Investigation of the Image Contrast in an Ultra-Low Voltage Scanning Electron Microscope Using an Auger Electron Spectrometer.

Surface-sensitive information on a bulk sample can be obtained by using a low incident electron energy (low accelerating voltage/landing voltage) in a scanning electron microscope (SEM). However, topography and composition contrast obtained at low incident electron energies may not be intuitive and should be analyzed carefully. By combining an Auger electron spectrometer (AES) with a low incident electron energy SEM (LE-SEM), we investigated the SEM contrast carefully by separating the secondary electron (SE) and back-scattered electron (BSE) components with high accuracy. For this, we modified an AES to measure the electron energy in the range of 0­0.6 keV with a sample bias voltage of 0 to −0.3 keV. We could clearly observe reversed brightness of gold and carbon (graphite) in BSE images when the energy of the incident electrons was reduced to 0.2­0.3 keV. In addition, reflected electron energy spectroscopy (REELS) is known to be a tool for chemical state analysis of the sample. We demonstrated that it is possible to study the electron states of graphite, diamond, and graphene by acquiring low incident energy REELS spectra from their surfaces with the newly modified AES. This will be a new method for analyzing the electron states of local areas of a surface.

Wisely Designed Phthalocyanine Derivative for Convenient Molecular Fabrication on a Substrate.

An axial-substituted silicon phthalocyanine derivative, SiPc(OR)2 (R = C4H9), that is soluble in organic solvent is conveniently synthesized. This silicon phthalocyanine derivative reacts with a hydroxyl group on a substrate and then with another phthalocyanine derivative under mild conditions. The accumulation number of the phthalocyanine molecules on the substrates is easily controlled by the immersion time. On the basis of AFM (atomic force microscopy) images, the surface of the phthalocyanine-modified glass substrate has uneven structures on the nanometer scale. ITO electrodes modified with the composition of the phthalocyanine derivative and PCBM show stable cathodic photocurrent generation upon light irradiation.

Dual-Functional Surfactant-Templated Strategy for Synthesis of an In Situ N2 -Intercalated Mesoporous WO3 Photoanode for Efficient Visible-Light-Driven Water Oxidation.

N2 -Intercalated crystalline mesoporous tungsten trioxide (WO3 ) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N2 intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N2 physisorption analysis showed that the specific surface area (57.3 m2 g-1 ) of WO3 templated with DDA (WO3 -DDA) is 2.3 times higher than that of 24.5 m2 g-1 for WO3 prepared without DDA (WO3 -bulk), due to the mesoporous structure of WO3 -DDA. The Raman and X-ray photoelectron spectra of WO3 -DDA indicated intercalation of N2 into the WO3 lattice above 450 °C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28 nm, from 459 nm (2.70 eV) to 487 nm (2.54 eV), due to N2 intercalation. This could be explained by the bandgap narrowing of WO3 -DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO3 . A WO3 -DDA-coated indium tin oxide (ITO) electrode calcined at 450 °C generated a photoanodic current under visible-light irradiation below 490 nm due to photoelectrochemical water oxidation, as opposed to below 470 nm for ITO/WO3 -bulk. The incident photon-to-current conversion efficiency (IPCE=24.5 %) at 420 nm and 0.5 V versus Ag/AgCl was higher than that of 2.5 % for ITO/WO3 -bulk by one order of magnitude due to N2 intercalation and the mesoporous structure of WO3 -DDA.

Grain-Boundary-Free Super-Proton Conduction of a Solution-Processed Prussian-Blue Nanoparticle Film.

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10-2  S cm-1 . Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 105 -fold enhancement of proton conductivity, reaching ca. 10-1  S cm-1 . The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.

Plasmon-assisted photocurrent generation from silver nanoparticle monolayers combined with porphyrins via their different chain-length alkylcarboxylates.

Three-typed porphyrin derivatives with a different chain-length alkylcarboxylic acid as their peripheral anchor group have been prepared. Anodic photocurrents were observed in a simple system where the porphyrin derivatives were directly anchored on an indium tin oxide (ITO) electrode. Cathodic photocurrents and their plasmon-assisted enhancement appeared from an Ag nanoparticle (Ag NP) composite monolayer combined with the porphyrin derivatives on the ITO electrode. In the photocurrent generation mechanism, Ag NPs played both the roles as photon- and energy-transfer to the porphyrin derivatives. The plasmon-assisted enhancement was affected by the chain-lengths of the peripheral anchor groups.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation.

