Publications (83)122.61 Total impact
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Article: Covalent assembly of silver nanoparticles on hydrogen-terminated silicon surface.
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ABSTRACT: Synthesis of ω-alkenyl-terminated silver nanoparticles (AgNPs) and then their immobilization on a hydrogen-terminated silicon surface in two-dimensional arrangement through covalent interaction are demonstrated. The thermal-induced hydrosilylation at mild conditions facilitate nanoparticles assembly through interaction between terminal alkenyl (CH(2)=CH-) groups of AgNPs and hydrogen-terminated silicon surface. The assembly of AgNPs on a silicon surface is characterized by FESEM and XPS. Adequate coating of 10-undecene-1-thiol (UDT) on AgNPs and mild temperature hydrosilylation impede the fusion or aggregation of nanoparticles, while they immobilized on a silicon surface, which is very crucial to preserve the discrete entities of nanoparticles. This elegant and facile approach provides stable monolayer of AgNPs with very good coverage area and promises potential to fabricate electronic devices and solar cells, where nanoparticles needs to be directly attached to the silicon surface without an interfacial oxide thin film.Journal of Colloid and Interface Science 06/2012; 382(1):22-7. · 3.07 Impact Factor -
Article: Site-selective assembly and reorganization of gold nanoparticles along aminosilane-covered nanolines prepared on indium-tin oxide.
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ABSTRACT: We have fabricated gold nanoparticle (AuNP) arrays on indium-tin oxide (ITO) substrates in a nearly one-dimensional fashion. AuNPs were site-selectively immobilized on ITO of which the surface had been patterned by a nanolithography process based on scanning probe microscopy. The fabricated nanoscale lines covered with aminosilane self-assembled monolayer served as chemisorption sites for citrate-stabilized AuNPs of 20 nm in diameter, accordingly, AuNP nanolines with a thickness of single nanoparticle diameter were spontaneously assembled on the lines. In this 1D array, the AuNPs were almost separated from each other due to the electrostatic repulsion between their negatively charged surface layers. Furthermore, a reorganization process of the immobilized AuNP arrays has been successfully demonstrated by replacing each AuNP's surface layer from citric acid to dodecanethiol. By this process, the AuNPs lost their electrostatic repulsion and became hydrophobic so as to be attracted to each other through hydrophobic interaction, resulting in reorganization of the AuNP array. By repeating the deposition and reorganization cycle, AuNPs were more densely packed. The optical absorption peak of the arrays due to their plasmonic resonance was found to shift from 526 to 590 nm in wavelength with repeating cycles, indicating that the resonance manner was changed from the single nanoparticle mode to the multiple particle mode with interparticle coupling.Langmuir 05/2012; 28(20):7579-84. · 4.19 Impact Factor -
Article: Molecular packing density of a self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane by a vapor phase process.
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ABSTRACT: The molecular density of an aminosilane self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPS) by a vapor phase method has been estimated to be about 3 AEAPS molecules per nm(2) based on chemical labeling, optical absorption spectroscopy and X-ray photoelectron spectroscopy.Chemical Communications 08/2011; 47(31):8841-3. · 6.17 Impact Factor -
Article: Formation of uniform ferrocenyl-terminated monolayer covalently bonded to Si using reaction of hydrogen-terminated Si(111) surface with vinylferrocene/n-decane solution by visible-light excitation.
