Optical near-field Raman microscopy

Of single-walled carbon nanotubes has been done. Scientists from the University of Rochester, Portland State University, and Harvard University combined near-field optics, surface-enhanced Raman scattering (SERS), and scanning probe techniques to achieve 25-nm resolution images using 633-nm laser light. The researchers fashioned a silver wire with an extremely sharp (10–15-nm radius) tip and placed it within about 1 nm of the sample, in this case a nanotube. When they directed the laser light to the tip, SERS took over: A greatly enhanced electric field at the tip excited the nanotube, which, in turn, emitted photons that were collected in the far field and analyzed. By scanning the tip over the sample, images like the one shown here were built up. The image is chemically specific—the only frequencies of light emitted correspond to vibrational excitations of the molecule being studied—and can be combined with spectroscopy. The researchers hope that better resolution will allow them to obtain detailed pictures of proteins in cell membranes. ( A. Hartschuh et al. , Phys. Rev. Lett. 90, 095503, 2003. http://dx.doi.org/10.1103/PhysRevLett.90.095503 )