A unique transformation of WO3 nanowires (NW-WO3) into hexagonal prisms (HP-WO3) was demonstrated by tuning the temperature of the (N2H4)WO3 precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO3 nanocrystals (ca. <100 nm width, 3-5 µm length) with anisotropic growth of monoclinic WO3 crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO3 nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO3 nanocrystals with a single-crystalline character. The HP-WO3 electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO3 electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO3 was 3.1-fold higher than 15% for the NW-WO3 electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO3 layer with the unidirectional nanowire structure is more efficient than that through the HP-WO3 layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO3 electrode is more efficient than the NW-WO3 electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO3 electrode. The efficient water oxidation reaction at the surface for the HP-WO3 electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO3 to suppress the electron-hole recombination at the surface.

High affinity anti-inorganic material antibody generation by integrating graft and evolution technologies: potential of antibodies as biointerface molecules.

Recent advances in molecular evolution technology enabled us to identify peptides and antibodies with affinity for inorganic materials. In the field of nanotechnology, the use of the functional peptides and antibodies should aid the construction of interface molecules designed to spontaneously link different nanomaterials; however, few material-binding antibodies, which have much higher affinity than short peptides, have been identified. Here, we generated high affinity antibodies from material-binding peptides by integrating peptide-grafting and phage-display techniques. A material-binding peptide sequence was first grafted into an appropriate loop of the complementarity determining region (CDR) of a camel-type single variable antibody fragment to create a low affinity material-binding antibody. Application of a combinatorial library approach to another CDR loop in the low affinity antibody then clearly and steadily promoted affinity for a specific material surface. Thermodynamic analysis demonstrated that the enthalpy synergistic effect from grafted and selected CDR loops drastically increased the affinity for material surface, indicating the potential of antibody scaffold for creating high affinity small interface units. We show the availability of the construction of antibodies by integrating graft and evolution technology for various inorganic materials and the potential of high affinity material-binding antibodies in biointerface applications.

Size-tunable synthesis of iron oxide nanocrystals by continuous seed-mediated growth: role of alkylamine species in the stepwise thermal decomposition of iron(II) oxalate.

The properties of inorganic nanoparticles (NPs) are governed by their size. Therefore, tuning the size of NPs is a fundamental technique in nanoscience. However, the size-tunable synthesis of inorganic NPs is generally carried out in a dilute solution, which produces large quantities of waste. Herein, we report the predictable size-tunable synthesis of Fe3O4 NPs by the stepwise thermal decomposition of iron(II) oxalate (Fe(ox)). Monodisperse Fe3O4 seed crystals were synthesized by the thermal decomposition of oleylamine-coordinated iron oxalate (Fe(ox)-OAm) in a small amount of oleylamine, followed by continuous seed-mediated growth of Fe3O4 NPs. The thermal decomposition behavior of Fe(ox) in oleylamine with and without N,N-diethyl-1,3-diaminopropane (dedap) revealed the important role of dedap in the stepwise thermal decomposition of Fe(ox). The size of the Fe3O4 NPs was easily tuned via the stepwise thermal decomposition of Fe(ox) by controlling the amount of decomposed Fe(ox) in a small amount of an alkylamine mixture. The particle diameter was predicted from the size of the Fe3O4 seed crystals and the amount of decomposed Fe(ox). Finally, the size dependency of magnetic properties of the synthesized Fe3O4 NPs was studied. This continuous seed-mediated growth method based on the stepwise thermal decomposition of metal oxalate can be applied to control the size of a variety of metal and metal oxide NPs.

An exclusive deposition method of silver nanoparticles on TiO2 particles via low-temperature decomposition of silver-alkyldiamine complexes in aqueous media.