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ABSTRACT: Electrochemically active self-assembled monolayers (SAM) have been successfully fabricated with atomic-scale uniformity on a silicon (Si)(111) surface by immobilizing vinylferrocene (VFC) molecules through Si-C covalent bonds. The reaction of VFC with the hydrogen-terminated Si (H-Si)(111) surface was photochemically promoted by irradiation of visible light on a H-Si(111) substrate immersed in n-decane solution of VFC. We found that aggregation and polymerization of VFC was avoided when n-decane was used as a solvent. Voltammetric quantification revealed that the surface density of ferrocenyl groups was 1.4×10(-10) mol cm(-2), i.e., 11% in substitution rate of Si-H bond. VFC-SAMs were then formed by the optimized preparation method on n-type and p-type Si wafers. VFC-SAM on n-type Si showed positive photo-responsivity, while VFC-SAM on p-type Si showed negative photo-responsivity.Journal of Colloid and Interface Science 06/2011; 361(1):259-69. · 3.07 Impact Factor -
Article: Preparation of Cu-Sn Layers on Polymer Substrate by Reduction-Diffusion Method Using Ionic Liquid Baths
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ABSTRACT: A novel metallization of non-conductive epoxy substrate with Cu-Sn “speculum alloy,” or “white bronze,” was performed through successive electrochemical processes: (i) conventional electroless deposition of pure Cu layer and (ii) subsequent electrochemical alloying of the resulting pure Cu layer with Sn using an ionic liquid bath at 150°C, a medium-low temperature. Availability of the Sn quasi-reference electrode for the alloying was verified, and the resulting compact and adhesive Cu-Sn layers, composed of Cu6Sn5 and/or Cu3Sn intermetallic phases, were examined as an alternative to nickel plating. The abundance of the two intermetallic phases was found to be dependent on the alloying potential and duration, and was discussed in terms of alloy formation thermodynamics of the Cu-Sn system.Journal of The Electrochemical Society. 05/2011; 158(6):D335-D341. -
Article: Alkyl and alkoxyl monolayers directly attached to silicon: chemical durability in aqueous solutions.
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ABSTRACT: For practical application of self-assembled monolayers (SAMs), knowledge of their chemical durability in acidic or basic solutions is important. In the present work, a series of SAMs directly immobilized on a silicon (111) surface through Si-C or Si-O-C covalent bonds without a native oxide layer were prepared by thermally activated chemical reactions of a hydrogen-terminated Si(111) substrate with linear molecules, i.e., 1-hexadecene, 1-hexadecanol, 1-dodecanol, and n-dodecanal, to investigate the durability of the SAMs to HF and Na2CO3 solutions. While grazing incidence X-ray reflectivity measurements showed that all the as-prepared SAMs had almost the same film density and molecular coverage, keeping the original step and terrace structure of Si(111) as is observed by atomic force microscopy, they gave different degradation behaviors, i.e., pitting and concomitant surface roughening in both solutions. 1-hexadecene SAM was stable against immersion in both solutions, while the other SAMs were damaged within 60 min, most likely due to the difference in chemical bonding modes at the SAM/Si interface, i.e., Si-C and Si-O-C.Langmuir 04/2009; 25(10):5516-25. · 4.19 Impact Factor -
Article: Room-temperature size evolution of thiol-protected gold nanoparticles assisted by proton acids and halogen anions.
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ABSTRACT: In the present work, a mild size-control method for thiol-protected Au NPs was developed. When thiol-protected Au NPs were reacted with tetra-n-octylammonium bromide and trifluoroacetic acid, the size of Au NPs was tuned in the range from 2 to 6 nm at room temperature. Larger Au NPs could be obtained by mild heating at 55 degrees C. This size evolution method assisted by proton acid and bromide anion is a first example of the size tuning of thiol-protected Au NPs at room temperature. Because of the mild reactivity of acid and bromide ions to organic molecules, various thiol derivatives sensitive to heat, base, and reducing agent can be utilized for this method.Journal of the American Chemical Society 02/2009; 131(5):1630-1. · 9.91 Impact Factor -
Article: Regulation of pattern dimension as a function of vacuum pressure: alkyl monolayer lithography.
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ABSTRACT: Photopatterning of a hexadecyl (HD) monolayer has been demonstrated using vacuum ultraviolet (VUV; lambda = 172 nm) light under controlled vacuum pressure with the objective of minimizing the pattern dimension. X-ray photoelectron spectroscopy (XPS) and lateral force microscopy (LFM) studies reveal that photodegradation of the HD monolayer not only is limited to the regions exposed to VUV but also spreads under the masked regions. The strong oxidants generated by VUV irradiation to atmospheric oxygen and water vapor diffuse toward the masked regions through the nanoscopic channels and photodissociate the monolayer under the masked area, near the photomask apertures, resulting in broadening of the photopattern. Such broadening decreases with decreased vacuum pressure inside the VUV chamber, associated with a decrease of oxidant concentration and reduction of their diffusion. Gold nanoparticles (AuNPs) were immobilized on the VUV patterned features to probe the dimension of the chemically active pattern. Field emission electron microscopy reveals the construction of 565 nm wide pattern features at a vacuum pressure of 10 Pa. This pattern widens to 1,030 nm at 10 (4) Pa using the same size apertures (500 nm) as printed on the photomask. This study provides insight for fabricating submicron patterns with high reproducibility and its exploitation for different applications, which includes the patterning of nanoparticles, biopolymers, and other nano-objects at submicron dimensions.Langmuir 10/2008; 24(20):12077-84. · 4.19 Impact Factor -
Article: Self-assembly of ionic liquid (BMI-PF6)-stabilized gold nanoparticles on a silicon surface: chemical and structural aspects.
