Short Nanowires Research Articles

Sustained Condensation Efficiency on 3D Hybrid Surfaces

Condensation plays a crucial role in various applications. While superhydrophobic surfaces have been employed to enhance condensation, their performance significantly deteriorates with increasing subcooling, limiting their practicality. Hybrid surfaces offer a potential solution for improved condensation at high subcooling, but current designs fail to sustain effective condensation as subcooling rises. This study presents a three‐dimensional (3D) hybrid surface integrating short hydrophobic silicon nanowire arrays with hydrophilic microchannels. The formation of bridging droplets across multiple channels is observed, but they are efficiently removed from the 3D hybrid surface. The 3D hybrid surface exhibits sustained, simultaneous dropwise and filmwise condensation under medium to high subcooling conditions. Notably, it maintains a stable heat transfer coefficient across these subcooling conditions without experiencing the typical decline due to flooding observed on conventional surfaces at elevated subcooling temperatures. When compared to a plain hydrophilic surface at high subcooling, the 3D hybrid surface achieved remarkable improvements of 198% in condensation heat flux and 216% in heat transfer coefficient. This 3D hybrid surface represents a significant breakthrough for enhancing condensation in practical systems operating under high subcooling conditions.

Improving Catalytic Performance via the Synergy of Tensile Lattice Strain and Plasmonic Enhancement in Defective AuPd@Pd Short Nanowires.

The synthesis of bimetallic nanocatalysts with strained crystal lattices has attracted considerable interest. This is because, beyond the electronic structure modifications realized through elemental doping, the strain effect offers an extra mechanism to fine-tune the electronic structures, thereby possibly improving the catalytic performances. We present a method for constructing defective AuPd@Pd short nanowires, achieved through a controlled galvanic replacement reaction between short AuCu nanowires and Pd precursors. Advanced structural analyses using spherical aberration-corrected transmission electron microscopy (AC-TEM) validated the expanded crystal lattice on the nanowire surface and also demonstrated pronounced plasmonic absorption in the UV-vis region. Leveraging both plasmonic absorption and strain effects, the AuPd@Pd short nanowires displayed a higher apparent rate constant compared to Pd nanoparticles. Integrating molecular dynamic simulations with density functional theory calculations revealed that the tensile strain on AuPd@Pd short nanowires benefited the catalytic activity by elevating the d-band center, thereby intensifying the adsorption of p-nitrophenol. The current research introduces a unique method for synthesizing noble metal nanocrystals with specific dimensions and elucidates the rational development of high-performance plasmonic nanocatalysts through synergistic exploitation of the beneficial strain effect.

Coordinating the pore size of paper substrates and aspect ratio of silver nanowires to improve printed electronics

The internet of things is advancing toward a world of ubiquitous electronic devices, composed in large part of low-cost printed electronics (PE) such as sensors. PE typically use plastic substrates, such as polyethylene terephthalate (PET), but these materials are not biodegradable. The proliferation of PE devices and their degradation to form micro- and nanoplastics pose significant environmental hazards. Paper is a promising substrate to replace PET for greener PE due to its recyclability, affordability, and compatibility with many printing processes. However, the porous cellulosic structure of paper can be an obstacle when trying to print active inks due to wicking of the ink into the paper pores, which disperses the functional ink and negatively impacts electronic performance. Filling the pores of paper with a polymer to planarize the surface is a commonly used remedy, although this approach can compromise recyclability. Here, we present an approach to manage the dispersion of silver nanowires, a widely used and printable 1D nanomaterial ink, in paper substrates. We deposit solutions of short (20–30 μms) and long (100–200 μms) silver nanowires onto various graded filter papers that differ in pore size and examine the trends in wicking distance, wicking speed, and electrical properties. We show that with careful selection of AgNW length and the pore size of the paper, it is possible to control the lateral spreading of the ink and minimize the concentration of the AgNWs needed to achieve a specific electrical performance.

Strengthened and toughened SiHfBCN-based high-temperature resistant adhesive with SiC NWs

To further improve the performance of binders, a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics (PDC) route using TiB2, Polysiloxane (PSO) and short SiC nanowires as fillers. The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature, as well as the reinforcing mechanism was studied. Compared with the adhesive without SiC nanowires, after curing (at 170 °C) and pyrolysis (at 1000 °C) in air, the appropriate adding of SiC nanowires upgrades the room temperature and high temperature (at 1000 °C in air) adhesive strength to (12.50 ± 0.67) MPa (up by about 32%) and (13.11 ± 0.79) MPa (up by about 106%), respectively. Attractively, under the synergistic impact of the nanowire bridging, nanowire breaking, nanowire drawing and crack deflection, the optimized adhesive exhibits multi-stage fracture, causing the increscent fracture displacement.

