Research 2014

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Top) Scanning electron microscopic (SEM) image of a microbull sculpture produced by raster scanning (left) and surface profile scanning (right). For the latter, only the crust was defined by the two-photon process, the inside was solidified by illumination under a mercury lamp. In this particular structure, the two-photon scanning time was reduced by 90% due to the use of surface profile scanning and subsequent solidification under a mercury lamp. Nanofabrication took 13 min. (Bottom) schematics of (a) raster, and (b) surface profile scanning.

Scanning electron microscope images of (a) selfstanding empty cubic structures (height∼4.6 μm) connected in pairs and (b) a silver-coated polymer structure composed of a cube (2 μm in size) holding up a spring (inner diameter 700 nm). The structures are made by a two-photon-induced photopolymerization technique combined with electroless plating.

Recent progress in the field of single- and two-photon nanofabrication, both 2- and 3-dimensional, in photopolymerizable resins and in films of photoisomerizable azopolymers are reviewed. The basic processes as well as technological advances and applications of nanofabrication by light are discussed. Recent advances and achievements in polymer photomechanics and light-activated molecular movement in azopolymers are also reviewed.

Laser nanofabrication in photoresists and azopolymers

Zouheir Sekkat and Satoshi Kawata

Laser Photonics Rev. 8, No. 1, 1–26 (2014) / DOI 10.1002/lpor.201200081

Related news at RISOU, Osaka University

AFM images of the surface deformation induced by Ez in the (a) 24 nm and (b) 40 nm thick films with 460 nm light irradiation.
For super-resolution microscopy, the authors developed a new strategy to realize a probe with a nonlinear fluorescence response, a stepwise two-photon absorption scheme, by using photoinduced charge separation; the first photon for the generation of the charge-separated state and the second photon for fluorescence excitation. Transient absorption spectra studies and simulation indicate that fluorescence is emitted through the photophysical pathways they proposed. Fluorescence imaging of biological cells showed marked improvements in image contrast and resolution, demonstrating the usefulness of the fluorescent probe in laser scanning confocal microscopy.

Nanomovement of Azo Polymers Induced by Longitudinal Fields

Hidekazu Ishitobi, Issei Nakamura, Taka-aki Kobayashi, Norihiko Hayazawa, Zouheir Sekkat, Satoshi Kawata, and Yasushi Inouye

ACS Photonics 2014, 1, 190−197

Fluorescence microscopy images recorded with a setup illustrated above at the interface of Pt electrode and solution containing ZnS-AgInS2 solid solution (ZAIS) NPs and quenchers: brightness variation when TMPDA is oxidized at +0.7 V (a), and when MP+ is reduced at -0.5 V (b).
A new method to visualize electrochemical reactions by fluorescence is demonstrated by using the photoluminescence quenching of semiconductor nanoparticles which changes according to the redox states of quenchers. The photoluminescence intensity of ZnS-AgInS2 solid solution semiconductor nanoparticles can be controlled by the electrochemical manipulation of quencher molecules. By using a fluorescence optical microscopy, the formation of Nernst diffusion layer is successfully observed as a photoluminescence intensity gradient.

Visualization of Electrochemical Reactions by Redox-dependent Quenching of Photoluminescence from ZnS-AgInS2 Solid Solution Semiconductor Nanoparticles


Electrochemistry, 82(5), 338–340 (2014)

Interaction analysis between SFNPs and proteins. Each SFNPs was mixed with protein. The fluorescent spectrum of
supernatant monitored by excitation wavelength at 400 nm. (a) αGlc-SFNP, (b) αGlcNAc-SFNP, (c) βGal-SFNP, (d) ZAIS/ZnS stabilized with TGA.

Confocal laser scanning microscopic imaging of HepG2 cells. Overlay images (top panel, A−G) and fluorescence images (lower panel H−N). HepG2 cells were incubated without SFNPs (A and H) and with αGlc-SFNPs (B and I), αGlcNAc-SFNPs (C and J), βGal-SFNPs (D and K), SAα2−3Gal-SFNPs (F and M), or SAα2−6Gal-SFNPs (G and N).
Sugar chains play a significant role in various biological processes through sugar chain–protein and sugar chain–sugar chain interactions. To date, various tools for analyzing sugar chains biofunctions have been developed. Fluorescent nanoparticles (FNPs) functionalized with carbohydrate, such as quantum dots (QDs), are an attractive imaging tool for analyzing carbohydrate biofunctions in vitro and in vivo. Most FNPs, however, consist of highly toxic elements such as cadmium, tellurium, selenium, and so on, causing problems in long-term bioimaging because of their cytotoxicity. In this study, we developed cadmium-free sugar-chain-immobilized fluorescent nanoparticles (SFNPs) using ZnS-AgInS2 (ZAIS) solid solution nanoparticles (NPs) of low or negligible toxicity as core components, and investigated their bioavailability and cytotoxicity. SFNPs were prepared by mixing our originally developed sugar-chain-ligand conjugates with ZAIS/ZnS core/shell NPs. In binding experiments with lectin, the obtained ZAIS/ZnS SFNPs interacted with an appropriate lectin to give specific aggregates, and their binding interaction was visually and/or spectroscopically detected. In addition, these SFNPs were 
successfully utilized for cytometry analysis and cellular imaging in which the cell was found to possess different sugar-binding properties. The results of the cytotoxicity assay indicated that SFNPs containing ZAIS/ZnS have much lower toxicity than those containing cadmium. These data strongly suggest that our designed SFNPs can be widely utilized in various biosensing applications involved in carbohydrates.

