Metal Hybrid Structures Research Articles

A tunable versatile metasurface in terahertz frequency based on graphene–metal hybrid structures

The increasing demands for device integration and reusability have led to the development of freely switchable and dynamically tunable diverse functions in both modern optics and wireless communications. This study proposes a versatile metasurface that integrates with four tunable functions in the terahertz region based on graphene patch and metal split-ring hybrid structures. By adjusting the Fermi level of the graphene patches through electrostatic gating, the proposed metasurface can effectively achieve free switching among four different functions and dynamic tuning of each function's characteristics over a broad frequency band. Moreover, the metasurface operates smoothly in reflection mode for x-polarization, y-polarization, and left-hand and right-hand circular polarization illuminations. All expected performances, including resonant absorption with tunable frequency (relative bandwidth is about 20 %) and regulable absorbance (from 10 % to 100 %), arbitrary interconversion of four polarization states (relative bandwidth is over 48 %), regulation of cross-polarization conversion rate (from 0 % to 100 %), tunable spatial power division (three-way outputs), and dual-channel high-efficiency signal modulation (modulation depth is over 81 %), are demonstrated through full-wave simulation experiments. This study opens up a new avenue for exploring tunable multifunctional integrated devices with graphene materials, with potential applications in various domains, such as wireless communication, terahertz sensing, and imaging.

Ultra‐high bonding strength of carbon fiber–doped polyamide–aluminum alloy composite structure achieved by changing crystallinity

AbstractLightweight and high‐strength polymer–metal hybrid structures are favored for reducing material and energy consumption. In this study, carbon fiber‐reinforced polyamide 6 (CFPA) composite materials were prepared through melt blending, and 30 wt% CFPA exhibited the highest shear strength and lowest shrinkage rate among other carbon fiber contents. With pretreatments of anodizing and etching treatment, injection molded direct joining was employed to create polyamide 6 (PA)/CFPA–Aluminum alloy (Al) composites. The impacts of the injection temperature and speed on the bonding strength of the PA/CFPA–Al composite materials were investigated. The characterization results confirmed that carbon fiber doping reduces the coefficient of linear thermal expansion (CLTE) and enhances crystallization ability of PA. The higher injection temperatures and lower injection speed significantly increase the crystallinity of PA and the infiltration of the molten polymer into the nanoporous anodic aluminum oxide films. When the injection temperature was 270°C and the speed was 6 mm/s, the bonding strength of the PA–Al hybrid structure reached a maximum of 36.6 MPa. When the injection temperature was 300°C, the bonding strength of the CFPA–Al hybrid structure reached a maximum of 40.8 MPa. Adhesive parts with high shear bonding strength are critical to satisfying engineering requirements and have significant potential, particularly in polymer–metal composite structures. The polymer‐metal hybrid structure can meet the high interfacial bonding strength required in most engineering applications.Highlights Injection temperature and speed in IMDJ affect PA crystallinity. Carbon fiber doping reduces the CLTE of PA and increases the shear strength. High temperatures and low injection speeds are beneficial to adhesives. The bonding strength of PA–Al reached a maximum of 36.6 MPa. The bonding strength of CFPA–Al reached a maximum of 40.8 MPa.

Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect

Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect

A graphene-metal hybrid biosensor for SEIRA spectroscopy applications

Detecting the building blocks of all living organisms plays a vital role in medical diagnosis and biological research. Infrared (IR) spectroscopy is one of the techniques for detecting biomolecules, such as DNA, RNA, and lipids, through their vibrational fingerprints. IR spectroscopy provides biosensing by directly measuring changes in absorption spectra; however, nanometric-size molecules reveal a weak signal-to-noise ratio with IR light, which is a disadvantage for sensitive bio-detection. Surface-Enhanced Infrared Spectroscopy (SEIRA) based on different structures and materials has been widely used to overcome this problem. In this study, a SEIRA platform based on a hybrid graphene-metal nanoantenna array is designed by combining the enhanced sensitivity of graphene with its electrical tunability and strong-field enhancement with metallic structures. The plasmonic resonance of graphene nano-slit is dynamically tuned to detect fingerprints of protein monolayer at different frequencies. The same detection behavior has been statically demonstrated by metallic antennas. Our results indicate that the sensitivity of the SEIRA sensor platform is quite high due to the combination of graphene and metal hybrid structure compared to the metal resonator alone because of the strong light confinement in the graphene layer. The proposed biosensor can detect the Amid-I and Amid-II bonds, which create relatively strong vibrational fingerprints, as well as the Amide-III bond, which is a very weak bond of a monolayer protein-goat-mouse Immunoglobulin (IgG) protein. It can also be a very useful characterization tool for identifying the molecular fingerprints of unknown chemicals and molecules with its capability to span a large spectral range either dynamically or statically. The strong light absorption via metallic structures compensates for the large areal coverage of graphene sheets, which is quite a challenge for dynamic tuning in real applications.

