Raman Enhancement Mechanism Research Articles

Contributions of Short-Range and Classical Electromagnetic Mechanisms to Surface-Enhanced Raman Scattering from Several Types of Biomolecules Adsorbed on Cold-Deposited Island Films

Surface-enhanced Raman scattering (SERS) spectra of three different classes of adsorbates have been analyzed: (1) native and denatured calf thymus DNA and adenine, as examples of molecules with electronic transitions in the UV region only; (2) flavine adenine dinucleotide (FAD) and doxorubicin (DOX), as examples of chromophores with low extinction transitions in the visible region; and (3) β-carotene, as an example of a chromophore with a very high extinction coefficient for an electronic transition in the visible region. These molecules were adsorbed on silver island films that had an extinction maximum in the 450–660 nm region of the electromagnetic spectrum. The short-range mechanism of Raman enhancement has been demonstrated to contribute primarily to enhanced Raman scattering from molecules in groups 1 and 2, whereas the pure (classical) electromagnetic mechanism dominates the enhancement of β-carotene resonance Raman scattering.

Obtaining Surface‐Enhanced Raman Spectra from the Passive Film on Iron

Surface‐enhanced Raman spectra (SERS) have been obtained from an iron electrode that contains on its surface a discontinuous layer of silver. The mechanism of Raman enhancement of this system has been explored through a systematic study of the time stability and the potential reversibility of SERS spectra as well as the relation between the amount of silver deposited and the intensity of SERS. It is concluded that the local electromagnetic field mechanism is the dominant contributor to enhancement in this system. It is also shown that the anodic polarization characteristics of the iron electrode are unaffected by the presence of the discontinuous silver layer. Comparisons between in situ and ex situ, as well asin situ and semi‐in situ Raman spectra have indicated the importance of characterizing the anodic passive film by in situtechniques. The limitation and possible extensions of the SERS technique in studies of passivity are also discussed.