Taichi Arakawa

Fabrication of Densely Packed Gold Nanoparticle Films and Their Fluorescence Enhancement Effect

Stable and densely packed two-dimensional films of gold nanoparticles (AuPs) were fabricated on a glass substrate, in which the gold nanoparticle film (AuPF) formed at a liquid/liquid interface was sandwiched between titanium oxide [Ti(O)] layers; the Ti(O) layer was prepared by a surface sol–gel process. The structure of AuPF on the substrate was measured and evaluated by absorption spectroscopy, quartz crystal microbalance (QCM) measurement, and scanning electron microscopy (SEM). Without the Ti(O) layer, the deposited gold nanoparticles moved to form aggregates on the substrate surface, as was verified from SEM measurements. A clear plasmon band due to AuPs was observed in the deposited AuPF both on the bare and Ti(O)-modified substrates. Tetratolylporphyrin (TTP) was cast on the surface of AuPFs. The excitation efficiencies of TTP on the as-described modified substrates were compared. The use of the Ti(O) layer was quite effective both for preserving the morphology of AuPF as well as for reducing the quenching effect of the photoexcited TPP by Au.

Silver-nanoparticle-assisted photocurrent generation in polythiophene-fullerene thin films

We have investigated the effect of silver nanoparticles (AgPs) on the photocurrent generation of a polyphiophene-fullerene photovoltaic film. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methylester (PCBM) were used for the electron donor and acceptor, respectively. First, AgPs were electrostatically deposited upon the surface of an indium tin oxide (ITO) electrode via a polycation. Then, a film of P3HT or a mixture of P3HT and PCBM was prepared by spin coating. The thickness of the film was evaluated by atomic force microscopy. Absorption and fluorescence spectral measurements were carried out to investigate the effects of AgPs. Photocurrent spectra were also measured, and the effects of AgPs on photocurrent enhancement were verified.

Facile Fabrication of Gold Nanoparticle–Titanium Oxide Alternate Assemblies by Surface Sol–Gel Process

Multistructured assemblies consisting of gold nanoparticles and titanium oxide were alternately fabricated by a surface sol–gel process. First, a quartz glass substrate was immersed into an organic solution of titanium butoxide [Ti(OBu)4]. Then, the substrate was rinsed with water, and dried in air, giving ultra-thin titanium oxide [Ti(O)]-modified quartz glass substrate. This modified glass substrate was immersed into an aqueous colloidal solution of gold nanoparticles (AuPs) that were stabilized with citrate ions, giving a AuP–Ti(O)-modified glass substrate. By repeating these surface sol–gel processes, the multistructured assemblies of AuPs and Ti(O), [AuP/Ti(O)]n/Glass (n=1–4) were fabricated. Plasmon band intensity increased with the number of surface sol–gel process cycles. The resultant assemblies were stable even after 11 days, or after treatment with an aqueous electrolyte solution. The alternate assembling of AuPs and Ti(O) was confirmed by quartz crystal microbalance measurements and absorption and X-ray photoelectron spectroscopies. Accordingly, we have succeeded in the preparation of stable AuP–Ti(O) composite films on the substrates.

Facile Fabrication and Photolectrochemical Properties of Porphyrin–Fullerene Assemblies by Self-Assembly and Surface Sol–Gel Processes

Ultrathin photoelectric conversion films consisting of a porphyrin–fullerene photoredox pair were fabricated by the combined use of room-temperature covalent-bonding and surface sol–gel processes. First, cysteamine was self-assembled on an indium–tin-oxide (ITO) electrode. The cysteamine-modified electrode was then immersed in C60 solution, giving immobilization of C60 via bond formation between the amino group of cysteamine and C60. Next, the C60-modified electrode was dipped in 2-ethanolamine solution to implant the hydroxy group to the immobilized C60 via the bond formation between C60 and the amino group; thus, the hydroxy group was exposed as the outermost layer. Then, Ti(OBu)4 and tetracarboxyporphyrin (TCPP) were alternately assembled on the C60 layer by the surface sol–gel process, to give an assembly of TCPP, titanium oxide species [Ti(O)], and C60 on the ITO electrode. The double layering of TCPP–Ti(O) was possible. The spectral characterization of the films was carried out. In the presence of sacrificial reagents, anodic photocurrents were generated from these modified electrodes. The incorporation of the C60 layer resulted in the substantial enhancement of the photocurrents as compared with that of the TCPP layer alone, suggesting effective electron-transfer reactions between TCPP and C60 that contribute to the photocurrent increase. The photocurrents increased by the double layering of the TCPP and Ti(O) layers.

Fabrication and Photocurrent Generation of Multilayer Assemblies Consisting of Silver-nanoparticles, Polydiacetylene, and Polyions

The fabrication of silver nanoparticle and polydiacetylene nanocrystal multilayer assemblies was successful on indium–tin-oxide transparent electrodes by repeating electrostatic layer-by-layer deposition. Adsorbed amount of silver nanoparticles and polydiacetylene nanocrystals was confirmed by visible absorption spectroscopy. The surface conditions and morphologies of the assemblies were investigated by scanning electron microscopy. In the presence of a sacrificial reagent, these multilayer assemblies generated a stable photocurrent. It has become apparent that polydiacetylene nanocrystals are not also photoexciting material in the present system, but also act as an electron relay or transport material. Therefore, photocurrent generation is assisted under the co-existence of polydiacetylene nanocrystals in the assemblies.

Fabrication and Photoelectrochemical Properties of Multilayer Assemblies Consisting of Silver-nanoparticles, Polydiacetylene, and Polyions

1 Department of Materials Science, School of Engineering, The University of Shiga Prefecture, 2500, Hassaka-cho, Hikone-City, Shiga 522-8533 Japan Phone: +81-749-28-8538, E-mail: akiyama.t@mat.usp.ac.jp 2 Department of Organic Device Engineering, Yamagata University, 4-3-16, Jyonan, Yonezawa-City, Yamagata 992-8510, Japan 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan 4 Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan 5 Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan