Core-shell Nanowires Research Articles

Bending and reverse bending during the fabrication of novel GaAs/(In,Ga)As/GaAs core–shell nanowires monitored by in situ x-ray diffraction

We report on the fabrication of a novel design of GaAs/(In,Ga)As/GaAs radial nanowire heterostructures on a Si 111 substrate, where, for the first time, the growth of inhomogeneous shells on a lattice mismatched core results in straight nanowires instead of bent. Nanowire bending caused by axial tensile strain induced by the (In,Ga)As shell on the GaAs core is reversed by axial compressive strain caused by the GaAs outer shell on the (In,Ga)As shell. Progressive nanowire bending and reverse bending in addition to the axial strain evolution during the two processes are accessed by in situ by x-ray diffraction. The diameter of the core, thicknesses of the shells, as well as the indium concentration and distribution within the (In,Ga)As quantum well are revealed by 2D energy dispersive x-ray spectroscopy using a transmission electron microscope. Shell(s) growth on one side of the core without substrate rotation results in planar-like radial heterostructures in the form of free standing straight nanowires.

Ultrathin PtNiW@WOx core-shell nanowires for enhanced CO-tolerant hydrogen oxidation: three-in-one catalyst design

Ultrathin PtNiW@WOx core-shell nanowires for enhanced CO-tolerant hydrogen oxidation: three-in-one catalyst design

New growth mechanism of InAs-GaSb core-shell nanowires with polygonal triangular pyramids and quantum dots grown by MOCVD

In this paper, new growth mechanism of InAs/GaSb heterojunction nanowires grown by MOCVD has been investigated. A spear-shaped structure was firstly formed at the top of nanowires and GaAsSb quantum dots were firstly grown on the side walls of the nanowires by self-catalyzed mode. It is found that the length of InAs-GaSb nanowires in core-shell structure plays an important role in the formation of polygonal triangular pyramids and quantum dots structures. The shorter InAs nanowires become, the larger the polygonal triangular pyramid will be formed while the longer InAs nanowires become, the smaller the polygonal triangular pyramid will be formed, and quantum dots will appear on the side walls of nanowires. This new mechanism and growth technology will be conducive to the preparation of quantum dots attached to the surface of nanowires.

2H–Si/Ge for Group-IV Photonics: on the Origin of Extended Defects in Core–Shell Nanowires

2H–Si/Ge for Group-IV Photonics: on the Origin of Extended Defects in Core–Shell Nanowires

Multiwall carbon nanotube-hyperbranched polymaleimide core–shell nanowires with hierarchical porous and polar structure as sulfur host for sustainable lithium-sulfur batteries

Lithium–sulfur (Li–S) batteries have gained considerable attention as a promising alternative to current advanced batteries because of their low cost, natural abundance, high energy density, and environmental benignity of sulfur. The commercial application of Li–S batteries is being seriously impeded by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of solid phase transformation. Herein, a novel composite material (PPI@MWCNT-Y) with a hierarchical porous skeleton and polar channel is prepared as a sulfur host using a convenient in-situ one-pot polymerization. PPI@MWCNT-Y is composed of conductive mesoporous multi-wall carbon nanotubes (MWCNTs) core and a microporous hyperbranched polymaleimide (PPI) shell formed by the self-polymerization of N,N′-1,4-phenylenedimaleimide (PDM). The mesoporous and conductive channels in PPI@MWCNT-Y improve the redox kinetics of the active materials by serving as a fast electron and Li-ions transportation pathway. The microporous structure and abundant adsorption sites (N and O atoms) within the PPI@MWCNT-Y served as physical and chemical barriers, preventing the loss of LiPSs, and suppressing the shuttle effect. Consequently, the S/PPI@MWCNT-38 composite exhibited a high discharge capacity of 1338 mAh g−1 at 0.2 C and a low-capacity decay rate of 0.088% for 400 cycles at 1 C.

