Nanowire Pairs Research Articles

Surface Plasmon Waveguide Based on Nested Dielectric Parallel Nanowire Pairs Coated with Graphene

A kind of surface plasmon waveguide composed of two nested cylindrical dielectric parallel nanowire pairs coated with graphene was designed and studied. The dependence of the mode characteristics and the normalized gradient force of the lowest two modes supported by the waveguide on the parameters involved were analyzed by using the multipole method. To ensure rigor, the finite element method was employed to verify the accuracy of the multipole method, thus confirming its results. The results show that the multipole method is a powerful tool for handling this type of waveguide. The real part of the effective refractive index, the propagation length, the figure of merit, and the normalized gradient force can be significantly affected by the operating wavelength, the Fermi energy of graphene, the waveguide geometric parameters, and the refractive index of the inner dielectric nanowire. Due to the employment of nested dielectric nanowire pairs coated with graphene, this waveguide structure exhibits significant gradient force that surpasses 100 nN·μm−1·mW−1. The observed phenomena can be attributed to the interaction of the field with graphene. This waveguide holds promising potential for applications in micro/nano integration, optical tweezers, and sensing technologies.

Transport-based fusion that distinguishes between Majorana and Andreev bound states

It has proven difficult to distinguish between topological Majorana bound states and nontopological Andreev bound states and to measure the unique properties of the former. In this work, we aim to alleviate this problem by proposing and theoretically analyzing a different type of fusion protocol based on transport measurements in a Majorana box coupled to normal leads. The protocol is based on switching between different nanowire pairs being tunnel coupled to one of the leads. For a Majorana system, this leads to switching between different states associated with parity blockade. The charge being transmitted at each switch provides a measurement of the Majorana fusion rules. Importantly, the result is different for a system with nontopological Andreev bound states. The proposed protocol only requires measuring a DC current combined with fast gate control of the tunnel couplings. Published by the American Physical Society 2024

Nanoscale contact state design for nodal energy transfer at crossed Ag nanowires

The thermal conduction properties of the cross-junction formed by one pair of Ag nanowires were characterized using experiments and simulations. By laser-sintering crossed nanowires on a substrate on which the Ag ion complex ink was dispersed, we succeeded in visualizing the heat flow trajectory of the junction according to the application of energy. To theoretically understand the energy transfer behavior at the junctions, Ag nanowires with penta-twinned cross-sections were modeled by all-atom molecular dynamics simulations. The equilibrium and non-equilibrium simulation results showed the structural stability at the interface junction, convergence of heat flux in an unsteady state, and effective thermal conductivity of the entire system in a steady state. In particular, we focused on the dependence of the diameter on the nanoscale region, which is the most important design variable for Ag nanowires. Accordingly, a structure–property relationship governed by the nanoscale geometry of the junction was identified.

Low‐Threshold Multiwavelength Plasmonic Nanolasing in an “H”‐Shape Cavity

AbstractMultiwavelength plasmonic nanolasers are central to the quest for ultradense and versatile photonic integrations. However, the insufficient optical feedback and mode selection strategies result in a high lasing threshold and multi‐mode operation with limited spectral purity and stability. Here, a multiwavelength near‐infrared plasmonic nanolaser with high mode purity by leveraging a nontrivial “H”‐shape plasmonic cavity is demonstrated. The nanolaser is constructed by inserting InGaAs/GaAs multi‐quantum‐disk (MQD) nanowires into a metallic Fabry‐Perot cavity consisting of a pair of Ag nanowires positioned on an ultrasmooth Au film. The design is endowed with strong optical feedback to enhance the energy transfer between the exciton and plasmon, rendering a significant reduction of the lasing threshold. More importantly, the “H”‐shape cavity is featured with a large flexibility in tuning the resonance wavelength, where multiwavelength lasing with the virtues of single‐mode is realized at room temperature. The results make a crucial step toward near‐infrared multiwavelength plasmonic nanolasers and open up exciting opportunities for applications such as ultracompact photonic integrated circuits and high‐throughput biochemical sensing.

