Single-crystalline Au Nanowires Research Articles

Epitaxially Integrated Hierarchical ZnO/Au/SrTiO3 and ZnO/Ag/Al2O3 Heterostructures: Three-Dimensional Plasmo-Photonic Nanoarchitecturing.

In this study, we fabricated three-dimensional (3D) hierarchical plasmo-photonic nanoarchitectures by epitaxially integrating semiconducting zinc oxide (ZnO) nanowires with vertically oriented plasmonic gold (Au) and silver (Ag) nanoplatforms and investigated their growth mechanisms in detail. We synthesized 3D hierarchical Au–ZnO nanostructures via a vapor–solid mechanism leading to the epitaxial growth of ZnO nanowires on vertically oriented single-crystalline Au nanowires on a strontium titanate (SrTiO3) substrate. The elongated half-octahedral Au nanowires with a rhombus cross-section were transformed into thermodynamically stable elongated cuboctahedral Au nanowires with a hexagonal cross-section during the reaction. After the transformation, ZnO thin films with six twinned domains were formed on the side planes of the elongated cuboctahedral Au nanowire trunks, and six ZnO nanowire branches were grown on the ZnO thin films. Further, 3D hierarchical Ag–ZnO nanostructures were obtained via the same vapor–solid mechanism leading to the epitaxial growth of ZnO nanowires on vertically oriented Ag nanoplates on an aluminum oxide (Al2O3) substrate. Therefore, the growth mechanism developed herein can be generally employed to fabricate 3D hierarchical plasmo-photonic nanoarchitectures.

Single-Crystalline Gold Nanowires Synthesized from Light-Driven Oriented Attachment and Plasmon-Mediated Self-Assembly of Gold Nanorods or Nanoparticles

Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water.

Facile Fabrication of Multi‐targeted and Stable Biochemical SERS Sensors

The direct transfer of single-crystalline Au nanowires (NWs) onto Au substrates was achieved by a simple attachment and detachment process. In the presence of a lubricant, Au NWs grown vertically on a sapphire substrate were efficiently moved to an Au substrate through van der Waals interactions. We demonstrate that the transferred Au NWs on the Au substrate can act as sensitive, reproducible, and long-term-stable surface-enhanced Raman scattering (SERS) sensors by detecting human α-thrombin as well as Pb(2+) and Hg(2+) ions. These three biochemically and/or environmentally important analytes were successfully detected with high sensitivity and selectivity by Au NW-SERS sensors bound by a thrombin-binding aptamer. Furthermore, the as-prepared sensors remained in working order after being stored under ambient conditions at room temperature for 80 days. Because Au NWs can be routinely transferred onto Au substrates and because the resultant Au NW-SERS sensors are highly stable and provide with high sensitivity and reproducibility of detection, these sensors hold potential for practical use in biochemical sensing.

High-quality nanomechanical resonator based on a defect-free gold nanowire

Nanomechanical resonators were fabricated using defect-free single-crystalline Au nanowires (NWs), and their mechanical properties were investigated by using the magneto-motive detection method. The fabricated Au NW resonators exhibited a resonance frequency of 33–119 MHz and a quality factor of 1800 ∼ 11000, depending on the resonator’s dimensions. Compared to its amorphous film counterpart, the Au NW resonator showed noticeable increases in both the resonance frequency and the quality factor. Also observed was a significant increase in the dynamic range for the NW resonator. These improvements could be attributed to low and uniform energy dissipation by the defect-free single-crystalline Au NW resonator. In addition, the length dependence of the nonlinear characteristics was observed. Mechanical softening was observed in the case of short (l = 2 µm and 3 µm) resonators while mechanical hardening was observed in the case of long (l = 4 µm) resonators.