High-performance composite transparent electrode composed of ultra-long silver nanowires and antimony-doped tin oxide nanoparticles

Composite transparent conductive electrodes (TCEs) consisting of silver nanowires (AgNWs) and conductive metal oxides are very promising for flexible optoelectronic devices due to their smooth surface morphology and high chemical stability. However, it is still challenging to ensure high optoelectronic performance and long-term stability in practical applications. Here, we solved these problems by coating antimony-doped tin oxide (ATO) nanoparticles dispersion on ultra-long AgNWs network using waterborne polyurethane (WPU) binder. Ultra-long nanowires occupy less wire-wire junctions and space than short nanowires, thus increasing the optoelectronic performance and flexibility of the composite TCE. WPU improves the adhesion and stability of ATO nanoparticles to the substrate and AgNWs network. The fabricated composite TCE showed a low sheet resistance of 11.9 Ω sq−1, good optical transmittance of 83% at 550 nm and a figure of merit (FOM) of 162 compared to PET/ITO electrode. It also showed excellent mechanical flexibility, adhesion to the substrate and solvent stability. Furthermore, the long-term conductivity was maintained under ambient conditions for 60 days.

Efficiency enhancement in a lensed nanowire solar cell

We investigate microlenses that selectively focus the light on only a small fraction of all nanowires within an arrayed InP nanowire solar cell. The nano-concentration improves both the short-circuit current (Jsc) and the open-circuit voltage (Voc) of the solar cell. For this purpose, polymethyl methacrylate microlenses with 6 μm diameter were randomly positioned on top of an arrayed nanowire solar cell with 500 nm pitch. The microlenses were fabricated by first patterning cylindrical micropillars, which were subsequently shaped as lenses by using a thermal reflow process. The quality of the microlenses was experimentally assessed by Fourier microscopy showing strong collimation of the emitted photoluminescence. By analyzing the slope of the integrated photoluminescence vs excitation density, we deduce a substantial enhancement of the external radiative efficiency of a nanowire array by adding microlenses. The enhanced radiative efficiency of the lensed nanowire array results in a clear enhancement of the open-circuit voltage for a subset of our solar cells. The microlenses finally also allow to increase the short-circuit current of our relatively short nanowires, providing a route to significantly reduce the amount of expensive semiconductor material.

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Nanofluids based on extended nanostructures, such as nanowires, have been demonstrated improved thermal conductivities (κ). However, the lack of a complete understanding at the microscopic level hinders the development of such nanofluids towards practical applications. We aim to provide it by investigating how the interface thermal resistance (R b ), ballistic phonon transport, and the solid-like liquid layer affect the heat conduction in nanowire-based nanofluids. By employing Non-Equilibrium Molecular Dynamics (NEMD), it is found that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the R b . This contradicts the predictions of the classical parallel heat conduction model, therefore, a novel model is proposed taking this coupled behavior into account. Using this model, it is shown that the high κ of the solid phase has a limited contribution to the effective κ of nanofluids having short nanowires due to the dominant R b effect. For the case of long nanowires, however, the individual nanowire κ becomes a vital parameter defining the effective κ. Further, NEMD calculations reveal that the κ of suspended nanowires in a liquid is markedly reduced, questioning the validity of classical effective medium theories which use the bulk parameters. This reduction is attributed to surface atoms’ restricted vibrational freedom and the nanowire’s phonon-boundary scattering. By substituting this reduced κ of the solid phase into the new mathematical model, the theoretical predictions align closely with the NEMD calculations, exhibiting deviations below 10%. The sole contribution from the solid-like liquid layer to the κ enhancement lies between 20%–30% in the nanofluids presently considered. Therefore, the findings of this study highlight the important roles play by the identified microscopic thermal characteristics in defining the effective κ of nanofluids based on nanowires.