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ABSTRACT: Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF(6)) ionic liquid. It was found that the BMI-PF(6) supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF(6)-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS-functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF(6). The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF(6) aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the MPS-functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.Langmuir 07/2008; 24(15):7785-92. · 4.19 Impact Factor -
Article: Structural organization of gold nanoparticles onto the ITO surface and its optical properties as a function of ensemble size.
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ABSTRACT: Self-assembly of citrate-stabilized gold nanoparticles (AuNPs) onto an optically transparent indium tin oxide (ITO) surface followed by neutralization of these particles using dodecanethiol as a surfactant have been demonstrated. X-ray photoelectron spectroscopic (XPS) studies revealed the partial removal of citrate ions from the immobilized AuNPs, which advances the dilution of electrostatic attraction between AuNPs and the APS (amino-terminated monolayer)-functionalized ITO surface. The resultant AuNPs restore their mobility to some extent and form small ensembles. Some of the immobilized AuNPs were completely removed from the surface due to neutralization, as confirmed by XPS studies. Interparticle distance and size of ensembles were manipulated by consecutive cycles of immobilization and neutralization of AuNPs. Controlled nanostructural fabrication progression, which leads to two-dimensional lateral growth of AuNPs, provides a method for systematically shifting the surface plasmon resonance band based on the increase in plasmon coupling among the closely placed AuNPs of an ensemble. The magnitude of shift increases with the size of ensemble. This manipulated chemical strategy offers a convenient and simple method to tune the optical properties of materials on a nanoscale.Langmuir 05/2008; 24(8):3787-93. · 4.19 Impact Factor -
Article: Thermal immobilization of ferrocene derivatives on (111) surface of n-type silicon: parallel between vinylferrocene and ferrocenecarboxaldehyde.
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ABSTRACT: Monolayers attached to a Si(111) surface through Si-C-C or Si-O-C covalent bonds were prepared by the thermally activated reaction (150 degrees C) of vinylferrocene (VFC) or ferrocenecarboxaldehyde (FCA) molecules with hydrogen-terminated Si(111) substrate in order to compare their reactivities. The resulting monolayers gave a couple of redox waves on voltammograms due to ferrocenyl moieties tethered at the surface. The voltammetric quantification revealed that the growth of electrochemically active layers was terminated within 5 h and the final surface coverages of the active ferrocenyl moieties were 58% and 16% for VFC- and FCA-based monolayers, respectively, indicating that the aldehyde molecule is less reactive. X-ray photoelectron spectroscopy and ellipsometry, however, gave an indication that the growth of the VFC layer did not self-terminate and proceeded beyond a monolayer, while this overgrown part of the layer was not electrochemically active.Langmuir 04/2007; 23(6):3193-8. · 4.19 Impact Factor -
Article: Photolithographic patterning of dendrimer monolayers and pattern-selective adsorption of linear macromolecules.
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ABSTRACT: Alkyl groups of n-octadecyltrimethoxysilane (ODS) in a self-assembled monolayer on a silicon substrate were oxidized to carboxyl groups by partial irradiation of vacuum ultra-violet light under the photomask, producing a COOH/ODS line pattern. After active esterification of carboxyl groups, two kinds of amine-terminated dendrimers, poly(propyleneimine) and poly(amido amine) (PAMAM) dendrimers, were immobilized on a COOH line through amide-bond so that photolithographic dendrimer/ODS pattern was finally fabricated. Preparation was certified by atomic force microscopy (AFM) and surface-enhanced infrared absorption spectroscopy at transmission mode. Adsorption of linear macromolecules was examined on PAMAM dendrimer/ODS pattern. After adsorption of poly-L-glutamic acid (PGA) at a pH below alpha-helix--random coil transition, rod-shape texture was observed only on the dendrimer line in an AFM image. This texture is an aggregate of alpha-helical PGA. Sodium hyaluronate and DNA were also adsorbed selectively on the dendrimer line, keeping the line profile, although characteristic textures were not observed.Journal of Nanoscience and Nanotechnology 12/2005; 5(11):1792-800. · 1.56 Impact Factor -
Article: Surface-potential reversibility of an amino-terminated self-assembled monolayer based on nanoprobe chemistry.
