Assembly Of Nanowires Research Articles

One‐Step Synthesis of Charge‐Transfer Salt Nanosensors on Microelectrode Patterns

AbstractDespite extensive research on nanowires and nanosensors, the lack of manufacturing methods limits nanosensor commercialization. Here a new way of making nanowire sensors is demonstrated. Nanowire crystals of charge‐transfer salt, tetrathiafulvalene bromide or (TTF)Br, are electrochemically deposited across lines of microelectrodes made by photolithography to complete the sensor circuitry. A novel concept is the direct synthesis of nanowires on sensor substrates using pre‐existing patterns to direct the nanowire nucleation and crystallization. The gas sensing capability of the nanowire assembly is demonstrated for the detection of ammonia at a concentration range of 1–100 ppm by measuring the changes in its electrical impedance. The selectivity toward ammonia against water vapor, one of the most persistent challenges for wide adoption of nanosensors for gas detection, can be tuned by (TTF)Br nanowire chemical composition during synthesis. This work demonstrates a proof of concept toward scalable manufacturing of nanosensor devices via one‐step, substrate‐directed nucleation and crystallization.

Fabrication and Characterization of an Aptamer-Based N-type Silicon Nanowire FET Biosensor for VEGF Detection

Cancer detection is an important part of modern medical diagnosis and many strategies based on nanotechnology had been developed in recent years. Of which, silicon nanowire (SiNW) field-effect transistor (FET) biosensor via DNA aptamer capture is considered as an interesting and viable option. Hence, in this report, we had assembled a n-type triple SiNW FET biosensor for the detection of vascular endothelial growth factor (VEGF) via surface functionalized DNA aptamer for a proof-of-concept. The SiNW FET biosensor was fabricated via "top-down" approach and the physical nature of the nanowire assembly was examined via atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). We had subsequently grafted VEGF specific DNA aptamer via conventional EDC/NHS chemistry and later measured the conductance of the nanowires in a four-point probe detector for VEGF detection. We had demonstrated that the detection of VEGF was possible even at a concentration of 2.59 nM which was highly comparable to the other common biosensors for detection of VEGF protein. In addition to being scalable with complementary metal–oxide–semiconductor (CMOS) technology, the findings as demonstrated from our simple SiNW FET biosensor setup had helped to provide better insights towards optimizing the approach for the development of the next generation of miniature biosensors.

Controllable growth and flexible optoelectronic devices of regularly-assembled Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks

Regularly assembled structures of nanowires, such as aligned arrays, junctions and interconnected networks, have great potential for the applications in logical circuits, address decoders, photoelectronic devices and transparent electrodes. However, for now it is still lack of effective approaches for constructing nanowire bifurcated junctions and crosslinked networks with ordered orientations and high quality. Herein, we report the controlled growth of Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks with well-aligned directions and high crystalline degree by utilizing the proportional lattice match between nanowires and substrates. Taking advantages of the “tip-to-stem splice” assembly of individual nanowires, the precise orientation alignments of Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks were successfully realized. The controlled growth mechanism and structural evolution process have been elucidated by detailed atomic structure characterizations and modeling. The highly crystal quality and direct energy bandgap of as-assembled photodetectors based on individual bismuth sulfide nanowires enabled high photoresponsivity and fast switch time under light illumination. The three-terminal devices based on nanowire bifurcated junctions present rapid carrier transport across the junction. The flexible photodetectors based on nanowire crosslinked networks show very minimal decay of photocurrent after long-term bending test. This work may provide new insights for the guided construction and regular assembly of low-dimensional ordered functional nanostructures towards advanced nanotechnologies.

Directional Assembly of ZnO Nanowires via Three-Dimensional Laser Direct Writing.

The precise placement of semiconductor nanowires (NWs) into two- or three-dimensional (2D/3D) micro-/nanoarchitectures is a key for the construction of integrated functional devices. However, long-pending challenges still exist in high-resolution 3D assembly of semiconductor NWs. Here, we have achieved directional assembly of zinc oxide (ZnO) NWs into nearly arbitrary 3D architectures with high spatial resolution using two-photon polymerization. The NWs can regularly align in any desired direction along the laser scanning pathway. Through theoretical calculation and control experiments, we unveiled the laser-induced assembly mechanism and found that the nonoptical forces are the dominant factor leading to the directional assembly of ZnO NWs. A ZnO-NW-based polarization-resolved UV photodetector of excellent photoresponsivity was fabricated to demonstrate the potential application of the assembled ZnO NWs. This work is expected to promote the research on NW-based integrated devices such as photonic integrated circuits, sensors, and metamaterial with unprecedented controllability of the NW's placement in three dimensions.

