Satoshi Tsukuda

Fullerene nanowires as a versatile platform for organic electronics

The development of organic semiconducting nanowires that act as charge carrier transport pathways in flexible and lightweight nanoelectronics is a major scientific challenge. We report on the fabrication of fullerene nanowires that is universally applicable to its derivatives (pristine C60, methanofullerenes of C61 and C71, and indene C60 bis-adduct), realized by the single particle nanofabrication technique (SPNT). Nanowires with radii of 8–11 nm were formed via a chain polymerization reaction induced by a high-energy ion beam. Fabrication of a poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) bulk heterojunction organic photovoltaic cell including PC61BM nanowires with precisely-controlled length and density demonstrates how application of this methodology can improve the power conversion efficiency of these inverted cells. The proposed technique provides a versatile platform for the fabrication of continuous and uniform n-type fullerene nanowires towards a wide range of organic electronics applications.

Fabrication of enzyme-degradable and size-controlled protein nanowires using single particle nano-fabrication technique

Protein nanowires exhibiting specific biological activities hold promise for interacting with living cells and controlling and predicting biological responses such as apoptosis, endocytosis and cell adhesion. Here we report the result of the interaction of a single high-energy charged particle with protein molecules, giving size-controlled protein nanowires with an ultra-high aspect ratio of over 1,000. Degradation of the human serum albumin nanowires was examined using trypsin. The biotinylated human serum albumin nanowires bound avidin, demonstrating the high affinity of the nanowires. Human serum albumin–avidin hybrid nanowires were also fabricated from a solid state mixture and exhibited good mechanical strength in phosphate-buffered saline. The biotinylated human serum albumin nanowires can be transformed into nanowires exhibiting a biological function such as avidin–biotinyl interactions and peroxidase activity. The present technique is a versatile platform for functionalizing the surface of any protein molecule with an extremely large surface area.

Effect of ion beam energy and polymer weight on the thickness of nanowires produced by ion bombardment of polystyrene thin films

Exposure of polystyrene to MeV-order heavy-ion beams produces nanowires by cross-linking along ion tracks. The chemical core of these ion tracks is visualized, and the dependence of the diameter of the nanowires on the linear energy transfer of the ion beam and molecular weight of the polymer are investigated precisely based on the model of transformation of a nanowire cross section into an ellipse. an equation is derived to predict the radius (5.6–27.6 nm) of the chemical core considering the energy density required for gelation of the polymer, and the validity of the relation is confirmed against experimental results.

Precise Control of Nanowire Formation Based on Polysilane for Photoelectronic Device Application

A High-energy single ion trajectory in a Si-based polymer thin film produces a cross-linked polymer nanowire with the length of 10–1000 nm and the thickness of 4.0–19.4 nm (radius of the cross section). The energy density deposited by incident ions and the molecular weight of the target polymer materials principally determine the thickness of the nanowires at any discrete radius in this range. Surface treatment of a substrate completely controls the adhesion of the nanowires, which makes it possible to pattern the nanowire distribution on the substrate. Nanogap platinum electrodes with 100 nm gap width are fabricated on the nanowire dispersed SiO2 substrate by a lift-off method with electron beam lithography techniques. Current-voltage analysis of the nanowires in the gap clearly indicates intrinsic semiconductive features based on crosslinked polysilanes.

Nano-wire formation and selective adhesion on substrates by single ion track reaction in polysilanes

High density energy deposition by ion beams causes non-homogeneous crosslinking reaction of polysilane derivatives within a nano-sized cylindrical area along an ion trajectory, and gives /spl beta/-SiC based nano-wires of which sizes (length, thickness) and number densities are completely under control by changing the parameters of incident ion beams and molecular sizes of target polymers. Recently the techniques of position-selective single ion hitting have been developed for MeV order ion beams, however it is not sufficient to control precisely the positions of the nano-wires on the substrates. In the present study, we report the selective adhesion of nano-wires on Si substrates by the surface treatments before polymer coating, which enables the patterning of planted nano-wires on substrates and/or electrodes as candidates for nano-sized field emissive cathodes or electro-luminescent devices.

