Search

When in contact with charged solid surfaces, ionic liquids (ILs) are known to form solvation structures consisting of alternating cation and anion layers. This phenomenon is considered to originate from the adsorption layer of counterions overcompensating the surface charge, so-called overscreening. However, the response of these layers to surfaces with near-zero or extremely high surface charge density (σ) remains inadequately understood. Here, we probe the solvation structure of ILs on alkali halide surfaces with varied surface orientations: nearly zero-charged RbI(100) and highly charged RbI(111), by employing frequency modulation atomic force microscopy with atomic resolution. Two commonly used ILs are examined in this study: 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C3mpyr][NTf2]) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]). On RbI(100) surfaces with near zero σ, we observe alternating cation and anion layers, diverging from the previously proposed monolayer model for IL/alkali halide(100) interfaces. These results support the argument that overscreening occurs under low σ, even approaching zero, and reconcile conflicting experimental conclusions about low σ systems. On RbI(111) surfaces with high σ, we identify solvation structures consisting of two consecutive counterion layers. This structure aligns with the theoretically predicted crowding; a phenomenon rarely observed in commonly used ILs due to typically unreachable σ in electrochemical IL/electrode systems. Our findings indicate that alkali halide(111) surfaces are potentially valuable for exploring the crowding phenomenon in ILs, addressing the current scarcity of experimental observations.

Self-assembled monolayers (SAMs) can be used for surface functional control to assist with pattern collapse prevention and as a protective layer to enable Area Selective Deposition (ASD). To be successful, these applications require the formation of a high-density, defect-free, so-called well-packed SAM at the nm scale. In this paper, we describe a method to map the nm scale defects of octadecyltrichlorosilane (ODTS) SAMs using a post-etching AFM analysis of the surface of the substrate and used this technique to develop a process to form high-density, defect-free SAM layer at the nm scale. This was achieved by optimizing the water concentration in the solvent for the precursor solution and annealing after SAM formation.

Atomic force microscopy (AFM) is a powerful technique to characterize solid/liquid interfacial structures on an atomic scale. However, conventional AFM using Si cantilevers can only be applied to optically transparent liquids. In this study, we applied a quartz tuning fork sensor to overcome this issue and succeeded in AFM imaging of the interfacial structures between molten Ga and solid Au–Ga alloys. The crystal structure of the alloy was identified as AuGa2from the atomic-resolution imaging results, and the AuGa2(111) surfaces were also found to be exposed. In situobservation of the alloy crystal growth was carried out, and its growth mode was discussed. We also found that the interfacial solvation structure of molten Ga can be visualized, which corresponded well to the atomic arrangement of the solid AuGa2. Since the molten- and solid-metal interfaces play crucial roles in many metallurgy applications, such as plating, soldering, and brazing, it is of great importance for both scientific and practical purposes to characterize these interfaces at the atomic scale. This study demonstrates the potential of AFM as a new analytical technique of molten- and solid-metal interfaces.

In this report, micropatterns of (3-aminopropyl)trimethoxysilane (APTMS) were developed on hydrophilic and hydrophobic surfaces after patterning using 172 nm vacuum ultraviolet (VUV) photolithography. Self-assembled monolayers (SAMs) formed on Si substrates through UV hydrosilylation of 1-hexadecene (HD) and 10-undecenoic acid (UDA) were used as hydrophilic and hydrophobic surfaces, respectively. For templating the HD- and UDA-SAMs, the VUV light was exposed to HD- and UDA-SAMs from the slits of photomasks in atmospheric and evacuated environments, respectively. Various oxygenated groups were generated at the exposed domains of HD-SAM, while the COOH groups were trimmed from the irradiated domains of UDA-SAM. The APTMS molecules were immobilized on the domains that were terminated by oxygenated groups after chemical vapor deposition (CVD). The thicknesses of the developed APTMS micropatterns increased significantly by raising the CVD temperature and in the presence of ambient air in the CVD Teflon container as well. The increase in thicknesses was ascribed to the formation of APTMS multilayers, which were mediated by H3N+ions. Also, the developed APTMS micropatterns on the UDA-SAM patterned by VUV light irradiation in a high-vacuum environment (HV-VUV) were thicker than those on the VUV/(O) patterned HD-SAM due to the presence of inactive oxygenated groups at the surface of VUV/(O)-terminated domains of HD-SAM such as COO–C and C–O–C groups. The presence of water or ambient air facilitated the silane coupling between the silyl groups with the oxygenated and amino groups The combination of VUV photolithography and the CVD method with control of the conditions would enable us to control the thicknesses and shapes of the developed APTMS micropatterns. These findings illustrate the applicability of VUV photolithography for templating hydrophobic and hydrophobic surfaces toward the development of organosilane architectures, which can be feasible for several applications.