An exclusive deposition method of Ag nanoparticles (NPs) on TiO2 particles has been developed. Ag NPs supported on TiO2 particles, Ag x /TiO2, with various Ag weight ratios versus total weights of Ag and TiO2 between x = 2 and 16 wt% are prepared via low-temperature thermal decomposition of Ag(i)-alkyldiamine complexes generated by a reaction between AgNO3 and N,N-dimethyl-1,3-propanediamine (dmpda) in an aqueous medium suspending TiO2 particles. The thermal decomposition of the Ag(i)-alkyldiamine complexes is accelerated by TiO2 particles in the dark, indicating that the reaction catalytically occurs on the TiO2 surfaces. Under optimised reaction conditions, the thermal decomposition of the complex precursors is completed within 3 hours at 70 °C, and Ag NPs are almost exclusively deposited on TiO2 particles with high conversion efficiencies (≥95%) of the precursor complexes. The thermal decomposition rates of the precursor complexes are strongly influenced by the chemical structure of a family of water-soluble dmpda analogues, and dmpda with both primary and tertiary amino groups is adopted as a suitable candidate for the exclusive deposition method. The number-averaged particle sizes of the Ag NPs are 6.4, 8.4, 11.8 and 15.2 nm in the cases of Ag x /TiO2, x = 2, 4, 8 and 16, respectively. To the best of our knowledge, the as-prepared Ag x /TiO2 samples show one of the highest catalytic abilities for the hydrogenation reduction of 4-nitrophenol into 4-aminophenol as a model reaction catalysed by Ag NPs.

Unique coexistence of dispersion stability and nanoparticle chemisorption in alkylamine/alkylacid encapsulated silver nanocolloids.

Surface encapsulation of metal nanoparticles (NPs) is fundamental to achieve sufficient dispersion stability of metal nanocolloids, or metal nanoink. However, the feature is incompatible with surface reactive nature of the metal NPs, although these features are both essential to realizing the functional applications into printed electronics technologies. Here we show that two different kinds of encapsulation for silver NPs (AgNPs) by alkylamine and alkylacid together are the key to achieve unique compatibility between the high dispersion stability as dense nanoclolloids and the AgNP chemisorption printing on activated patterned polymer surfaces. Advanced confocal dynamic light scattering study reveals that an additive trace amount of oleic acid is the critical parameter for controlling the dispersion and coagulative (or surface-reactive) characteristics of the silver nanocolloids. The composition of the disperse media is also important for obtaining highly concentrated but low-viscosity silver nanocolloids that show very stable dispersion. The results demonstrate that the high-resolution AgNP chemisorption printing is possible only by using unique silver nanocolloids composed of an exceptional balance of ligand formulation and dispersant composition.

Solvent-free synthesis of monodisperse Cu nanoparticles by thermal decomposition of an oleylamine-coordinated Cu oxalate complex.

Cu nanoparticles (NPs) are widely used in numerous applications because of their unique optical, catalytic, and electrical properties. However, the synthesis of monodisperse Cu NPs often involves harmful reducing agents under an inert atmosphere in a solution with low Cu ion concentrations. In this study, monodisperse Cu NPs were synthesized by the thermal decomposition of an oleylamine-coordinated Cu oxalate (Cu(ox)) complex (OA-Cu(ox)) in oleylamine in air with no reducing agent. The structure of OA-Cu(ox) was analyzed using Fourier-transform infrared spectroscopy. The decomposition temperature of the oxalate ion was reduced to 130 °C from that of Cu(ox) (300 °C) because of the coordination of the primary amino group of oleylamine with the Cu ion of Cu(ox). Furthermore, the decomposition temperature of OA-Cu(ox) strongly affected the size distribution of the synthesized Cu NPs. Monodisperse Cu NPs were successfully synthesized by the thermal decomposition of OA-Cu(ox) at temperatures higher than 240 °C with high yield (∼90%). The synthesized Cu NPs were readily dispersed in toluene.

N,N-Diethyl-diaminopropane-copper(ii) oxalate self-reducible complex for the solution-based synthesis of copper nanocrystals.

