Yoshikiyo Hatakeyama

Effects of sputtering conditions on formation of gold nanoparticles in sputter deposition technique

Sputter deposition of metals in a capture medium with extremely low vapor pressure is a simple and convenient method to generate metal nanoparticles (NPs) without chemical reactions. By careful selection of the capture medium and/or temperature of the medium for the deposition, the size of the synthesized NPs can be controlled. Sputtering conditions also play an important role in determining the size of the NPs. We synthesized Au NPs in a standard ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4) by systematically varying the sputtering conditions, which influence the formation processes and/or the size and size distributions of Au NPs. The Au NPs were characterized by small-angle X-ray scattering immediately after the synthesis of NPs in the capture medium. It is concluded that the temperature of the target and applied voltages have a strong influence on the size of Au NPs generated in the capture media, while the working distance between the target and the surface of the capture media, sputtering time, and discharge current have little or no influence. Lower temperature of the target and higher applied voltage are desired for generating size-controlled smaller NPs.

Anisotropic Mechanical Properties of Collagen Hydrogels Induced by Uniaxial-Flow for Ocular Applications

Engineering of well-organized tissue constructs is active in the field of material science for biomedical applications. Here, we propose a method for orienting collagen in transparent high-density collagen hydrogels using a simple rolling method. Structural organization and mechanical function were adjusted by regulating the thickness of the construct and the cross-linking reagent. Directionality of collagen alignment on the microscopic scale was achieved parallel to the extensional flow. The preferential alignment of collagen significantly affected the mechanical properties of the construct, with strong tensile strength in the direction parallel to the collagen, and high elastic strain in the perpendicular direction. The tensile strength in the parallel direction was effectively increased by 67% by increasing the cross-linking reagents by 33%, without affecting transparency which remained at 70–80% to visible light. The constructs exhibit good biocompatibility for as a substrate for the expansion of corneal epithelial cells isolated from human donor cornea, indicating the potential for tissue engineering and biomedical applications, particularly for ocular treatments.

Air oxidation of carbon spheres. II. Micropore development

The formation of micropores at the start of the oxidation of carbon spheres was studied by N2 gas adsorption, small-angle X-ray scattering and transmission electron microscopy with the aid of image processing. On the basis of a detailed analysis of the measurement results, it was suggested that the principal process in the formation of micropores was the opening of closed pores initially present in the carbon matrix of the spheres. The fact that these closed pores were formed during carbonization as the nano-texture of glass-like carbons suggests that the carbonization process may govern the size of the micropores formed at the start of the oxidation process employed for activating such activated carbon precursors.

Optical and Radiographical Characterization of Silica Aerogel for Cherenkov Radiator

We present optical and X-ray radiographical characterization of silica aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A novel pin-drying method enables us to produce highly transparent hydrophobic aerogels with high refractive index by shrinking wet-gels. In order to investigate the uniformity in the density (i.e., refractive index) of an individual aerogel monolith, we use the laser Fraunhofer method, an X-ray absorption technique, and Cherenkov imaging by a ring-imaging Cherenkov detector in a beam test. We observed an increase in density at the edge of the aerogel tiles, produced by pin-drying.

X-ray radiographic technique for measuring density uniformity of silica aerogel

Abstract This paper proposes a new X-ray radiographic technique for measuring density uniformity of silica aerogels used as radiator in proximity-focusing ring-imaging Cherenkov detectors. To obtain high performance in a large-area detector, a key characteristic of radiator is the density (i.e. refractive index) uniformity of an individual aerogel monolith. At a refractive index of n =1.05, our requirement for the refractive index uniformity in the transverse plane direction of an aerogel tile is | δ ( n − 1 ) / ( n − 1 ) | 4 % in a focusing dual layer radiator (with different refractive indices) scheme. We applied the radiographic technique to evaluate the density uniformity of our original aerogels from a trial production and that of Panasonic products (SP-50) as a reference, and to confirm they have sufficient density uniformity within ± 1 % along the transverse plane direction. The measurement results show that the proposed technique can quantitatively estimate the density uniformity of aerogels.