Formation of nanowires based on pi-conjugated polymers by high-energy ion beam irradiation

High-energy ion beam irradiation of cross-linking type polymers gives nanowires formed by cross-linking reactions along the ion track trajectories. A fairly simple technique has been developed to control the size and number density of nanowires based on polystyrene (PS) by selecting appropriate ion beam characteristics and molecular sizes of the target polymers. This technique has also been extended to the formation of nanowires based on polyaniline (PANi) and poly(3-hexylthiophene) (P3HT). Characteristic optical properties (absorption and photoluminescence) observed for the various sizes of nanowires based on P3HT on a quartz substrate are different than those from solid state P3HT, suggesting that the nanowires are not just the finely patterned analogs of the conjugated polymers.

Fabrication of Thermoresponsive Nanoactinia Tentacles by a Single Particle Nanofabrication Technique.

Nanowires that are retractable by external stimulus are the key to fabrication of nanomachines that mimick actinia tentacles in nature. A single particle nanofabrication technique (SPNT) was applied over a large area to the fabrication of retractable nanowires (nanoactinia tentacles) composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinylpyrrolidone) (PVP), which are thermoresponsive and hydrophilic polymers. The nanowires were transformed with increasing temperature from rod-like- to globule-forms with gyration radii of ∼1.5 and ∼0.7 μm, respectively. The transformation of the nanowires was reversible and reproducible under repeated cycles of heating and cooling. The reversible transformation was driven by hydration and dehydration of PNIPAM, the thermoresponsive segments, resulting in coil-to-globule transformation of the segments. The nanoactinia tentacle systems trapped the nanoparticles as a model of living cells under thermal stimulation, and the trapping was controlled by temperature. We present herein a unique nanomachine system which can be applicable to nanoparticle filtering/sensing systems and expandable to large-area functionalization and demonstrate polymer-based nanoactuators via scaling of molecular level coil-to-globule transformation into micron-sizes.

Formation of Au nanoparticle arrays on hydrogel two-dimensional patterns based on poly(vinylpyrrolidone)

In this study, we demonstrated the formation of Au nanoparticle (NP) arrays on two-dimensional gel patterns based on poly(vinylpyrrolidone) (PVP), which were fabricated by electron beam (EB) lithography. Au NPs were preferentially formed on PVP patterns by photoreduction in HAuCl4-containing MeOH solutions without any surface treatment. The number density of the Au NPs was highly controlled by changing the UV irradiation time; therefore, increasing the UV irradiation time produced Au NP arrays with highly packed Au NPs on the PVP patterns. The size of the cross-linking networks of PVP, which depended on the cross-linking density induced by EB irradiation, plays a very important role in the formation of Au NPs in the Au ion-containing solution under UV irradiation. We discussed the difference in the fabricated Au NP arrays at different EB exposure doses in terms of the interaction between the gel networks and the Au NPs formed.

Fabrication of Au nanoparticles on poly(vinylpyrrolidone) nanowires exhibiting reversible frequency change of localized surface plasmon resonance

Au nanoparticles (NPs) are formed on gel nanowires (NWs) based on poly(vinylpyrrolidone) (PVP) via photoreduction in a HAuCl4-containing MeOH solution. The particle size and number density of the Au NPs increase with the photoreduction time. At a photoreduction time of 15 min, the surfaces of the PVP NWs are almost completely covered by Au NPs. The hybrid material exhibited visible optical absorption based on the localized surface plasmon resonance (LSPR) of the Au NPs. The peak LSPR absorption wavelength under dry conditions red-shifted slightly as the particle size and number density increased owing to increased coupling of the plasmonic bands of each particle. In water, the LSPR wavelength is blue-shifted compared with under dry conditions because of an increase in the interparticle distance between the Au NPs owing to the swelling of the PVP gel NWs; this causes a decrease of the plasmonic coupling of the particles. The absorption peak wavelength shifts reversibly when the hybrid NWs is alternately ex...

Colloidal Zn(Te,Se)/ZnS Core/Shell Quantum Dots Exhibiting Narrow-Band and Green Photoluminescence

Colloidal CdSe quantum dot (QD) phosphors have attracted considerable attention as green and red phosphors for blue backlight downconversion in next-generation liquid-crystal displays because of their excellent emission features including tunable emission wavelength and narrow emission bands. Alternatives to CdSe, which do not contain toxic cadmium, are strongly desired to ensure safety and reduce the environmental load of consumer products. Herein, we synthesized colloidal Zn(Te,Se)/ZnS core/shell QDs and demonstrated narrow-band green photoluminescence (PL) emission. A full width at half-maximum of 30 nm was achieved for PL emission at 535 nm from Zn(Te0.77Se0.23)/ZnS core/shell QDs with a core QD diameter of 4.3 nm. This emission characteristic was as good as that of CdSe QDs.