Ionic liquids (ILs) have been intensively studied as new electrolytes for lithium-ion batteries (LIBs). Structural analysis of interfaces between an IL-based electrolyte and an LIB electrode would provide beneficial information for improving LIBs. In this study, we investigated the interfacial structures between an IL, 1-methyl-1-propyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide, and a H-terminated Si(111) electrode in the presence and absence of Li salt by frequency modulation atomic force microscopy utilizing a quartz tuning fork sensor. Two-dimensional frequency shift mapping imaging of the solvation structure at the interface showed that the layered solvation structure was only observed in the absence of Li salts in the ILs, which was in good agreement with our previous studies performed on IL/lithium titanate interfaces. Combined with electrochemical measurements, the partial disappearance of the layered solvation structure in the Li salt-doped IL was strongly suggested to be due to the Li-ion insertion/extraction at the IL/Si interface.

Assisted chemical etching using non-noble metal catalysts is attracting new attention for the fabrication of semiconductor micro/nanostructures. Here, we perform silicon etching in a vapor phase using molybdenum disulfide (MoS2) flakes exfoliated from a natural bulk crystal. The edge plane of MoS2works as a catalytic active site, while its basal plane is inert. This unique feature distinguishes MoS2from other catalysts used in assisted chemical etching. Therefore, MoS2can be a promising candidate for elucidating the mechanism behind assisted chemical etching using non-noble metal catalysts. When the MoS2-loaded silicon substrate is exposed to an HF/H2O vapor, the whole silicon substrate under the MoS2flakes is selectively etched, forming etched hollows despite the presence of the catalytic active sites located only at the edge. This vapor-phase etching using MoS2flakes is expected to stimulate new fundamental research on chemical etching assisted by other non-noble metal materials.

Microcontact printing (μCP) techniques have sparked a surge of interests in microfabrication since they help produce arrays on a wide range of target substrates in a facile and efficient manner. Polydimethylsiloxane (PDMS), as a well-established material for stamps, has constraints resulting from its hydrophobicity and softness, and the replication of PDMS stamps usually requires rigid masters or processes using a photoresist. Herein, a novel μCP stamp based on cyclo-olefin polymer (COP) is produced through vacuum ultraviolet (VUV) lithography. 2,4,6,8-Tetramethylcyclotetrasiloxane is selectively deposited at the affinity-patterns on the COP surface, and these patterned siloxane films are converted into SiOxmeanwhile protecting the COP beneath them from the VUV photoetching. By this means, a patterned relief is fabricated on the COP plates, resulting in a hydrophilic SiOx/COP μCP stamp with punch heights of ∼180 nm. The novelty arises from the simplicity of the master- and photoresist-free microstructuring, and the higher stiffness of SiOx/COP stamps prevents the deformation during pressing. Finally, an example μCP is given to transfer titania precursor gel and produce TiO2micropatterns on flexible polymer substrates. The SiOx/COP stamps and the μCP of TiO2provide simple and cost-effective patterning techniques, which should contribute to the future design and creation of flexible devices.

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS2nanosheets comprising 4–10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on MoS2nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS2surface are coupled with the electron-rich nitrogen center of ODA and yield ODA-functionalized MoS2(MoS2–ODA). The MoS2–ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL–1) to mineral oil. It is shown that even at low concentration, MoS2–ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS2-based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.

The interfacial structures and mechanical response of the highly viscous poly(dimethylsiloxane) (PDMS, 9750 mPa s, Mn∼ 59,000) on solid surfaces were investigated by frequency-modulation atomic force microscopy using a quartz tuning fork sensor. A layered density distribution on a PDMS/mica interface was visualized on a sample that has set for 29 h by two-dimensional frequency shift (Δf) mapping, and the result exhibited that the layered structure was metastable. It was also found that the damping coefficient of tip vibration (Δγ) increased in the region of ∼1 nm from the solid surface, which suggests the limited mobility of the liquid molecules closest to the solids. After settling for more extended time or heating the sample, the layered density distribution was suppressed, and the conservative repulsive force near the solid surface in 2–3 nm was observed over longer distances by settling for a more extended time or heating. The suppression of the layered density distribution showed a similar temperature dependence with the bulk viscoelastic relaxation. In contrast, the elongation of conservative repulsive force near the solid surface showed steeper temperature dependence than that of the bulk, which suggests that it was rate-limited by the attraction between the solid surface and the closest liquid molecules.

