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T. Umakoshi and P. Verma
The thermal evaporation of plasmonic materials relies on the process of random
deposition of plasmonic nanoparticles. Therefore, one of the issues is the low yield
of plasmonically active tips. No near-field light is excited unless a plasmonic particle
sits at the tip apex. Therefore, precisely optimized deposition process is of great
importance. In this regard, highly reproducible fabrication of plasmonic tips by the
thermal evaporation has been reported [49, 50]. One straight forward way to have a
plasmonic particle at the tip apex is to attach a gold nanoparticle directly on a tip apex
using glue (Fig. 7d) [51]. Direct growth of silver nanoparticle on the tip apex through
photochemical reaction was an alternate way that was also reported [52]. Figure 7e
shows a SEM image of a tip where a silver nanoparticle was grown directly at the
tip apex by the photochemical reaction. It is also possible to fabricate a plasmonic
nanostructure at the tip apex by means of nano-lithographic techniques [53, 54].
However, as the fabrication process become rather complicated, the simple thermal
evaporation technique has been still widely accepted in the field. As a part of the
AFM family, shear force microscopy (SFM) has also been used in TERS. In this case,
a tuning fork is utilized instead of the cantilever. An electrochemically etched tip,
which is similar to the one used in STM-based TERS, is attached on the tuning fork,
and the tip is controlled through the shear force between the tip and sample [55].
In recent years, some makers have started to manufacture TERS apparatus. For the
researchers who are not familiar with TERS, this brings in some good opportunities
for them to use TERS for their researches without the need of any expertise in
related instrumentation. We also see that the number of publications in TERS research
utilizing commercial instrumentation is gradually increasing. We believe that TERS
would contribute more and more to various research fields in the near future.
4 Developments and Applications of TERS
4.1 Applications of TERS for Novel Nano-Materials
We described basic instrumentations for TERS in the previous section. At last,
we introduce some important evolution of TERS, especially focusing on the latest
research developments to describe recent situation of TERS.
After the first report of TERS in 2000 [13–15], one of the most common samples
studied was CNTs, which is a robust one-dimensional advanced nano-material, wellsuited to demonstrate the strength of TERS. Some beautiful TERS images of CNTs
have been reported from several groups [43, 49, 54, 56], an example of which is
shown in Fig. 2. It made the research communities realize the strong imaging capabilities of TERS microscopy. Detailed structures as well as local optical responses of
CNTs were visualized at nanoscale. For example, optical response change is clearly
observed in Raman spectrum if some strain exists in CNTs. As Raman scattering
originates from molecular bond vibrations, strains induced in molecular bonds drastically affect Raman scattering, which appears as broadening, position shift, and/or
T. Umakoshi and P. Verma
The thermal evaporation of plasmonic materials relies on the process of random
deposition of plasmonic nanoparticles. Therefore, one of the issues is the low yield
of plasmonically active tips. No near-field light is excited unless a plasmonic particle
sits at the tip apex. Therefore, precisely optimized deposition process is of great
importance. In this regard, highly reproducible fabrication of plasmonic tips by the
thermal evaporation has been reported [49, 50]. One straight forward way to have a
plasmonic particle at the tip apex is to attach a gold nanoparticle directly on a tip apex
using glue (Fig. 7d) [51]. Direct growth of silver nanoparticle on the tip apex through
photochemical reaction was an alternate way that was also reported [52]. Figure 7e
shows a SEM image of a tip where a silver nanoparticle was grown directly at the
tip apex by the photochemical reaction. It is also possible to fabricate a plasmonic
nanostructure at the tip apex by means of nano-lithographic techniques [53, 54].
However, as the fabrication process become rather complicated, the simple thermal
evaporation technique has been still widely accepted in the field. As a part of the
AFM family, shear force microscopy (SFM) has also been used in TERS. In this case,
a tuning fork is utilized instead of the cantilever. An electrochemically etched tip,
which is similar to the one used in STM-based TERS, is attached on the tuning fork,
and the tip is controlled through the shear force between the tip and sample [55].
In recent years, some makers have started to manufacture TERS apparatus. For the
researchers who are not familiar with TERS, this brings in some good opportunities
for them to use TERS for their researches without the need of any expertise in
related instrumentation. We also see that the number of publications in TERS research
utilizing commercial instrumentation is gradually increasing. We believe that TERS
would contribute more and more to various research fields in the near future.
4 Developments and Applications of TERS
4.1 Applications of TERS for Novel Nano-Materials
We described basic instrumentations for TERS in the previous section. At last,
we introduce some important evolution of TERS, especially focusing on the latest
research developments to describe recent situation of TERS.
After the first report of TERS in 2000 [13–15], one of the most common samples
studied was CNTs, which is a robust one-dimensional advanced nano-material, wellsuited to demonstrate the strength of TERS. Some beautiful TERS images of CNTs
have been reported from several groups [43, 49, 54, 56], an example of which is
shown in Fig. 2. It made the research communities realize the strong imaging capabilities of TERS microscopy. Detailed structures as well as local optical responses of
CNTs were visualized at nanoscale. For example, optical response change is clearly
observed in Raman spectrum if some strain exists in CNTs. As Raman scattering
originates from molecular bond vibrations, strains induced in molecular bonds drastically affect Raman scattering, which appears as broadening, position shift, and/or