PD Research Report for the 2016 year
Name（Research group） Sanpon VANTASIN, (Ozaki Laboratory, Graduate School of Science andTechnology)
Research Theme

Tip-enhanced Raman scattering spectroscopy of nanostructured graphene

Research PeriodApril, 2016 ~ November, 2016

Research Results（about 2,500 characters in Japanese, about 65 lines times 90 characters in English）
The origin of unique features of nanomaterials is in their nanostructures. For example, nanostructures ongraphene sheet can drastically alter the properties of graphene. Therefore, characterization techniques
which can reveal the true nature of nanomaterials must have nanoscale spatial resolution. Raman
spectroscopy is an established characterization method for wide ranges of material because its ability toprovide rich molecular information from vibrational modes. However, spatial resolution of Raman
spectroscopy is limited by diffraction limit of light (around 300 nm). The resolution in Z axis withinpolymer is even worse, as it might be larger than 10µm, due to the diffraction at air-polymer interface.
These limits prevent the individual characterization of nanostructures in nanomaterials. We demonstrated
the use of tip-enhanced Raman spectroscopy (TERS) to overcome these limits. TERS employs near-fieldplasmonic enhancement at the apex of metallic nanotips. Since the enhancement is confined to small
area of less than 100 nm, TERS can archives resolution surpassing diffraction limit. We used TERS tocharacterize nanostructures on epitaxial graphene. The results show that TERS can reveal thecompressive strain relaxation on graphene nanoridges and decreased graphene content on nanocrack,
which cannot be measured using conventional Raman spectroscopy. The strain relaxation is the solid
evidence to the long-suspected mechanism of ridge forming by compressive strain. By analyzing
nanoridges on graphene microisland, we can also rule out the possibility of alternative mechanism ofridge formation by silicon vapor trapping.
The TERS measurement of nanostructures revealed that each kind of nanostructures uniquely affects
graphene properties. Nanostep does not affect strain at all, since it is the inherent structure of SiC
substrate rather than graphene itseft. Nanoridge shows a relaxation in compressive strain compared toneighbor areas. This is shown in Figure 1. Nanocrack shows a missing of graphene content.

Figure 1. (a) AFM topology of graphene nanoridge. (b) 3D image of (a). (c) G’ band in Raman and TERS
spectra from each measurement point in (a). (d) graph of strains calculated from band position in (c)Addition to TERS research, I also conducted 3D surface-enhanced Raman spectroscopy (SERS) research.

This three-dimensional SERS imaging allows the characterization of obscure inhomogeneity of thesample. This work is published in Angewandte Chemie International Edition in May, 2016.

Figure 2. A) A SERS spectrum of PATP from the center of a hexapod silver microstructure. B) Optical
microscope image of the particle. C),D) Top and diagonal views 3D SERS images constructed by PATP a1
mode at 1074 cm-1, using the same particle as B). E) Examples of 2D slices in the Z axis of B). Only one infive slices (corresponding to 1.5 µm distance) are shown. Noted that C), D) and E) use the same color scale.

Publication list (during postdoctoral period):(1) Vantasin, S.; Ji, W.; Tanaka, Y.; Kitahama, Y.; Wang, M.; Wongravee, K.; Gatemala, H.; Ekgasit,S.; Ozaki, Y. 3D SERS Imaging Using Chemically Synthesized Highly Symmetric Nanoporous
Silver Microparticles. Angew. Chem. Int. Ed. 2016, 55 (29), 8391–8395.
Conference list (during postdoctoral period):
1. 26th IUPAC International Symposium on Photochemistry, April 3–8, 2016, Osaka, Japan
2. Nanoimaging and Nanospectroscopy IV, August 28 – September 1, 2016, San Diego, CA, USA
3. The 10th Annual Meeting of Japan Society for Molecular Science, September 13-15, 2016, Kobe,
Japan
4. SCIX 2016, September 18-23, 2016, Minneapolis, MN, USA