Merging Nanowires and Formation Dynamics of Bottom‐Up Grown InSb Nanoflakes

AbstractIndium Antimonide (InSb) is a semiconductor material with unique properties, that are suitable for studying new quantum phenomena in hybrid semiconductor‐superconductor devices. The realization of such devices with defect‐free InSb thin films is challenging, since InSb has a large lattice mismatch with most common insulating substrates. Here, the controlled synthesis of free‐standing 2D InSb nanostructures, termed as “nanoflakes”, on a highly mismatched substrate is presented. The nanoflakes originate from the merging of pairs of InSb nanowires grown in V‐groove incisions, each from a slanted and opposing {111}B facet. The relative orientation of the two nanowires within a pair, governs the nanoflake morphologies, exhibiting three distinct ones related to different grain boundary arrangements: no boundary (type‐I), Σ3‐ (type‐II), and Σ9‐boundary (type‐III). Low‐temperature transport measurements indicate that type‐III nanoflakes are of a relatively lower quality compared to type‐I and type‐II, based on field‐effect mobility. Moreover, type‐III nanoflakes exhibit a conductance dip attributed to an energy barrier pertaining to the Σ9‐boundary. Type‐I and type‐II nanoflakes exhibit promising transport properties, suitable for quantum devices. This platform hosting nanoflakes next to nanowires and nanowire networks can be used to selectively deposit the superconductor by inter‐shadowing, yielding InSb‐superconductor hybrid devices with minimal post‐fabrication steps.

Controlled evolution of three-dimensional magnetic states in strongly coupled cylindrical nanowire pairs

Cylindrical magnetic nanowires are promising systems for the development of three-dimensional spintronic devices. Here, we simulate the evolution of magnetic states during fabrication of strongly-coupled cylindrical nanowires with varying degrees of overlap. By varying the separation between wires, the relative strength of exchange and magnetostatic coupling can be tuned. Hence, we observe the formation of six fundamental states as a function of both inter-wire separation and wire height. In particular, two complex three-dimensional magnetic states, a 3D Landau Pattern and a Helical domain wall, are observed to emerge for intermediate overlap. These two emergent states show complex spin configurations, including a modulated domain wall with both Néel and Bloch character. The competition of magnetic interactions and the parallel growth scheme we follow (growing both wires at the same time) favours the formation of these anti-parallel metastable states. This works shows how the engineering of strongly coupled 3D nanostructures with competing interactions can be used to create complex spin textures.

Analyzing the synchronism of stacking-fault formation in side-by-side SiC nanowire pairs using the Levenshtein distance: stochastic versus deterministic processes.

Pairs of silicon carbide nanowires were grown side by side synchronously from the same metal catalyst nanoparticles. The stacking sequences of each pair were read by high-resolution transmission electron microscopy, and the similarity of each stacking sequence was measured using the Levenshtein distance. No synchronism was detected in the pairs of stacking sequences, and the results indicated that the formation of stacking faults in silicon carbide nanowires was not deterministic, but purely stochastic.

Photonic Nanolaser with Extreme Optical Field Confinement.

We proposed a photonic approach to a lasing mode supported by low-loss oscillation of polarized bound electrons in an active nano-slit-waveguide cavity, which circumvents the confinement-loss trade-off of nanoplasmonics, and offers an optical confinement down to sub-1-nm level with a peak-to-background ratio of ∼30 dB. Experimentally, the extremely confined lasing field is realized as the dominant peak of a TE_{0}-like lasing mode around 720-nm wavelength, in 1-nm-level width slit-waveguide cavities in coupled CdSe nanowire pairs. The measured lasing characteristics agree well with the theoretical calculations. Our results may pave a way towards new regions for nanolasers and light-matter interaction.

Lasing action in a strongly coupled silicon nanowire pair.