S-L-S 성장기구를 이용한 양질의 골드 나노선 합성

Single crystalline Au nanowires were successfully synthesized in a tube-type furnace. The Au nanowires were grown by vapor phase synthesis technique using solid-liquid-solid (SLS) mechanism on substrates of corning glass and Si wafer. Prior to Au nanowire synthesis, Au thin film served as both catalyst and source for Au nanowire was prepared by sputtering process. Average length of the grown Au nanowires was approximately 1 on both the corning glass and Si wafer substrates, while the diameter and the density of which were dependent on the thickness of the Au thin film. To induce a super-saturated states for the Au particle catalyst and Au molecules during the Au nanowire synthesis, thickness of the Au catalyst thin film was fixed to 10 nm or 20 nm. Additionally, synthesis of the Au nanowires was carried out without introducing carrier gas in the tube furnace, and synthesis temperature was varied to investigate the temperature effect on the resulting Au nanowire characteristics.

Insulating State and Breakdown of Fermi Liquid Description in Molecular-Scale Single-Crystalline Wires of Gold

Electrical transport measurements on ultrathin single-crystalline Au nanowires, synthesized via a wet chemical route, show an unexpected insulating behavior. The linear response electrical resistance exhibits a power-law dependence on temperature. In addition, the variation of current over a wide range of temperature and voltage obeys a universal scaling relation that provides compelling evidence for a non-Fermi liquid behavior. Our results demonstrate that the quantum ground state in ultrathin nanowires of simple metallic systems can be radically different from their bulk counterparts and can be described in terms of a Tomonaga-Luttinger liquid (TLL), in the presence of remarkably strong electron-electron interactions.

The Role of Oxidative Etching in the Synthesis of Ultrathin Single-Crystalline Au Nanowires

The fabrication of ultrathin single-crystal Au nanowires with high aspect ratio and that are stable in air is challenging. Recently, a simple wet-chemical approach using oleylamine has been reported for the synthesis of Au nanowires with micrometer length and 2 nm in diameter. Despite efforts to understand the mechanism of the reaction, an ultimate question about the role of oxygen (O(2)) during the synthesis remained unclear. Here we report that the synthesis of ultrathin Au nanowires employing oleylamine is strongly affected by the amount of O(2) absorbed in the reaction solution. Saturating the solution with O(2) leads to both a high-yield production of nanowires and an increase in their length. Nanowires with diameters of about 2 nm and lengths of 8 μm, which corresponds to an aspect ratio of approximately 4000, were produced. The role of oxygen is attributed to the enhanced oxidation of twin defects on Au nanoparticles formed in the first stage of the reaction. Understanding the role of oxidative etching is crucial to significantly increasing the yield and the length of ultrathin Au nanowires.

Superconducting Junction of a Single-Crystalline Au Nanowire for an Ideal Josephson Device

We report on the fabrication and measurements of a superconducting junction of a single-crystalline Au nanowire, connected to Al electrodes. The current-voltage characteristic curve shows a clear supercurrent branch below the superconducting transition temperature of Al and quantized voltage plateaus on application of microwave radiation, as expected from Josephson relations. Highly transparent (0.95) contacts very close to an ideal limit of 1 are formed at the interface between the normal metal (Au) and the superconductor (Al). The very high transparency is ascribed to the single crystallinity of a Au nanowire and the formation of an oxide-free contact between Au and Al. The subgap structures of the differential conductance are well explained by coherent multiple Andreev reflections (MAR), the hallmark of mesoscopic Josephson junctions. These observations demonstrate that single crystalline Au nanowires can be employed to develop novel quantum devices utilizing coherent electrical transport.

Elastic properties of nanowires

AbstractThe elastic properties of metallic and semiconducting nanowires were analyzed by different techniques employing static and dynamic loads. The reliability of the methods is verified by analyzing well defined microstructures and a good agreement for the values of the Young's modulus determined by the different methods was achieved. For the investigated materials systems (Au, W, Si, InN), basically no differences in the Young's moduli were observed between microstructures, bulk material, and nanowires with radii of 20–300 nm. Microstructure, morphological undulation, defects, and contaminations, however, can drastically change the apparent Young's moduli of nanowires. Examples are given, where an apparent increasing or decreasing of the Young's modulus with decreasing diameter is caused by such effects. The same effects have also influence on the fracture strength in nanowires. While perfect Au nanowires exhibit fracture strengths exceeding the bulk values up to two orders of magnitude, any anomaly causes earlier failure. In addition, failure mechanisms are observed to be dependent on the microstructure. While single crystalline Au nanowires have shown a pure elastic deformation upon load, polycrystalline nanowires show a remarkable plastic deformation before breaking.