Progress towards innovative and energy efficient logic circuits

The integration of superconductive nanowire logic memories and energy efficient computing Josephson logic is explored. Nanowire memories are based on the integration of switchable superconducting nanowires with a suitable magnetic material. These memories exploit the electro-thermal operation of the nanowires to efficiently store and read a magnetic state. In order to achieve proper memory operation a careful design of the nanowire assembly is necessary, as well as a proper choice of the magnetic material to be employed. At present several new superconducting logic families have been proposed, all tending to minimize the effect of losses in the digital Josephson circuits replacing resistors by adequate combinations of inductors in the logic gates. Among those, the nSQUID concept relies on the propagation of vortices along underdamped Josephson transmission lines. While, in principle, this logic family provides very low dissipation, several issues, such as speed and stability, have yet to be addressed. The current status of design and testing of n-SQUID logic gates and circuits as well as of the design and implementation of the nanowire memories is reported

Bioinspired fiberboard-and-mortar structural nanocomposite based on ultralong hydroxyapatite nanowires with high mechanical performance

Natural materials have enlightened us to assemble brittle building blocks into specific architectures with both high strength and toughness. As the main inorganic component of the bone and tooth, hydroxyapatite (HAP) materials have a high biocompatibility, but usually have a high brittleness. It is still a big challenge to artificially prepare biomaterials with the combination of high strength and high toughness, similar to natural materials constructed with brittle HAP building blocks. In this work, considering that enamel and nacre are typical examples of natural biomaterials with high strength and high toughness, respectively, we combine the structural merits of both enamel (highly ordered bundles) and nacre (brick-and-mortar structure) to construct a new kind of highly ordered ultralong HAP nanowire fiberboard-and-mortar alignment hierarchical structure (HFMAS) by the multiscale and multilevel assemblies of ultralong HAP nanowires from the nanoscale to microscale to macroscale and from one-dimensional (1-D) to 2-D to 3-D levels. The as-prepared hierarchical HFMAS nanocomposite can achieve a confluence of strengthening and toughening mechanisms of enamel and nacre, and exhibits superior mechanical properties such as high strength (308 MPa), Young's modulus (34.7 GPa), and toughness (4.77 MPa·m1/2), which are far better than those of many synthetic HAP-organic composites and other materials reported in the literature. Moreover, the as-prepared HFMAS nanocomposite exhibits a low density (1.8 g cm−3), good resistance to great impact, good damping capacity and durability. The as-prepared HFMAS nanocomposite is promising for various applications such as the protective armor, mechanical damping, and building materials.

In-situ reflectometry to monitor locally-catalyzed initiation and growth of nanowire assemblies

We investigate in-situ laser reflectometry for measuring the axial growth rate in chemical vapor deposition of assemblies of well-aligned vertical germanium nanowires grown epitaxially on single crystal substrates. Finite difference frequency domain optical simulations were performed in order to facilitate quantitative analysis and interpretation of the measured reflectivity data. The results show an insensitivity of the reflected intensity oscillation period to nanowire diameter and density within the range of experimental conditions investigated. Compared to previous quantitative in-situ measurements performed on III–V nanowire arrays, which showed two distinct rate regimes, we observe a constant, steady-state nanowire growth rate. Furthermore, we show that the measured reflectivity decay can be used to determine the germanium nanowire nucleation time with good precision. This technique provides an avenue to monitor growth of nanowires in a variety of materials systems and growth conditions.

Ultrathin PtCo nanorod assemblies with self-optimized surface for oxygen reduction reaction

Controllable synthesis of Pt-based materials at the nanoscale can efficiently tailor their electrocatalytic performance, enabling enhancement in both activity and durability. Herein, we report the synthesis of ultrathin PtCo nanorod assemblies (NRAs) terminated with high index facets through a grain-boundary corrosion approach. Atomic insight reveals that grain boundaries and other defects are formed in PtCo nanowire assemblies (NWAs) during the hydrothermal reaction. With a further increase in reaction time, selective dissolution at these sites generated PtCo NRAs composed of shorter nanorod assemblies with larger surface areas and high index facets termination. The carbon-supported catalyst of PtCo NRAs exhibits high mass activity of 0.914 A/mgPt at 0.9 V vs RHE for ORR, 2.4 times higher than those of the smooth PtCo NWAs (0.377 A/mgPt), 5.7 times higher than those of the commercial Pt/C (0.161 A/mgPt). Most significantly, the PtCo NRAs show high stability with about 25.6% loss of mass activity after 10,000 cycles, while only 22.3% loss of mass activity from 10,000 cycles to 50,000 cycles of accelerated durability test. The high durability is mainly attributed to the jagged surface resulted from the surface reconstruction of PtCo NRAs during the electrochemical process. This self-optimization phenomenon may lead to a new effective long-life electrocatalyst.

