Resonance Raman spectroscopy is an ideal tool for studying nanowires such as those produced by filling single walled carbon nanotubes. It allows us to investigate not only the low energy vibrational and other excitations of the nanowires it also allows us to determine optical transition energies. This is because the magnitude of peaks within a Raman spectra are greatly enhanced when either the energy of the light which will be Raman scattered or the Raman scattered light coincides with the energy of an optical transition. This effect means that in a sample with more than one type of nanowire present it is possible to associated electronic energies with specific nanowire types assuming, as is commonly the case, that the different types have different vibrational modes. Resonance Raman spectroscopy involves measuring Raman spectra with a range of laser energies and requires a tuneable Raman spectrometer.
Shown below are examples of Raman spectra for HgTe filled single walled carbon nanotubes in and out of resonance. The non-resonant peak is the Radial Breathing mode of one of the single walled carbon nanotubes present in the sample.