Nanowire Backbones Research Articles

Highly Stretchable or Transparent Conductor Fabrication by a Hierarchical Multiscale Hybrid Nanocomposite

As is frequently seen in sci‐fi movies, future electronics are expected to ultimately be in the form of wearable electronics. To realize wearable electronics, the electric components should be soft, flexible, and even stretchable to be human‐friendly. An important step is presented toward realization of wearable electronics by developing a hierarchical multiscale hybrid nanocomposite for highly flexible, stretchable, or transparent conductors. The hybrid nanocomposite combines the enhanced mechanical compliance, electrical conductivity, and optical transparency of small CNTs (d ≈ 1.2 nm) and the enhanced electrical conductivity of relatively bigger Ag nanowire (d ≈ 150 nm) backbone to provide efficient multiscale electron transport path with Ag nanowire current backbone collector and local CNT percolation network. The highly elastic hybrid nanocomposite conductors and highly transparent flexible conductors can be mounted on any non‐planar or soft surfaces to realize human‐friendly electronics interface for future wearable electronics.

Vapor-solid growth of p-Te/n-SnO2 hierarchical heterostructures and their enhanced room-temperature gas sensing properties.

We have synthesized brushlike p-Te/n-SnO2 hierarchical heterostructures by a two-step thermal vapor transport process. The morphologies of the branched Te nanostructures can be manipulated by adjusting the source temperature or the argon flow rate. The growth of the branched Te nanotubes on the SnO2 nanowire backbones can be ascribed to the vapor-solid (VS) growth mechanism, in which the inherent anisotropic nature of Te lattice and/or dislocations lying along the Te nanotubes axis should play critical roles. When exposed to CO and NO2 gases at room temperature, Te/SnO2 hierarchical heterostructures changed the resistance in the same trend and exhibited much higher responses and faster response speeds than the Te nanotube counterparts. The enhancement in gas sensing performance can be ascribed to the higher specific surface areas and formations of numerous Te/Te or TeO2/TeO2 bridging point contacts and additional p-Te/n-SnO2 heterojunctions.

Synthesis and photoluminescence properties of string-like ZnO/SnO nanowire/nanosheet nano-heterostructures

Abstract String-like ZnO/SnO nanowire/nanosheet nano-heterostructures were synthesized by a two-stage vapor transport and condensation method. ZnO nanowire backbones and SnO nanosheets were single crystalline. Several pieces of SnO nanosheets were threaded by a single ZnO nanowire, forming string-like nano-heterostructures. A preliminary growth model was proposed to explain the formation of the nano-heterostructures. PL measurements showed the band related emission of ZnO had a blue shift for ZnO/SnO nano-heterostructures, which was due to the doping of Sn in ZnO nanowires. A broad emission ranging from 450 to 730 nm of the ZnO/SnO nano-heterostructures might be related to defects in both ZnO nanowires and SnO nanosheets. This special nanostructure may find applications in gas sensors, photodetectors, etc.

Misfit-Guided Self-Organization of Anticorrelated Ge Quantum Dot Arrays on Si Nanowires

Misfit-strain guided growth of periodic quantum dot (QD) arrays in planar thin film epitaxy has been a popular nanostructure fabrication method. Engineering misfit-guided QD growth on a nanoscale substrate such as the small curvature surface of a nanowire represents a new approach to self-organized nanostructure preparation. Perhaps more profoundly, the periodic stress underlying each QD and the resulting modulation of electro-optical properties inside the nanowire backbone promise to provide a new platform for novel mechano-electronic, thermoelectronic, and optoelectronic devices. Herein, we report a first experimental demonstration of self-organized and self-limited growth of coherent, periodic Ge QDs on a one-dimensional Si nanowire substrate. Systematic characterizations reveal several distinctively different modes of Ge QD ordering on the Si nanowire substrate depending on the core diameter. In particular, Ge QD arrays on Si nanowires of around 20 nm diameter predominantly exhibit an anticorrelated pattern whose wavelength agrees with theoretical predictions. The correlated pattern can be attributed to propagation and correlation of misfit strain across the diameter of the thin nanowire substrate. The QD array growth is self-limited as the wavelength of the QDs remains unchanged even after prolonged Ge deposition. Furthermore, we demonstrate a direct kinetic transformation from a uniform Ge shell layer to discrete QD arrays by a postgrowth annealing process.

