Formation Of Wires Research Articles

Quinoacridine Derivatives with One-Dimensional Aggregation-Induced Red Emission Property

A new series of acceptor-donor-acceptor (A-D-A) type quinoacridine derivatives (1-3) with aggregation-induced red emission properties were designed and synthesized. In these compounds, the electron-withdrawing 2-(3,5-bis(trifluoromethyl)phenyl)acetonitrile groups act as electron-accepting units, while the alkyl-substituted conjugated core acts as electron-donating units. The restriction of intramolecular rotation was responsible for the AIE behavior of compounds 1-3. All compounds were employed as building blocks to fabricate one-dimensional (1-D) organic luminescent nano- or microwires based on reprecipitation or slow evaporation approaches. Morphological transition from zero-dimensional (0-D) hollow nanospheres to 1-D nanotubes has been observed by recording SEM and TEM images of aggregated sates of compound 2 in THF/H(2)O mixtures at different aging time. It was demonstrated that the synthesized compounds with different lengths of alkyl chains displayed different wire formation properties. The single-crystal X-ray analysis of compound 2 provided reasonable explanation for the formation of 1-D nano- or microstructures.

Effect of Counter Electrode in Electroformation of Giant Vesicles

Electroformation of cell-sized lipid membrane vesicles (giant vesicles, GVs), from egg yolk phosphatidylcholine, was examined varying the shape of the counter electrode. Instead of a planar ITO (indium tin oxide) electrode commonly used, platinum wire mesh was employed as a counter electrode facing lipid deposit on a planar formation electrode. The modification did not significantly alter GV formation, and many GVs of 30–50 μm, some as large as 100 μm, formed as with the standard setup, indicating that a counter electrode does not have to be a complete plane. When the counter electrode was reduced to a set of two parallel platinum wires, GV formation deteriorated. Some GVs formed, but only in close proximity to the counter electrode. Lower electric voltage with this setup no longer yielded GVs. Instead, a large onion-like multilamellar structure was observed. The deteriorated GV formation and the formation of a multilamellar structure seemed to indicate the weakened effect of the electric field on lipid deposit due to insufficient coverage with a small counter electrode. Irregular membranous objects formed by spontaneous swelling of lipid without electric voltage gradually turned into multilamellar structure upon following application of voltage. No particular enhancement of GV formation was observed when lipid deposit on a wire formation electrode was used in combination with a large planar counter electrode.

Selective Artificial Transmembrane Channels for Protons by Formation of Water Wires

Lined up water molecules: Artificial transmembrane channels from pillar[5]arene monomeric and dimeric derivatives have been prepared. Single-channel conductance measurements and isotope effect experiments under acidic conditions showed selective proton transport through the channels, which were mediated by water wires formed in the pillar[5]arene backbones (see picture).

Selective Artificial Transmembrane Channels for Protons by Formation of Water Wires

Aufgereihte Wassermoleküle: Künstliche transmembrane Kanäle aus monomeren und dimeren Pillar[5]aren-Derivaten wurden hergestellt. Leitfähigkeitmessungen an einzelnen Kanälen und Experimente mit isotopenmarkierten Systemen im sauren Milieu offenbaren einen selektiven Protonentransfer durch die Kanäle, der durch „Wasserdrähte“ im Pillar[5]aren-Rückgrat vermittelt wird (siehe Schema).

Pd-Ag Alloy Dendritic Nanowires: Fabrication and Application in Hydrogen Sensor

Dendritic Pd-Ag alloy nanowires (Pd-Ag DNWs) with different bimetallic composition have been directly self-assembled on the microelectrodes from mixed solutions of palladium and silver ions by applying an alternating current (AC) field. The size and morphology of the final product were controlled via adjusting the electrodeposition parameters and the metal ion concentration ratio. The influence of three factors on the bimetallic composition in alloy nanowires was examined. Structural characterizations suggest that there was a preferential growth along (200) and (111) directions, leading to the formation of Pd-Ag nanodendritic wires with 150-200 nm in stem and branch diameter. The mechanism of forming the DNWs is discussed. The DNWs were studied as sensing materials for the detection of hydrogen, and they were found to exhibit good sensitivity and reproducibility. The Pd-Ag sensing materials with 22.2 wt% Ag content possessed were also found to display a rapid response time of less than 1 min for 4% (V/V) hydrogen concentration.