Aerogels have attracted great interest for their unique properties, but their mechanical brittleness and poor functionality highly limit their practical applications. Herein, we report unprecedented superelastic multifunctional aminosilane-crosslinked reduced graphene oxide (AC–rGO) aerogels that are prepared via a facile and scalable strategy involving simultaneous crosslinking and reducing of graphene oxide nanosheets with different kinds of aminosilanes via C–N coupling and hydrolytic polycondensation reactions. It is found that 3-aminopropyl(diethoxy)methylsilane (APDEMS) is the better choice to enhance hydrophobicity, elasticity, and other properties of the resulting aerogels compared with (3-aminopropyl)triethoxysilane. One APDEMS molecule plays three roles as a crosslinker, a reductant, and a hydrophobizing agent. An outstanding combination of high surface area, ultralow density, superhydrophobicity, supercompressibility, superelasticity, low thermal conductivity, ultrahigh absorption capacity for organic liquids, efficient three-component separation, and strain/pressure sensing has been achieved in a single APDEMS-crosslinked rGO aerogel for the first time. In addition, a flexible, highly sensitive, and moisture-resistant AC–rGO aerogel-based strain/pressure-sensing array for the effective detection of strain (0–80%)/pressure (10 Pa to 10 kPa) distributions and object shapes has been demonstrated.

In this work, graphene oxide (GO) monolayers were immobilized on a hydrogen terminated silicon (H-Si) substrate by applying 4-vinylaniline (VAn) molecules as the intermediate linkers. Surface property measurements confirmed the formation of VAn layers on the substrate and the packing density of molecules increased with the reaction time. Atomic force microscopy (AFM) images showed that GO sheets were deposited on the modified surface with coverage of more than 90%.VAn SAMs were first photochemically assembled onto a H-Si substrate by visible light irradiation. GO sheets were then coupled onto the synthesized substrate via interaction between GO and the aniline group of VAn molecule.

This work describes the UV alkoxylation of a series of 1,2-epoxyalkanes on the hydrogen-terminated silicon (H–Si) substrate. The formation of alkoxy self-assembled monolayers (SAMs) and the nature of bonding at the surface of H–Si were examined using water contact angle goniometer, spectroscopic ellipsometer, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy. UV exposure to 1,2-epoxyalkane mesitylene solution for 60 min formed alkoxy-SAMs onto H–Si with hydrophobic properties. The local molecular environment of the alkyl chains transitioned from a disordered, liquid-like state to an ordered, crystalline-like structure with increasing the chain length. XPS and FTIR indicated that the reaction of H–Si with 1,2-epoxyalkane produced Si–O–C linkages. The Si–H bond homolysis and electron/hole were the plausible mechanistic routes for the grafting of 1,2-epoxyalkanes.

Chemical etching of semiconductor surfaces assisted by various types of carbon-based materials is drawing much attention for the fabrication of those micro-nano structures. We herein demonstrated to apply graphene oxide (GO), a 2D nano-carbon material, as a catalyst for the InP etching reaction, and a possible mechanism of GO-assisted InP etching was suggested by combining XPS analyses. The solubility of the InP oxide layer towards the etching solution affected the rate-determining step of InP etching reaction. When the oxidant reduction reaction catalyzed by GO was the rate-determining step, the etching reaction under GO was enhanced. Furthermore, the etching behavior was different in utilizing different oxidants, which means that the catalytic activity of GO for the oxidant reduction also affects the etching behavior.

Spinel-type lithium titanate (Li4Ti5O12(LTO)) is known as a negative electrode material for lithium-ion batteries (LIBs). In this study, the surface structure of the LTO(111) electrode in an ionic liquid (IL) electrolyte was investigated by electrochemical atomic force microscopy (EC-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, so-called the qPlus sensor, was used as an AFM force sensor instead of a Si cantilever, and the AFM equipment was embedded in a vacuum chamber to decrease the water concentration included in the IL electrolyte. The in situ analysis of the surface structure before and after the insertion of Li ions into the LTO electrode revealed that the atomic steps on the LTO(111) surface were kept even after the insertion of Li ions. We also succeeded in atomic-resolution topographic imaging on the LTO(111) electrode before and after Li-ion insertion. The hexagonally arranged bright spots with a period of ∼0.3 nm were clearly imaged after Li-ion insertion, which corresponded well to the structure of the ion arrangement of the Li7Ti5O12(111) surface. Namely, after Li-ion insertion, it was revealed that the LTO electrode changed its crystal structure from spinel-type Li4Ti5O12to rocksalt-type Li7Ti5O12while maintaining the surface structure with atomic steps.

Microprocessing of graphene oxide (GO) films is of fundamental importance in fabricating graphene-based devices. We demonstrate the photoetching of GO sheets using vacuum-ultraviolet (VUV, λ = 172 nm) light under controlled atmospheric pressure. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and differential interference contrast microscopy (DIC) studies revealed that the photoetching of GO films successfully proceeded in the regions exposed to VUV irradiation in the oxygen-containing atmosphere. Precise photoetching of the GO sheets was achieved at a vacuum pressure of 5 × 103Pa with VUV light irradiation for 20 min. This was followed by VUV irradiation in a high vacuum (<10–3Pa) and sonication in water. The photoetched GO sheets then transformed into reduced GO (rGO) patterns. The minimum feature fabricated by this method was 2 μm wide lines aligned at an interval of 4 μm. This method provides a cost-effective way to fabricate rGO patterns with fewer boundaries between rGO sheets and offers a better integrity of rGO, which can be promising for further applications in micro mechanics, micro electrochemistry, optoelectronics, etc.

