Fabrication of the Cerium Oxide Nanocrystal Film with Heterogeneous Ligand Structures
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1207-N07-30
Fabrication of the Cerium Oxide Nanocrystal Film with Heterogeneous Ligand Structures Daisuke Hojo1, Takanari Togashi1, and Tadafumi Adschiri1 1
Advanced Institute for Materials Research, Tohoku University Sendai 980-8577, Japan
ABSTRACT Sufficiently dense films of cerium oxide nanocrystals modified with decanoic acid, with sizes of ~9 nm, were fabricated on the surface by modifying a silicon substrate with 3,4dihydroxyhydrocinnamic acid, where catechol group lied at the top. By doing this, no further pretreatment for the modified cerium oxide nanocrystals is required to fix them chemically on the substrate. Selective adhesion between nanocyrstals and the substrate for the two-dimensional assembly can be attributed to the chemical bonding formed by on-site ligand exchange between carboxyl and catechol groups. INTRODUCTION Highly crystalline metal oxide nanoparticles have been extensively investigated in various fields such as electrochemistry and optics and used in catalysis. Characteristics of nanometer-sized materials, e.g., catalytic or magnetic effects, are expected to be different from those of bulk materials.[1] Recently, the assembling of a highly crystalline metal oxide nanoparticle layer at room temperature has attracted considerable attention.[2,3] Highly crystalline metal oxide films have a high potential for use in high refractive index films and highpermittivity insulating materials. However, such high-quality films are fabricated by subjecting them to high-temperature treatments, which damage heat-sensitive substrates such as plastic polymers. If the process of fabricating a thin film can be divided into the processes—synthesis of highly crystalline nanoparticles at high temperature and assembly of the nanocrystals on substrates at room temperature, highly crystalline metal oxide thin films can be fabricated on such heat-sensitive substrates. For the fabrication of two-dimensional structures or monolayercontrolled thin films of nanoparticles on the surface, the interactions between nanoparticles should be decreased whereas the interactions between nanoparticles and the substrate should be carefully designed.[2-11] The efficient method to chemically fix high-dispersible nanoparticles to the substrate is anticipated for uniform two-dimensional assembly. Here, we report a new, simple, and efficient method for assembling cerium oxide nanocrystals modified with decanoic acid two-dimensionally on the surface by modifying substrates with 3,4-dihydroxyhydrocinnamic acid (DHCA). By doing this, no further pretreatment for the modified nanocrystals is required to fix them chemically on the substrate. We have modified highly crystalline cerium oxide nanoparticles with carboxyl acid during their syntheses in supercritical water (SCW).[12-14] These modified nanocrystals can be monodispersed in organic solvents such as tetrahydrofuran (THF), toluene, or cyclohexane.[12-14] In order to chemically anchor high-dispersible decanoic acid-cerium oxide hybrid nanocrystals, we used onsite ligand exchange betwe
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