An experimental study of the effects of degrees of confinement on the response of thermoplastic fibre–metal laminates subjected to blast loading

A series of tests on the dynamic response of thermoplastic fibre–metal laminates (TFMLs) subjected to blast loading with three different degrees of confinement (unconfined, vented and fully confined) were performed. The deflection time histories, the residual deformation, the internal delamination and damage mode of the TFMLs were recorded or observed by employing the digital image correlation, the 3D scanning and X-ray computed tomography techniques. Based on equivalent material properties combined with dimensionless damage numbers φq, the deformation of fibre–metal hybrid structures of different configurations can be effectively predicted and verified by experimental data. In addition, the effective load applied to the hybrid structure within the saturation response time is a key factor in determining the blast performance at different degrees of confinement. Vented explosions can result in the same dynamic response as fully confined explosions with even more severe internal delamination. The presence of quasi-static pressure in fully confined explosions can contribute more than 20% to the final deformation. The results can provide a basis for further understanding of the dynamic response and failure behaviour of fibre–metal hybrid structures subjected to blast loading with different degrees of confinement.

Effect of interfacial thermal history on bonding mechanism of laser assisted joining of QP980-CFRTP with adjustable flat-top rectangular laser beam

Carbon fiber reinforced thermoplastic composite (CFRTP) - metal hybrid structures, which have been increasingly used in the industry, can significantly reduce structure weight and energy consumption. In this paper, an adjustable flat-top rectangular diode laser beam was used as a heat source to join the quenched and portioned QP980 steel and CFRTP in a lap joint configuration. Compared to conventional laser beam scanning process in the literatures, the rectangular laser beam provides a relatively uniform temperature distribution at interface. The relationship between interfacial thermal history and the joint performance was explored. Experimental results showed that thermal history had a significant impact on interfacial chemical compositions and the formation of joint defects via affecting the resin state, resulting in change of the joint fracture behaviors. Furthermore, higher interfacial temperature and sufficient heating/holding time contributed to the complete melting and diffusing of resin matrix on QP980 surface, filling the micro pores of the interface, and promoting the chemical bonding between QP980 and CFRTP. On this basis, a novel strategy to achieve excellent interfacial bonding via adjusting the interfacial thermal history was proposed to produce a high-quality joint with the peak load higher than 10 kN and the shear strength of 22 MPa.

Heteroatom Introduction to Reconstruct Interfacial Chemical Structures for High-Reliability CFRTP/A6061-T6 Hybrid Structures.

The application of carbon-fiber-reinforced thermoplastic (CFRTP)/metal hybrid structures is a vital step for realizing the lightweight design concepts in aerospace. However, the CFRTP/metal hybrid structures are usually not reliable enough in practical applications due to the high differences in chemical and physical properties between these two materials. The current work provides a bottom-up strategy of introducing heteroatoms into CFRTP/metal interfaces to reconstruct the interfacial chemical structures and thus manufacture high-reliability hybrid structures. Based on the principle of utmost using reaction sites at metal surfaces, the heteroatoms of oxygen and hydrogen are specially designed and introduced to the CFRTP/A6061-T6 (6061) interfaces by simple and green plasma polymerization. The introduced oxygen and hydrogen heteroatoms react with the aluminum and oxygen of the oxidation film at 6061 surfaces to produce great interfacial Al-O covalencies and hydrogen bonds. The reconstructing interfacial chemical structures strengthen the joint strength of CFRTP/6061 hybrid structures from 8.82 to 23.97 MPa. Our heteroatom introduction strategy is expected to get a fresh insight into the interfacial design concept and has several important implications for the future application of high-reliability CFRTP/metal hybrid structures.