Design of SnO2/ZnO hierarchical nanostructures for enhanced ethanol gas-sensing performance

Abstract Designing nanostructured materials to enhance gas-sensing performance is of important key for the next-generation sensor platforms. In this paper, a design of hierarchical SnO2/ZnO nanostructures for scalable fabrication of high-performance ethanol sensors is developed based on a combination of two simple synthesis pathways. High-quality single crystalline SnO2 nanowire (NW) backbones were first synthesized using the thermal evaporation method, whereas ZnO nanorod (NR) branches were subsequently grown perpendicularly to the axis of SnO2 NWs via the hydrothermal approach. The successful synthesis of SnO2/ZnO hierarchical nanostructures is confirmed by the results of scanning electron microscope, X-ray diffraction and photoluminescence spectrum. The ethanol-sensing properties of the SnO2/ZnO hierarchical nanostructures sensors were systematically investigated and compared to those of the bare SnO2 NWs sensor. The effect of growth manipulation of the SnO2/ZnO hierarchical nanostructures on the ethanol sensing characteristics was also studied. The results revealed that the design of the hierarchical nanostructures enhanced the ethanol gas response and selectivity for interfering gases such as NH3, CO, H2, CO2, and LPG. These enhancements are attributed to the enhancement of homogenous and heterogeneous NW–NW contacts. In addition, the results of this study may serve as a basis for designing various novel hierarchical nanostructures for other applications, including photocatalysis, battery electrode, solar cell, and nanosensors.

3D branched nanowire heterojunction photoelectrodes for high-efficiency solar water splitting and H2 generation

We report the fabrication of a three dimensional branched ZnO/Si heterojunction nanowire array by a two-step, wafer-scale, low-cost, solution etching/growth method and its use as photoelectrode in a photoelectrochemical cell for high efficiency solar powered water splitting. Specifically, we demonstrate that the branched nanowire heterojunction photoelectrode offers improved light absorption, increased photocurrent generation due to the effective charge separation in Si nanowire backbones and ZnO nanowire branching, and enhanced gas evolution kinetics because of the dramatically increased surface area and decreased radius of curvature. The branching nanowire heterostructures offer direct functional integration of different materials for high efficiency water photoelectrolysis and scalable photoelectrodes for clean hydrogen fuel generation.

Three-Dimensional High-Density Hierarchical Nanowire Architecture for High-Performance Photoelectrochemical Electrodes

Three-dimensional (3D) nanowire (NW) networks are promising for designing high-performance photoelectrochemical (PEC) electrodes owing to their long optical path for efficient light absorption, high-quality one-dimensional conducting channels for rapid electron-hole separation and charge transportation, as well as high surface areas for fast interfacial charge transfer and electrochemical reactions. By growing titanium dioxide (TiO(2)) nanorods (NRs) uniformly on dense Si NW array backbones, we demonstrated a novel three-dimensional high-density heterogeneous NW architecture that could enhance photoelectrochemical efficiency. A 3D NW architecture consisting of 20 μm long wet-etched Si NWs and dense TiO(2) NRs yielded a photoelectrochemical efficiency of 2.1%, which is three times higher than that of TiO(2) film-Si NWs having a core-shell structure. This result suggests that the 3D NW architecture is superior to straight NW arrays for PEC electrode design. The efficiency could be further improved by optimizing the number of overcoating cycles and the length/density of NW backbones. By implementing these 3D NW networks into electrode design, one may be able to advantageously impact PEC and photovoltaic device performance.

