title: Fundamental differences between micro- and nano-Raman spectroscopy.
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.
authors: Physics Department, North Carolina State University, Raleigh, NC 27695-8202, USA.
authors: E J
authors: EJ
authors: Ayars
authors: C L
authors: CL
authors: Jahncke
authors: M A
authors: MA
authors: Paesler
authors: H D
authors: HD
authors: Hallen