Metal oxalates (C2O42-, ox) have been explored as promising precursors for the direct transformation of their oxalate moieties into metallic or metal oxide crystals via thermal decomposition without the formation of any byproducts due to releasing CO2 gas. The copper(ii) oxalate (Cu(ox)) crystal is a coordination polymer composed of an infinite coordination network with a thermal decomposition temperature around 300 °C; however, their insoluble nature in any solvents and relatively high decomposition temperature do not allow the solution-based syntheses of surface-modified metallic Cu nanocrystals (NCs) in the presence of various surfactants such as long-chain alkylamines and alkylcarboxylates which have been used for increasing the dispersibility of NCs in organic solvents. In this study, the insoluble nature of Cu(ox) is overcome by mixing Cu(ox) crystals and N,N-diethyl-1,3-diaminopropane (dedap) to form a discrete complex, [Cu(ox)(dedap)2], whose structure is determined by X-ray crystallographic analysis. The obtained complex is well soluble in polar solvents and miscible with surfactants. Furthermore, it is decomposed at a moderate temperature of <170 °C with the evolution of CO2 gas; as a result, Cu NCs dispersible in organic solvents have been synthesized in suitable surfactants, such as the mixture of oleic acid, dodecylamine, and octylamine utilized as a reaction solvent. In addition, their potential application of the surface-modified Cu NCs as a conductive-ink has been preliminarily tested. The Cu film sintered at 280 °C exhibits a resistivity of 40 µΩ cm.

Characterization of Interfacial Charge-Transfer Photoexcitation of Polychromium-Oxo-Electrodeposited TiO2 as an Earth-Abundant Photoanode for Water Oxidation Driven by Visible Light.

Polychromium-oxo-deposited TiO2 (CrIII x Oy /TiO2 ) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an CrIII x Oy layer with approximately 2-3 nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the CrIII x Oy /TiO2 electrodes. However, the wavelength (below 620 nm) for photocurrent generation at CrIII x Oy /TiO2 -rutile was longer than that (below 560 nm) at CrIII x Oy /TiO2 -P25 by 60 nm, which is in agreement with the difference (0.2 eV) in the conduction band (CB) edge energy between rutile and anatase TiO2 . This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited CrIII x Oy layer to the TiO2 CB. The photocurrent generated for CrIII x Oy /TiO2 -rutile was higher than that for CrIII x Oy /TiO2 -anatase, which is ascribed to 1) more effective CrIII x Oy deposition on the rutile particles, 2) a larger electrolyte/CrIII x Oy interface for water oxidation as a result of smaller rutile particles (ca. 30-40 nm) compared with larger P25 particles (ca. 40-80 nm), and 3) more effective use of visible light owing to the low energy IFCT transition of rutile.

Nanoparticle chemisorption printing technique for conductive silver patterning with submicron resolution.

Silver nanocolloid, a dense suspension of ligand-encapsulated silver nanoparticles, is an important material for printing-based device production technologies. However, printed conductive patterns of sufficiently high quality and resolution for industrial products have not yet been achieved, as the use of conventional printing techniques is severely limiting. Here we report a printing technique to manufacture ultrafine conductive patterns utilizing the exclusive chemisorption phenomenon of weakly encapsulated silver nanoparticles on a photoactivated surface. The process includes masked irradiation of vacuum ultraviolet light on an amorphous perfluorinated polymer layer to photoactivate the surface with pendant carboxylate groups, and subsequent coating of alkylamine-encapsulated silver nanocolloids, which causes amine-carboxylate conversion to trigger the spontaneous formation of a self-fused solid silver layer. The technique can produce silver patterns of submicron fineness adhered strongly to substrates, thus enabling manufacture of flexible transparent conductive sheets. This printing technique could replace conventional vacuum- and photolithography-based device processing.

Construction of hybrid films of silver nanoparticles and polypyridine ruthenium complexes on substrates.

Hybrid films of functional molecules and metal nanoparticles have been considered to be novel photo-functional devices. Here we have successfully constructed hybrid films of silver nanoparticles and ruthenium polypyridine derivatives on substrates. In order to hybridise them on a surface, a self-assembled monolayer method via chemical bond formation and electro-reductive polymerisation (thick layers) via physical attachment have been employed. These methods have the advantage of convenient and reproducible fabrication of complicated hybrid films. Furthermore, it has been clarified that these hybrid films show unique photo-functional behaviours, such as enhanced photocurrent generation.

Potential Tuning of Nanoarchitectures Based on Phthalocyanine Nanopillars: Construction of Effective Photocurrent Generation Systems.