Formation of hook-shaped and straight silica wires by a thermal vapor method

Hook-shaped and straight silica wires have been successfully synthesized on silicon wafer through a simple thermal vapor method with or without assistance of Al, respectively. The hook-shaped silica wires have amorphous structures with nearly 100 μm long and about 4 μm in average diameters, while the straight silica wires are hundreds of micrometers long and approximately 50–300 nm in diameters. The composition analysis revealed that larger Al/SiO x islands can form on the silicon substrate with Al catalysts, whereas tiny silica clusters form without Al catalysts. They could act as the nucleation centers for the growth of silica wires with different shapes. The formation process of hook-shaped silica microwire results from a thermal gradient on the silicon substrate. The thermal gradient may be caused by the cold gas flowing during the process or other factors that lead to uneven temperature. On the contrary, straight growth of silica submicrowire is unacted on the thermal gradient factor due to the tiny silica clusters as nucleation centers. The present simple and low-cost process of producing hook-shaped and straight silica wires in bulk may lead to potential applications in catalysts, electrode materials, biosensing, etc.

Formation of nanoscale gold chain on a Si(110) surface: A density functional investigation

The adsorption of gold (Au) atoms on a Si(110) surface is theoretically investigated by employing the first-principles plane wave pseudopotential method and the density functional scheme. We have examined the atomic geometries of stable atomic Au wire formation, leading to (1 × 2) and (2 × 5) reconstructions of the Si(110) surface, corresponding to the Au coverages of 0.25 monolayer and 0.4 monolayer, respectively. Both reconstructions are found to have metallic nature, with at least two dispersive bands crossing the Fermi level. The effective mass values of the near-Fermi bands are estimated and compared with the available experimental findings.

Structural and optical properties of m-plane GaN/AlGaN quantum wires grown by metalorganic chemical vapor deposition

We have investigated the structural and optical properties of GaN quantum wires grown by metalorganic chemical vapor deposition on m-plane AlGaN templates. The quantum wire formation can be attributed to the surface morphology of the AlGaN buffer layer and to the anisotropic lattice mismatch between wires and template. The quantum wires exhibit a triangular cross-sectional geometry with width and height fluctuations. The appearance of individual spectrally narrow emission lines in the micro-photoluminescence spectra clearly demonstrates the localizations in the quantum wires. We correlate the narrow emission lines with the structural fluctuations in the cross-sectional geometry of the quantum wires.

Clean Coupling of Unfunctionalized Porphyrins at Surfaces To Give Highly Oriented Organometallic Oligomers

The direct coupling of complex, functional organic molecules at a surface is one of the outstanding challenges in the road map to future molecular devices. Equally demanding is to meet this challenge without recourse to additional functionalization of the molecular building blocks and via clean surface reactions that leave no surface contamination. Here, we demonstrate the directional coupling of unfunctionalized porphyrin molecules--large aromatic multifunctional building blocks--on a single crystal copper surface, which generates highly oriented one-dimensional organometallic macromolecular nanostructures (wires) in a reaction which generates gaseous hydrogen as the only byproduct. In situ scanning tunneling microscopy and temperature programmed desorption, supported by theoretical modeling, reveal that the process is driven by C-H bond scission and the incorporation of copper atoms in between the organic components to form a very stable organocopper oligomer comprising organometallic edge-to-edge porphyrin-Cu-porphyrin connections on the surface that are unprecedented in solution chemistry. The hydrogen generated during the reaction leaves the surface and, therefore, produces no surface contamination. A remarkable feature of the wires is their stability at high temperatures (up to 670 K) and their preference for 1D growth along a prescribed crystallographic direction of the surface. The on-surface formation of directional organometallic wires that link highly functional porphyrin cores via direct C-Cu-C bonds in a single-step synthesis is a new development in surface-based molecular systems and provides a versatile approach to create functional organic nanostructures at surfaces.

