Enhanced Infrared Absorption of SERS-Active Lines of Ethylene on Cu

Abstract

Vibrational modes of adsorbates on rough metal films can show surface enhanced Raman scattering (SERS) as well as surface enhanced infrared (IR) absorption (SEIRA). Both effects are a consequence of field enhancement and of a so-called chemical effect. Our experiments show that chemical contributions to SERS and to SEIRA from ethylene on Cu may have the same origin. We investigated ethylene adsorbed on ultrathin Cu films at about 100 K and below with IR transmission spectroscopy. At exposures up to 2 L the IR spectra show lines only at the positions of the very intense SERS E-bands. At higher exposures lines at the frequencies of the infrared active vibrations of ethylene molecules develop. All lines are stronger than one expects from molecular IR activities. Co-adsorption experiments performed with ethylene and CO show that E-lines in SEIRA do not occur after pre-coverage of Cu with CO.

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

“…For copper, since the frequency dependence of P bulk is weak, we can take d c as the critical thickness for percolation. 21,40,41 For all films of this ACBT study, the final thickness d is more than 30% above d c . For estimating the corresponding volume filling F…”

“…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.…”

Post-annealing temperature dependence of infrared absorption enhancement of polymer on evaporated silver films

“…Although transmittance decreases with the increase in wavenumber in 6 and 7 nm films, transmittance decreases by the low wavenumber side conversely for 8 to 10 nm films. The wavenumber dependence of transmittance changes with film thickness based on the influence of surface scattering and anomalous absorption by the metal film: it is considered to originate in film percolation [15,16]. Transmittance decreases concomitant with the decrease in wavenumber if the metal's dielectric constant is considered.…”

“…On the other hand, at 6 and 10 nm, in contrast to the case of 4 nm, transmittance decreases according to the decreased wavenumber. As mentioned above, the relation between wavenumber and transmittance has been clarified in precedent studies [15,16]. The abovementioned evidence clarifies that the thin film in this research before annealing has a discrete island for 4 nm film; it is a nearcontinuous film for 6 and 10 nm films.…”

SERS and infrared reflection‐absorption spectroscopy of NO on cold‐deposited Cu

“…2 Surface enhanced infrared absorption (SEIRA) spectroscopy of adsorbates on metal-island films (usually measured in transmission, but in principle also measurable as a contribution to the infrared reflectionabsorption spectroscopy (IRRAS) signal) 3 has both local field enhancement 4 and electronic contributions, as demonstrated, for instance, in Ref. 5, but a consistent model covering both the enhancement effects is still missing, especially in view of the recent work on single-crystalline Au electrodes. 6 -8 Whereas the bulk of the experimental SERS and SEIRA investigations is performed at electrode surfaces or with samples in air, we have specialized in the studies of samples in ultra-high vacuum (UHV) because this has many advantages for mechanistic research: The coverage can easily be controlled by the interplay of exposure and temperature; for instance, different species in the first and in the second layer can be chosen arbitrarily.…”