Effect of Scattering Efficiency in the Tip-Enhanced Raman Spectroscopic Imaging of Nanostructures in the Sub-diffraction Limit

Abstract

The experimental limitations in signal enhancement, and spatial resolution in spectroscopic imaging have been always a challenging task in the application of nearfield spectroscopy for nanostructured materials in the subdiffraction limit. In addition, the scattering efficiency also plays an important role in improving signal enhancement and contrast of the spectroscopic imaging of nanostructures by scattering of light. We report the effect of scattering efficiency in the Raman intensity enhancement, and contrast generation in nearfield tipenhanced Raman spectroscopic (TERS) imaging of one dimensional inorganic crystalline nanostructures of Si and AlN having large variation in polarizability change. The Raman enhancement of pure covalently bonded Si nanowire (NW) is found to be two orders of higher in magnitude for the TERS imaging, as compared to that of AlN nanotip (NT) having a higher degree of ionic bonding, suggesting the importance of scattering efficiency of the materials in TERS imaging. The strong contrast generation due to higher signal enhancement in TERS imaging of Si NW also helped in achieving the better resolved spectroscopic images than that of the AlN NT. The study provides 2 an insight into the role of scattering efficiency in the resolution of near-field spectroscopic images.

Polarized Tip-Enhanced Raman Spectroscopy in Understanding Metal-to-Insulator and Structural Phase Transition in VO2

“…Polarized Raman spectroscopy not only confirms the crystalline phase and crystallographic orientation of the sample but also helps in understanding the lattice dynamics by finding the mode symmetries . The tip-enhanced Raman spectroscopy (TERS) is capable of enhancing the spatial resolution in the subdiffraction limit. , The TERS study mainly utilizes the advantages of optical confinement using plasmonic metal nanostructures, especially Au and Ag. , The major reports based on TERS studies are mainly focused on covalently bonded materials such as bio-organic or carbon molecules with an enhancement factor (EF) of 8 orders. , However, it is being used extensively for characterizing noncarbonaceous materials including partially ionic compounds. − Moreover, as the TERS is accomplished with directional field enhancement, the identification of corresponding phonon mode frequency is also made possible using polarized measurement …”

Advanced Characterization Methods for Electrical and Sensoric Components and Devices at the Micro and Nano Scales

“…A wide range of materials has been studied with TERS: polymers, organic molecules, inorganic nanoclusters, nanowires,, etc. CNTs are one of the materials most well studied with TERS, including the remarkable work of Chen, Hayazawa, and Kawata with STM‐TERS to visualize defects in the individual CNTs and the works of Rodriguez, Zahn, and coworkers on identifying and imaging with AFM‐TERS carbon allotropes, characterizing defects in the CNT transistors channel, etc .…”

Single-Walled Carbon Nanotubes as One-Dimensional Scattering Surfaces for Measuring Point Spread Functions and Performance of Tip-Enhanced Raman Spectroscopy Probes

“…In addition, the sample chemistry influences the scattering efficiency. For example, predominantly, covalent nanoparticles have been shown to have significantly higher scattering cross sections compared to ionic nanoparticles due to an increased polarizability, resulting in a 2 orders of magnitude increase in the enhancement factor . Highly anisotropic molecules such as nanotubes are sensitive to polarization .…”

“…For example, predominantly, covalent nanoparticles have been shown to have significantly higher scattering cross sections compared to ionic nanoparticles due to an increased polarizability, resulting in a 2 orders of magnitude increase in the enhancement factor. 27 Highly anisotropic molecules such as nanotubes are sensitive to polarization. 28 Finally, Raman enhancement has been shown to be dependent on conduction electron properties.…”