Core-shell Nanowires Research Articles

SiO2/SiC Nanowire Surfaces as a Candidate Biomaterial for Bone Regeneration

Tissue engineering (TE) and nanomedicine require devices with hydrophilic surfaces to better interact with the biological environment. This work presents a study on the wettability of cubic silicon-carbide-based (SiC) surfaces. We developed four cubic silicon-carbide-based epitaxial layers and three nanowire (NW) substrates. Sample morphologies were analyzed, and their wettabilities were quantified before and after a hydrogen plasma treatment to remove impurities due to growth residues and enhance hydrophilicity. Moreover, sample biocompatibility has been assessed with regard to L929 cells. Our results showed that core–shell nanowires (SiO2/SiC NWs), with and without hydrogen plasma treatment, are the most suitable candidate material for biological applications due to their high wettability that is not influenced by specific treatments. Biological tests underlined the non-toxicity of the developed biomaterials with regard to murine fibroblasts, and the proliferation assay highlighted the efficacy of all the surfaces with regard to murine osteoblasts. In conclusion, SiO2/SiC NWs offer a suitable substrate to develop platforms and membranes useful for biomedical applications in tissue engineering due to their peculiar characteristics.

On-Chip Monolithically Integrated UltravioletLow-Threshold Plasmonic Metal-Semiconductor Heterojunction Nanolasers.

The metal-semiconductor heterojunction is imperative for the realization of electrically driven nanolasers for chip-level platforms. Progress in developing such nanolasers has hitherto rarely been realized, however, because of their complexity in heterojunction fabrication and the need to use noble metals that are incompatible with microelectronic manufacturing. Most plasmonic nanolasers lase either above a high threshold (101 -103 MW cm-2 ) or at a cryogenic temperature, and lasing is possible only after they are removed from the substrate to avoid the large ohmic loss and the low modal reflectivity, making monolithic fabrication impossible. Here, for the first time, record-low-threshold, room-temperature ultraviolet (UV) lasing of plasmon-coupled core-shell nanowires that are directly grown on silicon is demonstrated. The naturally formed core-shell metal-semiconductor heterostructure of the nanowires leads to a 100-fold improvement in growth density over previous results. This unprecedentedly high nanowire density creates intense plasmonic resonance, which is outcoupled to the resonant Fabry-Pérot microcavity. By boosting the emission strength by a factor of 100, the hybrid photonic-plasmonic system successfully facilitates a record-low laser threshold of 12kW cm-2 with a spontaneous emission coupling factor as high as ≈0.32 in the 340-360nm range. Such architecture is simple and cost-competitive for future UV sources in silicon integration.

Ag2Cu(VO3)4/PEDOT:PSS core-shell nanowire for lithium-ion batteries

Recently, multi-component transition-metal vanadium oxides (MTVOs) have shown great potential as a new class of active materials for lithium-ion batteries (LIBs). Compared with simple vanadium oxides, the presence of multi-component transition-metal elements in MTVOs can greatly improve the capacity and cycling stability. Here, we synthesized Ag2Cu(VO3)4 (SCVO) via a simple hydrothermal method. To further improve the specific capacity and electrical conductivity, SCVO/PEDOT:PSS core-shell nanowires were constructed by a dip-coating approach. Electrochemical measurements revealed that SCVO/PEDOT:PSS nanowires exhibit higher initial Coulombic efficiency and better cycling stability as anode material for LIBs.

Ultrathin Ag@ZnO Core–Shell Nanowires for Stable Flexible Transparent Conductive Films

Ultrathin Ag@ZnO Core–Shell Nanowires for Stable Flexible Transparent Conductive Films

Atomic Layer Deposition and Strain Analysis of Epitaxial GaN-ZnO Core-Shell Nanowires.

We demonstrate the epitaxial coating of GaN NWs with an epitaxial ZnO shell by atomic layer deposition at 300 °C. Scanning transmission electron microscopy proves a sharp and defect-free coherent interface. The strain in the core-shell structure due to the lattice mismatch and different thermal expansion coefficients of GaN and ZnO was analyzed using 4D-STEM strain mapping and Raman spectroscopy and compared to theoretical calculations. The results highlight the outstanding advantages of epitaxial shell growth using atomic layer deposition, e.g., conformal coating and precise thickness control.

