Anomalous infrared transmission of adsorbates on ultrathin metal films: Fano effect near the percolation threshold

Krauth, Oliver; Fahsold, G.; Magg, Norbert; Pucci, Annemarie

doi:10.1063/1.1309133

Cited by 59 publications

(45 citation statements)

References 22 publications

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“…This asymmetrical band has been described in an earlier report [13]. Probably, in past studies [32,33,34,35], the existence of Fano Resonance was assumed from this asymmetrical band. The absorption intensity of this sample is the maximum in the sample in this study, and it is starting percolation of the silver film (Figs.…”

Section: Experimental Seira Spectra Of Methanolsupporting

confidence: 66%

Surface plasmonic contribution to SEIRA and asymmetrical band

Nakashima¹,

Kita²,

Suzuki³

2014

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The Surface Enhanced InfraRed Absorption (SEIRA) band reaches its the maximum intensity and the band shape becomes asymmetric at the just percolated metal thin films. To explain for them, various models (e.g. the Fano model) have been proposed. However, no model can explain them completely. In this paper, we conducted a classical model calculations (Fresnel's formula and the Bruggemann effective medium theory) for SEIRA and asymmetric bands. The calculated SEIRA spectra were good agreement with the experimentally spectra. Therefore, the asymmetrical SEIRA band might not be attributable to Fano model. Moreover, we specifically addressed the relation between effective dielectric constants of a metal-insulator composite thin film and SEIRA band shape change. Although the sign of the real part switched from positive to negative and although the imaginary part became metallic, the asymmetrical band shape did not change. The sign of the real part is 28 Hiroshi Nakashima et. al.expected to be negative and the imaginary part would be metallic if the asymmetrical band shape change results from surface plasmon. Therefore, the asymmetrical band shape might not be attributable to surface plasmon.

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Section: Experimental Seira Spectra Of Methanolsupporting

confidence: 66%

Surface plasmonic contribution to SEIRA and asymmetrical band

Nakashima¹,

Kita²,

Suzuki³

2014

aap

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“…We know that the intensities of these resonances are strongly increased due to SEIRA on rough metal films. 8,41,49 On Cu films, this enhancement is stronger for CO than for C 2 H 4 . As a result, CO adsorption from the residual gas (prior to C 2 H 4 exposure) leads to SEIRA lines (at ϳ2100 cm −1 ) of similar strength as the SEIRA lines (between 900 cm −1 and 1600 cm −1 ) from roughly monolayer coverage of C 2 H 4 .…”

Section: B Adsorbate Exposurementioning

confidence: 96%

“…The occurrence of SEIRA at normal incidence of light and its strength is a consequence of metal film roughness. 7,41,49 For Cu/ Si no SEIRA is observed.…”

Section: Figmentioning

confidence: 98%

Influence of morphology on adsorbate-induced changes in thin-film dynamic conductivity

et al. 2004

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For ultrathin copper films of various morphology we studied adsorbate-induced changes in broadband infrared transmission at normal incidence of light. Smooth Cu films on Si(111) and mesoscopically rough Cu films on KBr(001) were exposed to CO and to C 2 H 4 . We observed significant broadband changes for each of these gases and for both surfaces. Applying a Drude-type model we calculated the optical spectra in accord with the experiment. We find that the effects related to a change in the electronic relaxation rate are weakly influenced by the mesoscopic roughness of the film, while the effects related to charge transfer are strongly enhanced due to such roughness. This paper shows that the real adsorbate-induced changes can be determined for both the homogeneous films and the inhomogeneous films beyond percolation. The increased surface area owing to mesoscopic roughness is merely one contribution to larger adsorbate-induced effects of inhomogeneous films. The other more interesting contribution is due to depolarization in rough metal films that is responsible for strong enhancement of charge transfer effects.

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“…For iron at 430 K and Cu at 300 K, infrared absorption by CO stretching mode is not observed during deposition, in spite of the effect of surface-enhanced infrared absorption (SEIRA) that is typical for CO on rough metal films. 16,17 Only for the iron film grown at 300 K were SEIRA lines of CO observed (<2000 cm 1 ). Their intensity and position well match our findings for saturation exposures of iron films at room temperature, which will be published in another paper because it seems not to be relevant for the observed growth phenomena.…”

Section: Methodsmentioning

confidence: 96%

Infrared spectroscopic study of the CO‐mediated decrease of the percolation threshold during the growth of ultrathin metal films on MgO(001)

Lust

Priebe

Fahsold

et al. 2002

Surface & Interface Analysis

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Metals are known to grow three-dimensionally on clean ionic crystal surfaces with low surface energies. As a consequence, the naturally grown films consist of islands and are non-conductive up to the percolation threshold, which is at ∼1 nm for iron films grown on MgO(001) at room temperature and is much larger for noble metals and higher temperatures, respectively. In this paper we show that CO exposure at ∼10 −8 mbar during deposition modifies the growth on MgO(001) for iron and copper. The development of infrared transmission spectra versus metal film thickness clearly is changed by CO exposure. The spectral differences correspond to a significant percolation threshold decrease induced by CO. Infrared conductivity parameters calculated from transmittance spectra indicate that the surface relaxation of the free charge carriers is decreased due to CO exposure during growth but the plasma frequency is unchanged.

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Anomalous infrared transmission of adsorbates on ultrathin metal films: Fano effect near the percolation threshold

Cited by 59 publications

References 22 publications

Surface plasmonic contribution to SEIRA and asymmetrical band

Surface plasmonic contribution to SEIRA and asymmetrical band

Influence of morphology on adsorbate-induced changes in thin-film dynamic conductivity

Infrared spectroscopic study of the CO‐mediated decrease of the percolation threshold during the growth of ultrathin metal films on MgO(001)

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