Remnants of the nonrelativistic Casimir effect on the lattice

The Casimir effect is a fundamental quantum phenomenon induced by the zero-point energy for a quantum field. It is well-known for relativistic fields with a linear dispersion relation, while its existence or absence for nonrelativistic fields with a quadratic dispersion is an unsettled question. Here, we investigate the Casimir effects for various dispersion relations on the lattice. We find that Casimir effects for dispersions proportional to an even power of momentum are absent in a long distance but a remnant of the Casimir effect survives in a short distance. Such a remnant Casimir effect will be experimentally observed in materials with quantum fields on the lattice, such as thin films, narrow nanoribbons, and short nanowires. In terms of this effect, we also give a reinterpretation of the Casimir effect for massive fields.

Dynamics and Reversible Control of the Bloch-Point Vortex Domain Wall in Short Cylindrical Magnetic Nanowires

Fast and efficient switching of nanomagnets is one of the main challenges in the development of future magnetic memories. We numerically investigate the evolution of static and dynamic spin-wave (SW) magnetization in short (50--400 nm in length and 120 nm in diameter) cylindrical ferromagnetic nanowires, where competing magnetization configurations of a single vortex (SV) and a Bloch-point vortex domain wall (BP-DW) can be formed. For a limited nanowire length range (between 150 and 300 nm), we demonstrate reversible transitions induced by a microwave field (forwards) and by opposite spin currents (backwards) between topologically different SV and BP-DW states. By tuning the nanowire length, the excitation frequency, the microwave pulse duration, and the spin-current value, we show that the optimum (low-power) manipulation of the BP-DW can be achieved with a microwave excitation tuned to the main SW mode for nanowire lengths around 230--250 nm, where single-vortex domain-wall magnetization reversal via nucleation and propagation of a SV-DW transition takes place. An analytical model of the dynamics of the Bloch point provides an estimate of the gyrotropic mode frequency close to that obtained via micromagnetic simulations. A practical implementation of the method in a device is proposed, involving microwave excitation and the generation of opposite spin currents via the spin-orbit torque. Our findings open up an alternative pathway for the creation of topological magnetic memories.

Quantized Spin Pumping in Topological Ferromagnetic-Superconducting Nanowires.

Semiconducting nanowires with strong spin-orbit coupling in the presence of induced superconductivity and ferromagnetism can support Majorana zero modes. We study the pumping due to the precession of the magnetization in single-subband nanowires and show that spin pumping is robustly quantized when the hybrid nanowire is in the topologically nontrivial phase, whereas charge pumping is not quantized. Moreover, there exists one-to-one correspondence between the quantized conductance, entropy change and spin pumping in long topologically nontrivial nanowires but these observables are uncorrelated in the case of accidental zero-energy Andreev bound states in the trivial phase. Thus, we conclude that observation of correlated and quantized peaks in the conductance, entropy change and spin pumping would provide strong evidence of Majorana zero modes, and we elaborate how topological Majorana zero modes can be distinguished from quasi-Majorana modes potentially created by a smooth tunnel barrier at the lead-nanowire interface. Finally, we discuss peculiar interference effects affecting the spin pumping in short nanowires at very low energies.

Enhanced light absorption of kinked nanowire arrays for high-performance solar cells

A kinked InP nanowire array solar cell architecture is proposed for high-performance solar cells. Coupled three-dimensional optoelectronic simulations are performed to investigate the optical absorption and photovoltaic conversion properties. The results show that the kinked morphology significantly enhances the absorption by increasing the optical path, exciting more resonance modes, and reducing the transmission into the substrate. Moreover, the kinked morphology also increases the absorption in the intrinsic region by suppressing the absorption loss in the top doped region. For short nanowires with a total length of 1–1.5 μm, the kinked structures exhibit remarkable efficiency exceeding 14%, significantly higher than the vertical nanowires. Nanowires with different kinked angles are studied, and a moderate kinked angle is beneficial for obtaining optimal performance. This work demonstrates the potential of kinked nanowires in ultra-thin low-cost high-efficiency solar cells.