Palladium atomic layers coated on ultrafine gold nanowires boost oxygen reduction reaction

Palladium-based nanocatalysts play an important role in catalyzing the cathode oxygen reduction reaction (ORR) for fuel cells working under alkaline conditions, but the performance still needs to be improved to meet the requirements for large-scale applications. Herein, Au@Pd core–shell nanowires have been developed by coating Pd atomic layers on ultrafine gold nanowires and display outstanding electrocatalytic performance towards alkaline ORR. It is found that Pd overlayers with atomic thickness can be coated on 3 nm Au nanowires under CO atmosphere and completely cover the surfaces. The obtained ultrafine Au@Pd nanowires exhibit an electrochemical active area (ECSA) of 68.5 m2/g and a mass activity of 0.91 A/mg (at 0.9 V vs. RHE), which is around 3.1 and 15.2 times higher than that of commercial Pd/C. The activity loss of the ultrafine Au@Pd nanowire after 10,000 cycles of accelerated degradation tests is only ∼20 %, demonstrating its much better stability compared to commercial Pd/C. Further characterizations combined with density functional theory (DFT) calculations demonstrate that the electronic interactions between Pd atomic layers and underlying Au can increase the electronic density of Pd and promote the efficient activation of oxygen, thus leading to the improved ORR performance.

High-Yield Synthesis of SiC@SiO2 Core–Shell Nanowires on Graphite Substrates for Energy Applications

High-Yield Synthesis of SiC@SiO₂ Core–Shell Nanowires on Graphite Substrates for Energy Applications

Fabrication of CuO (p)–ZnO (n) Core–Shell Nanowires and Their H2-Sensing Properties

Unlike the conventional one-dimensional (1D) core–shell nanowires (NWs) composed of p-type shells and n-type cores, in this work, an inverse design is proposed by depositing n-type ZnO (shell) layers on the surface of p-type CuO (core) NWs, to have a comprehensive understanding of their conductometric gas-sensing kinetics. The surface morphologies of bare and core–shell NWs were investigated by field emission scanning electron microscope (FE-SEM). The ZnO shell layer was presented by overlay images taken by electron dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The pronounced crystalline plane peaks of ZnO were recorded in the compared glancing incident X-ray diffraction (GI-XRD) spectra of CuO and CuO–ZnO core–shell NWs. The ZnO shell layers broaden the absorption curve of CuO NWs in the UV-vis absorption spectra. As a result of the heterostructure formation, the intrinsic p-type sensing behavior of CuO NWs towards 250 and 500 ppm of hydrogen (H2) switched to n-type due to the deposition of ZnO shell layers, at 400 °C in dry airflow.

Silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays with low water adhesion and high antibacterial activity

Nanostructured surfaces based on silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays, which can assure protection against various environmental factors such as water and bacteria were developed by combining dry preparation techniques namely thermal oxidation in air, radio frequency (RF) magnetron sputtering and thermal vacuum evaporation. Thus, high-aspect-ratio ZnO nanowire arrays were grown directly on zinc foils by thermal oxidation in air. Further ZnO nanowires were coated with a CuO layer by RF magnetron sputtering, the obtained ZnO–CuO core–shell nanowires being decorated with Ag nanoparticles by thermal vacuum evaporation. The prepared samples were comprehensively assessed from morphological, compositional, structural, optical, surface chemistry, wetting and antibacterial activity point of view. The wettability studies show that native Zn foil and ZnO nanowire arrays grown on it are featured by a high water droplet adhesion while ZnO–CuO core–shell nanowire arrays (before and after decoration with Ag nanoparticles) reveal a low water droplet adhesion. The antibacterial tests carried on Escherichia coli (a Gram-negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium) emphasize that the nanostructured surfaces based on nanowire arrays present excellent antibacterial activity against both type of bacteria. This study proves that functional surfaces obtained by relatively simple and highly reproducible preparation techniques that can be easily scaled to large area are very attractive in the field of water repellent coatings with enhanced antibacterial function.