SiC@NiO Core-Shell Nanowire Networks-Based Optoelectronic Synapses for Neuromorphic Computing and Visual Systems at High Temperature.

1D nanowire networks, sharing similarities of structure, information transfer, and computation with biological neural networks, have emerged as a promising platform for neuromorphic systems. Based on brain-like structures of 1D nanowire networks, neuromorphic synaptic devices can overcome the von Neumann bottleneck, achieving intelligent high-efficient sensing and computing function with high information processing rates and low power consumption. Here, high-temperature neuromorphic synaptic devices based on SiC@NiO core-shell nanowire networks optoelectronic memristors (NNOMs) are developed. Experimental results demonstrate that NNOMs attain synaptic short/long-term plasticity and modulation plasticity under both electrical and optical stimulation, and exhibit advanced functions such as short/long-term memory and "learning-forgetting-relearning" under optical stimulation at both room temperature and 200°C. Based on the advanced functions under light stimulus, the constructed 5×3 optoelectronic synaptic array devices exhibit a stable visual memory function up to 200°C, which can be utilized to develop artificial visual systems. Additionally, when exposed to multiple electronic or optical stimuli, the NNOMs effectively replicate the principles of Pavlovian classical conditioning, achieving visual heterologous synaptic functionality and refining neural networks. Overall, with abundant synaptic characteristics and high-temperature thermal stability, these neuromorphic synaptic devices offer a promising route for advancing neuromorphic computing and visual systems.

1T'-transition metal dichalcogenide monolayers stabilized on 4H-Au nanowires for ultrasensitive SERS detection.

Unconventional 1T'-phase transition metal dichalcogenides (TMDs) have aroused tremendous research interest due to their unique phase-dependent physicochemical properties and applications. However, due to the metastable nature of 1T'-TMDs, the controlled synthesis of 1T'-TMD monolayers (MLs) with high phase purity and stability still remains a challenge. Here we report that 4H-Au nanowires (NWs), when used as templates, can induce the quasi-epitaxial growth of high-phase-purity and stable 1T'-TMD MLs, including WS2, WSe2, MoS2 and MoSe2, via a facile and rapid wet-chemical method. The as-synthesized 4H-Au@1T'-TMD core-shell NWs can be used for ultrasensitive surface-enhanced Raman scattering (SERS) detection. For instance, the 4H-Au@1T'-WS2 NWs have achieved attomole-level SERS detections of Rhodamine 6G and a variety of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins. This work provides insights into the preparation of high-phase-purity and stable 1T'-TMD MLs on metal substrates or templates, showing great potential in various promising applications.

High energy capability in poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposite incorporated with Ag@polyaniline@covalent organic framework core–shell nanowire

The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core–shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core–shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core–shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core–shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite.

Design and synthesis of NiCo2O4@Au@NiO sandwiched coaxial core–shell nanowire arrays on carbon fabric for high-performance supercapacitor

Design and synthesis of NiCo2O4@Au@NiO sandwiched coaxial core–shell nanowire arrays on carbon fabric for high-performance supercapacitor

Transition from anisotropic to isotropic optical absorption in core-shell square nanowires tuned by anti-crossing engineering.

The transition from anisotropic to isotropic optical properties in nanostructures plays an important role in developing next-generation intelligent photonic devices. Currently, core-shell nanostructures, frequently accompanied by different growth rates, are typically characterized by anisotropic optical properties at mid-infrared wavelengths. This inherent anisotropy, however, poses formidable challenges in achieving optical isotropy. In this work, an electric field is employed to transform the optical anisotropy of the off-centered core-shell square nanowires into optical isotropy. Based on the finite difference method, the results show that by tuning the electric field reasonably, the anti-crossing behavior of energy levels can be induced to align the energy structures in both eccentric and concentric nanowires. Although the optical anisotropy is strongly dependent on the distance and direction of the core shift, we marks, to the best of our knowledge, the first demonstration that the restored electronic states can effectively neutralize the polarization sensitivity, achieving isotropic optical absorption with wavelengths longer than 10 μm. Our finding indicates that the anti-crossing behavior of energy levels can serve as a viable mechanism to achieve switchable optical isotropy.