Nanopillars composed of a photoresponsive phthalocyanine derivative have been conveniently fabricated using a continuous silane coupling reaction on a substrate. The chemical potentials of phthalocyanine nanopillars (PNs) are precisely controlled by changing the number of phthalocyanine derivatives on the substrate. In addition, photocurrent generation efficiencies have been strongly influenced by the number of phthalocyanine derivatives. High photocurrent conversion cells in a solid state have been obtained by the combination of PNs and a fullerene derivative.

Synthesis of water-dispersible silver nanoparticles by thermal decomposition of water-soluble silver oxalate precursors.

Silver oxalate, one of the coordination polymer crystals, is a promising synthetic precursor for transformation into Ag nanoparticles without any reducing chemicals via thermal decomposition of the oxalate ions. However, its insoluble nature in solvents has been a great disadvantage, especially for systematic control of crystal growth of the Ag nanoparticles, while such control of inorganic nanoparticles has been generally performed using soluble precursors in homogeneous solutions. In this paper, we document our discovery of water-soluble species from the reaction between the insoluble silver oxalate and N,N-dimethyl-1,3-diaminopropane. The water-soluble species underwent low-temperature thermal decomposition of the oxalate ions at 30 °C with evolution of CO2 to reduce Ag+ to Ag0. Water-dispersible Ag nanoparticles have been successfully synthesized from the water-soluble species in the presence of gelatin via similar thermal decomposition at 100 °C. The gelatin-protected and water-dispersible Ag nanoparticles with a mean diameter of 25.1 nm appeared. In addition, antibacterial activity of the prepared water-dispersible Ag nanoparticles has been preliminarily investigated.

Hydrothermal synthesis of inorganic-organic hybrid gadolinium hydroxide nanoclusters with controlled size and morphology.

A series of gadolinium hydroxide [Gd(OH)3] nanoclusters having different morphologies was synthesized in the presence of 3,4-dihydroxy hydrocinnamic acid (DHCA), an organic modifier, under subcritical water conditions. These well-shaped Gd(OH)3 clusters are composed of many nanorods in a parallel orientation, rather than a disordered aggregation of nanorods, which are linked together by organic DHCA molecules. Here DHCA works as an inter-linker to form these cluster-like structures through coordination bonds. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and SQUID magnetometry. We investigated the effect of the concentrations of DHCA and KOH on the size and morphology of the Gd(OH)3 clusters. Their possible formation mechanism is also briefly discussed.

Molecular nanostamp based on one-dimensional porphyrin polymers.

Surface design with unique functional molecules by a convenient one-pot treatment is an attractive project for the creation of smart molecular devices. We have employed a silane coupling reaction of porphyrin derivatives that form one-dimensional polymer wires on substrates. Our simple one-pot treatment of a substrate with porphyrin has successfully achieved the construction of nanoscale bamboo shoot structures. The nanoscale bamboo shoots on the substrates were characterized by atomic force microscopy (AFM), UV-vis spectra, and X-ray diffraction (XRD) measurements. The uneven and rigid nanoscale structure has been used as a stamp for constructing bamboo shoot structures of fullerene.

Surfactant-assisted one-pot synthesis of superparamagnetic magnetite nanoparticle clusters with tunable cluster size and magnetic field sensitivity.

Magnetic nanoparticles (MNPs) have many potential biomedical applications. Improvements in their magnetic properties and solubility are necessary for these applications to realize their full potential. In this study, MNPs in the form of raspberry-like magnetite (Fe(3)O(4)) nanoparticle clusters, consisting of tiny Fe(3)O(4) particles with a diameter of approximately 20 nm, were prepared under hydrothermal conditions at 200 °C in the presence of 3,4-dihydroxyhydroxysinnamic acid (DHCA). The primary particles were connected by DHCA molecules to form the clusters, which were well dispersed in water media because a COOH group from DHCA appeared on their surfaces. The cluster size could be tuned from 50 to 400 nm without changing the primary particle size by controlling the reaction time. Therefore, all prepared clusters displayed superparamagnetic properties at room temperature. In addition, the sensitivity of Fe(3)O(4) to an external magnetic field could also be controlled by the cluster size.