Construction of pH-universal hydrogen evolution freeway in MoO3-MoNi4@Cu core–shell nanowires via synergetic electronic and geometric effect

Construction of pH-universal hydrogen evolution freeway in MoO3-MoNi4@Cu core–shell nanowires via synergetic electronic and geometric effect

A high κ, transparent, and stretchable Cu@TiO2 core@shell nanowire/poly(dimethylsiloxane) composite film for sensitive wearable touch sensor

Touch sensors are crucial for the development of advanced wearable devices and enhancement of the user experience through human-machine interaction. The properties of dielectric films, including their high dielectric constants (high-κ), low loss tangents (tan⁡δ), transparency, and stretchability are key factors that impact the accuracy, reliability, and display visibility of wearable touch sensors. Here, we present an approach for fabricating a Poly(dimethylsiloxane) (PDMS)-based dielectric film that can achieve a dielectric constant 6 times larger than that of pure PDMS film by loading a very low wt% (3%) of copper@titanium dioxide (Cu@TiO2) core-shell nanowires (NWs) to PDMS matrix. TiO2 was deposited on surfaces of Cu NWs by a hydrothermal reaction to form the covering shell, and it is experimentally and theoretically proved that the shell can suppress the scattering from metal surfaces, resulting in improving the transparency, and reducing the dielectric loss of the film (tan⁡δ=0.01–0.06). The nanocomposite film also exhibits outstanding mechanical property (standing up to a tensile strain of 200%). The demonstration of a transparent, highly sensitive and low noise multi-touch sensor using high-κ film suggests that this film has potential application in next-generation of wearable electronic devices for human-machine interaction.

Ultrahigh-Temperature-Tolerant NiO@Ag NW-Based Transparent Heater with High Stability, Durability, Ultraflexibility, and Quick Thermal Response

High-performance electrical heaters with high transmittance, fast response speed, superior heat resistance, ultraflexibility, high working temperature, and sufficient stabilities are highly desirable for application in heating systems in areas such as healthcare and aerospace. Herein, we demonstrate an ultrahigh-temperature-tolerant flexible transparent heater (FTH) consisting of a NiO@Ag core–shell nanowire (NiO@Ag NW) network and a colorless polyimide (cPI) film. NiO nanoshells are formed uniformly on the surface of Ag NWs through the solution process, which enhances the stability of Ag NWs. The heating behaviors and transmittance can be controlled by the NiO@Ag NW spin-coating cycle. The NiO@Ag NW-based FTHs show a fast thermal response of ∼15 s, a high transmittance of 86.2% in the visible region, and a large thermal figure of merit of 30.7 m2·°C/W under optimal preparation conditions. The saturation temperature of FTHs has barely changed after 20 taping tests and 1000 bending cycles at a bending radius of 0.5 mm. Particularly, the heating temperature of FTHs can reach 266 °C in the air under an applied voltage of 9 V. Moreover, the FTHs possess sufficient heating reliability, stability, and repeatability during the long-term and repeated heating cycles. In addition, the FTHs are resistant to a number of harsh environments.

Pd@PtRuNi core–shell nanowires as oxygen reduction electrocatalysts

Fuel cells, as the alternative to fossil energy, have engaged widespread attention by reason of the high conversion efficiency from the chemical energy to the electric energy combined with low pollution emissions. The cathodic ORR catalysts with excellent performance and cost-effectiveness are the dominant point towards the massive development of fuel cells. Here, our group select the Pd NWs as the template and construct the Pd@PtRuNi core–shell bilayer nanostructure to expand platinum atom utilization. Pd@PtRuNi bilayer core–shell NWs unfold elevated mass activity of at 0.9 V versus RHE in alkaline media, 2.03- and 6.23-fold of pristine Pd NWs and benchmark commercial Pt/C, respectively. Meanwhile, the cyclic stability tests reveal the excellent durability of Pd@PtRuNi NWs, whose mass activity is only 13.58% degradation after accelerated durability tests. The catalytic activity and durability towards ORR are better than the U.S. 2025 DOE target ( and less than 40% activity attenuation at 0.9 V after 30 000 potential cycles). The elevated catalytic properties can be traceable to the synergism between the ligand effect of Ni and Ru and one-dimensional structure superiority, which optimizes the electronic structure of active sites, promotes the charge transfer and restrains the agglomeration and detachment.