Achieving excellent interfacial bonding of QP980 steel to CFRTP by laser joining via carbon fiber reinforced mechanical anchorage

Carbon fiber reinforced thermoplastic composites (CFRTP)-metal hybrid structures can significantly reduce weight and cost while maintaining good performance. In this paper, a diode laser was used to join QP980 steel-CFRTP at a lap joint configuration. Furthermore, an ultrafast laser ablation process was used to produce periodic micro-groove structures on the surface of QP980 in order to generate mechanical anchors and improve QP980-CFRTP interfacial bonding performance. The relationship between the shear strength of QP980-CFRTP joints and laser heat input as well as QP980 surface micro-groove depth were evaluated. It was found that both heat input and micro-groove depth significantly affected the state of resin near the bonding interface. The suitable heat input and the micro-groove depth produced the optimized mechanical anchorage structures without the formation of the pores and porosities. Furthermore, a new method was proposed to significantly improve the joint performance where the orientation of fiber and the micro-grooves were intentionally designated as the same and perpendicular to loading direction in order to form carbon fiber reinforced interfacial mechanical anchorage structures. By optimized heat input, micro-groove depth and orientation, the peak load of the joint was dramatically improved by 515% compared with that without laser ablation treatment.

Research Progress on Characterization and Regulation of Forming Quality in Laser Joining of Metal and Polymer, and Development Trends of Lightweight Automotive Applications

Metal–polymer hybrid structures have been widely used in research into their lightweight automotive applications, because of their excellent comprehensive properties. As an efficient technology for automatic connection of dissimilar materials, laser joining has great application potential and development value in the field of lightweight automotive design. However, due to the physical and chemical differences between metals and polymers, the formation quality of the hybrid joint is seriously affected by defects, low bonding strength, and poor morphology. Meanwhile, it is difficult to meet the demands for lightweight automobiles by considering only bonding strength as the target for forming quality. Therefore, the technological characteristics of metal–polymer hybrid structures for use in lightweight automotive applications are analyzed, the advantages and problems of laser-joining technology are discussed, and the characterization indexes and regulation measures of forming quality in laser joining are summarized. This paper which provides reference and guidance for reliable forming, intelligent development, and lightweight application of laser joining for polymer–metal hybrid structures.

Microstructure and Mechanical Properties of Aluminum Alloy/Stainless Steel Dissimilar Ring Joint Welded by Inertia Friction Welding

In recent years, studying the weldability of a dissimilar metal hybrid structure, with the potential to make full use of their unique benefits, has been a research hotspot. In this article, inertia friction welding was utilized to join Φ130 forged ring of 2219 aluminum alloy with 304 stainless steel. Optical observation (OM), electron back scattering diffraction (EBSD), and scanning electron microscopy (SEM) were utilized to examine the joint microstructure in depth. Depending on the research, a significant thermal–mechanical coupling effect occurs during welding, resulting in inadequate recrystallization on aluminum-side thermo-mechanically affected zone (TMAZ) and forming zonal features. The crystal orientation and grain size of each TMAZ region reflect distinct differences. On the joint faying surface, the growth of intermetallic compounds (IMCs) is inhibited by a fast cooling rate and metallurgical bonding characteristics were found depending on the discontinuous distribution of IMCs. The average joint tensile strength can reach 161.3 MPa achieving 92.2% of 2219-O; fracture occurs on aluminum-side base metal presenting ductile fracture characteristics.

Fabrication and characterization of low-sheet-resistance and stable stretchable electrodes employing metal and metal nanowire hybrid structure

Stretchable electrodes with high stretching capability and low sheet resistance were developed using a metal/silver nanowires (AgNWs)/metal hybrid structure on a poly-dimethylsiloxane substrate. A low sheet resistance around 100 mΩ square−1 was achieved using the hybrid structures of Ag/AgNWs/Ag and Cu/AgNWs/Cu electrodes. The stretching capability under single and multi-cycling strain conditions was greatly improved due the AgNWs in-between top and bottom metal electrodes. The random connection of AgNWs generates new current path over the various cracks and wavy structures of the metal electrodes, which improve the initial resistance, the stretching capability under single strain up to 16%, and the resistance stability under 100 times cycling strain for the electrodes. Using a simple resistor model, it was shown that the hybrid structure is effective to improve the stretching capability of the stretchable metal electrodes due to the random connection of AgNWs in-between the metal electrodes.

