This review shows updated experimental cases of tip-enhanced Raman scattering (TERS) operated in
solution/liquid systems. TERS in solution/liquid is still infancy, but very essential and challenging
because crucial and complicated biological processes such as photosynthesis, biological electron
transfer, and cellular respiration take place and undergo in water, electrolytes, or buffers. The
measurements of dry samples do not reflect real activities in those kinds of systems. To deeply
understand them, TERS in solution/liquid is needed to be developed. The first TERS experiment in
solution/liquid is successfully performed in 2009. After that time, TERS in solution/liquid has gradually
been developed. It shows a potential to study structural changes of biomembranes, opening the world of
dynamic living cells. TERS is combined with electrochemical techniques, establishing electrochemical
TERS (EC-TERS) in 2015. EC-TERS creates an interesting path to fulfil the knowledge about
electrochemical-related reactions or processes. TERS tip can be functionalized with sensitive molecules
to act as a “surface-enhanced Raman scattering (SERS) at tip” for investigating distinct properties of
systems in solution/liquid e.g., pH and electron transfer mechanism. TERS setup is continuously under
developing. Versatile geometry of the setup and a guideline of a systematic implementation for a setup
of TERS in solution/liquid are proposed. New style of setup is also reported for TERS imaging in
solution/liquid. From all of these, TERS in solution/liquid will expand a nano-scaled exploration into
solution/liquid systems of various fields e.g., energy storages, catalysts, electronic devices, medicines,
alternative energy sources, and build a next step of nanoscience and nanotechnology.
Tip-enhanced Raman scattering (TERS) can be observed highly sensitive spectral image with high spatial resolution.
However, it shows low reproducibility due to difference and change in optical properties of the metallic tips. For surfaceenhanced
Raman scattering (SERS), the spectra can be reproduced by the scattering spectra due to localized surface
plasmon resonance (LSPR) of the individual metallic nanostructures, which observed with a dark field illumination, and
the calculated electromagnetic field around the nanostructures. In the present study, we tried to relate TERS spectra with
the LSPR spectra and the calculation, in a similar way of SERS. By conventional dark field illumination, LSPR
scattering spectra at the apex of the tip were measured and were compared with the corresponding TERS spectra. By
excitation using polarization parallel to the tip, the polarized LSPR peak was stronger than that by perpendicular
polarization. Also in the case of TERS, the similar trend was observed. It was confirmed whether the vertical
polarization to the sample plane (Z-polarization) is effective or not by the polarized LSPR and TERS spectra. By
excitation at different wavelengths, moreover, TERS enhancement factors were compared. In the calculation for TERS,
the nanostructure like a monopole antenna was adopted, because the EM field is enhanced not at both sides, but at only
apex. The dependence on taper and curvature of the tip were compared with the calculated results for the nanostructure
like a conventional dipole antenna.
Despite often illustrated as a perfect two-dimensional sheet, real graphene sample is not always flat. Nanostructures can be occurred on graphene sheet, especially for epitaxial graphene. The nanostructures alter the electrical and mechanical properties of graphene. This is crucial for epitaxial graphene since its main potential is in the electronics and optics application. This study investigates nanostructures on epitaxial graphene by tip-enhanced Raman spectroscopy, which is a technique that can provide Raman spectra with great spatial resolution, exceeding the diffraction limit of light. The results suggest that the compressive strain on nanoridges is weaker compared to neighbor flat area, supporting the ‘ridge as compressive strain relaxation’ mechanism. TERS measurement of nanoridges on epitaxial graphene microisland also indicates that the ‘Si vapor trapping’ mechanism for ridge formation is unlikely to occur.
This study presents the synthesis, SERS properties in three dimensions, and an application of 3D symmetric nanoporous silver microparticles. The particles are synthesized by purely chemical process: controlled precipitation of AgCl to acquire highly symmetric AgCl microparticle, followed by in-place to convert AgCl into nanoporous silver. The particles display highly predictable SERS enhancement pattern in three dimensions, which resembles particle shape and retains symmetry. The highly regular enhancement pattern allows an application in the study of inhomogeneity in two-layer polymer system, by improving spatial resolution in Z axis.