Study of Hybrid Dust Sample Collection System Toward Mars Aeroflyby Sample Collection Mission

New sample collector system is proposed for the sample return mission on Mars under consideration in JAXA. The new sample collector consists of silica aerogels and carbon aerogels to compensate each other for their unique characteristics. In order to demonstrate the concept and verify the technical difficulties, several experiments are conducted in this study. Heating tests are carried out to see whether the sample collector can be applied to the aerodynamic heating environment. From the heating tests, no significant difference is observed in the sample collector between before and after heating. Unlike the silica aerogels, the surface alteration that makes the dust capturing difficult are not observed on the surface of carbon aerogels. The light gas gun experiments are also performed to simulate the dust particle capturing by using the sample collector. It is confirmed from the study that 10-30μm dust particles with the relative velocity of 4km/s could be successfully captured by using the present sample collector. After the light gas gun experiments, several particles are picked out from the sample collector by using a nano-manipulating system. The SEM and EDS analysis is successfully performed for particles picked out from the sample collectors. Consequently, it is concluded that the dust particles would be analyzed by the present analysis scheme, if the present sample collector would be applied to the MASC mission.

Titanium oxide nanoparticle dispersions in a liquid monomer and solid polymer resins prepared by sputtering

A transparent resin containing titanium oxide nanoparticles (NPs) was prepared using a molten matrix sputtering (MMS) technique. The low vapour pressure of the liquid, pentaerythritol ethoxylate (PEEL) substrate permits the use of this vacuum technique directly with liquid PEEL under stirring conditions in order to obtain uniform dispersions of NPs. We found that it is possible to synthesize titanium oxide, TiOx, NPs with diameters of less than 5 nm with a controlled composition by simply adjusting the sputtering atmosphere. Furthermore, as the electronic structure of the TiOx NPs changes depending on the particle size, crystallinity and degree of oxidation, we were able to modify the optical properties of PEEL and the resin by embedding TiOx NPs in the matrix. The enhancement of the refractive index of a resin containing TiO2 NPs was also demonstrated. This synthetic method is promising for the advanced preparation of high purity TiOx NPs without using a reducing agent and leaving by-products for various applications in optical devices, energy conversion, and light harvesting in the UV visible region.

Development of large area silica aerogel used as RICH radiator for the Belle II experiment

This paper presents the recent progress in the development of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter that will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH counter is designed to identify charged pions and kaons and to have a separation capability of more than 4σ at momenta up to 4 GeV/c. In a focusing-dual-layer radiator with different refractive indices, a prototype A-RICH counter satisfied the required performance using our conventional aerogel tiles with refractive indices n of 1.045 and 1.055, transmission lengths ΛT of 30-40 mm, and designed final dimensions of 18 × 18 × 2 cm3. Moreover, we achieved better π/K separation performance using n ~ 1.06 aerogels with relatively small dimensions but long transmission length (ΛT > 50 mm) produced by a novel pin-drying method. We need to fill the large end cap area of 3.5 m2 with two-layer aerogel tiles and to minimize the number of tiles with realistic dimensions to reduce the tile boundaries, at which the number of detected photoelectrons decreases. Therefore, we studied large area aerogel production by both conventional and pin-drying methods as a key to achieving high performance over the actual detector. This paper discusses the crack-free yield, optical transparency, and uniformity in refractive index within a monolith of recently produced large area aerogels.

Small-Angle X-ray Scattering

Abstract Most of the pores in carbon materials are formed during the pyrolysis and carbonization of the precursors and govern some physicochemical properties of the resultant carbon materials. Therefore, the characterization of pore structure in some carbon materials is very important for their applications, such as adsorbents, catalyst supports, etc., as well as control of the materials during pyrolysis and carbonization. Small-angle X-ray scattering (SAXS) is the technique used to characterize closed pores as well as open pores, although other techniques are possible for evaluating only open pores. In this chapter, the SAXS technique is explained by focusing on the applications to carbon materials by introducing some of the specific examples.

Low-Temperature Production of Genuinely Amorphous Carbon from Highly Reactive Nanoacetylide Precursors

Copper acetylide is a well-known explosive compound. However, when the size of it crystals is reduced to the nanoscale, its explosive nature is lost, owing to a much lower thermal conductance that inhibits explosive chain reactions. This less explosive character can be exploited for the production of new carbon materials. Generally, amorphous carbon is prepared by carbonization of organic compounds exposed to high temperature, which can induce partial crystallization in graphite. In this work, we present a new method in which the carbonization reaction can proceed at a lower annealing temperature (under 150°C) owing to the highly reactive nature of copper acetylide, thus avoiding crystallization processes and enabling the production of genuinely amorphous carbon materials.