Enhancing electroreduction activity and selectivity of N2-to-NH3 through proton-feeding adjustments in Ag@AgP2@Ni-CoP@C core-shell nanowires

The synthesis of NH3via electrochemical N2 fixation at ambient conditions has been proposed as a promising alternative to the traditional Haber-Bosch process. However, the development of highly efficient and selective electrocatalysts remains a challenge. In this study, uniform Ag@AgP2 @Ni-CoP@C core-shell nanowires were synthesized using a template-engaged strategy. The merging of conductive Ag core with active AgP2 and porous carbon-coated Ni-doped CoP shells favors the mass and electron transfers, effectively lowering the activation energy toward the reduction of N2 to NH3. Density functional theory (DFT) calculations further indicates that the sandwiched AgP2 layer plays crucial roles in promoting electrocatalytic kinetics and suppressing the competitive hydrogen evolution reactions. Benefiting from these advantages, the titled catalyst achieved a high NH3 yield of 16.84 μg h−1 mg–1cat. at −0.4 V (vs. reversible hydrogen electrode, RHE) and a high Faradaic efficiency of 21.7 % at −0.3 V vs. RHE, as well as high electrochemical and structure stability.

Fire-resistant and hydrophobic paper based on Si3N4@PDMS core-shell nanowires with 3D interlocking structure

Paper with simultaneous fire-resistance and hydrophobicity have greatly potential applications in the fields of packing, storage and delivering information, which attracts increasing attention recently. Different from the traditional cellulose-based paper which is extremely easily damaged by water and fire, a new type of highly flexible, fire-resistant and hydrophobic paper based on Si3N4 nanowires and polydimethylsiloxane (PDMS) is reported. Specially, the Si3N4@PDMS core-shell nanowires with 3D interlocking structure are designed, in which the Si3N4 nanowires act as the inorganic fire-resistant frameworks and the PDMS shell with low surface energy provides the hydrophobic surface. The Si3N4@PDMS core-shell nanowires are intertwined and interlaced to form a highly flexible Si3N4@PDMS paper. The tensile strength of Si3N4@PDMS paper is 6.19 MPa, indicating the good mechanical property. The obtained Si3N4@PDMS paper has the characteristics of writability, fire-resistance and hydrophobicity. The high thermal stability of Si3N4 nanowires makes Si3N4@PDMS paper exhibit excellent fire resistance. No obvious change is observed for the commercial paper with Si3N4@PDMS paper as the fire-shielding layer after heating for 30 min. In addition, the contact angles of water droplets are all greater than 110° over the surfaces of Si3N4@PDMS paper after mechanical damages, chemical corrosions and thermal treatments. Si3N4@PDMS paper can be used in oil/water separation and oil collection. More importantly, Si3N4@PDMS paper can be used for writing without being damaged by fire or water. The present work may inspire the development and application of functional paper and is expected to become a breakthrough in the traditional paper industry.

Multilayer Graphene-Coated Silicon Carbide Nanowire Formation Under Defocused Laser Irradiation

Graphene-coated silicon carbide (SiC@C) core–shell nanostructures have attracted attention in the fields of energy storage and nanoelectronics. In this study, multilayer graphene-coated silicon carbide (SiC) nanowires were obtained through the laser irradiation of a mixture target of graphite powder and silicon (Si) grinding sludge discharged from Si wafer manufacturing. Laser irradiation was performed using an ytterbium (Yb) fiber pulsed laser with a pulse width of 10 ms and a wavelength of 1070 nm with various defocus distances. The effect of laser defocusing on the morphology of the generated nanostructures was investigated. Results showed that nanowires were produced under the defocused conditions, and nanoparticles were observed at the on-focus position. The products obtained under all defocused conditions showed a core–shell structure, and the SiC nanowires were covered by graphene layers. The aspect ratio of the nanowires increased with the defocus distance. Observation of the laser-induced plume using a high-speed camera showed that when the laser was defocused, the plume propagation speed slowed down, and the shape of the plume changed to a swirling vortex. The nanowire formation was closely related to the propagation speed and shape variation of the plume. This successful production of SiC@C core–shell nanowires from Si waste opens up the possibility of the sustainable development of new materials for energy storage and nanoelectronics.