High-index dielectric nanostructures are of particular interest for nanoscale lasing due to their low absorption losses. However, the relatively weak near-field restricts the isolated dielectric cavities as low-threshold integrated on-chip laser sources. Here, we demonstrate lasing action in a silicon nanowire pair with 32 nm gap coated with dye-doped shell on the silicon-on-insulator platform. It is found that the quality factor Q is dominated by the coupling of the silicon nanowire pair, which depends on the gap size, the nanowire width, and the dye thickness. A lasing peak at the wavelength of 529 nm with FWHM of 0.6 nm is experimentally realized by the Si nanowire pair width, and the corresponding pumping power threshold is ∼34 µW/cm2. The proposed strategy, based on the well-established Si planar process, lays the groundwork for practical integrated nanolasers that have potential applications in photonic circuits.

Strong Magnetic Plasmon Resonance in a Simple Metasurface for High-Quality Sensing

We present a simple metasurface consisting of a periodic array of two closely spaced Ag nanowires standing on Ag substrate, to achieve a very strong magnetic plasmon (MP) resonance. We show that the strong MP resonance in the simple metasurface is essentially an antisymmetric resonance caused by the near-field plasmon hybridization in the pair of metallic nanowires. The magnetic field intensity and the spectral linewidth of the MP resonance can be effectively tuned by changing the height of nanowires and the spacing between the two closely spaced nanowires. More importantly, owing to the huge magnetic field enhancement, the ultra-narrow linewidth and the nearly-zero reflection at the strong MP resonance, the metasurface has very high sensitivity (S = 750 nm/RIU, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sub> = 45/RIU) and figure of merit (FOM = 94, FOM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sub> = 750000). The results suggest that the proposed simple metasurface may find great potential applications in label-free biosensing.

Structural color from a coupled nanowire pair beyond the bonding and antibonding model

Optical resonances in nanostructures can be harnessed to produce a wide range of structural colors. Conversely, the analysis of structural colors has been used to clarify the nature of optical resonances. Here, we show that silicon nanowire (NW) pairs can display a wide range of structural colors by controlling their radiative coupling. This is accomplished by exciting a series of Fabry–Pérot-like modes where light is repeatedly scattered between two NWs. These modes are beyond the expectation from the conventional chemical bonding model under a quasi-electrostatic approximation, in which only bonding and antibonding modes can be formed in a pair system through modal hybridization. The additional eigenmodes found in a two-resonator system originate from the nonlinear, frequency-dependent coupling strength derived from the radiative nature of low-Q resonators. The Fabry–Pérot modes can be tuned across the entire visible frequency range by varying the distance between two NWs, leading to what we believe is a new type of universal building blocks that can provide structural color within a subwavelength footprint. The presented results pave the way toward the design and usage of highly tunable resonances that exploit the radiative coupling of high-index nanostructures.

Fully in situ Nb/InAs-nanowire Josephson junctions by selective-area growth and shadow evaporation.

Josephson junctions based on InAs semiconducting nanowires and Nb superconducting electrodes are fabricated in situ by a special shadow evaporation scheme for the superconductor electrode. Compared to other metallic superconductors such as Al, Nb has the advantage of a larger superconducting gap which allows operation at higher temperatures and magnetic fields. Our junctions are fabricated by shadow evaporation of Nb on pairs of InAs nanowires grown selectively on two adjacent tilted Si (111) facets and crossing each other at a small distance. The upper wire relative to the deposition source acts as a shadow mask determining the gap of the superconducting electrodes on the lower nanowire. Electron microscopy measurements show that the fully in situ fabrication method gives a clean InAs/Nb interface. A clear Josephson supercurrent is observed in the current–voltage characteristics, which can be controlled by a bottom gate. The large excess current indicates a high junction transparency. Under microwave radiation, pronounced integer Shapiro steps are observed suggesting a sinusoidal current–phase relation. Owing to the large critical field of Nb, the Josephson supercurrent can be maintained to magnetic fields exceeding 1 T. Our results show that in situ prepared Nb/InAs nanowire contacts are very interesting candidates for superconducting quantum circuits requiring large magnetic fields.