Cadmium-Free Sugar-Chain-Immobilized Fluorescent Nanoparticles Containing Low-Toxicity ZnS-AgInS2 Cores for Probing Lectin and Cells

Hiroyuki Shinchi, Masahiro Wakao, Nonoka Nagata, Masaya Sakamoto,  Eiko Mochizuki, Taro Uematsu, Susumu Kuwabata, and Yasuo Suda

Bioconjugate Chem. 2014, 25, 286−295

We have developed a technique based on two-photon polymerization 
lithography to fabricate arbitrary 3D structures in which aligned SWCNTs are embedded. SWCNTs are aligned along nanowires or laser scanning directions while they are embedded in the structure, as evidenced by polarized Raman microspectroscopy. The alignment is induced by spatial confi nement, volume shrinkage, and optical gradient force. The obtained composites, which exhibit the nematic order parameters up to 0.4, should lead to an enhancement of mechanical, electrical, thermal, and optical properties, as anisotropic properties resemble those of individual SWCNTs, thereby opening up possibilities of making devices and systems consisting of macroscopic ensembles of aligned SWCNT. Our method can also attain vertical alignment of SWCNTs if the laser is scanned along vertical direction. Further, the alignment along vertical direction would be also enhanced with tailoring polarization of the laser beam parallel to z -direction that is created by focusing radially polarized laser beam. Our method, thus, enables alignment control in any desired directions in arbitrary 3D nanostructures, which should lead to new applications such as actuators and metamaterials. 

Direct Laser Writing of 3D Architectures of Aligned Carbon

Shota Ushiba, Satoru Shoji, Kyoko Masui, Junichiro Kono, and 
Satoshi Kawata

Adv. Mater. 2014, 26, 5653–5657

Schematic of the electro-optic effect in the miscible polymer/LC nanocomposite.

Demonstration of an optical amplitude modulator. Transient transmission curves of a He-Ne laser obtained from samples 
after polymerization between crossed polarizers being driven by a 10 kHz sine wave.

We report a microsecond electro-optic response in an anisotropic-polymer/liquid-crystal composite, which forms a homogeneously mixed structure in the nanoscale range owing to the high miscibility between them. The nanocomposite was fabricated by photopolymerizing a nematic liquid crystal (NLC) mixture doped with a cross-linkable mesogenic monomer at a concentration of 30 wt%. Our system is inherently different from polymer-dispersed liquid crystals in that the LC molecules are almost miscible in the anisotropic polymer matrix and do not form observable domains. When an electric field is applied to such a nanocomposite, the molecular alignment of the polymer matrix is retained, while the non-polymerizable NLC reorients along the electric field, leading to a shift in the birefringence. Furthermore, the reorientation of the NLC molecules in a space sufficiently smaller than the wavelength of visible light results in scattering-free characteristics over the entire visible wavelength range and a short decay response time of 15 μs. 

Nematic liquid crystal nanocomposite with scattering-free, microsecond electro-optic response

Yo Inoue, Hiroyuki Yoshida, and Masanori Ozaki

Optical Materials Express, Vol. 4, Issue 5, pp. 916-923 (2014)
Some highlights of our research results and activities are introduced. They include Plasmonic Imaging, Nano Plasmonic Devices, Biosensor Devices, Solar Cells, Functional Nanomaterials, Plasmaphotonics and CsLiB6O10 Crystal. Also introduced are activities for photonics industrialization and a platform for innovation: "Photonics Cannery" as well as international/domestic conferences/workshops, Photonics Days and weekly tea gathering. Contributions of Osaka University OSA/SPIE Student Chapter are also essential such as Asia Student Photonics Conferences and the Kid’s Photonics School “Super HIKARI JUKU”, an outreach program of the Photonics Center.

The Photonics Center 
at Osaka University

Satoshi Kawata and Hiroshi Iwasaki

AAPPS BULLETIN february 2014 vol. 24 no. 1 P. 32

Schematic view of MPS-GaN sub. and experimental setup. (a) The multipoint-seed GaN substrate was produced by patterning a GaN template. The solution was stirred using the motion shown in the illustration. (b) Schematic illustration of point seed arrangement.

Dependence of peak top angle of XRC on measurement point. The inverse of the slope of a line represents the radius of lattice curvature. The solid circles, open circles, and solid squares represent the shift in XRC peak top angle of the GaN template, MPS-GaN sub., and coalesced GaN crystal after separation from the sapphire substrate, respectively.
Low-curvature and large-diameter GaN wafers are in high demand for the development of GaN-based electronic devices. Recently, we have proposed the coalescence growth of GaN by the Na-flux method and demonstrated the possibility of enlarging the diameter of high-quality GaN crystals. In the present study, 2 in. GaN wafers with a radius of curvature larger than 100m were successfully produced by the Na-flux coalescence growth technique. FWHMs of the 002 and 102 GaN X-ray rocking curves were below 30.6 arcsec, and the dislocation density was less than the order of 102cm-2 for the entire area of the wafer.

Fabrication of low-curvature 2 in. GaN wafers by Na-flux coalescence growth technique

Mamoru Imade, Masayuki Imanishi, Yuma Todoroki, Hiroki Imabayashi, Daisuke Matsuo, Kosuke Murakami, Hideo Takazawa, Akira Kitamoto, Mihoko Maruyama, Masashi Yoshimura, and Yusuke Mori

Applied Physics Express 7, 035503 (2014)