Integrated Fabrication and Magnetic Positioning of Metallic and Polymeric Nanowires Embedded in Thin Epoxy Slabs

This paper describes a process for the fabrication and positioning of nanowires (of Au, Pd, and conjugated polymers) embedded in thin epoxy slabs. The procedure has four steps: (i) coembedding a thin film of metal or conducting polymer with a thin film of nickel metal (Ni) in epoxy; (ii) sectioning the embedded structures into nanowires with an ultramicrotome ("nanoskiving"); (iii) floating the epoxy sections on a pool of water; and (iv) positioning the sections with an external magnet to a desired location ("magnetic mooring"). As the water evaporates, capillary interactions cause the sections to adhere to the substrate. Both the Ni and epoxy can be etched to generate free-standing metallic nanowires. The average translational deviation in the positioning of two nanowires with respect to each other is 16 +/- 13 mum, and the average angular deviation is 3 +/- 2 degrees . Successive depositions of nanowires yield the following structures of interest for electronic and photonic applications: electrically continuous junctions of two Au nanowires, two Au nanowires spanned by a poly(3-hexylthiophene) (P3HT) nanowire; single-crystalline Au nanowires that cross; crossbar arrays of Au nanowires; crossbar arrays of Au and Pd nanowires; and a 50 x 50 array of poly(benzimidazobenzophenanthroline ladder) (BBL) nanowires. Single-crystalline Au nanowires can be placed on glass wool fibers or on microfabricated polymeric waveguides, with which the nanowire can be addressed optically.

Facile Synthesis of Ultrathin and Single‐Crystalline Au Nanowires

Au nanowires have attracted significant interest in nanomaterials research owing to their chemical stability and high conductivity for potential nanoelectronic applications. However, previous syntheses yielded only polycrystalline Au nanowires with diameters larger than 10 nm. Very recent advances in solution-phase synthesis have led to the formation of ultrathin single-crystalline Au nanowires with diameters of less than 10 nm. This Focus Review summarizes the synthesis, characterization, and transport studies of these ultrathin single-crystalline Au nanowires for potential electronic device applications.

Ultrathin Au Nanowires and Their Transport Properties

This paper presents a facile synthesis of single-crystalline Au nanowires by reduction of HAuCl4 in oleic acid and oleylamine. The diameter of these micron-meter-long Au nanowires is controlled to be 3 and 9 nm by volume ratio of oleylamine and oleic acid. When linked between two gold electrodes, the 9 nm Au nanowire shows good electron conductivity with its breakdown current density reaching 3.5 x 10(12) A/m2. This demonstrates that the chemically made ultrathin Au nanowires can be used as a molecular-scale interconnect for nanoelectronic applications.

Synthesis of gold nanowires with controlled crystallographic characteristics

The controlled fabrication of poly- and single-crystalline Au nanowires is reported. In polycarbonate templates, prepared by heavy-ion irradiation and subsequent etching, Au nanowires with diameters down to 25 nm are electrochemically synthesized. Four-circle X-ray diffraction and transmission electron microscopy measurements demonstrate that wires deposited potentiostatically at a voltage of -1.2 V at 65 °C are single-crystalline and oriented along the [110] direction. By reverse-pulse electrodeposition, wires oriented along the [100] direction are grown. The wires are cylindrical over their whole length. The morphology of the caps growing on top of poly- and single-crystalline wires is a strong indication of the particular crystalline structure of the nanowires.