Fundamental differences between micro- and nano-Raman spectroscopy |
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Authors: | E. J. Ayars,C. L. Jahncke&dagger ,M. A. Paesler,& H. D. Hallen |
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Affiliation: | Physics Department, North Carolina State University, Raleigh, NC 27695-8202, U.S.A.;Physics Department, St. Lawrence University, Canton, NY 13617, U.S.A. |
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Abstract: | 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. |
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Keywords: | Infra-red spectroscopy near-field optical microscopy Raman spectroscopy |
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