Rational growth of branched nanowire heterostructures with synthetically encoded properties and function

Branched nanostructures represent unique, 3D building blocks for the "bottom-up" paradigm of nanoscale science and technology. Here, we report a rational, multistep approach toward the general synthesis of 3D branched nanowire (NW) heterostructures. Single-crystalline semiconductor, including groups IV, III-V, and II-VI, and metal branches have been selectively grown on core or core/shell NW backbones, with the composition, morphology, and doping of core (core/shell) NWs and branch NWs well controlled during synthesis. Measurements made on the different composition branched NW structures demonstrate encoding of functional p-type/n-type diodes and light-emitting diodes (LEDs) as well as field effect transistors with device function localized at the branch/backbone NW junctions. In addition, multibranch/backbone NW structures were synthesized and used to demonstrate capability to create addressable nanoscale LED arrays, logic circuits, and biological sensors. Our work demonstrates a previously undescribed level of structural and functional complexity in NW materials, and more generally, highlights the potential of bottom-up synthesis to yield increasingly complex functional systems in the future.

Solution heteroepitaxial growth of dendritic SnO2/TiO2hybrid nanowires

Abstract

Chemical Mimicry: Hierarchical 1D TiO2@ZrO2 Core−Shell Structures Reminiscent of Sponge Spicules by the Synergistic Effect of Silicatein-α and Silintaphin-1

In nature, mineralization of hard tissues occurs due to the synergistic effect of components present in the organic matrix of these tissues, with templating and catalytic effects. In Suberites domuncula, a well-studied example of the class of demosponges, silica formation is mediated and templated by an axial proteinaceous filament with silicatein-α, one of the main components. But so far, the effect of other organic constituents from the proteinaceous filament on the catalytic effect of silicatein-α has not been studied in detail. Here we describe the synthesis of core-shell TiO(2)@SiO(2) and TiO(2)@ZrO(2) nanofibers via grafting of silicatein-α onto a TiO(2) nanowire backbone followed by a coassembly of silintaphin-1 through its specifically interacting domains. We show for the first time a linker-free, one-step funtionalization of metal oxides with silicatein-α using glutamate tag. In the presence of silintaphin-1 silicatein-α facilitates the formation of a dense layer of SiO(2) or ZrO(2) on the TiO(2)@protein backbone template. The immobilization of silicatein-α onto TiO(2) probes was characterized by atomic force microscopy (AFM), optical light microscopy, and high-resolution transmission electron microscopy (HRTEM). The coassembly of silicatein-α and silintaphin-1 may contribute to biomimetic approaches that pursue a controlled formation of patterned biosilica-based biomaterials.

Hierarchical SnO2 Nanostructures: Linear Assembly of Nanorods on the Nanowire Backbones

Single-crystalline SnO2 nanorods were successfully assembled on SnO2 nanowire backbones through a sequential gold-catalyzed thermal evaporation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed that uniform secondary nanorod branches were epitaxially grown from two side surfaces of the nanowire backbones. These branch rods are parallel to each other with 2-fold symmetry with respect to the backbones. The crystal structure of these as-prepared SnO2 centipede-like nanostructures was identified to coincide to the normal rutile structure. The photoluminescence (PL) properties of single centipede-like SnO2 structures were studied by confocal microscopy, which showed that these structures can act as good optical waveguides. Cathodoluminescence (CL) spectra of the SnO2 branched structures obtained in the SEM−CL system featured a blue emission band around 462 nm that is attributed to a defect-state-related emission.

Catalyst-free synthesis and cathodoluminescent properties of ZnO nanobranches on Si nanowire backbones

We report the catalyst-free synthesis of ZnO nanobranches on Si nanowires using metalorganic chemical vapor deposition. The formation of single-crystalline ZnO nanobranches on Si nanowire backbones has been confirmed by lattice resolved transmission electron microscopy. Depending on the growth parameters, especially the growth temperature, the morphology and size of the ZnO nanobranches evolved from nanothorn-shaped (at 350 °C) to nanoneedle-shaped structures (at 500 °C). When the growth temperature was further increased to 800 °C, thin ZnO nanowire branches grew out of the Si nanowire backbones coated with thin ZnO shells, whereas no ZnO branch was formed on bare Si nanowires due to limited nucleation. The growth behavior was further exploited to fabricate ZnO/Si nanowire networks by growing the ZnO nanowires selectively on laterally aligned Si–ZnO core-shell nanowire arrays. In addition, cathodoluminescent properties of ZnO nanobranches on Si nanowire backbones are discussed with respect to position and size.

