Masaki Sugimoto

Formation of Nanowires along Ion Trajectories in Si Backbone Polymers

Here we report the formation of nanowires of crosslinked polymers with a cylindrical structure via high-energy ion beam irradiation of thin films of Si backbone polymers. Our results show that the spatial distribution and size of the isolated nanowires can be controlled fairly well by this technique, unlike techniques for producing carbon nanotubes or wires. The radius of the wires varies from a few nanometers to 15 nm, and is precisely controlled by simply changing the parameters of incident ion beam or molecular weight of the target polymer. The thickness of the target film determines the length of each wire, which can also be controlled by the present technique. Nanostructured materials such as carbon nanotubes have been developed in recent years, and are regarded as potential one-dimensional quantum wires. [1‐5] The following methods of synthesizing the tubes have been suggested: arc-discharge, laser-vaporization, ion-beam assisted deposition, and catalytic pyrolysis. However, it is still difficult to control the size, spatial distribution, and structure of the tubes using these techniques. Polysilane derivatives are themselves one-dimensional semiconducting wires that exhibit interesting features. [6‐10] We reported the radiation effects of ion beams on polysilanes and the dependence of reaction processes on linear energy transfer (LET: energy deposition rate of incident particles per unit length) of the characteristic radiation. [11] Polymers appeared to become crosslinked by high LET ion beam irradiation, despite predominant main chain scission reactions observed for low LET radiation. The difference in radiation-induced reactions was ascribed to a variation of density of reactive intermediates. The spatial distribution of deposited energy by charged ions plays a significant role in promoting chemical reactions in the target materials. [12‐16] We suggested that the ion

Fine SiC fiber synthesized from organosilicon polymers: relationship between spinning temperature and melt viscosity of precursor polymers

A very fine silicon carbide (SiC) fiber with diameter of 6 μm, about a half of that of a commercially available SiC fiber, was synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS). The fine SiC fiber was obtained by optimizing the composition and the spinning temperature of PCS-PVS polymer blends. In order to determine these optimum conditions, the relationship between temperature and melt viscosities of the polymer blends was investigated. As a result, it was found that the optimum spinning temperature range was within a temperature range where the melt viscosity is 5–10 Pa · s. Moreover, by blending PVS with PCS, the spinning temperature of the polymer blends was lowered, the spinnability of polymer system was improved, and finer polymer fiber was obtained compared with PCS. The optimum content of PVS in the polymer blend was 15–20 wt%.

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.

Degradation mechanisms of silicone rubber (SiR) by accelerated ageing for cables of nuclear power plant

The degradation behavior of SiR for the cable insulation by accelerated thermal and radiation ageing was studied and the degradation mechanism was proposed. The degradation was observed by the change of tensile properties, the distribution of crosslinking, and the change of weight. The chemical reaction under the both ageing in oxidation conditions was crosslinking and the oxidation mechanism was found to be the same between thermal and radiation ageing. The yield of crosslinking was proportional to the ageing time and also the dose. The effect of irradiation temperature on oxidation was accelerated with an increase of temperature above around 120°C, which might be due to the specific radiation chemical reactions. Therefore, the degradation by simultaneous ageing at higher temperatures above 155°C was much higher than that for sequential ageing, such as irradiation followed by thermal ageing or thermal ageing followed irradiation. At a high temperature, the degradation by thermal ageing under vacuum (without oxidation) was more progressed than that for the ageing in air (with oxidation). The reason was assumed to be the thermal decomposition of crosslinks between SiR molecules formed by the chemical crosslinking agent. The hardness (Shore hardness) reflected well the degradation of the SiR material for any ageing conditions.

Let effects of ion beam irradiation on poly(di-n-hexylsilane)

Abstract Thin films of poly(di-n-hexylsilane) were irradiated with 2–20 MeV H + , He + and He 2+ ion beams. The beams caused heterogeneous reactions of crosslinking and main chain scission in the films. The relative efficiency of the crosslinking was drastically changed in comparison with that of main chain scission. The anomalous change in the molecular weight distribution was analyzed with increasing irradiation flux, and the ion beam induced reaction radius; the track radius was determined for the radiation sources by the function of molecular weight dispersion. The values obtained ranged from 5.9 ± 1.5 nm for 2 MeV He + to 1.0 ± 0.5 nm for and 20 MeV H + ion beam irradiation.

The distribution profile of the chemical structural changes in ion-irradiated polyolefins

The distribution profiles of the chemical structural changes induced in low density polyethylene(LDPE) irradiated by various ion-beams were obtained by micro-FT-IR measurement. Predominant species induced by ion-beam irradiation were trans-vinylene, hydroxyl group and carbonyl group. It was found that the depth profiles of these species resemble the Bragg curve, but they are rather different from the depth profile of the stopping power calculated by TRIM code. The terminal of the chemical reaction was observed to be deeper than the range calculated by TRIM code for all ion particles. This suggests that the energy profile in the region which the energy of the ion particle becomes lower is very complicated.

Fiber reinforced plastics using a new heat-resistant silicon based polymer

Fiber reinforced plastics (FRPs), reinforced with carbon fiber, SiC fiber and glass fiber, were prepared by using a new thermosetting silicon-containing polymer, poly[(phenylsilylene) ethynylene-1,3-phenyleneethynylene](MSP), as a matrix resin. In MSP composite processing, no solvent is needed, no by-products are generated, and the curing temperature is low (150–210°C). The FRPs (MSP composite) showed high heat-, burn- and radiation-resistant properties. Bending strengths (110–140 MPa) and modulus (30 GPa) at 200°C and 400°C were almost equal with those at room temperature, and were not affected by 100 MGy of irradiation. Dynamic viscoelasticity and creep properties of MSP composite were also determined and compared with those of a polyimide composite.

Fine silicon carbide fibers synthesized from polycarbosilane-polyvinylsilane polymer blend using electron beam curing

A fine SiC fiber is synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS) with electron beam curing under vacuum. The obtained SiC fiber from the PCS-PVS blend polymer has smaller average diameter of 8.5 μm than that of 11.8 μm from PCS, and shows higher average tensile strength of 3.2 GPa than that of 2.8 GPa from PCS after heat treatment at 1673 K in Ar gas atmosphere. However, the SiC fiber from the polymer blend decreases in tensile strength after heat treatment above 1773 K due to β-SiC crystal growth near the fiber surface, because of a small amount of oxygen incorporated in the fiber.