Mariko Miyachi

π-Conjugated Nickel Bis(dithiolene) Complex Nanosheet

A π-conjugated nanosheet comprising planar nickel bis(dithiolene) complexes was synthesized by a bottom-up method. A liquid-liquid interfacial reaction using benzenehexathiol in the organic phase and nickel(II) acetate in the aqueous phase produced a semiconducting bulk material with a thickness of several micrometers. Powder X-ray diffraction analysis revealed that the crystalline portion of the bulk material comprised a staggered stack of nanosheets. A single-layer nanosheet was successfully realized using a gas-liquid interfacial reaction. Atomic force microscopy and scanning tunneling microscopy confirmed that the π-conjugated nanosheet was single-layered. Modulation of the oxidation state of the nanosheet was possible using chemical redox reactions.

A New Method To Generate Arene-Terminated Si(111) and Ge(111) Surfaces via a Palladium-Catalyzed Arylation Reaction

Formation of silicon-aryl and germanium-aryl direct bonds on the semiconductor surface is a key issue to realize molecular electronic devices, but the conventional methods based on radical intermediates have problems to accompany the side reactions. We developed the first example of versatile and efficient methods to form clean organic monolayers with Si-aryl and Ge-aryl bonds on hydrogen-terminated silicon and germanium surfaces by applying our original catalytic arylation reactions of hydrosilanes and hydrogermanes using Pd catalyst and base in homogeneous systems. We could immobilize aromatic groups with redox-active and photoluminescent properties, and further applied in the field of rigid π-conjugated redox molecular wire composites, as confirmed by the successive coordination of terpyridine molecules with transition metal ions. The surfaces were characterized using cyclic voltammetry (CV), water contact angle measurements, X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, and atomic force microscopy (AFM). Especially, the AFM analysis of 17 nm-long metal complex molecular wires confirmed their vertical connection to the plane surface.

Nanoparticle Assemblies via Coordination with a Tetrakis(terpyridine) Linker Bearing a Rigid Tetrahedral Core

Controlling particle-particle interactions is a major challenge in achieving the programmable assembly of nanoparticles, which shows great potential for device fabrication and detection systems. We present here a simple chemical method that allows the formation of Pd nanoparticle assemblies using a tetrakis(terpyridine) linker with a rigid tetrahedral core.

Bio-inspired photoresponse of porphyrin-attached gold nanoparticles on a field-effect transistor.

A bio-inspired photoresponse was engineered in porphyrin-attached Au nanoparticles (AuNPs) on a field-effect transistor (FET). The system mimics photosynthetic electron transfer, using porphyrin derivatives as photosensitizers and AuNPs as photoelectron counting devices. Porphyrin-protected AuNPs were immobilized onto the gate of an FET via the formation of self-assembled monolayers. Photoinduced electron transfer from the porphyrin led to single electron transfer at the Au nanoparticles, which was monitored via a changing gate voltage on the FET in the presence of organic electrolyte. The further attachment of other functional molecules to this system should enable various other potential functionalities. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

Synthesis of Diazenido-Ligated Vanadium Nanoparticles

Metallic vanadium nanoparticles stabilized with 4-octylphenyldiazenido groups (particle size: 1.7 ± 0.2 nm) were synthesized via the reduction of VCl4 with superhydride (LiBHEt3) in the presence of 4-octylphenyldiazonium salt in an Ar-filled glovebox. The resulting particles were characterized using TEM, elemental analysis, and XPS measurements. The unusual reaction on the surface resulted in the passivation of V-N═N-Ar covalent bonds.

Observation of O K-Edge X-Ray Magnetic Circular Dichroism of CO Adsorbed on an Ultrathin Co/Cu(001) Film

We have for the first time observed K-edge X-ray magnetic circular dichroism of submonolayer amounts of adsorbates on ferromagnetic thin metal films. The O K-edge X-ray magnetic circular dichroism (XMCD) of CO adsorbed on fcc Co grown epitaxially on Cu(001) showed a positive sign for the O1s →2 π* transition, which implies an opposite orbital moment of O to the Co magnetization.

Effective Method for Micro-Patterning Arene-Terminated Monolayers on a Si(111) Electrode

Microstructured electrodes are significant to modern electrochemistry. A representative aromatic group, 4-ferrocenylphenyl one, was covalently bound to a micropatterned silicon electrode via the arylation of a hydrogen-terminated silicon(111) surface formed selectively on a Si wafer. Starting from a silicon(100)-on-insulator (SOI) wafer, the aromatic monolayer was attached sequentially by spin-coating a resist, electron beam lithography, Cr/Au deposition, lift-off, anisotropic etching with aqueous KOH solution, and Pd-catalyzed arylation. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) are used to characterize the coupling reaction between 4-ferrocenyl group and silicon substrate, and to confirm performance of the final modified microsized electrode. These data show that this synthetic protocol gives chemically well-defined and robust functionalized monolayers on a silicon semiconducting surface with a small electrode.

Preparation of Pd Nanoparticles with Tetrahedral, Spherical, Plate, and Feather Shapes by Capping with 1-Pentyl Isocyanide

In this study, we synthesized n-alkyl-isocyanide-protected palladium colloidal nanoparticles with different shapes. The 1-pentyl-isocyanide-protected Pd nanoparticles prepared by the reduction of the Pd complex with ethylene glycol had various geometric shapes. Transmission electron micrographs showed that tetrahedral particles were predominant, although some spherical, plate-, and feather-shaped particles were also observed. The enriched nanotetrahedra were isolated as a black powder by reprecipitation with methanol–chloroform and the particle size was controlled by the reaction conditions.

Electrochemical fabrication of one-dimensional porphyrinic wires on electrodes

[5,15-Di(4-aminophenyl)-10,20-diphenylporphyrinato]zinc(II) was found to electropolymerize on electrodes such as glassy carbon (GC), indium tin oxide (ITO), and tin oxide, to form a redox-active, stable, and reproducible π-conjugated polymer. Electrochemical and UV/vis spectroscopic studies showed that the electropolymerization involves azobenzene linkage formation via radical intermediates. The electrode modified with the porphyrinic wire featured strong light absorptions in the visible region, thereby serving as a photoanode for a photocurrent generation system.

Conjugates between photosystem I and a carbon nanotube for a photoresponse device.

Photosystem I (PS I) is a large pigment–protein complex embedded in the thylakoid membranes that performs light-driven electron transfer across the thylakoid membrane. Carbon nanotubes exhibit excellent electrical conductivities and excellent strength and stiffness. In this study, we generated PSI–carbon nanotube conjugates dispersed in a solution aimed at application in artificial photosynthesis. PS I complexes in which a carbon nanotube binding peptide was introduced into the middle of the PsaE subunit were conjugated on a single-walled carbon nanotube, orienting the electron acceptor side to the nanotube. Spectral and photoluminescence analysis showed that the PS I is bound to a single-walled carbon nanotube, which was confirmed by transmission electron microscopy. Photocurrent observation proved that the photoexcited electron originated from PSI and transferred to the carbon nanotube with light irradiation, which also confirmed its orientated conjugation. The PS I–carbon nanotube conjugate will be a useful nano-optoelectronic device for the development of artificial systems.