Tin versus indium catalyst in the growth of silicon nanowires by plasma enhanced chemical vapor deposition on different substrates

• Silicon nanowires (NWs) grown on various substrates via Vapor–Liquid–Solid method. • Best crystallized SiNWs obtained using tin catalyst on silicon germanium substrate. • Morphology and crystalline nature strongly depend on the junction substrate-catalyst. • Substrate surface energy affects growth by regulating catalyst repartition. The plasma-assisted Vapor-Liquid-Solid technique has been used to grow Silicon nanowires (SiNWs) on different substrates coated with 1 nm of tin and indium, to study the impact of the surface energy of the substrates on the morphology and structure of the NWs. The characteristics of the prepared Si NWs were analyzed by field emission scanning electron microscopy, X-ray diffraction (XRD) and Raman spectroscopy. The morphological characteristics differ in the density, diameter and length of the synthesized SiNWs. The mean diameters of these SiNWs range from 36 to 51 nm at the bottom and from 15 nm to 34 nm at the tip, while their average length varies from 0.2 μm up to 0.54 μm depending on the substrate and catalyst. The presence of strong peaks in all XRD patterns indicates that the as-grown SiNWs are highly crystalline. The XRD and Raman characteristics of the Sn and In catalyzed SiNWs formed on different substrates show that the crystalline grain size is influenced by the substrate nature and catalyst material, which can be related to the substrate surface energy. In particular shorter NWs with improved crystallinity (larger grain size) are obtained when using Sn as a catalyst on an amorphous silicon-germanium (a-SiGe) substrates, while the small grains were obtained on the same substrate when indium was used as a catalyst.

Effects of switching layer morphology on resistive switching behavior: A case study of electrochemically synthesized mixed-phase copper oxide memristive devices

Resistive switching (RS) behavior can serve as a building block in the development of non-volatile memory and neuromorphic computing applications. Thus far, various device parameters have been modulated appropriately to achieve the desired characteristics from RS devices. However, no clear guideline for device parameter modulation has been reported. Herein, we systematically investigate the effect of the switching layer morphology and thickness, as well as the choice of the bottom electrode, on RS properties by using electrochemically synthesized mixed-phase copper oxide (CuxO) as a model material for memristive devices. By controlling various electrochemical parameters, we have fabricated CuxO switching layers with various morphologies (microcrystal, microcubic, compact thin film, short dendritic nanowire, granular, and nanoparticle). Interestingly, the CuxO-based RS devices fabricated by means of electrodeposition (CuxO/FTO) exhibit the forming-free digital RS property, which is suitable for non-volatile memory, whereas those fabricated by utilizing anodization (CuxO/Cu) exhibit the analog RS property, which makes them suitable for use in synaptic learning applications. A convolutional neural network (CNN) was implemented using experimental synaptic weights of the anodized CuxO RS device for image edge detection application. In addition, conduction mechanisms and possible RS mechanisms are suggested for both types of devices. These results indicate that the electrochemically synthesized switching layers are promising for use in both non-volatile memory and neuromorphic computing applications.

Spontaneous Parametric Down-Conversion from GaAs Nanowires at Telecom Wavelength

We report on the generation of photon pairs at 1550 nm from free-standing epitaxially grown self-assisted micrometre long GaAs nanowires. The efficiency of the spontaneous parametric down-conversion process has a rate of 320 GHz/Wm normalized to the transmission of the setup, the pump intensity, and the volume of the nanostructure. GaAs is a high index dielectric that can support electromagnetic Mie modes, therefore we model how shorter nanowires could improve the second-harmonic signal and we found that sub-micro long nanowires (600 nm length and 250 nm diameter) can support quality factors up to 15 at the pump wavelength (780 nm). We anticipate that the near field enhancement compared to micrometre long nanowires will boost the second-harmonic generation and, correspondingly, the biphoton rate efficiency.

Population dependence of THz charge carrier mobility and non-Drude-like behavior in short semiconductor nanowires.

We investigate THz radiation absorption by charge carriers, focusing on the mobility in nanorods and wires. We show that for short rods the mobility is limited by the high spacing of the charge carrier energy levels, while for longer wires (greater 25 nm) finite dephasing results in considerably higher low frequency mobility. Analyzing the length, temperature and population dependence, we demonstrate that, apart from the temperature dependent dephasing, the mobility becomes strongly charge carrier population dependent. The latter results in no simple linear relationship between carrier density and conductivity. Additionally their thermal distribution determines the mobility, measured in experiments. We further show that Drude or Plasmon models apply only for long wires at elevated temperatures, while for short length quantization results in considerable alterations. In contrast to those phenomenological models, i.e. a negative imaginary part of the frequency-dependent conductivity in a nanosystem can be understood microscopically. Based on the results, we develop guidelines to analyze 1D terahertz conductivity spectra. Our approach provides also a new tool to optimize the mobility by nanowire length as well as to analyze the dephasing, not by conventional wave mixing techniques, but by coherent optical pump-THz probe spectroscopy.

