the past six decades are in part inconsistent and exhibit significant discrepancies. The measurement is experimentally challenging with the values of dielectric function spanning over five orders of magnitude from the mid-infrared to the visible/ultraviolet spectral range. Using broadband spectroscopic ellipsometry, we determine the complex valued dielectric function of evaporated and template stripped polycrystalline silver films from 0.05 eV (λ = 25 µm) to 4.14 eV (λ = 300 nm) with a statistical uncertainty of less than 1%. From Drude analysis of the 0.1 -3 eV range, values of the plasma frequency ω p = 8.9 ± 0.2 eV, dielectric function at infinite frequency ∞ = 5 ± 2, and relaxation time τ = 1/Γ = 17 ± 3 fs are obtained, with the absolute uncertainties estimated from systematic errors and experimental repeatability. Further analysis based on the extended Drude model reveals an increase in τ with decreasing frequency in agreement with Fermi liquid theory, and extrapolates to τ 22 fs for zero frequency. A deviation from simple Fermi liquid behavior is suggested at energies below 0.1 eV (λ = 12 µm) with the onset of a further increase in τ connecting to the DC value from transport measurements of ∼ 40 fs. The results are consistent with a wide range of optical and plasmonic experiments throughout the infrared and visible/ultraviolet spectral range. The influence of grain boundaries, defect scattering, and surface oxidation is discussed. The results are compared with our previous measurements of the dielectric function of gold [Phys. Rev. B 86, 235147 (2012)].

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Section: Methodsmentioning

confidence: 99%

Optical dielectric function of silver

et al. 2015

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“…Their Raman bands, which appear around 188, 243, and 273 cm -1 for Ag 2 S and 432, 460, 595, 623, 970 (strong), and 1079 cm -1 for Ag 2 SO 4 [2], can coincide with spectral regions of interest such as the radial breathing mode of carbon nanotubes (CNT) [3]. It was also shown that the electric field enhancement decreases with the aging of the silver surface [4]; the thickness of Ag 2 S increases over time as it is not a self-limiting process confined to the surface [5]. Thus, experiments with silver probes are almost exclusively performed on the day of the probe preparation as described in previous works [6].…”

Section: Introductionmentioning

confidence: 96%

Chemical stability of plasmon-active silver tips for tip-enhanced Raman spectroscopy

Kalbacova¹,

Rodriguez²,

Desale³

et al. 2015

Nanospectroscopy

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Silver nanostructures are used in tip- and surface-enhanced Raman spectroscopy due to their high electric field enhancement over almost the entire visible spectral range. However, the low chemical stability of silver, compared to other noble metals, promotes silver sulfide and sulfate formation which decreases its plasmonic activity. This is why silver tips are usually prepared on the same day of the experiments or are disregarded in favour of gold that is chemically more stable. Since silver degradation cannot be avoided, we hypothesized that a protection layer may be able to minimize or control degradation. In this contribution, we report the successful preparation of 4-biphenylthiol and 4’-nitro-4-biphenylthiol self-assembled monolayers on silver tips in order to protect them against tarnishing and to investigate the effect on the life-time of the plasmonic activity. The electrochemically etched wire surface was probed via Raman spectroscopy and scanning electron microscopy. The best long term stability and resistance against corrosion was shown by a monolayer of 4-biphenylthiol formed from dimethylformamide which did not display any degradation of the metallic tip during the observed period. Here, we demonstrate an easy and straightforward approach towards increasing the chemical stability of silver TERS-active probes.

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“…For example, the sterling standard stipulates a 7.5 % copper concentration. Unlike other precious metals such as gold and platinum, silver is known to tarnish with time forming Ag 2 S when exposed to low concentrations (<1 ppb) of H 2 S in ambient environments [1][2][3]. While Ag 2 S is the main component in silver tarnish, sulfate, chloride, oxide, and oxygenated carbon species can also be present [4].…”

Section: Introductionmentioning

confidence: 99%

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers

et al. 2015

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Introduction: Silver, prized throughout history for its luster and shine, develops a black Ag 2 S tarnish layer that is aesthetically displeasing when exposed to atmospheric pollutants. Tarnishing, and subsequent polishing, leads to irreversible material loss and object damage. Currently, nitrocellulose coatings are often used to prevent silver from tarnishing, however non-uniform coatings and degradation over time limit their effectiveness. Atomic layer deposition (ALD) has been explored as a new method for creating dense, uniform, and conformal coatings on 3-dimensional (3D) objects that are more effective than nitrocellulose in preventing silver from tarnishing. Results:To create high quality ALD coatings on 3D objects, slowing down the ALD process is critical to ensure proper precursor exposure. Non-ideal deposition of organo-oxy-metallic compounds can occur with fast deposition rates that do not allow sufficient flow around 3D objects. The coatings can be removed by dissolving the Al 2 O 3 ALD films in aqueous NaOH. Thicker ALD films prevent defects from occurring on non-ideal surfaces and effectively prevent silver objects from tarnishing under ambient aging conditions. Conclusion:Thick ALD films, deposited with sufficiently long precursor pulse and purge times, may be effective in preventing complex, 3D non-mixed media silver cultural heritage objects from tarnishing.

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Formation and Growth of Tarnish on Evaporated Silver Films

Cited by 154 publications

References 28 publications

Optical dielectric function of silver

Optical dielectric function of silver

Chemical stability of plasmon-active silver tips for tip-enhanced Raman spectroscopy

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers

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