Surfaces of cyclo-olefin polymers (COPs) are photoactivated by vacuum ultraviolet (VUV) light and can be bonded with a practical bonding strength at low temperatures below Tg. The VUV irradiation condition was optimized, the maximum interfacial toughness was obtained for 5?min of irradiation and a longer irradiation time resulted in a decrease in toughness. We also found that a high-humidity environment caused the decrease in toughness. We investigated the mechanism of the low-temperature bonding of COP by characterizing the fracture surfaces using high-resolution scanning electron microscopy and imaging the bonded interfaces using energy-filtering transmission electron microscopy and scanning transmission electron microscopy. The fracture surfaces exhibited a large number of nanofibrils, whose features are similar to those we previously observed in the polymer–polymer interfaces that were welded in melt conditions. We conclude that the interfacial failure occurs where the polymer chains connected at the interface by hydrogen bonding are pulled out. Thus, the entanglement is important in the bonding of polymers by surface-activation processes.

Electrochemical exfoliation of graphite is a method for synthesizing graphene oxide (GO) with fewer structural defects than GO synthesized by conventional chemical oxidation. Photoreduction of GO has been focused on due to their facile procedures, and environmental friendliness. In this report, electrochemically-exfoliated graphene oxide (EGO) was irradiated by vacuum ultraviolet (VUV) light at 140 °C under a high vacuum environment, named thermal-assisted VUV light treatment. Conductive atomic force microscopy was used to investigate the electrical characteristics of individual sheets on the nanometer scale. The electrical conductivity of the treated sheet (1.4 × 105 S m-1) was higher than the pristine EGO by an order of magnitude. The chemical and structural analysis showed that the EGO was reduced and their p-conjugated domains were restored through a hybrid of photochemical and thermal treatment. These results indicate that our hybrid approach has the potential for reducing the EGO.

Ionic liquid (IL)/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as catalysis, corrosion, electrochemistry, and lubrication. Hence, understanding the effect of substrate surface nature on the interfacial properties has a significant impact on improving technological processes in which interfacial properties are dominant. In this work, we investigated interfacial structures between 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) IL and KBr crystal surfaces by frequency modulation atomic force microscopy utilizing a quartz tuning fork sensor. KBr(100) and (111) surfaces were used as the substrates, where the (100) surface is electrically neutral, and the (111) surface is highly charged. We investigated the influence of surface charge on their surface structures and interfacial solvation structures by atomic-scale topographic imaging and frequency shift versus distance curve measurement. The behavior of IL at these two interfaces was found to be significantly different due to these different surface properties.

Ionic liquids (ILs) form layered solvation structures at IL/electrode interfaces relevant to many electrochemical applications. Recently, we observed a partially disturbed solvation structure at the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI)/spinel lithium titanate oxide (Li4Ti5O12, LTO) electrode interface containing Li-salt and considered the Li+-ion transfer occurring at the interface as one plausible reason for this partial destruction. In this study, we investigated EMI-TFSI/LTO(111) interfaces with the addition of K-salt or Mg-salt by frequency modulation atomic force microscopy utilizing a quartz tuning fork. It is assumed that no ion-transfer occurs at these two interfaces. The laterally consecutive solvation structures were observed at both interfaces, which strongly supported our hypothesis. Additionally, a kink in the solvation structure was observed at the interface containing Mg-salt. These results offer a comprehensive understanding of the perplexing IL/electrode interfaces with an addition of metal salt.

The surface potentials and local conductivity of self-assembled monolayers (SAMs) formed using aromatic molecules covalently bonded to n-type silicon (111) via Si–C and Si–O bonds were measured using Kelvin probe force microscopy (KPFM) and conductive AFM (CAFM). Surface potential measurements were done using micropatterned SAMs with hexadecyl SAM as a reference to eliminate surface potential variations due to the cantilever tips. Micropatterning was conducted via vacuum ultraviolet photolithography at ?= 172 nm. Ellipsometry, X-ray photoelectron spectroscopy, static water contact angle and atomic force microscopy tests show that the aromatic SAMs were well-organized despite the short molecular lengths of the precursors. KPFM results show that Si–C bonded SAMs have higher surface potentials compared to Si–O SAMs, which is in agreement with dipole moments estimated by Molecular Orbital Package semi-empirical computations. CAFM scans showed conductive domains for the aromatic SAM regions, and Si–O SAMs exhibited a higher current than Si–C SAMs.

