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Register a new userThe dipole-quadrupole theory of surface-enhanced Raman scattering
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Authors
A.M. Polubotko
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The review is devoted to explanation of SERS in terms of the dipole and quadrupole light-molecule interactions arising in surface fields strongly varying in space in the region of the strongly irregular surface roughness. The main SERS characteristics, the theory of electromagnetic fields near some model kinds of rough surfaces and some other systems, the theory of SERS Raman tensor for arbitrary and symmetrical molecules, selection rules and analysis of the SER spectra, some anomalies in the SER spectra of symmetrical molecules for some specific conditions, electrodynamic forbiddance of the quadrupole scattering mechanism for the methane molecule and molecules with cubic symmetry groups are considered. The huge enhancement and blinking of the SERS signal arising in the phenomenon of Single Molecule detection by the SERS method are explained. The above theory is compared with some another SERS mechanisms, and the phenomena accompanying SERS are accounted for. It is demonstrated that the theory is in a good agreement with the experiment and explains quite a number of characteristics related to the SERS phenomenon.
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We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.
The Dipole-Quadrupole theory of Surface Enhanced Hyper Raman Scattering (SEHRS), created by the authors is expounded in details. Peculiarities of the behavior of electromagnetic field on rough metal surfaces are considered. It is demonstrated that there is an enhancement of the dipole and quadrupole light-molecule interaction near the places with a large curvature. The expression for the SEHRS cross-section of symmetrical molecules, which consists of several contributions is obtained. Selection rules for the scattering contributions are obtained and a qualitative classification of the contributions after an enhancement degree is performed. Analysis of experimental spectra of pyrazine and phenazine, and also some another molecules is performed too. It is demonstrated a full coincidence of experimental regularities in these spectra with the theory suggested.
Surface Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF) are studied within the framework of modified Spontaneous Emission (SE), and similarities and differences are highlighted. This description sheds new light into several aspects of the SERS electromagnetic enhancement. In addition, combined with the optical reciprocity theorem it also provides a rigorous justification of a generalized version of the widely used SERS enhancement factor proportional to the fourth power of the field ($|E|^4$). We show, in addition, that this approach also applies to the calculation of Surface-Enhanced Fluorescence cross-sections thus presenting both phenomena SERS and SEF within a unified framework.
A method is proposed to pin down an unambiguous proof for single molecule surface enhanced Raman spectroscopy (SERS). The simultaneous use of two analyte molecules enables a clear confirmation of the single (or few) molecule nature of the signals. This method eliminates most of the uncertainties associated with low dye concentrations in previous experiments. It further shows that single-molecule signals are very common in SERS, both in liquids and on dry substrates.
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