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ABSTRACT: Nanoprobe chemistry offers a promising approach for the construction of nanostructures consisting of organic molecules by employing the tip of a scanning probe microscope. In a previous report, we demonstrated that a nitroso-terminated surface on an organosilane self-assembled monolayer could be converted into an amino-terminated surface by applying such a nanoprobe electrochemical technique. This paper reports on surface-potential reversibility originating from a reversible chemical reaction between amino and nitroso groups. In addition, we demonstrate surface-potential memory based on this chemical reversibility. Amino-terminated SAMs were prepared from p-aminophenyl-trimethoxysilane through chemical vapor deposition. Surface potentials were acquired by Kelvin force microscopy. When scanning probe lithography was conducted with a gold tip at positive-bias voltages, the surface potential of the scanned area shifted dramatically in the negative direction. Scanning with negative-bias voltages led to positive shift in the surface potential of the scanned area. The surface potential could be recovered even after multiple scannings with positive and negative applied bias voltages. On the basis of this discovery, we also succeeded in demonstrating surface-potential memory via our nanoprobe electrochemical technique.The Journal of Physical Chemistry B 07/2005; 109(23):11602-5. · 3.70 Impact Factor -
Article: Organosilane self-assembled monolayers directly linked to the diamond surfaces
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ABSTRACT: An amino-terminated self-assembled monolayer (SAM) was prepared from p-aminophenyltrimethoxysilane ( H <sub>2</sub> N ( CH )<sub>6</sub> Si ( OCH <sub>3</sub>)<sub>3</sub>, APhS ) on diamond substrates irradiated by vacuum ultraviolet (VUV) light (wavelength: 172 nm ) through chemical vapor deposition. Furthermore, the APhS - SAM was irradiated by VUV light in air. After the VUV irradiation, only one layer of siloxane ( SiO <sub>x</sub>) was left as a result of the selective decomposition of organic compounds. APhS - SAM was reprepared on the SiO <sub>x</sub> surface. The evidence as to the respective processes was clearly obtained by x-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Based on the chemical bonding states analysis, APhS - SAMs were confirmed to be directly linked to the diamond substrates and SiO <sub>x</sub> layers with bonding types of Si – O – C and Si – O – Si , respectively. The compositions obtained by XPS measurement indicate that the thickness of the SiO <sub>x</sub> layer was increased gradually by repeating the APhS - SAM formations and VUV irradiations in this order. Finally, we are successful in controlling the nano-scale thickness of the SiO <sub>x</sub> layer, which is the interface between APhS - SAM s and diamond substrates.Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 10/2004; · 1.25 Impact Factor -
Article: Photodegradation micropatterning of adsorbed collagen by vacuum ultraviolet light.
