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1Polarization-dependent TERS analysis of a single AlN nanowire with nanoscale spatial resolution
I. Milekhin1,2*, V. Mansurov2, T. Malin2, K. Zhuravlev2, A. Milekhin2, A. Latyshev1,2
1-Novosibirsk State University, Pirogov, 1, 630090 Novosibirsk, Russia 2- A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentieva, 13, 630090, Novosibirsk, Russia
Tip-enhanced Raman scattering (TERS) is a relatively new and rapidly developing method, which combines the advantages of conventional Raman spectroscopy for chemical analysis, a high sensitivity of surface-enhanced Raman spectroscopy, and the nanoscale spatial resolution provided by atomic force microscopy (AFM). The emerging region of the enhanced electromagnetic field between the metalized AFM tip and the sample surface ("hot spot") makes it possible to overcome the diffraction limit and significantly enhance the phonon response. TERS is based on the ability to control the location of the hot spot between the tip and the sample surface, and simultaneously perform TERS mapping.
a)
X=638 nm
■51200 Si SO phonons
ra c CT 'w S 800 01 LLI 1— near-field 1
400 \ias-Seli«
400
600 800 Raman shift/ cm-1
1000
b) d)
Fig. 1. A) AFM image of a single AlN nanowire mechanically transferred onto Au/Si substrate. B) Comparison of TERS spectra of the nanowire recorded in the near- and far-fields. C),d) TERS maps (taken in the spectral range shown by rectangular in (b)) of the AlN nanowire presented in (a). The laser light is polarised along (c) and perpendicular (d) to the TERS probe axis.
In this work, we present the results of a TERS experiment with a single AlN nanowire grown by molecular beam epitaxy and subsequently transferred to a gold surface (Fig. 1a). The TERS method allows one to remarkably enhance its optical response and investigate both bulk-like and surface optical (SO) modes of a single AlN nanowire located in the gap between a gold substrate and the tip of a metalized (Ag) AFM probe (Fig. 1b). The TERS tip provides a high sensitivity to AlN SO phonons and allows to achieve 10 nm spatial resolution under ambient conditions. The laser with an excitation energy of 1.94 (638 nm) was used in the TERS experiment for a single AlN nanowire. TERS mapping (Fig. 1c, d) at different light polarizations makes it possible to determine the spatial localization of surface optical phonons in the nanostructure. Our results open up the possibility for TERS diagnostics of single AlN nanostructures to identify the MBE growth features and visualize edge effects.
Acknowledgements
The work was supported by the Ministry of Science and Higher Education of the Russian Federation, project No. FSUS-2024-0020.The authors are grateful to Shared research center "VTAN" at NSU.