Hydroxyapatite nanomaterials with tailored length regulated by different fatty acids

The morphology and structures of hydroxyapatite (HA) nanomaterials greatly influence their physicochemical properties and bio-applications. In this study, HA nanostructures with tailored length regulated by different fatty acids were prepared via a solvothermal route. By using ricinoleic acid, linoleic acid and oleic acid as the template, the growth of HA crystals was regulated and the morphology of HA nanomaterials was transformed from long nanowires to short nanowires and then nanorods. The underlying mechanism for the formation of HA nanomaterials synthesized by different kinds of fatty acids under solvothermal condition was proposed. This study provides a simple and environmentally friendly way to obtain HA nanomaterials with tailored length for biomedical applications.

Synergistic effect of endocellular calcium ion release and nanotopograpy of one-dimensional hydroxyapatite nanomaterials for accelerating neural stem cell differentiation

Neural stem cells (NSCs) based nerve repair is the most promising approach for neurodegenerative disease therapy. However, the long-time requirement for NSCs differentiation into mature neurons challenges the clinical applications of NSCs because of the missing of the best opportunity for nerve repair. In this work, we synthesized four kinds of one-dimensional (1D) hydroxyapatite (HAp) nanomaterials with different morphologies of short nanorod, long nanorod, short nanowire, and long nanowire. And we found that rapid differentiation of NSCs could be realized just by the endocytosis of 1D HAp nanomaterials with different lengths. Both the endocellular calcium ion (Ca2+) release of HAp nanosturctures suffered a low pH in endosomes and their nanotopography can regulate the neural differentiation of NSCs, and their synergistic effect is the main reason for the acceleration of NSCs differentiation. The safe, rapid and low-cost approach for promoting NSCs differentiation supposed in this work will have great potential in clinical applications for therapy of neurodegenerative diseases.

Study on the optoelectronic properties of Ag, Pt, Na and Li particles adsorbed on GaAs nanowire arrays

In this paper, COMSOL Multiphysics software based on finite element method was used to design a GaAs nanowire array simulation model absorbed with metal nanoparticles. We studied the effects of the size, position and number of metal nanoparticles on their light absorption, and in this experiment, precious metal (Ag, Pt) and alkali metal (Na, Li) particles adsorbed on nanowires. The results show that the adsorption of metal particles is helpful to improve the light binding capacity of short wavelength nanowire arrays. With the change of the radius, position and number of particles, the nanowires absorbed by Li and Ag nanoparticles showed better light absorption characteristics. The optical trapping effect can be effectively enhanced by increasing the size of particles, the number of surrounding particles and the number of particles which distributed along the nanowire direction appropriately.

Electron conducting Ag2Te nanowire/polymer thermoelectric thin films

Herein, we report the electrical conductivity and Seebeck coefficients of air-stable, thin films of poly([N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)) embedded with β-Ag2Te nanowires. Three different length nanowires (∼2600, ∼800, and ∼300 nm) were synthesized and combined with the polymer to yield composite thin films. The room temperature electrical conductivity values of thin films made from the longest nanowires were 5 orders of magnitude larger than the shorter nanowires. The electrical conductivity data were modeled to a series and parallel-connected composite network. The films with the longest nanowires best fit a series-connected model, while the shorted nanowires best fit a parallel connected model. Specifically, the electrical conductivity of the thin films containing the longest Ag2Te nanowires increased from 0.16 to 0.61 S/cm when the weight percent Ag2Te increased from 45 to 85%. The magnitude of the Seebeck coefficient remained relatively unchanged (about −130 μV/K) as the amount of Ag2Te in the films increased. A power factor of ∼1 μW/mK2 was determined for the 85 wt. % Ag2Te films at room temperature. These results reveal the important role of the nanowire length in the thermoelectric performance of composite thin films.

Spin–Orbit Coupling-Induced Effective Interactions in Superconducting Nanowires in the Strong Correlation Regime

In the second order of the operator form of the perturbation theory, the effective interactions in a superconducting nanowire have been obtained at the strong electron correlations, when the spin–orbit coupling parameter is comparable with the hopping integral. Using the exact diagonalization technique, in short nanowires with the open boundary conditions at the strong Coulomb repulsion, the excitations corresponding to the Majorana edge states with the energy below the value of a bulk superconducting gap have been demonstrated.