Langmuir 06/2004; 20(10):4299-301. · 4.19 Impact Factor -
Article: Ultra-Water-Repellent Poly(ethylene terephthalate) Substrates
11/2003; -
Article: Gas Barrier Performance of Surface-Modified Silica Films with Grafted Organosilane Molecules
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ABSTRACT: Surface-modified polymeric substrates with excellent gas barrier performances have been fabricated by coating the substrates with a silica film by means of plasma-enhanced chemical vapor deposition (PECVD) and the subsequent deposition of an organosilane layer on the silica film by a low-temperature CVD method. The hydrophobic organosilane layer on the silica-deposited substrates prevented adsorption of oxygen and water molecules on the substrate surfaces. Consequently, oxygen and water vapor transmission rates were markedly decreased down to 60% as compared to the substrates without the hydrophobic layers. In particular, the fluoroalkylsilane-coated substrate showed a water vapor transmission rate of 0.32 g/(m2·day), which was drastically low compared with that of the alkylsilane-coated substrate.08/2003; -
Article: Oxide Nanoskin Formed on Poly(methyl methacrylate)
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ABSTRACT: A silicon oxide (SiOx) layer of molecular-scale thickness, which we have named an “oxide nanoskin”, has been successfully formed on a poly(methyl methacrylate) (PMMA) substrate through the vapor-phase chemisorption of organosilane and subsequent photooxidation using 172-nm vacuum ultraviolet (VUV) light. First, a hydrophilized PMMA sample was exposed to the vapor of a precursor, that is, tetraethoxysilane (TEOS). As was confirmed by water contact-angle measurements and X-ray photoelectron spectroscopy (XPS), chemisorption of the TEOS molecules was accomplished after 3 h of vapor treatment. Next, VUV irradiation was conducted for more than 10 min, and the chemisorbed TEOS molecules were photochemically converted to SiOx, as was evidenced by XPS. The resulting oxide layer was confirmed by transmission electron microscopy to be continuous with a thickness of 3 nm or less. As a control experiment, a SiOx layer was deposited by the same procedure on a Si substrate covered with a native oxide. As was determined by ellipsometry, the thickness of the oxide deposited on the substrate was found to be only about 0.45 nm, which was much smaller than that of the SiOx layer fabricated on the PMMA substrate. As a result of the formation of this oxide nanoskin layer, the charge density and surface acidity of the PMMA sample became almost equal to those of a native oxide-covered Si substrate. The PMMA surface covered with the oxide nanoskin layer showed excellent hydrophilicity even after being aged in air for 30 days.07/2003; -
Article: Photoreactivity of Alkylsilane Self-Assembled Monolayers on Silicon Surfaces and Its Application to Preparing Micropatterned Ternary Monolayers
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ABSTRACT: The photoreactivity of an n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) on a Si substrate was investigated under the irradiation of vacuum ultraviolet (VUV) light of 172 nm in wavelength. The results of water contact angle, film thickness, and X-ray photoelectron spectroscopy analysis showed that the ODS-SAM decomposed gradually due to the VUV light exposure. Oxidized products, that is, −COOH groups, had formed before the ODS-SAM was completely decomposed and removed from the substrate. Coplanar ternary organosilane SAM microstructures have been successfully fabricated by employing the reaction between −OCH3 functional groups with −COOH groups on the VUV-modified ODS-SAM.02/2003; -
Article: Imaging micropatterned organosilane self‐assembled monolayers on silicon by means of scanning electron microscopy and Kelvin probe force microscopy
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ABSTRACT: Field-emission scanning electron microscopy (FE-SEM) and surface potentiometry based on scanning probe microscopy, i.e. Kelvin probe force microscopy (KFM), have been applied to study microstructures consisting of organosilane self-assembled monolayers (SAMs) terminated with -CH3 or -CF3 groups. Onto cleaned Si substrates covered with a thin oxide layer of 2 nm thick, SAMs were formed by chemical vapour deposition using n-octadecyltrimethoxysilane (CH3(CH2)17Si(OCH3)3, ODS) or fluoroalkylsilane (CF3(CF2)7(CH2)2Si(OCH3)3, FAS) as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures composed of ODS, FAS or both were fabricated. Micropatterns of the SAMs on SiO2/Si substrates were clearly imaged by FE-SEM at an acceleration voltage of the electron beam below 1 kV, but image contrasts became faint with an increase in the acceleration voltage. At a voltage of 5 kV there was almost no detectable contrast. An FE-SEM image of the ODS–FAS microstructure acquired at an acceleration voltage of 0.8 kV clearly demonstrated that the region covered with ODS was brighter and thus, emitted secondary electrons more efficiently than the region covered with FAS. Furthermore, as indicated in a KFM image, the region covered with FAS had a surface potential ∼180 mV lower than that of the region covered with ODS. The origin of these image contrasts between ODS- and FAS-SAMs was the large difference in electronic states between ODS and FAS owing to the electron negativity of fluorine atoms. Copyright © 2003 John Wiley & Sons, Ltd.Surface and Interface Analysis 01/2003; 35(1):94 - 98. · 1.18 Impact Factor
Top co-authors
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Institutions
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2012
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Indian Institute of Petroleum (IIP)
Dehra Dūn, Uttarakhand, India
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2007–2012
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Kyoto University
- Department of Materials Science and Engineering
Kyoto, Kyoto-fu, Japan
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2000–2005
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Nagoya University
- • Graduate School of Science
- • Graduate School of Engineering
Nagoya-shi, Aichi-ken, Japan
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