The Optics Laboratory
Group of Hans Hallen, Physics Department, North Carolina State University

Nano-Raman Spectroscopy

Raman spectroscopy enables the study of vibrations in molecules and solids through the interaction of light with the vibrations. Some of the energy of a photon sets off a quantum of vibration, a phonon, in the material. Due to energy conservation, the photon leaves with less energy than it came with -- its color is shifted towards the red, or longer, wavelengths. We measure this (slight) change in color to find the energy of the vibration. Some vibration modes of a material do not interact with light in this manner, or do so only under special conditions. This information about the vibration also brings deeper understanding. A complementary technique in which the photon is completely absorbed (looses all its energy) interacts with the vibrations in a different manner. It is called infrared (IR) spectroscopy.

Raman spectroscopy was first invented about 90 years ago, in 1928, by Chandrasekhara Venkata Raman. The advent of the laser popularized the method, and use grew. About 45 years ago, Edgar Etz and his colleagues invented micro-Raman spectroscopy, which allowed study of small sample regions. One of the concerns at the time (private communication with Dr. Etz) was that micro-Raman spectroscopy might not be the same as traditional Raman spectroscopy, since it was performed through a microscope and on such a small (micron-sized) volume of material. They concluded and it is now universally agreed that micro-Raman and traditional Raman spectroscopies are the same. In the early 1990's, we were the first to push Raman spectroscopy one step further in resolution, to nano-Raman spectroscopy and nano-Raman imaging (also called near-field Raman) [15]. We faced a similar question: is nano-Raman the same as the other Raman spectroscopies? The answer this time is "No!" There are important differences in the way the light interacts with the vibrations, such as which vibration modes can be excited with the Raman technique. Some of the differences are easily understood, and are described here. Others required looking at Raman in a fundamentally different manner, which we call Gradient Field Raman (GFR) and describe on another web page. [7] [4] [5] [10]

 Introduction to Raman and IR spectroscopy

 Nano-Raman Imaging [14] [12]

 Comparison of near-field (nano) and far-field (micro and traditional) Raman [2] [6] [8] [11]

 Surface Enhancement and a Truly Near-Field Plasmon Effect [1] [3] [9] [13]

  • [1] H. D. Hallen, "Nano-Raman Spectroscopy: Surface Plasmon Emission, Field Gradients, and Fundamentally Near Field Propagation Effects," NanoBiotechnology 3, 197-202, 2007 [online], -- An invited paper. [local preprint]
  • [2] H.D. Hallen, E.J. Ayars and C.L. Jahncke, "The effects of probe boundary conditions and propagation on nano-Raman spectroscopy," J. Microsc. 210, 252 - 4, 2003 [online]. [local preprint]
  • [3] H.D. Hallen and C.L. Jahncke, "The electric field at the apex of a near-field probe: implications for nano-Raman spectroscopy," J. Raman Spectrosc. 34, 655 - 62, 2003 [online], -- An invited paper. [local preprint]
  • [4] C. L. Jahncke, E. J. Ayars and H. D. Hallen, "Raman selection rules in the presence of an electric field gradient," Microscopy and Microanalysis 8, 1518-1519, 2002 [online]. [local preprint]
  • [5]C.L. Jahncke , E.J. Ayars and H.D. Hallen, "Gradient-Field Raman: Selection Rules in the Near Field," in Proc. of the 7th International Conference on Near-field Optics, NFO-7, Rochester, NY, pp. 142, August, 2002. [local preprint]
  • [6] E.J. Ayars, C.L. Jahncke, M.A. Paesler and H.D. Hallen, "Fundamental differences between micro- and nano-Raman spectroscopy," J. Microscroscopy 202, 142 - 7, 2001 [online]. [local preprint]
  • [7] E.J. Ayars, H.D. Hallen and C.L. Jahncke, "Electric field gradient effects in Raman spectroscopy," Phys. Rev. Lett. 85, 4180 - 3, 2000 [online]. [local preprint]
  • [8]E.J. Ayars , C.L. Jahncke , M.A. Paesler and H.D. Hallen, "Fundamental differences between micro- and nano-Raman spectroscopy," in The 6th International Conference on Near Field Optics and Related Techniques, University of Twente, The Netherlands, August, 2000. [local preprint]
  • [9] E.J. Ayars and H.D. Hallen, "Surface enhancement in near-field Raman spectroscopy," Appl. Phys. Lett. 76, 3911 - 13, 2000 [online]. [local preprint]
  • [10]E. J. Ayars , M. A. Paesler and H. D. Hallen, "Near-field Raman spectroscopy: electric field gradient effects," in Proceedings of IUMAS 2000, The 2000 Meeting of the International Union of Microbeam Analysis Societies, Kailua-Kona, Hawaii 165:1, pp. 115, July, 2000 [online], -- An invited paper. [local preprint]
  • [11] H.D. Hallen, M.A. Paesler and C.L. Jahncke, "Raman spectroscopy: Probing the border between near-field and far-field spectroscopy," in Proceedings of SPIE - The International Society for Optical Engineering, San Diego, CA, United states 3467, pp. 199 - 201, 1998 [online], -- An invited paper. [local preprint]
  • [12] C.L. Jahncke, H.D. Hallen and M.A. Paesler, "Nano-Raman spectroscopy and imaging with a near-field scanning optical microscope," J. Raman Spectrosc. 27, 579 - 86, 1996 [online], -- An invited paper. [local preprint]
  • [13] C.L. Jahncke and H.D. Hallen, "Near-field Raman spectra: Surface enhancement, z-polarization, fiber Raman background and Rayleigh scattering," in Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, Boston, MA, USA 1, pp. 176 - 177, 1996 [online]. [local preprint]
  • [14] C.L. Jahncke, M.A. Paesler and H.D. Hallen, "Raman imaging with near-field scanning optical microscopy," Appl. Phys. Lett. 67, 2483 - 5, 1995 [online]. [local preprint]
  • [15] H.D. Hallen, A.H. La Rosa and C.L. Jahncke, "Near-field scanning optical microscopy and spectroscopy for semiconductor characterization," Physica Status Solidi (A) Applied Research 152, 257 - 268, 1995 [online]. [local preprint]
  •  More info is in the papers.

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