Integrating Multiple Advantages into 1 Nm Pt3Ni Bimetallic Alloy Nanowires for Oxygen Reduction Reaction

Exploiting highly active and durable oxygen reduction reaction (ORR) electrocatalyst is still imperative for clean and efficient energy conversion device, such as fuel cells and metal-air batteries. For this purpose and maximize the utilization of noble Pt, we present here a facile, scalable strategy for the high-precise synthesis of 1 nm thick Pt3Ni bimetallic alloy nanowires (Pt3Ni BANWs). The seed-mediated growth mechanism of Pt3Ni BANWs is identified by examining the morphology and composition of the intermediate products collect at different reaction stages. As expected, the Pt3Ni BANWs delivered enhanced mass activity (0.546 A mg-1 Pt, exceeding the DOE 2020 target) in comparison to Pt nanowires assembly (Pt NWA, 0.098 A mg-1 Pt) and Pt/C (Pt, 0.135 A mg-1 Pt) due to the rational integration of multiple compositional and structural advantages, such as alloy feature, ultrathin 1D nanostructure and high-index facets. Moreover, the Pt3Ni BANWs displayed enhanced durability (37% MA retention) than Pt NWA and Pt after 50,000 potential cycles. All these results indicate that the ultrathin Pt3Ni BANWs are potential candidates for catalyzing ORR with acceptable activity and durability. The present work could not provide a facile strategy but also a general guidance for the design of superb performance Pt-based nanowire catalysts for ORR. Figure 1. Progressive formation mechanism of the ultrathin Pt3Ni BANWs. Keywords: Oxygen Reduction Reaction, Pt-Ni alloy, Nanowires, Seed-mediated growth

Self-Assembly Anisotropic Magnetic Nanowire Films Induced by External Magnetic Field.

Self‐assembly generated materials induced by an external magnetic field have attracted considerable interest following the development of nanodevices. However, the fabrication of macroscopic and anisotropic magnetic films at the nanoscale remains a challenge. Here, anisotropic magnetic films are successfully prepared using a solution‐based nanowire assembly strategy under a magnetic field. The assembly process is manipulated by changing the thickness of silica shell coated on the surface of magnetic nanowires. The anisotropic magnetic films show highly anisotropic magnetization under different angles of magnetic field and better magnetization properties than that of disordered magnetic films. The well‐defined nanowire arrays enable magnetization anisotropic property which may be useful in the magnetic energy conversion technologies and biomedical sciences which lie far beyond those achievable with traditional magnetic materials.

Assembly of Gold Nanowires on Gold Nanostripe Arrays: Simulation and Experiment

Nanowires (NWs) have a large aspect ratio and large available surface area, which have made them a potential platform for applications in biosensors as well as electronic/optic and power storage de...

Radial Nanowire Assemblies under Rotating Magnetic Field Enabled Efficient Charge Separation.

Developing efficient charge separation strategies is essential to achieve high-power conversion efficiency in the fields of chemistry, biology, and material science. Herein, we develop a facile strategy for fabrication of unique wafer-scale radial nanowire assemblies by exploiting shear force in rotary solution. The assembly mechanism can be well revealed by the large-scale stochastic dynamics simulation. Free electrons can be rapidly generated to produce quantitatively tunable current output when the radial nanowire assemblies rotate under the magnetic field. Moreover, the photoconductive performance of the radial semiconductor nanowire assemblies can be remarkably enhanced as the electron-hole recombination was retrained by the efficient charge separation under the rotating magnetic field. Such large-scale unique nanowire assemblies will facilitate the design of an efficient charge separation process in biosystem, sensors, and photocatalysis.