Chiral Magnonics: Reprogrammable Nanoscale Spin Wave Networks Based on Chiral Domain Walls.

SummarySpin waves offer promising perspectives as information carriers for future computational architectures beyond conventional complementary metal-oxide-semiconductor (CMOS) technology, owing to their benefits for device minimizations and low-ohmic losses. Although plenty of magnonic devices have been proposed previously, scalable nanoscale networks based on spin waves are still missing. Here, we demonstrate a reprogrammable two-dimensional spin wave network by combining the chiral exchange spin waves and chiral domain walls. The spin-wave network can be extended to two dimensions and offers unprecedented control of exchange spin waves. Each cell in the network can excite, transmit, and detect spin waves independently in the chiral domain wall, and spin-wave logics are also demonstrated. Our results open up perspectives for integrating spin waves into future logic and computing circuits and networks.

Similarity analysis of stacking sequences in a SiC nanowire pair grown from the same catalyst nanoparticle using Levenshtein distance.

Stacking faults are easily formed in silicon carbide (SiC) crystals, and this is also the case for SiC nanowires. The stacking faults exercise influences on SiC's properties, therefore it is important to understand their formation mechanism and to control their formation for applications of SiC and its nanowires. In this study, we propose a method for investigating stacking faults' formation mechanism in nanowires and provide its proof of concept. Stacking sequences in a pair of SiC nanowires that were grown from the same metal catalyst nanoparticle were quantified as a pair of binary sequences, and Levenshtein distances between partial sequences extracted from the two sequences were measured to detect similarity between them, and the result was compared with that obtained using a surrogate data of one sequence. The similarity analysis using Levenshtein distances works as a probe for investigating possible influences of some phenomena in the catalyst nanoparticle on the formation of stacking faults. The analysis did not detect a correlation between the two sequences. Although a possibility that the formation of stacking faults in the nanowires were owing to some phenomena in the catalyst nanoparticle cannot be denied, the extrinsic cause in the catalyst nanoparticle was not detected through our analysis in this case.

Orientation Distribution Dependence of Piezoresistivity of Metal Nanowire-Polymer Composite

In this study, we investigate the piezoresistivity of metal nanowire networks embedded in a polymer, which has been widely used as a highly-stretchable strain sensor, by varying the orientation distribution of nanowires. For simplicity, we assume the affine transform of the nanowire network upon stretching and compute the effective conductivity of the nanowire network by recognizing the percolation network connecting low and high voltage boundaries. Orientation-dependence is then studied firstly by varying the range of polar angle and secondly by changing the degree of alignment along loading direction. Since nanowires are embedded in thin nanowire-polymer film in most stretchable sensor applications, instead of having random orientation distribution over full solid angle, nanowires have a limited range of polar angle distribution around 90° (when the surface normal vector of a thin film is given as the zenith direction). We show that the gauge factor (relative resistance change over applied mechanical strain) decreases as the polar angle distribution gets narrower. We then study the effect of nanowire alignment on the piezoresistive response, by assuming partial alignment distribution along the tensile direction. We find that a wide range of the gauge factor, from negative to positive, appears as the initial partial alignment angle varies, and explained such response by analyzing the relative electrical path change between a pair of nanowires. Our study deepens the understanding on the percolation-network based piezoresistive sensors and provides a guideline for designing a stretchable strain sensor with the desired gauge factor.

涂覆石墨烯层的双椭圆形纳米线模式特性

涂覆石墨烯层的双椭圆形纳米线模式特性

High-Performance Transmission of Surface Plasmons in Graphene-Covered Nanowire Pairs with Substrate

Graphene was recently proposed as a promising alternative to support surface plasmons with superior performances in the mid-infrared range. Here, we theoretically show that high-performance and low-loss transmission of graphene plasmons can be achieved by adding a silica substrate to the graphene-covered nanowire pairs. The effect of the substrate layer on mode properties has been intensively investigated by using the finite element method. Furthermore, the results show that inserting a low index material layer between the nanowire and substrate could compensate for the loss accompanied by the substrate, thus the mode properties could be adjusted to fulfill better performance. A reasonable propagation length of 15 μm and an ultra-small normalized mode area about ~10−4 could be obtained at 30 THz. The introduction of the substrate layer is crucial for practical fabrication, which provides additional freedom to tune the mode properties. The graphene-covered nanowire pairs with an extra substrate may inspire potential applications in tunable integrated nanophotonic devices.