Improved electro‐actuation property of dielectric elastomer composites regulated by one‐dimensional CaCu3Ti4O12@TiO2 core–shell construction

AbstractDielectric elastomers (DEs) are typical electro‐active polymers that can achieve an electro‐actuated deformation under an applied electric field. However, obtaining a large low‐field‐actuated strain of DEs is still a key challenge, which is critical to their practical application range. Herein, a typical CaCu3Ti4O12@TiO2 (CCTO@TiO2) core–shell‐structured nanowires were synthesized by the micro‐emulsion method. Additionally, a series of polydimethylsiloxane (PDMS)‐based DE composites combining variable proportions of CCTO@TiO2 were prepared. The CCTO@TiO2 nanowires with the design of both decreasing dielectric constant from core to shell and a high aspect ratio can provide larger heterogeneous interfaces for the DE composites, leading to a promoted interfacial polarization. The maximum electro‐actuated strain of 37.66% is achieved from the DE composite incorporated with 20 wt% CCTO@TiO2 when subjected to a relatively low electric field of 40 V/μm, which is 14 times higher than that of pure PDMS (strain ~2.5%). Moreover, the composite exhibits the largest electro‐actuated strain (45.83%) under the electric field approaching its breakdown strength of 43.57 V/μm. The results demonstrate that the one‐dimensional core–shell nanowires have a positive effect on improving the low‐field‐actuated strain of DE composites. This research reveals an effective and feasible method to prepare the DE composites exhibiting enhanced low‐field electro‐actuated characteristics.

Adaptive Epidermal Bioelectronics by Highly Breathable and Stretchable Metal Nanowire Bioelectrodes on Electrospun Nanofiber Membrane

AbstractThe potential of the electrospun nanofiber membrane (ENM)‐based soft electronics in epidermal bioelectronics has gained huge attention with their conformal compatibility with the human body and associated performance improvements. This study presents a novel filtration‐based direct local nanowire patterning method on the ENM using dispenser systems, aiming to fabricate stretchable, breathable, and highly conductive epidermal electronics harnessing various types of metal nanowires, including Ag, Ag@Au core–shell, and Ag@(Au–Pt) core–shell nanowires. By utilizing capillary force from a support bed beneath the ENM, efficient fluid flow can be achieved, eliminating the requirement for expensive vacuum equipment typically employed in filtration processes. In the postprocessing phase, the photothermal effect of a laser is harnessed to improve the mechanical stability of the nanowire–ENM interface. The maskless fabrication process is instrumental in crafting epidermal bioelectronics in that the design can be spontaneously replicated according to diverse human body geometries in situ. The selective insulation process can be also executed with the same dispenser system, streamlining the overall fabrication system. Applications are demonstrated showcasing the advantages of the presented fabrication system and the resulting devices, including an in vivo epicardial signal recording electrode, an epidermal electrochemical biosensor, and a customized epidermal electromyography (EMG)‐based human–machine interface (HMI).

On electron and hole accumulation in a core-shell nanowire: Study by a Monte Carlo simulation

A Monte-Carlo simulation is used to study carrier accumulation inside a Ge–Si core-shell nanowire inside an n-doped Si substrate in the electron beam induced current technique. An ideal and a like-real nanowires are studied. For the like-real nanowire, imperfections are described by square wave functions representing modulation of Ge and Si radial dimensions. Carriers are created using an electron beam energy of 5 keV in the perpendicular configuration. A part of holes is collected by a nanoscale electrode. Another part is accumulated inside the core. Electrons are accumulated inside the shell since the core-shell is assumed to exhibit type II confinement of band edge alignment. The results show that the hole collection efficiency increases, at the expense of carrier trapping in the nanowire, with the distance depth between the nanowire and the nanocontact until a threshold distance of ∼50 nm from which the induced current reaches a saturation. While the accumulation of both holes and electrons inside the nanowire continues to decline. The only difference between an ideal and a like-real nanowire is underlined by more electrons inside the ideal than the like-real one. The accumulated hole number is weak and shows no difference between the two nanowires.