Water-in-salt (WiS), which contains salt with a high salt concentration (>5 mol kg-1), is attractive for novel electrolytes in electrochemical applications such as lithium-ion batteries and electrochemical deposition because of its high electrochemical stability. Structural analysis on the WiS/solid interfaces would be beneficial for understanding these processes. In this study, we investigated interfacial solvation structures of WiSs by frequency modulation atomic force microscopy utilizing a quartz tuning fork sensor. Two types of WiSs, a lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)-WiS and a LiCl-WiS, were prepared. We found that the interfacial solvation structures of the WiSs on mica surfaces were quite different by using a 2D frequency shift mapping technique. We discussed the differences in their interfacial solvation structures by comparing their bulk solution properties measured by Raman spectroscopy.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.

Structural analysis of interfaces between ionic liquid (IL) and alkali-halide (100) surface was demonstrated by frequency modulation atomic force microscopy (FM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, the so-called qPlus sensor, was used as a force sensor. Atomic-resolution topographic imaging on a KCl(100) surface was successfully achieved in a viscous IL. The square lattice structure with a period of ∼0.4 nm was clearly imaged, which indicated that only K+or Cl–ions were imaged. An abrupt shift of the tip position occurred during the topographic imaging, suggestting that the dissolution of KCl atomic layers was detected by the FM-AFM. In addition, two-dimensional force mapping was carried out, and the presence of the KCl-based layered structure on the interface was recognized.

Vinylferrocene-terminated Si(111) was prepared by illuminating visible light onto a hydrogen-terminated Si(111) surface that was immersed in either diethyl ether-vinylferrocene or dibutyl ether-vinylferrocene solution. The use of either diethyl ether or dibutyl ether as grafting medium yielded a neutral ferrocenyl monolayer that was electrically connected with the silicon substrate. Both preparation media produce samples that have good electrochemical characteristics e.g., low peak potential separation and linear plot of peak current density with scan rate. The use of dibutyl ether as grafting solution resulted to a fast grafting rate, in which the optimum grafting time for samples with n-type and p-type substrates were 0.5 h and 1 h, respectively. Meanwhile, the use of diethyl ether resulted to the presence of lumps of deposited materials on the grafted surface. Nevertheless, even if these materials may be considered as impurities, these did not distort significantly the electrochemical characteristics of the sample.

Solvation structures on liquid/solid interfaces are essential for understanding the mechanisms of various electrochemical reactions. Here, we demonstrate structural analysis on interfaces of ionic liquids (ILs) and electrodes by frequency modulation atomic force microscopy (FM-AFM). A quartz-based force sensor was used instead of a Si cantilever in order to achieve highly-stable and highly-sensitive measurement in ILs. Two-dimensional (2D) force mapping was performed with control of the electrode potential. The potential-dependent solvation structures on the interface were investigated and structural change of the solvation layers was successfully imaged.

Ordered and high-density AuNP structures were successfully immobilized on Si(111) substrates via a photochemical reaction, using the immersion method and the LB method, respectively. Because of partial oxidation of the substrate, island-like structures were formed using the immersion method. While that in the LB method, because AuNPs were immobilized in nitrogen atmosphere and not in liquid solution, oxidation was minimized thus a more compact structure was obtained. Furthermore, the plasmonic properties of the AuNP structure were found to be tunable by controlling the particle density and the interparticle distance.

It is essential to immobilize gold nanoparticles (AuNPs) firmly onto a certain substrate in a closely packed manner to apply plasmonic functions of AuNP in photonic/electronic devices. AuNP-Si systems are of particular interest for the integration of plasmonics to semiconductor electronics. Here we report on the arrangement of AuNPs into a 2-D array that was covalently bonded to a Si substrate without surface oxide. This process was achieved by simply irradiating visible light to a hydogen-terminated Si substrate immersed in a solution of AuNPs covered with a self-assembled monolayer (SAM) of 11-mercaptoundecene (MUD). These MUD-AuNPs were attached to the substrate by forming Si–C bonds as a result of the photochemical reaction between Si–H groups on the substrate and vinyl groups of the MUD-SAMs. The reaction proceeded most effectively at a wavelength band around 520 nm adjusted to the plasmonic resonance peak of the MUD-AuNPs(20 nm in diameter)/toluene solution centered at 535 nm, demonstrating that the photochemical reaction was assisted by localized surface plasmon, which allowed the AuNPs to be photon collectors.

Cu-Zn alloy formation on a non-conductive epoxy substrate was demonstrated through successive electrochemical processes: (i) conventional electroless Cu deposition on the substrate using an aqueous bath, and (ii) electrochemical alloying of the resulting Cu layer with Zn using a reduction-diffusion (RD) method in a Zn2+-containing ionic liquid bath at 150degC. The obtained Cu-Zn alloy layers were adhesive and were uniformly grown with maintaining the surface morphology of the initial electroless Cu. The Cu-Zn phases, i.e. g-Cu5Zn8, b'-CuZn, and/or a-Cu(Zn), which define the color of the layers were dependent on applied potential during the RD alloying. Thermodynamics of the alloy formation was also discussed.

