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Keywords:

  • Raman microscopy;
  • gallium nitride;
  • semiconductor nanowires;
  • tip-enhanced Raman scattering

Abstract

Raman imaging of a single [110] GaN nanowire using a combination of an atomic force microscope (AFM) and an inverted confocal microscope was investigated. The Raman spectra and associated maps of this single object, the diameter of which was of 200 nm, were collected in both confocal mode and with the interaction of an AFM tip to benefit from local tip enhancement effect. Beyond the pure tip-enhanced Raman scattering (TERS) effect, the setup was developed to integrate a commercial AFM and spectrometer to permit simultaneous topography and vibrational imaging with spatial and spectral resolutions determined by the respective instruments. Data exchange and communication of the Raman spectrometer and the AFM were optimized to display both height and Raman intensity for a set of Z positions at the AFM tip for each (x,y) position on the sample. The experiments were conducted with both a straight tip coated with gold at an excitation of λ = 647 nm and with a tilted tip coated with silver at an excitation wavelength of λ = 514 nm. The TERS signal was observed for a given phonon mode of the [110] nanowire, providing an optical resolution that corresponds to the size of the object. Copyright © 2009 John Wiley & Sons, Ltd.