Takuma Hachisu

New trends in nanoparticles: syntheses and their applications to fuel cells, health care, and magnetic storage

This paper reviews important research on chemical and electrochemi- cal synthesis and application of nanoparticles, especially our recent results in this field: (i) catalytic metal nanoparticles for micro-fuel cells, (ii) magnetic oxide nanoparticles for drug delivery systems, and (iii) magnetic metal nanoparticles for magnetic recording media. To fulfill the requirements of each application, we chose and modified those synthetic methods for obtaining suitable properties, e.g., mor - phology, catalytic activity, and magnetic properties. (i) For micro-fuel cells, elec- trodeposition is attractive because of its selective deposition onto current collectors and possible elimination of an annealing process. As a result, we have successfully synthesized Pt, PtRu alloy, and PdCo alloy, which consisted of dendritic structures macroscopically and of interconnected nanoparticles microscopically. (ii) For drug delivery systems, since magnetic nanoparticles should possess ferromagnetism, be dispersible in water, and be nontoxic, Fe3O4 nanoparticles synthesized by hydroly- sis in aqueous media are suitable. As a result, we have successfully controlled the size (10-40 nm in diameter) and the magnetic properties of Fe3O4 nanoparticles by means of adjusting the molar ratio of ferrous to ferric ions in the precursor solution. (iii) For magnetic recording materials, since magnetic nanoparticles should possess high coercivity, a controlled shape, and a uniform small size, we have modified a chemical method for synthesizing FePt by adjusting the growth temperature. As a result, we have succeeded in synthesizing FePt nanoparticles with a controlled shape (cubic) and a uniform size (ca. 5.6 nm).

(Invited) Development on Self-Assembly Technique for Arrangement of Chemically Synthesized FePt Nanoparticles

This paper reviews our study of bit patterned media (BPM) using L10 (face centered tetragonal)-FePt nanoparticles. For the practical use of L10-FePt nanoparticles to BPM, some breakthroughs are required: a highly ordered two-dimensional array of nanoparticles on a substrate, a controlled orientation of the axis of easy magnetization in vertical direction on a substrate. Previously, we reported about the achievement for uniformity FePt nanoparticles by controlling chemical synthesis conditions. Moreover, we confirmed the selective chemical interaction Pt in the surface of FePt nanoparticles and SH group with (3-mercaptopropyl)tri-methoxysilane (MPTMS). This study presented a new hybrid technique combining the selective chemical bonding and a substrate with a geometrical grid in order to control the array of FePt nanoparticles with uniform direction of their magnetization. We succeed in preparing uniform array of nanoparticles on geometrical grid with size of 200 nm square prepared using ultraviolet nanoimprint lithography (UV-NIL).

Arrangement of FePt Nanocubes Utilizing Chemical Binding Selectivity

This study on future ultrahigh density magnetic recording devices aims to develop a technique for arranging FePt nanocubes on a substrate by using organosilane as an interlayer. An array of FePt nanocubes was formed by chemical synthesis, utilizing the Pt-S binding between the SH functional group in (3-mercaptopropyl)trimethoxysilane and Pt in the FePt nanocubes. The morphology of the FePt nanocube array on the substrate was characterized using atomic force microscopy and plan-view scanning electron microscopy, which revealed that the array was a monolayer. After SiO 2 was coated by chemical vapor deposition as a protective layer for sintering prevention, annealing was carried out at 900°C for 3 h in a reducing atmosphere to transform the crystal structure of the FePt nanocubes to the L1 0 phase. X-ray diffraction results revealed that the annealed FePt nanocube array had a FePt(110) orientation and L1 0 phases such as (001) and (110). The Pt-S binding did not obstruct the L1 0 ordering of FePt. Consequently, a method for arranging nanoparticles by using the organic molecules with functional groups that can interact with nanoparticle selectivity as an interlayer can be applied as a formation technique for arranging a wide range of nanoparticles.