Liquid droplet dynamics and complex morphologies in vapor–liquid–solid nanowire growth

Abstract

Polarization and Excitation Dependence of Photoluminescence of InAs Quantum Wires and Dots Grown on GaAs(631)

We studied the optical properties of self-assembled InAs nanostructures grown by molecular beam epitaxy on GaAs substrates with (631) crystallographic orientation by photoluminescence (PL) spectroscopy. The growth of InAs proceeded on GaAs(631) buffer layers conformed by corrugated surfaces with a high degree of lateral periodicity (uniformly spaced nano grooves). The grooved surface is sustained even after the growth of InAs with thicknesses below 2 monolayers (ML), indicating the formation of InAs quantum wires. The one-dimensional confinement is corroborated by PL polarized along the [113] and [8,19,9] orthogonal directions. The calculated polarization degree, Πd, was 0.13 and 0.125 for InAs thicknesses of 1 and 1.5 ML, respectively. As the InAs thickness is increased, the InAs film reaches the critical thickness and quantum dots aligned along the grooved surface are formed, as observed by atomic force microscopy. Excitation-power-dependent luminescence is observed to a larger extent for low-energy PL lines in addition to a blue shift related to the band-filling effect.

Rapid Fabrication of Silver Nanowires through Photoreduction of Silver Nitrate from an Anodic-Aluminum-Oxide Template

A method for rapidly fabricating dense and high-aspect-ratio silver nanowires, with wire diameter of 200 nm and wire length more than 30 µm, is reported. The fabrication process simply involves filling the silver nitrate solution into the pores of an anodic-aluminum-oxide (AAO) membrane through capillary attraction and irradiating the dried template AAO membrane using a pulsed ArF excimer laser. Through varying the thickness and pore diameter of the employed AAO membrane, the primary dimensions of the targeted silver nanowires can be plainly specified; and, by amending the initial concentration of the silver nitrate solution and adjusting the laser operation parameters, laser fluence and number of laser pulses, the surface morphology and size of the resulting nanowires can be finely regulated. The wire formation mechanism is considered through two stages: the period of precipitation of silver particles from the dried silver nitrate film through the laser-induced photoreduction; and, the phase of clustering, merging and fusing of the reduced particles to form nanowires in the template pores by the thermal energy owing to photothermal effect. This approach is straightforward and takes the advantage that all the fabrication processes can be executed in an ambient environment and at room temperature. In addition, by the excellence in local processing that the laser possesses, this method is suitable for precisely growing nanowires.

Microwave-Assisted Green Synthesis of Silver Nanostructures

Over the past 25 years, microwave (MW) chemistry has moved from a laboratory curiosity to a well-established synthetic technique used in many academic and industrial laboratories around the world. Although the overwhelming number of MW-assisted applications today are still performed on a laboratory (mL) scale, we expect that this enabling technology may be used on a larger, perhaps even production, scale in conjunction with radio frequency or conventional heating. Microwave chemistry is based on two main principles, the dipolar mechanism and the electrical conductor mechanism. The dipolar mechanism occurs when, under a very high frequency electric field, a polar molecule attempts to follow the field in the same alignment. When this happens, the molecules release enough heat to drive the reaction forward. In the second mechanism, the irradiated sample is an electrical conductor and the charge carriers, ions and electrons, move through the material under the influence of the electric field and lead to polarization within the sample. These induced currents and any electrical resistance will heat the sample. This Account summarizes a microwave (MW)-assisted synthetic approach for producing silver nanostructures. MW heating has received considerable attention as a promising new method for the one-pot synthesis of metallic nanostructures in solutions. Researchers have successfully demonstrated the application of this method in the preparation of silver (Ag), gold (Au), platinum (Pt), and gold-palladium (Au-Pd) nanostructures. MW heating conditions allow not only for the preparation of spherical nanoparticles within a few minutes but also for the formation of single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites. The morphologies and sizes of the nanostructures can be controlled by changing various experimental parameters, such as the concentration of metallic salt precursors, the surfactant polymers, the chain length of the surfactant polymers, the solvents, and the operation reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization have been obtained more consistently via MW heating than by heating with a conventional oil-bath. The use of microwaves to heat samples is a viable avenue for the greener synthesis of nanomaterials and provides several desirable features such as shorter reaction times, reduced energy consumption, and better product yields.

