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Fundamental differences between micro‐ and nano‐Raman spectroscopy
Author(s) -
Ayars E. J.,
Jahncke C. L.,
Paesler M. A.,
Hallen H. D.
Publication year - 2001
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.2001.00878.x
Subject(s) - raman spectroscopy , near field scanning optical microscope , spectroscopy , coherent anti stokes raman spectroscopy , polarization (electrochemistry) , electric field , optics , materials science , microscopy , near and far field , optical microscope , raman scattering , analytical chemistry (journal) , optoelectronics , chemistry , scanning electron microscope , physics , quantum mechanics , chromatography
Electric field polarization orientations and gradients close to near‐field scanning optical microscope (NSOM) probes render nano‐Raman fundamentally different from micro‐Raman spectroscopy. With x ‐polarized light incident through an NSOM aperture, transmitted light has x, y and z components allowing nano‐Raman investigators to probe a variety of polarization configurations. In addition, the strong field gradients in the near‐field of a NSOM probe lead to a breakdown of the assumption of micro‐Raman spectroscopy that the field is constant over molecular dimensions. Thus, for nano‐Raman spectroscopy with an NSOM, selection rules allow for the detection of active modes with intensity dependent on the field gradient. These modes can have similar activity as infra‐red absorption modes. The mechanism can also explain the origin and intensity of some Raman modes observed in surface enhanced Raman spectroscopy.