SEHRS surface-enhanced hyper-Raman

SEHRS Surface enhanced hyper-Raman spectroscopy scattering... 

Since the HRS scattering cross section is so small, enhancement of the signal intensity is indispensable for a practical use of the HRS technique in the field of molecular science. As already mentioned, one of the methods for signal enhancement is to use plasmonic resonances of metal nanostructures [20, 21, 25]. This enhancement technique is called surface-enhanced hyper-Raman scattering (SEHRS) because it is similar to that of surface-enhanced Raman scattering (SERS). In SERS or SEHRS, both excitation absorption and scattered emission benefit from plasmonic field enhancement. Therefore, the plasmonic enhancement factor M is described as... 

Hulteen, J.C., Young, M.A., and Van Duyne, R.P. (2006) Surface-enhanced hyper-Raman scattering (SEHRS) on Ag film over nanosphere (EON) electrodes surface symmetry of centrosymmetric adsorbates. Langmuir, 22, 10354-10364. 

Surface Enhanced Hyper-Raman Spectroscopy (SEHRS)... 

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]. 

Surface Enhanced Hyper-Raman Spectroscopy (SEHRS) Hyper-Raman scattering is a nonlinear three-photon energy conversion process, that offers complementary informahon to Raman spectroscopy and has some advantages... 

Vibrational hyper-Raman scattering [40-43]. Another nonlinear phenomenon observed for metal/molecule system is the surface-enhanced hyper-Raman scattering (SEHRS), consisting in the emission from a sample irradiated with iight at a frequency radiation with frequency 2 > com, where com is a frequency t3q)ical of the molecule (such as a vibrational frequency). For h3q)er-Raman signals enhancement factors of 10 have been measured [41]. 

The discovery and understanding of SERS was important not only because it made Raman a more viable analytical method but also because it introduced the concept of surface-enhanced spectroscopies in general. With the SERS precedent, surface-enhanced resonance Raman spectroscopy (SERRS) and surface-enhanced hyper-Raman spectroscopy (SEHRS) have both been discovered and put to use as analytical tools. In fact, enhancement factors as large as 10 have been measured in SEHRS experiments (see Section VII.B). This immense enhancement was only recently surpassed by the 10 " enhancement measured in single molecule SERS (see Section X). 

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