Neuromorphic computing based on an antiferromagnet-heavy metal hybrid structure under the action of laser pulses

The paper proposes a model of a neuromorphic processor, consisting of excitatory and processing neurons that are oscillators and detectors. The concept of neuromorphic computing, implemented by generating a spin current due to optical excitation of magnetic oscillations in an antiferromagnet is considered. The inverse spin Hall effect causes the generation of an electric current in the heavy metal layer. A constant driving current flows through the common bus. Magnetic oscillations in the receiving neuron occur due to the spin Hall effect. A biaxial nickel oxide crystal was used as a material for the base cells of AFM insulators and platinum was utilized as a heavy metal. The use of optical excitation can significantly increase the processing speed of neuromorphic computing with low power consumption. The presented model implements the simplest operations of neuromorphic computations, such as logical “OR”, “AND”.

Assessment of dissimilar joining between metal and polymer hybrid structure with different joining processes

In this century, innovation and technology are required to fabricate the hybrid joint of metal and polymers. Due to their lightweight and anti-corrosion properties, the mixed components are increasingly used to produce lightweight hybrid structures such as aerospace and automobiles. It is essential to develop welding techniques for joining dissimilar materials and instead use them in engineering structures. The bonding mechanism of the weld joint has varied depending upon the welding process. In the present review, the bonding mechanism of various hybrid joints like Friction stir welding (FSW), Friction stir spot joining, Friction riveting, laser welding, ultrasonic welding and induction welding is discussed in detail. The defects observed in the different welding process is discussed in details. The mechanical properties and microstructure analysis of different hybrid joints are reviewed in detail for a different combination of hybrid joints.

Encapsulating FeCo alloys by single layer graphene to enhance microwave absorption performance

Graphene/magnetic metal hybrid nanostructures are promising candidates of novel microwave absorption materials. Although many efforts have been devoted to fabricate various graphene/magnetic metal hybrid composites, the microwave absorption performance of these materials is still far from industrial demand due to the not well balance between electric field and magnetic field characteristics. Herein, we report single layer graphene encapsulating FeCo alloy nanoparticles (FeCo@Cs) with excellent microwave absorption performance, which deliver a reflection loss value exceeding −10 dB in the whole Ku-band, whole X-band, whole C2-band, and even in the whole C1-band by varying the absorber thickness. The control experiments and numerical simulations demonstrate that the introduction of graphene coating on FeCo alloy nanoparticles can improve the microwave absorption performance greatly by increasing the electrical loss. Moreover, decreasing the coating thickness to single layer graphene can render a good match between electric field and magnetic field, and thus resulting in an electrifying microwave absorption performance. This work gives new insights into the absorption enhancement of graphene/magnetic metal hybrid structures and contributes to guide the design and development of highly efficient microwave absorption materials for practical application.

Finite transverse conductance in topological insulators under an applied in-plane magnetic field

Recently, in topological insulators (TIs) the phenomenon of planar Hall effect wherein a current driven in presence an in-plane magnetic field generates a transverse voltage has been experimentally witnessed. There have been a couple of theoretical explanations of this phenomenon. We investigate this phenomenon based on scattering theory on a normal metal (NM)-TI-normal metal hybrid structure and calculate the conductances in longitudinal and transverse directions to the applied bias. The transverse conductance depends on the spatial location between the two NM-TI junctions where it is calculated. It is zero in the drain electrode when the chemical potentials of the top and the bottom TI surfaces (μ t and μ b respectively) are equal. The longitudinal conductance is π-periodic in ϕ-the angle between the bias direction and the direction of the in-plane magnetic field. The transverse conductance is π-periodic in ϕ when μ t = μ b whereas it is 2π-periodic in ϕ when μ t ≠ μ b. As a function of the magnetic field, the magnitude of transverse conductance increases initially and peaks. At higher magnetic fields, it decays for angles ϕ closer to 0, π whereas oscillates for angles ϕ close to π/2. The conductances oscillate with the length of the TI region. A finite width of the system makes the transport separate into finitely many channels. The features of the conductances are similar to those in the limit of infinitely wide system except when the width is so small that only one channel participates in the transport. When only one channel participates in transport, the transverse conductance in the region 0 < x < L is zero for μ t = μ b and the transverse conductance in the region x > L is zero even for the case μ t ≠ μ b. We understand the features in the obtained results.