The Role of Local Hydration and Hydrogen-Bonding Dynamics in Ion and Solute Release from Ion-Coupled Secondary Transporters

Recent progress in crystallographic studies of sodium-coupled secondary transporters has revealed striking similarities in the structural organization of ion and solute binding. Previous reports suggested that the Na2 sodium binding site in the neurotransmitter sodium symporter (NSS) leucine transporter (LeuT) is conserved across sodium/proton coupled secondary transporters of many distantly related families. This site is implicated in the conformational dynamics controlled by the binding and release of both translocated solute and ion(s) through a mechanism that largely remains unknown. In this study, we used extensive equilibrium molecular dynamics simulations, potential of mean force (PMF) computations, and quasi-harmonic analysis of the LeuT transporter with and without sodium ion bound at the Na2 site to delineate the role of this site in the conformational dynamics of the protein. PMF computations show that in presence of the sodium ion in Na2 the conserved T354 residue is locked into a single rotameric state in contrast to two degenerate states available in the absence of ion in Na2. Molecular dynamics (MD) simulations suggest the formation of a stable water wire from the cytoplasm to the Na2 site in the occluded state. It is plausible that local hydration plays an important role in transport cycle facilitating release of the ion from Na2. An unbinding of the ion from the Na2 site leads to a tightening of the extracellular thin gates and a destabilization of the intracellular thin gate and thus may promote an unbinding of the cotransported substrate. The study lends additional support to the hypothesis that one of the main drivers in the transport cycle of Na-coupled secondary transporters is the binding of the Na2 ion that controls dynamical equilibrium between an inward-facing to an outward-facing conformation.

Thickness dependent self limiting 1-D tin oxidenanowire arrays by nanosecond pulsed laser irradiation

Fast, sensitive and discriminating detection of hydrogen at room temperature is crucial for storage, transportation, and distribution of hydrogen as an energy source. One dimensional nanowires of SnO2 are potential candidates for improved H2 sensor performance. The single directional conducting continuous nanowires can decrease electrical noise, and their large active surface area could improve the response and recovery time of the sensor. In this work we discuss synthesis and characterization of nanowire arrays made using nanosecond ultraviolet wavelength (266 nm) laser interference processing of ultrathin SnO2 films on SiO2 substrates. The laser energy was chosen to be above the melting point of the films. The results show that the final nanowire formation is dominated by preferential evaporation as compared to thermocapillary flow. The nanowire height (and hence wire aspect ratio) increased with increasing initial film thickness h0 and with increasing laser energy density Eo. Furthermore, a self-limiting effect was observed where-in the wire formation ceased at a specific final remaining thickness of SnO2 that was almost independent of h0 for a given Eo. To understand these effects, finite element modeling of the nanoscale laser heating was performed. This showed that the temperature rise under laser heating was a strong non-monotonic function of film thickness. As a result, the preferential evaporation rate varies as wire formation occurs, eventually leading to a shut-off of evaporation at a characteristic thickness. This results in the stoppage of wire formation. This combination of nanosecond pulsed laser experiments and thermal modeling shows that several unique synthesis approaches can be utilized to control the nanowire characteristics.