Huge local magnetic field enhancement at optical frequencies in metamaterials through coupling with photonic band gap

We theoretically study the coupling of magnetic plasmon polaritons (MPPs) with photonic band gap (PBG) in a system composed of a one-dimensional (1D) silver nanowire pair array lying on a one-dimensional photonic crystal (1D PC). The near-field plasmon interactions in individual silver nanowire pairs induce MPPs. The 1D PC consisting of dielectric multilayer stacks with alternating refractive indices forms a PBG in the reflection spectrum. When the position of the PBG of the 1D PC is tuned to be close to the MPPs, the MPPs and the PBG can couple together to lead to a hybrid mode within the PBG. At the hybrid mode resonance, the magnetic fields in the center of Ag nanowire pairs are enhanced to nearly 4.3 times larger than those in the nanowire pair array directly lying on a substrate. Our numerical results hold important applications in magnetic sensors and magnetic nonlinearity.

Electron-beam excitation of supermodes of a photonic molecule built on twin high refractive index dielectric nanowires

We study the radiation that occurs if a modulated beam of electrons flows between two identical high-index dielectric nanowires, which form a photonic molecule, in the visible wavelength range. The electromagnetic field of such a two-dimensional beam has the shape of the surface wave propagating along its trajectory. This wave induces the polarization and surface currents on the nearby obstacles, and hence, radiation occurs even if the beam does not touch the obstacle. Here, a pair of dielectric nanowires behaves as optically coupled open resonators, thanks to which the diffraction radiation is enhanced near the wavelengths of the natural modes. As known, the latter are so-called supermodes built on the modes of each wire, with the account of two-fold symmetry of the pair. To solve accurately the scattering problem, we use a semianalytical technique based on the Fourier expansions in the local coordinates of each wire and the addition theorems for the cylindrical functions. This leads to the efficient code having mathematically guaranteed convergence. We compute spectral characteristics of the diffraction radiation, analyze their dependences on the electron-beam parameters, and visualize the near-field and far-field patterns. A new form of the optical theorem adapted to the modulated electron-beam excitation is derived and exploited. Possible applications of the studied effects in the design of optical beam position monitors are discussed.

Stretchable SnO2-CdS interlaced-nanowire film ultraviolet photodetectors

Stretchable ultraviolet photodetectors with fast response have wide applications in wearable electronics and implantable biomedical devices. However, most of the conventional binary oxide nanowires based photodetectors exhibit slow response due to the presence of a large number of surface defects related to trapping centers. Herein, with interlaced SnO2-CdS nanowire films as the sensing materials, we fabricated stretchable ultraviolet photodetectors with significantly improved response speed via a multiple lithographic filtration method. Systematic investigations reveal that the interlaced-nanowire based photodetectors have lower dark current and much higher response speed (more than 100 times) compared with pure SnO2 nanowire based photodetectors. The relevant carrier generation and transport mechanism were also discussed. In addition, due to the formation of waved wrinkles on the surface of the nanowires/PDMS layer during the prestretching cycles, the SnO2-CdS interlaced nanowire photodetectors display excellent electrical stability and stretching cyclability within 50% strain, without obvious performance degradation even after 150 stretching cycles. As a simple and effective strategy to fabricate stretchable ultraviolet photodetectors with high response speed, the interlaced-nanowire structure can also be applied to other nanowire pairs, like ZnO-CdS interlaced-nanowires. Our method provides a versatile way to fabricate fast speed ultraviolet photodetectors by using interlaced metal oxide nanowires-CdS nanowires structures, which is potential in future stretchable and wearable optoelectronic devices.