Imaging of single GaN nanowires by tip‐enhanced Raman spectroscopy

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.

Tip-enhanced Raman spectroscopy: principles and applications

“…Marquestaut et al studied isolated GaN nanowires, and reported that the near-field enhancement factor depends on the symmetry of the specific vibrational mode [103]. Böhmler et al were able to image single CdSe nanowires using tip-enhanced Raman and PL spectroscopy, thus differentiating the PL energy emission of nanowires with different diameters [104].…”

Double strain state in a single GaN/AlN nanowire: Probing the core-shell effect by ultraviolet resonant Raman scattering

“…Moreover, further ideas have been recently proposed for the Raman study of single NWs or Nanotubes. 18,19 It has been shown that strong enhancement of the Raman scattering could occur depending on the NW diameter, excitation wavelength and incident polarization. 18 The increased sensitivity of this technique by Tip-Enhanced Raman Spectroscopy (TERS) has also been reported for single GaN NW.…”

“…18 The increased sensitivity of this technique by Tip-Enhanced Raman Spectroscopy (TERS) has also been reported for single GaN NW. 19 Even if near-field Raman scattering (surface-enhanced and tip-enhanced Raman scattering) are still challenging techniques for semiconducting nanostructures studies, recent advances exploiting plasmonic effects are promising in view of the careful analysis of narrowest single NWs on specific substrates. 20,21 Here, we report on the UV μ-Raman spectroscopy of a single GaN/AlN NW grown by Molecular Beam Epitaxy (MBE).…”

Studying Surface Chemistry beyond the Diffraction Limit: 10 Years of TERS

“…Recently, TER spectra of semiconductor materials, such as SiC surfaces [55] or GaN nanowires, [56] and the TER response of graphene of varying thickness have been studied with nanometer spatial resolution, [55,57] extending the application of TERS toward inorganic substrates with exciting physico-chemical properties.…”