Gold at the root or at the Tip of ZnO Nanowires: A Model

Growth studies of ZnO nanowires nucleated from predefined Au particles on planar substrates or on nanowire backbones show that Au particles are observed either at the root for planar substrates or the tip for wires nucleated from nanowire backbones (see image). In contrast to the well-accepted cases of the vapor–solid–solid process for Si and III-V compound nanowires, the size of the Au particle at the tip does not determine the size of the ZnO nanowire.

Synthesis and characterization of axially periodic Zn2SnO4 dendritic nanostructures

Zn2SnO4 (ZTO) nanowires with a unique dendritic nanostructure were synthesized via a simple one-step thermal evaporation and condensation process. The morphology and microstructure of the ZTO nanodendrite have been investigated by means of field emission scanning electron microscopy (SEM), x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). SEM observation revealed the formation of branched nanostructures and showed that each branch exhibited a unique periodic structure formed by a row of overlaid rhombohedra of ZTO nanocrystals along the axis of the nanobranch. HRTEM studies displayed that the branches grew homoepitaxially as single-crystalline nanowires from the ZTO nanowire backbone. A possible growth model of the branched ZTO nanowires is discussed. To successfully prepare branched structures would provide an opportunity for both fundamental research and practical applications, such as three-dimensional nanoelectronics, and opto-electronic nanodevices.

Branched SnO2 nanowires on metallic nanowire backbones for ethanol sensors application

We report the synthesis of hierarchically branched semiconducting SnO2 nanowire on metallic Sb-doped SnO2 nanowires by the sequential seeding of multiple nanowire generations with Au nanoparticles as catalysts. Such semiconducting nanowire/metallic backbone complex structures increase the potential functionality of SnO2 nanowires. Branched SnO2 nanowire films are used as sensing materials for high-performance ethanol sensor fabrication. The nanowire sensors show sub-ppm sensitivity and fast response and recovery times at 300°C. A linear equation relationship between sensitivity and the ethanol vapor concentration was observed.

High-Performance Transparent Conducting Oxide Nanowires

We report the growth and characterization of single-crystalline Sn-doped In2O3 (ITO) and Mo-doped In2O3 (IMO) nanowires. Epitaxial growth of vertically aligned ITO nanowire arrays was achieved on ITO/yttria-stabilized zirconia (YSZ) substrates. Optical transmittance and electrical transport measurements show that these nanowires are high-performance transparent metallic conductors with transmittance of approximately 85% in the visible range, resistivities as low as 6.29 x 10(-5) Omega x cm and failure-current densities as high as 3.1 x 10(7) A/cm2. Such nanowires will be suitable in a wide range of applications including organic light-emitting devices, solar cells, and field emitters. In addition, we demonstrate the growth of branched nanowire structures in which semiconducting In2O3 nanowire arrays with variable densities were grown epitaxially on metallic ITO nanowire backbones.

Rational Growth of Branched and Hyperbranched Nanowire Structures

Branched and hyperbranched nanowire structures were synthesized via a multistep nanocluster-catalyzed vapor-liquid-solid approach. Scanning electron microscopy studies of silicon nanowire structures prepared in this way confirmed the formation of branched nanostructures and showed that the branch density could be controlled by the nanocluster catalyst concentration. This same approach was also used to grow branched gallium nitride nanowires. High-resolution transmission electron microscopy studies of the branched silicon nanowire structures revealed that the branches grew epitaxially as single-crystal nanowires from the silicon nanowire backbone. In addition, hyperbranched silicon nanowire structures were prepared in a controlled manner by repeating the catalyst deposition and nanowire growth steps. The ability to prepare rationally branched and hyperbranched nanowires should open up new opportunities for both fundamental research and applications, including three-dimensional nanoelectronics.