Formation of a Molecular Wire Using the Chemically Adsorbed Monomolecular Layer Having Pyrrolyl Groups

A molecular wire containing polypyrrolyl conjugate bonds has been prepared by a chemical adsorption technique using 1,1,1-trichloro-12-pyrrolyl-1-siladodecane (PNN) and an electrooxidative polymerization technique, and the conductivity of the molecular wire without any dopant has been measured by using AFM/STM at room temperature. When sample dimension measured was about 0.3 nm (thickness of the conductive portion in the PNN monomolecular layer) ×100 μm (the average width of an electric path) ×2 mm (the distance between Pt positive electrode and the AFM tip covered with Au), the conductivity of the polymerized PNN molecular wire at room temperature was larger than 1.6 × 105 S/cm both in an atmosphere and in a vacuum chamber of 10−5 Torr. The activation energy obtained by Arrhenius' plots was almost zero in the temperature range between 320 and 450 K.

Effect of Additive-Free Plating and High Heating Rate Annealing on the Formation of Low Resistivity Fine Cu Wires

Low resistivity Cu wires were developed by the combination of lessening impurities through additive-free plating and high heating rate annealing. Resistivities of Cu wires made with the new method were about 30% lower than those made by conventional plating with additives and annealing at the same temperature in H2. Low resistivity Cu wires were realized even at temperatures 100K lower than conventional annealing temperatures due to substantial grain growth by the high heating rate annealing in the Cu wires made with the additive-free plating. [doi:10.2320/matertrans.M2011098]

Formation of p-Silicon Wire by Electrochemical Etching Using Positive Photoresist as an Etch Mask in Organic Electrolyte

Formation of p-Silicon Wire by Electrochemical Etching Using Positive Photoresist as an Etch Mask in Organic Electrolyte

高純度めっき材料を用いた低抵抗率Cu配線形成プロセスの8インチウエハによる検証

We have confirmed the effectiveness of ultra-high purity plating material on the formation of low resistivity Cu wires for 22 nm level ULSIs using 8 inch wafer. The resistivity of the 30 nm wide Cu wires formed by ultra-high purity process is found to be 30% lower than those for Cu wires fabricated by the conventional process. It was also found that the grain size of the ultra- high purity processed Cu wires is larger than that of the conventional processed Cu wires by 30%, and the grain size is much more uniform. This innovative new process is expected to be one of the powerful candidates as the Cu wire forming process for 22 nm level ULSIs.

The World Constructed by Self-organization of Some Amphiphils-with a Focus on Vesicle Formation-

The world constructed by self-organization of some amphiphils was discussed on the basis of micelle formation, vesicle formation, and oriented-nano-wire formation. First, the micelle formation of a both water- and oil- soluble surfactant, Aerosol OT, was discussed. Solution states of micelles and monomer were discussed on the basis of thermodinamic and NMR spectroscopic analyses of micelle formation. Next, micelle-vesicle transition was discussed. It was proposed that the phospholipid LUV formation by removing detergents and destruction by adding detergents occurred via 4 stages. The 4 stage model instead of the 3 stage model could not only elucidate the complicated phenomena observed during micelle-vesicle transition, but predicted the size and properties of the vesicles formed by detergent removal from mixed micelles. Next, the vesicle formation of a fatty acid with a single hydrophobic chain different from phospholipid, which has two hydorophobic chains, was discussed. The vesicle formation was strongly affected by the presence of preformed vesicles and the size was biased on the preformed vesicles. It was shown there exist two pass ways in the process of micelle-vesicle transition by pH jump. One is fission of the preformed vesicles after transfer of monomers from newly added oleate micelles and the other is transition from the mixed micelles after partial solubilization by the oreate micelles. Then, the vesicle formation of HCO-10, which has 3 hydrophobic chains, the mixed vesicle formation of phosphatidylethanolamine and lysophosphtidylcholine, which can not form vesicles, and the phospholipid vesicle formation and destruction by removing and adding PEG-lipid, were discussed. Lastly, oriented nano wire formation of mulamyldipeptid-conjugated lipids with ca 5 nm of diameter was discussed.