Atomic Structure of Ultrathin Gold Nanowires

Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1–2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications

Low-Temperature Solution-Phase Growth of Silicon and Silicon-Containing Alloy Nanowires

Low-temperature synthesis of crystalline silicon and silicon-containing nanowires remains a challenge in synthetic chemistry due to the lack of sufficiently reactive Si precursors. We report that colloidal Si nanowires can be grown using tris­(trimethylsilyl)­silane or trisilane as the Si precursor by a Ga-mediated solution–liquid–solid (SLS) approach at temperatures of about 200 °C, which is more than 200 °C lower than that reported in the previous literature. We further demonstrate that the new Si chemistry can be adopted to incorporate Si atoms into III–V semiconductor lattices, which holds promise to produce a new Si-containing alloy semiconductor nanowire. This development represents an important step toward low-temperature fabrication of Si nanowire-based devices for broad applications

Structure-Sensitive CO₂ Electroreduction to Hydrocarbons on Ultrathin 5‑fold Twinned Copper Nanowires

Copper is uniquely active for the electrocatalytic reduction of carbon dioxide (CO₂) to products beyond carbon monoxide, such as methane (CH₄) and ethylene (C₂H₄). Therefore, understanding selectivity trends for CO₂ electrocatalysis on copper surfaces is critical for developing more efficient catalysts for CO₂ conversion to higher order products. Herein, we investigate the electrocatalytic activity of ultrathin (diameter ∼20 nm) 5-fold twinned copper nanowires (Cu NWs) for CO₂ reduction. These Cu NW catalysts were found to exhibit high CH₄ selectivity over other carbon products, reaching 55% Faradaic efficiency (FE) at −1.25 V versus reversible hydrogen electrode while other products were produced with less than 5% FE. This selectivity was found to be sensitive to morphological changes in the nanowire catalyst observed over the course of electrolysis. Wrapping the wires with graphene oxide was found to be a successful strategy for preserving both the morphology and reaction selectivity of the Cu NWs. These results suggest that product selectivity on Cu NWs is highly dependent on morphological features and that hydrocarbon selectivity can be manipulated by structural evolution or the prevention thereof

Crystal Structure Control of Zinc-Blende CdSe/CdS Core/Shell Nanocrystals: Synthesis and Structure-Dependent Optical Properties

Nearly monodisperse zinc-blende CdSe/CdS core/shell nanocrystals were synthesized by epitaxial growth of 1–6 monolayers of CdS shell onto presynthesized zinc-blende CdSe core nanocrystals in one pot. To retain the zinc-blende structure, the reaction temperature was lowered to the 100–140 °C range by using cadmium diethyldithiocarbamate as a single-source precursor and primary amine as activation reagents for the precursor. Although the wurtzite counterparts grown under the same conditions showed optical properties similar to those reported in the literature, zinc-blende CdSe/CdS core/shell nanocrystals demonstrated surprisingly different optical properties, with ensemble single-exponential photoluminescence decay, significant decrease of photoluminescence peak width by the shell growth, and comparatively high photoluminescence quantum yields. The lifetime for the single-exponential ensemble photoluminescence decay of zinc-blende CdSe/CdS core/shell nanocrystals with 3–4 monolayers of CdS shell was reproducibly found to be approximately 16.5 ± 1.0 ns

Synthesis of Ultrathin Copper Nanowires Using Tris(trimethylsilyl)silane for High-Performance and Low-Haze Transparent Conductors

Colloidal metal nanowire based transparent conductors are excellent candidates to replace indium–tin–oxide (ITO) owing to their outstanding balance between transparency and conductivity, flexibility, and solution-processability. Copper stands out as a promising material candidate due to its high intrinsic conductivity and earth abundance. Here, we report a new synthetic approach, using tris­(trimethylsilyl)­silane as a mild reducing reagent, for synthesizing high-quality, ultrathin, and monodispersed copper nanowires, with an average diameter of 17.5 nm and a mean length of 17 μm. A study of the growth mechanism using high-resolution transmission electron microscopy reveals that the copper nanowires adopt a five-fold twinned structure and evolve from decahedral nanoseeds. Fabricated transparent conducting films exhibit excellent transparency and conductivity. An additional advantage of our nanowire transparent conductors is highlighted through reduced optical haze factors (forward light scattering) due to the small nanowire diameter

Solution-Processed Copper/Reduced-Graphene-Oxide Core/Shell Nanowire Transparent Conductors

Copper nanowire (Cu NW) based transparent conductors are promising candidates to replace ITO (indium–tin-oxide) owing to the high electrical conductivity and low-cost of copper. However, the relatively low performance and poor stability of Cu NWs under ambient conditions limit the practical application of these devices. Here, we report a solution-based approach to wrap graphene oxide (GO) nanosheets on the surface of ultrathin copper nanowires. By mild thermal annealing, GO can be reduced and high quality Cu r-GO core–shell NWs can be obtained. High performance transparent conducting films were fabricated with these ultrathin core–shell nanowires and excellent optical and electric performance was achieved. The core–shell NW structure enables the production of highly stable conducting films (over 200 days stored in air), which have comparable performance to ITO and silver NW thin films (sheet resistance ∼28 Ω/sq, haze ∼2% at transmittance of ∼90%)

Benzoin Radicals as Reducing Agent for Synthesizing Ultrathin Copper Nanowires

In this work, we report a new, general synthetic approach that uses heat driven benzoin radicals to grow ultrathin copper nanowires with tunable diameters. This is the first time carbon organic radicals have been used as a reducing agent in metal nanowire synthesis. <i>In-situ</i> temperature dependent electron paramagnetic resonance (EPR) spectroscopic studies show that the active reducing agent is the free radicals produced by benzoins under elevated temperature. Furthermore, the reducing power of benzoin can be readily tuned by symmetrically decorating functional groups on the two benzene rings. When the aromatic rings are modified with electron donating (withdrawing) groups, the reducing power is promoted (suppressed). The controllable reactivity gives the carbon organic radical great potential as a versatile reducing agent that can be generalized in other metallic nanowire syntheses

Ultrathin Epitaxial Cu@Au Core–Shell Nanowires for Stable Transparent Conductors

Copper nanowire networks are considered a promising alternative to indium tin oxide as transparent conductors. The fast degradation of copper in ambient conditions, however, largely overshadows their practical applications. Here, we develop the synthesis of ultrathin Cu@Au core–shell nanowires using trioctylphosphine as a strong binding ligand to prevent galvanic replacement reactions. The epitaxial overgrowth of a gold shell with a few atomic layers on the surface of copper nanowires can greatly enhance their resistance to heat (80 °C), humidity (80%) and air for at least 700 h, while their optical and electrical performance remained similar to the original high-performance copper (e.g., sheet resistance 35 Ω sq^–1 at transmittance of ∼89% with a haze factor <3%). The precise engineering of core–shell nanostructures demonstrated in this study offers huge potential to further explore the applications of copper nanowires in flexible and stretchable electronic and optoelectronic devices