Functionalized graphene fiber modified by dual nanoenzyme: Towards high-performance flexible nanohybrid microelectrode for electrochemical sensing in live cancer cells

The development of flexible miniaturized electrochemical sensors based on functionalized microelectrode systems has gained numerous attentions for their promising application in potable, implantable and wearable medical devices. In this work, we report a facile strategy to construct a new type of high-performance microelectrode based on wet-spinning graphene fiber (GF) functionalized by dual nanoenzyme composed of ultrafine Au nanoparticles (Au-NPs) wrapped flower-like MnO2 nanowires (MnO2-NWs) assembly (MnO2-NWs@Au-NPs), and explore its practical application in electrochemical detection of biomarker hydrogen peroxide (H2O2) released from live cancer cells. Benefiting from the advantage of the unique hierarchical nanohybrid structure and dual nanoenzyme activity, the resultant MnO2-NWs@Au-NPs modified GF microelectrode shows superior catalytic activity towards the electrochemical redox reaction of H2O2. When used in amperometric detection of H2O2, the nanohybrid microelectrode exhibits high sensitivity and selectivity as well as good mechanical stability and biocompatibility, and can be used in real-time in situ detection of H2O2 released from human breast cancer cells, which contributes to the development of high-performance hierarchically nanostructured microelectrode in electrochemical sensing system for sensitive detection of various targets in biological samples.

Cu2O/TiO2 Nanowire Assemblies as Photocathodes for Solar Hydrogen Evolution: Influence of Diameter, Length and NumberDensity of Wires

Abstract The performance of free-standing parallel-aligned nanowire arrays and interconnected networks of single-crystalline cuprous oxide (Cu2O) coated with titanium oxide (TiO2) as photocathodes for solar energy harvesting was analyzed. The nanostructures were synthesized by electrodeposition in polymer membranes prepared by ion-track technology. To enhance the photoelectrochemical stability of the nanowires in aqueous solution, they were conformally coated with a 10 nm thick TiO2 layer by atomic layer deposition. The diameter, size, geometry and number density of the parallel nanowires were systematically varied. The generated photocurrents show a clear increase as a function of wire diameter and wire number. In turn, the photocurrent does not get larger with increasing wire length. Highly interconnected networks of nanowires under 45° from various directions enabled further increase of wire density number and exhibited higher photocurrent densities compared to parallel arrays.

Probing the Role of Metal Coordination and pH in Assembly and Function of Cytochrome Nanowires

Geobacter sulfurreducens produces protein nanowires for extracellular electron transfer during respiration and interspecies electron exchange to survive in environments that lack soluble electron acceptors. It was previously thought that nanowires were Type IV pili comprised by PilA monomers, but we showed via electron cryo-microscopy (cryo-EM) that nanowires instead constitute a helical polymer of the six-heme outer membrane cytochrome OmcS, yielding a periodic arrangement of hemes over the micrometer scale of the filaments (Cell, 2019, 177, 361). This 3.7 Å-resolution structure revealed several features which appear to stabilize this polymer, including close stacking of covalently bound heme ligands within ∼ 3.5-6 Å of each other, and axial coordination of a heme metal center in each subunit by a histidine residue in the adjacent subunit. These OmcS filaments represent to our knowledge the first micrometer-scale cytochrome polymer naturally evolved for electron transfer, but the mechanism of this polymerization remains unknown. Furthermore, lowering the pH of nanowire samples enhances their conductivity and improves heme stacking, yet the structural changes in OmcS underlying this conformation change are unclear. Here, we develop a method to obtain OmcS nanowires and monomers in high purity. We then combine cryo-EM with spectroscopic methods such as UV-vis and circular dichroism to examine the changes in OmcS polymers and their inter-subunit interactions as a result of changes to pH, further enabling tuning of the conductivity of purified microbial nanowires. Furthermore, we explore the spectroscopic features and biochemical properties of OmcS monomers after reversing their polymerization, to obtain a mechanistic understanding of nanowire assembly that will aid engineering of synthetic protein nanowires for bioelectronics. This research was supported by Career Award from Burroughs Welcome Fund, NIH New Innovator award NSF CAREER award and DARPA (to N.S.M.).