Ag Nanoparticle-Decorated GaN/β-Ga2O3 Core–Shell Nanowires as Catalysts for Highly Efficient CO2-to-CO Photocatalytic Conversion

Ag Nanoparticle-Decorated GaN/β-Ga₂O₃ Core–Shell Nanowires as Catalysts for Highly Efficient CO₂-to-CO Photocatalytic Conversion

Morphology dependent EMI shielding performance of Ag-Ni core-shell nanowires

The proposed work reports a facile chemical reduction method for synthesizing the hierarchical silver-nickel core-shell nanowire structures with controllable morphologies by varying the Ag concentration. The growth of Ni shells around the Ag core to make thorny and smooth Ag-Ni core-shell nanowires is studied for addressing electromagnetic interference (EMI). The synthesized Ag-Ni nanowires show better EMI shielding effectiveness (SE) than Ni nanowires with much-improved absorption loss (SEA). Due to high electrical conductivity (8630 S cm−1), magnetic permeability (44.1 emu/g), and heterojunction core-shell interfaces, the bimetallic nanowires flakes exhibit exceptional average EMI SE of 90.5 dB in the X-band frequency range (8–12 GHz) with a thickness of 0.11 mm, taking specific EMI SE to 822.72 dB/mm. In addition, the EMI shielding performance of the smooth Ag-Ni nanowires showed a 45% enhancement in SEA with marginal change in reflection loss (SER) compared to the thorny ones, indicating high absorption of EM waves. The unique core-shell nanowires with high aspect ratio with tunable physical properties can be ideal candidates for futuristic applications in microwave absorption and electromagnetic interference shielding.

Investigation of some thermal properties of iron and chromium-based core-shell nanowires

Fe and Cr based core–shell nanowires (CSNWs) are modeled as cylindrical structures in which the atoms are arranged in a bcc crystal structure. Two different sizes with diameters of 2.5 nm and 4.5 nm for nanowires (NWs) are created and their lengths are set as four times their diameters. Their structural and thermodynamic properties are investigated through the molecular dynamics (MD) simulation technique in the canonical (NVT) statistical ensemble implemented in the open-source Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software package. Atomic interactions between the atoms are described by using the many-body potentials based on the Embedded Atom Model (EAM). The melting temperatures of the NWs have been determined by investigating the behavior of the potential energy, specific heat capacity, radial distribution function, Lindemann melting criterion, the mean square displacement, and diffusion coefficients as a variation of temperature. The same melting temperatures are acquired from all these temperature-dependent physical properties for all NWs considered in this study. To the best of our knowledge, our simulation results are presented for the first time in this work and have the potential to guide experimental studies.

Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells.

III-V nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core-shell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.

Spin-Resolved Magneto-Tunneling and Giant Anisotropic g-Factor in Broken Gap InAs-GaSb Core-Shell Nanowires.

We experimentally and computationally investigate the magneto-conductance across the radial heterojunction of InAs-GaSb core-shell nanowires under a magnetic field, B, up to 30 T and at temperatures in the range 4.2-200 K. The observed double-peak negative differential conductance markedly blue-shifts with increasing B. The doublet accounts for spin-polarized currents through the Zeeman split channels of the InAs (GaSb) conduction (valence) band and exhibits strong anisotropy with respect to B orientation and marked temperature dependence. Envelope function approximation and a semiclassical (WKB) approach allow to compute the magnetic quantum states of InAs and GaSb sections of the nanowire and to estimate the B-dependent tunneling current across the broken-gap interface. Disentangling different magneto-transport channels and a thermally activated valence-to-valence band transport current, we extract the g-factor from the spin-up and spin-down dI/dV branch dispersion, revealing a giant, strongly anisotropic g-factor in excess of 60 (100) for the radial (tilted) field configurations.