Comparison of two methods for one-dimensional Ga2O3-ZnGa2O4 core–shell heterostructure synthesis

While gallium oxide Ga2O3 has recently shown promise as a new ultra-wide bandgap semiconductor in the form of thin films and nanowires (NWs), its widespread applicability is limited due to lack of native p-type conductivity, thus requiring fabrication of heterojunctions. A potential matching material is spinel zinc gallate ZnGa2O4. In this work we demonstrated and compared two novel approaches of one-dimensional Ga2O3-ZnGa2O4 core–shell NW heterostructure preparation: (a) a direct deposition of a ZnGa2O4 coating using a reactive magnetron co-sputtering; (b) annealing of a sacrificial few-nm-thick ZnO coating, deposited via atomic layer deposition, at high temperature to enable solid state reaction between ZnO and Ga2O3. The as-grown nanostructures were characterized via scanning and transmission electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Room temperature optical features were disclosed using photoluminescence and optical absorption. While both methods are viable for production of the heterostructures, smoother and more uniform ZnGa2O4 coating around Ga2O3 NWs was obtained via sacrificial layer conversion in comparison to the sputter-deposited one. These heterostructures could potentially be used for photocatalysis and nanoscale ultra-wide bandgap electronics.

Achieving the high-energy-density asymmetric supercapacitor by hierarchical molybdenum-vanadium-sulphide@covalt sulphide core–shell nanoporous hybrid as cathode and iron oxide@carbon-nanofibers/nitrogen-doped reduced graphene oxide aerogel as anode

In recent decades, supercapacitors have attracted much research as low-cost, reliable, and environment-friendly energy storage devices. However, the low energy density and low operating voltage limit its wide applications. Herein, a novel 1D–2D constructed 3D multicomponent Mox:Vy–S@Co9S8 core–shell nanowires array is designed and fabricated as the cathode material through a simple and economical two-step hydrothermal reaction and electrodeposition process. The constructed 3D Mo0.5V0.5–S@Co9S8 electrode exhibits excellent charge storage capability; an area capacity of 0.91 mA h cm−2 with a corresponding specific capacity of 480.9 mA h g−1 at 2 mA cm−2. Moreover, a solid-state ASC (SS–ASC) is assembled with the as-obtained Fe2O3@CNFs/N–rGO aerogel as the anode, the constructed 3D Mox:Vy–S@Co9S8 NWAs as cathode, and KOH–PVA–gel as a gel electrolyte. As proof of concept, the assembled SS–ASC display an excellent operating voltage window of ~1.7 V and an outstanding energy density of ~108.47 W h kg−1 at ~520.65 W kg−1 power density. Also, when connected in series, the two SS–ASC devices can run an electronic clock for 30 min, demonstrating the practicability of the constructed 3D Mox:Vy–S@Co9S8 NWAs as a promising electrode material for the development of the high energy density ASC.

Flux-periodic oscillations in proximitized core–shell nanowires

Flux-periodic oscillations of the superconducting gap in proximitized core–shell nanowires are explored. Periodicity of oscillations in the energy spectrum of a cylindrical nanowire is compared with nanowires having hexagonal and square cross-section geometry, along with the effects of Zeeman and Rashba spin–orbit interaction. A transition between h/e and h/2e periodicity is found and shown to be dependent on the chemical potential, with correspondence to degeneracy points of the angular momentum quantum number. For a thin shell of a square nanowire, solely h/e periodicity is found in the infinite wire spectrum and shown to result from energy separation between the lowest groups of excited states.

Constructing a Si-CuO core-shell nanowire heterojunction photoanode for enzyme-free and highly-sensitive glucose sensing

Constructing novel heterojunctions has become an effective strategy to improve the performance of photoelectrochemical (PEC) biosensors, but most of the glucose-sensing photoelectrodes involve enzyme modification and disordered or semi-closed surface topography which restricts the working environment and sensing performance. Herein, the dense and burr-like CuO nanospikes (CuONSs) are grown on all over the whole surfaces of the relatively-sparse and ordered Si nanowires (SiNWs) by a combination of magnetron sputtering and hydrothermal growth. The optimized SiNWs-CuONSs heterojunction with a core–shell structure achieves the enzyme-free PEC detection of glucose with a sensitivity of 2324.09 μA mM−1 cm−2 in the concentration range of 0–1.0 mM and a detection limit of 0.74 μM (Signal/Noise = 3). The excellent sensing performance is ascribed to that (1) the SiNWs with a large specific surface area acting as host have open-style surface topography, ensuring the analyte flowability; (2) the CuONSs with a desired glucose-catalytic activity are hierarchical, providing a great number of active sites; and (3) the SiNWs-CuONSs heterojunction has a satisfactory optical absorption and a high efficiency of the photogenerated-hole transfer. This work demonstrates that the enzyme-free and highly-sensitive glucose detection can be realized by morphology-controllable heterojunction, and provides an alternative route to noninvasive sensing.