Anodic dissolution of elemental Mg was examined in an ionic liquid, trimethyl-n-hexylammonium bis[(trifluoromethyl)-sulfonyl]amide (TMHA-Tf2N), containing a simple salt, Mg(Tf2N)2, having a common anion. faradaic anodic dissolution was markedly stimulated in the presence of water dissolved within its solubility limit. The dissolution current efficiency for elemental Mg was found to be almost 100% without decreasing the water content, indicating that spontaneous reaction of Mg with water was limited and water molecules play a catalytic role in the overall dissolution mechanism, where a magnesium(II) oxide/hydroxide is involved. The Mg2+/Mg0 redox potentials, or onset potentials for Mg dissolution, vs. Li+/Li0 redox with and without water were also estimated from a set of sampled-current voltammograms obtained by a potential-step method.

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 150degC, 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.

Anodic dissolution behavior of magnesium (Mg) metal was examined in an ionic liquid bath containing Mg(II) ions as Mg(Tf2N)2. A set of sampled-current voltammograms obtained by a potential-step method revealed that the Mg2+/Mg0 redox potential in the ionic liquid was +1.41 V vs. Li+/Li0, and was little affected by residual water in the ionic liquid. It was found, in contrast, that the residual water increased faradaic current density for the anodic dissolution of Mg and also the apparent exchange current density of the Mg2+/Mg0 redox.

Cu-Zn alloy metallization of a non-conductive epoxy substrate was demonstrated through successive electrochemical processes: (i) conventional electroless Cu deposition on the substrate using an aqueous bath, and (ii) electrochemical alloying of the resulting Cu layer with Zn by a reduction-diffusion (RD) method using an ionic liquid bath at 150 {degree sign}C. The resulting Cu-Zn alloy layers were adhe-sive and were uniformly grown by maintaining the surface mor-phology of the initial electroless Cu. The Cu-Zn phases, i.e. g-Cu5Zn8, b'-CuZn, and/or a-Cu(Zn), which define the color of the layers were dependent on applied potential during the RD alloying.

We have immobilized 1,2-epoxydodecane (EDD) on hydrogen-terminated silicon (H-Si) substrates by UV photochemical grafting. The surface properties of the fabricated samples showed the formation of highly dense alkoxy monolayers resulting from the reaction between the H-Si and the epoxide moieties of the EDD molecules.

The redox behavior of the binary self-assembled monolayers (SAMs) of 11-ferrocenyl-1-undecanethiol and 1-undecanthiol on gold substrate was investigated in an ionic liquid (IL), trimethyl-n-hexylammonium bis[(trifluoromethyl)sulfonyl]amide (TMHA-Tf2N) and HClO4 aqueous solution. It was found that the total amount of charge for the redox of ferrocenyl groups in the ionic liquid is about 70% of that in the HClO4 solution, indicating that less number of ferrocenyl groups are involved in the redox in the ionic liquid. A set of impedance measurements indicated that the electron transfer rate between the SAMs and the substrate is lower in the ionic liquid than that in aqueous solution, suggesting a slow and incomplete reconstruction of TMHA-Tf2N ions at the SAMs/ionic liquid surface.

Cu-Sn alloy metallization of a non-conductive epoxy substrate was demonstrated through successive electrochemical processes: (i) conventional electroless Cu deposition on the substrate and (ii) electrochemical alloying of the resulting Cu layer with Sn through a reduction-diffusion method using an ionic liquid bath at 150 aC. The resultant Cu-Sn alloy layer, composed of Cu6Sn5 and/or Cu3Sn intermetallic phases, was compact, smooth, and adhesive. Dependence of the intermetallic phases on applied potential and alloying time was also examined to discuss the alloy formation mechanism, demonstrating that Cu-Sn alloy layers composed of desired phases could easily be prepared by controlling these parameters.

Hexagonal nanoholes, in which an array of Au nanoparticles was located, were successfully fabricated on the basis of scanning probe anodization lithography. The lithography has been conducted to draw nanopatterns on a hexadecyl self-assembled monolayer covalently bonded to a Si substrate through Si−C bonds. Using a conductive atomic force microscope (AFM) probe as a point contact electrode, current was locally injected into the monolayer-Si sample. The monolayer was decomposed on the location where current injected. Subsequently, at this point, the substrate Si was anodized resulting in the formation of an oxide nanodot. Next, the oxide nanodot was selectively etched with HF in order to make a nanohole while the surrounding monolayer remaining unetched. As a result, a nanohole was formed at the current injected point. Employing the remained monolayer as an etch mask, the nanohole was further etched with NH4F in order to prepare a well-defined hydrogen-terminated surface in the nanohole. The nanohole became hexagonal due to the anisotropic nature of Si etching with NH4F. The lateral size of the fabricated nanohexagonal holes were in the range of 180 ∼ 320 nm. Finally, electroless plating was applied to the sample. Au nanoparticles were selectively nucleated on the surface of the nanohole’s bottom and walls. The particles with a diameter less than 10 nm were well-separated each other with a nucleation density of 150,000 μm−2. The NH4F etching was successful in order to control the nucleation manner for the fabrication of the Au nanoparticle array.