BP/GaN and BP/GaP core/shell nanowires: theoretical insights into photovoltaic and gas-sensing abilities.

DFT-based calculations were undertaken to, first, fully optimize and study the structural and electrical properties of bare BP nanowire (NW) in its hexagonal wurtzite (WZ) phase. The bare BP NW was found to have an indirect bandgap of 1.362 eV. Hence, the optimization of BP/GaN and BP/GaP core/shell nanowires (CSNWs) was performed to check if an indirect-to-direct band transition occurred. Both the CSNWs showed direct bandgaps of 0.225 eV and 1.252 eV, respectively. The Shockley-Queisser limits for the bare BP NW and BP/GaP CSNW were calculated and compared to gauge their respective photovoltaic efficiencies. The bare BP NW and BP/GaP CSNW yielded almost identical SQ efficiencies of 33.80% and 33.55%, respectively. However, as far as the nano- and micro-photovoltaic cell applications are concerned, the BP/GaP CSNW would be preferable, owing to its direct bandgap. Furthermore, the adsorption of some small oxide gases like carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (NO2) and sulfur dioxide (SO2) gases on BP/GaN and BP/GaP CSNWs was studied. On the basis of the charge transfer and work function mechanisms, NO2 and SO2 gases showed selectivity to be detected by both the CSNWs. However, the very highly escalated desorption times for these gases would reduce the repeatability of sensors. Conversely, both BP/GaN and BP/GaP CSNWs could find applications in the fabrication of entrapment devices for NO2 and SO2. The current-voltage (I-V) curves for the CSNWs before and after adsorption were also plotted and analyzed. The occurrence of negative differential conductance (NDC) can be observed in both the CSNWs. The CO2, NO2 and SO2 gases show significantly higher values of current than the pristine BP/GaN CSNW for voltages beyond 0.5 V. Thus, these gases are good proponents to be detected by BP/GaN CSNWs with negligible selectivity amongst them. However, CO@BP/GaN is a stand-out case with a characteristically unique NDC region at 0.9 V. In the case of BP/GaP CSNWs, CO and CO2 gases can be selectively detected, with a unique NDC region for CO at 0.9 V. Thus, the BP/GaP CSNW, in particular, stands out as an extremely versatile material that can be used to fabricate nano-photovoltaic and nano-sensing devices of the next generation.

Carrier modulation of one-dimensional MAPbxSr1-x(IyCl1-y)3 core-shell perovskite nanowires.

Low dimensional hybrid organic-inorganic perovskites (HOIPs) have become one of the most promising materials in solar cells, photodetectors, and lasers due to their low exciton binding energy, high bipolar carrier mobility, and long carrier lifetime. The effective separation and collection of photo-generated electrons and holes have always been crucial for a perovskite as a working medium for optoelectronic devices. However, the surface state of pristine perovskite nanowires causes recombination of electrons and holes at the edge of the energy band, leading to deactivation of charge carriers. In this work, we constructed MAPbxSr1-xI3 core-shell nanowires, which adjust the band gap and control the spatial distribution of charge carriers by changing the Pb composition ratio, achieving spontaneous separation of electron-hole pairs to avoid surface recombination. In addition, MAPbxSr1-x(IyCl1-y)3 core-shell nanowires with different component ratios (x, y) can be constructed by further doping the Cl element, and the spatial distribution of charge carriers in the nanowires can be flexibly manipulated to achieve exchange between type-I and type-II band alignment orders. This study provides a feasible method for enhancing the carrier separation of organic-inorganic hybrid perovskites and improving the performance of optoelectronic devices.