Hard and semi-hard magnetic materials based on cobalt and cobalt alloys

Cobalt (Co) is one of the most important 3d transition metal elements used in the development of magnetic materials, especially in hard magnetic materials, from the early Co-based steel magnets to the rare-earth permanent magnets based on the 3d-4f compounds. Like iron (Fe), Co possesses a high saturation magnetization (MS) and a high Curie temperature (TC). Unlike Fe, Co has high magnetocrystalline anisotropy due to its spin-orbit coupling. As a result, it can be used to achieve a high degree of magnetic hardening in its elemental, alloy or compound materials. For instance, Co-based magnetic recording media is based on its elemental material. On the other hand, nano-structuring of Co-based alloys gives important hard magnetic materials including Alnico magnets and Fe–Cr–Co magnets, which are probably the earliest nanostructured hard magnetic materials. Recent progress in the development of Co-containing nanoscale hard magnetic materials has been very encouraging and promising based on the outstanding magnetic properties we have seen in L10 CoPt, tetragonally distorted FeCo and Co-based intermetallics. Particularly, the morphology of the nanoparticles has also been modulated to develop high coercivity via utilizing shape anisotropy, leading to extraordinarily high coercivity in Co nanowire assemblies. This review presents an overview of the development of Co-based hard and semi-hard magnetic materials and their intrinsic and extrinsic magnetic properties in view of fundamental understanding and technological applications.

Chirality Evolution from Sub-1 Nanometer Nanowires to the Macroscopic Helical Structure.

The chirality evolution from the molecular level to the macroscopic level remains elusive for inorganic hierarchical structures. Without adding any chiral ligands or dopants, we prepared the macroscopic helical assemblies of sub-1 nm nanowires through a facile evaporation-induced self-assembly process with 100% efficiency, benefiting from the self-adjustment and self-recognition of sub-1 nm nanowires. Furthermore, we observed circularly polarized luminescence signals from the helical assemblies composed of nanowires and achiral organic fluorescent dyes, stemming from chirality transfer from the helical assemblies to achiral organic molecules. Molecular dynamics simulations found that the chirality of nanowires played a key role in the formation of macroscopic helical assemblies. Our work clarifies the chirality evolution and transfer of inorganic nanomaterials in part without being studied previously.

Photomechanical molecular crystals and nanowire assemblies based on the [2+2] photodimerization of a phenylbutadiene derivative

Crystalline (E)-4-fluoro-cinnamaldehyde malononitrile undergoes a [2+2] photocycloaddition, leading to a robust photomechanical response and improved force generation by nanowire ceramic composites.

Synthesis of orthogonally assembled 3D cross-stacked metal oxide semiconducting nanowires.

Assemblies of metal oxide nanowires in 3D stacks can enable the realization of nanodevices with tailored conductivity, porous structure and a high surface area. Current fabrication methods require complicated multistep procedures that involve the initial preparation of nanowires followed by manual assembly or transfer printing, and thus lack synthesis flexibility and controllability. Here we report a general synthetic orthogonal assembly approach to controllably construct 3D multilayer-crossed metal oxide nanowire arrays. Taking tungsten oxide semiconducting nanowires as an example, we show the spontaneous orthogonal packing of composite nanorods of poly(ethylene oxide)-block-polystyrene and silicotungstic acid; the following calcination gives rise to 3D cross-stacked nanowire arrays of Si-doped metastable ε-phase WO3. This nanowire stack framework was also tested as a gas detector for the selective sensing of acetone. By using other polyoxometallates, this fabrication method for woodpile-like 3D nanostructures can also be generalized to different doped metal oxide nanowires, which provides a way to manipulate their physical properties for various applications.

Assembly of silver nanowires and PEDOT:PSS with hydrocellulose toward highly flexible, transparent and conductivity-stable conductors

• Flexible and transparent conductor film was assembled via an integration strategy. • The CRC-film exhibited super-stable conductivity even in harsh environments. • The CRC-film-based strain sensor was demonstrated. Improving the conductivity stability of flexible conductors has a positive impact on the working performance and service life of portable electronic devices. However, designing a conductor material with both conductivity-stable and flexible performance is still not an easy task because of the conductive network damage under large deformation or high humidity conditions. Here, we surmount this challenge by developing an interfacial assembly/encapsulation integration strategy for the construction of flexible, transparent, and conductivity-stable film. Under the synergistic effect of coordination complexation and hydrogen bonding, silver nanowires (AgNWs) are sandwiched encapsulated by regenerated cellulose film (as flexible substrate) and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) nanosheets (as sealing coat). The resulting hybrid film has a robust interfacial structure and prominently stable properties. Even when subjected to harsh condition such as a high-moisture environment of 90% relative humidity and 65 °C temperature for up to 60 days, repeated bending for 500 times, peeling over 400 times or soaking in water for 30 days, the film still exhibits a high and stable conductivity, better than most previously reported values for AgNWs-based films. With this strategy as base, we demonstrate a flexible, transparent and biocompatible strain-to-electricity sensor with high working stability and performance.