Gold nanoparticles (AuNPs) reveal fascinating electronic and optical properties, when they organize into one-dimensional architectures. Here, we developed a simple approach to immobilize the AuNPs in a well-aligned one-dimensional arrangement on a silicon surface. A conformationally ordered hexadecyl (HD) monolayer attached to a silicon substrate through Si−C covalent linkage was used as a chemical template to construct the nanopattern in a linear fashion by intermittent-contact mode scanning probe anodization. A positive bias voltage was applied to the silicon substrate at 10% relative humidity and constructs the highly reproducible <30 nm wide SiO 2pattern. The site selective assembly of the amino terminated monolayer on the SiO 2pattern guided the anchoring of citrate stabilized AuNPs in linear arrangements with controlled interparticle distance, as determined by electrostatic interactions, whereas the HD-covered surface remained unexposed to the AuNPs.

Electrochemical alloying of Cu substrates with Sn through a reduction-diffusion method was investigated using an ionic liquid, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide, as a solvent for an electrolytic bath. The use of the ionic liquid made it possible to raise the processing temperature up to 190 aC and form silver-gray Cu-Sn "speculum metal" layers faster than with an aliphatic quaternary ammonium-based ionic liquid, trimethyl-n-hexylammonium bis[(trifluoromethyl)sulfonyl]amide. The layers obtained at 170-190 aC showed clear composition gradients where the outer and inner parts of the Cu-Sn layer have compositions corresponding to Cu6Sn5 and Cu3Sn phases, respectively.

Electrochemical alloying of Cu substrate through a reduction-diffusion method was investigated using ionic liquid, trimethyl-n-hexylammonium bis[(trifluoromethyl)sulfonyl]amide, as a solvent for an electrolytic bath. The use of the ionic liquid rendered it possible to raise the processing temperature beyond 100 aC so as to form the Cu-Sn layers faster than in the case of an aqueous media. The layers obtained from Cu thin layer under potentiostatic condition were silver-gray speculum metal composed of Cu6Sn5, Cu3Sn, and Cu10Sn3 intermetallic phases, while those prepared under galvanic contact condition involved a b-Sn phase containing a trace amount of copper. The formation of each Cu-Sn phase was discussed in terms of thermodynamics of alloy formation.

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 ‐CH3or ‐CF3groups. 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.

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.

The decomposition mechanism of p-chloromethylphenyltrimethoxysiloxane (CMPS) self-assembled monolayers (SAMs) due to vacuum ultraviolet (VUV) irradiation at a wavelength of 172 nm has been studied based on water repellency, X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM). The CMPS-SAMs were prepared through chemical vapor deposition at 100 °C. The water contact angle increased dramatically within the first 30 min, reaching a plateau at this point. The saturated water contact angle was 76°. Next, the CMPS-SAMs were irradiated at under 10 Pa from 0 to 30 min. The CMPS-SAMs irradiated for 15 and 30 min were covered with carboxylated hydrocarbon fragments and silanol groups, respectively. KPFM measurements for micro-patterned SAMs, i.e. CMPS/CO₂H and CMPS/SiOH, showed that the surface potential of the carboxylated and silanol regions were −16 and +19 mV vs. CMPS-SAM, respectively. The former negative surface potential difference originated in the electronegativity of the CO₂H fragments. These results provide us with a route to prepare an organic template for various fields such as bio-sensors, chemical sensors and electrolytes.

Self‐assembly of organosilane molecules at the vapour/solid interface under atmospheric pressure conditions was explored in order to form a monolayer on oxide‐covered silicon substrates. Three types of precursors were employed: n‐octadecyltrimethoxysilane (ODS: H3C(CH2)17Si(OCH3)3), n‐(6‐aminohexyl)aminopropyltrimethoxysilane (AHAPS: H2N(CH2)6NH(CH2)3Si(OCH3)3) and fluoroalkylsilane (FAS: heptadecafluoro‐1,1,2,2‐tetrahydro‐decyl‐1‐trimethoxysilane, F3C(CF2)7(CH2)2Si(OCH3)3). Characteristics of these self‐assembled monolayers (SAMs) formed at a temperature of 100–150°C were studied based on ellipsometry and x‐ray photoelectron spectroscopy. Chemical properties of the monolayers were characterized further by water contact angle and ζ‐potential measurements. The SAMs formed from ODS and FAS were hydrophobic so as to show water contact angles of >100°, whereas that of the SAM formed from AHAPS was ∼60°. ζ‐potentials and isoelectric points (IEPs) of SiO2substrates covered with each of the SAMs were measured and compared with a naked SiO2substrate. The IEPs of the SiO2substrate covered with the ODS‐ or FAS‐SAM was pH 3.5–4.0, which was almost the same as those of polyethylene and polytetrafluoroethylene plates, whereas that of the naked SiO2substrate was pH ∼2.0, as predicted from results on silica particles. In the case of the AHAPS‐SAM, its surface was positively charged under acidic conditions due to protonation of surface amino groups. Consequently, the AHAPS‐SAM‐covered substrate showed an IEP of pH 7.5–8.0. Copyright © 2002 John Wiley & Sons, Ltd.

Self-assembly of organosilane molecules at the vapour/solid interface under atmospheric pressure conditions was explored in order to form a monolayer on oxide-covered silicon substrates. Three types of precursors were employed: n-octadecyltrimethoxysilane (ODS: H3C(CH2)17Si(OCH3)3), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS: H2N(CH2)6NH(CH2)3Si(OCH3)3) and fluoroalkylsilane (FAS: heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane, F3C(CF2)7(CH2)2Si(OCH3)3). Characteristics of these self-assembled monolayers (SAMs) formed at a temperature of 100–150°C were studied based on ellipsometry and x-ray photoelectron spectroscopy. Chemical properties of the monolayers were characterized further by water contact angle and ζ-potential measurements. The SAMs formed from ODS and FAS were hydrophobic so as to show water contact angles of >100°, whereas that of the SAM formed from AHAPS was ~60°. ζ-potentials and isoelectric points (IEPs) of SiO2 substrates covered with each of the SAMs were measured and compared with a naked SiO2 substrate. The IEPs of the SiO2 substrate covered with the ODS- or FAS-SAM was pH 3.5–4.0, which was almost the same as those of polyethylene and polytetrafluoroethylene plates, whereas that of the naked SiO2 substrate was pH ~2.0, as predicted from results on silica particles. In the case of the AHAPS-SAM, its surface was positively charged under acidic conditions due to protonation of surface amino groups. Consequently, the AHAPS-SAM-covered substrate showed an IEP of pH 7.5–8.0. Copyright © 2002 John Wiley & Sons, Ltd.

Molecular-resolution imaging on an alkanethiol self-assembled monolayer (SAM) in an ionic liquid (IL) was demonstrated using frequency modulation atomic force microscopy (FM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, the so-called qPlus sensor, was used as a force sensor. Etch pits, which are a typical structure of alkanethiol SAMs, individual alkanethiol molecules, and single molecular defects were clearly imaged; that is, true molecular-resolution imaging was successfully achieved. We also carried out force curve measurement using the FM-AFM and the presence of a solvation layer on the IL/SAM interface was recognized.

Platinum (Pt) micropatterns were fabricated photocatalytically on titanium oxide (TiO2) surface by projecting a reduced light image of a photomask. Negative and positive Pt patterns on TiO2with the spatial resolution better than 10 µm were obtained by photoreduction of PtCl42-to Pt in aqueous K2PtCl4solution and photoetching of the deposited Pt in aqueous HCl solution, respectively.

The photoconductivity of native oxide on titanium (Ti) was studied by scanning tunneling microscopy and spectroscopy (STM and STS). The enhanced tunneling current was observed when the oxide surface was illuminated by ultraviolet light. Nanofabrication of Ti by STM tip-induced anodization was also presented. The chemical composition of the fabricated pattern surface was identified to be titanium dioxide (TiO2) by STS and Auger electron spectroscopy. The anodized surface could be photocatalitically modified with poly-aniline through the photoactivity of TiO2.

The application of scanning probe anodization to nanolithography is described. The electrochemical processing of material surfaces at nanometer scale both laterally and vertically was conducted by scanning probe anodization, which used the tip-sample junction of a scanning probe microscope connected with an adsorbed water column as a minute electrochemical cell. Silicon (Si) samples whose surfaces were terminated with hydrogen (Si−H samples) or covered with an organosilane monolayer were used. Silicon oxide (SiOx) patterns were prepared on the Si−H sample surfaces by the use of anodization of Si, while in the second case the organosilane layer was selectively degraded by anodic corrosion. Furthermore, pattern transfer processes that fabricated metal nanostructures using these patterned SiOxor organosilane layers as templates were developed. These processes are based on area-selective electroless plating where selectivity depends on the difference in the chemical reactivity between the surface modified by scanning probe anodization and the unmodified surface.