An Insightful Picture of Nonlinear Photonics in 2D Materials and their Applications: Recent Advances and Future Prospects

AbstractThe nonlinear optical (NLO) materials are playing a crucial role in almost all aspects of photonics including imaging frequency, manipulation, photon generation, transmission and detection. The nonlinear optics aims to investigate light response in NLO media, in which the NLO response is normally weak and low energy efficient. A comprehensive summary, discussion, and correlation of the light–matter interaction in the 2D nano‐platform, like graphene and TMDCs, would be inspirational and timely needed. In this contribution, a broad overview and discussion about recent experimental evolution regarding the NLO response and its corresponding applications in various 2D materials are presented. A wide material library including graphene, transition metal dichalcogenides, black phosphorus, MXenes, semimetals, polymer materials, and hybrid structures (0D, 1D, 3D) are discussed. In this review, the qualitative description of NLO is firstly illustrated, followed by various fundamental NLO processes being highlighted. Fundamental limits of nonlinear optics and some of NLO applications are prospected. It is hoped that this comprehensive review will shed a light on the development of nonlinear optics with 2D materials to be applied in the field of photonics and optoelectronics.

Dynamically reversible and strong circular dichroism based on Babinet-invertible chiral metasurfaces.

We propose a Babinet-invertible chiral metasurface for achieving dynamically reversible and strong circular dichroism (CD). The proposed metasurface is composed of a VO2-metal hybrid structure, and when VO2 transits between the dielectric state and the metallic state, the metasurface unit cell switches between complementary structures that are designed according to Babinet's principle. This leads to a large and reversible CD tuning range between ±0.5 at 0.97 THz, which is larger than the one found in the literature. We attribute the CD effect to extrinsic chirality of the proposed metasurface. We envision that the Babinet-invertible chiral metasurface proposed here will advance the engineering of active and tunable chiro-optical devices and promote their applications.

Efficient single-photon emission from a nanowire quantum dot coupled to a plasmonic nanoantenna

Integration of a single III-V quantum dot with a plasmonic nanoantenna is still underexplored as a means towards efficient single-photon sources. Here, we propose two new concepts based on a nanowire quantum dot (NWQD) emitter coupled with a plasmonic bowtie antenna and an NWQD-plasmonic metal hybrid structure. Based on finite element method modeling, we show how these devices can achieve an enhancement in single-photon emission rate and directional radiation. The plasmonic bowtie can increase the spontaneous emission of NWQD with a small diameter, overcoming their otherwise dominating intrinsic spontaneous emission suppression. Further, the NWQD-plasmonic hybrid structure can act as a single-mode waveguide. These features would facilitate nano-photonic device integration as desired for applications of bright single-photon sources, plasmonic lasers, and on-chip opto-electronic nanodevices.

Static and fatigue behaviours of a bolted GFRP/steel double lap joint

To provide a safe and reliable connection using bolts for glass fibre-reinforced polymer (GFRP)/metal hybrid structures in civil engineering, the static and fatigue behaviours of a bolted GFRP/steel double-lap joint (DLJ) with a clamping force of 10 N m were investigated experimentally under monotonic tensile loading and repetitive tensile loading with a load ratio of R = 0.1, respectively. The dominant failure modes, fatigue life and stiffness degradation law were obtained for the bolted DLJ. The fatigue damage evolution of the bolted DLJ was also clarified. The F–N curve and a non-linear stiffness degradation model were obtained from the experimental results for the bolted GFRP/steel DLJ. Finally, a comparison between the fatigue behaviour of the bolted GFRP/steel DLJ and that of a GFRP/GFRP DLJ was performed to identify the differences. The results indicated that the stiffness degradation law of the bolted GFRP/steel DLJ could be accurately characterized by the non-linear stiffness degradation model. The GFRP/steel DLJ exhibited a longer fatigue life than the GFRP/GFRP DLJ because the compressive stresses in the inner surface of the bolt-hole of the outer GFRP laminates were much smaller in the bolted GFRP/GFRP joint than the bolted GFRP/GFPR DLJ under the same applied maximum load. The stiffness degradation rate of the GFRP/steel DLJ under fatigue loading was almost the same as that of the GFRP/GFRP DLJ during their service lives.

Switchable broadband and wide-angular terahertz asymmetric transmission based on a hybrid metal-VO2 metasurface.

We propose a switchable broadband and wide-angular terahertz asymmetric transmission based on a spiral metasurface composed of metal and VO2 hybrid structures. Results show that asymmetric transmission reaching up to 15% can be switched on or off for circularly polarized terahertz waves when the phase of VO2 transits from the insulting state to the conducting state or reversely. Strikingly, we find that relatively high asymmetric transmission above 10% can be maintained over a broad bandwidth of 2.6-4.0 THz and also over a large incident angular range of 0°-45°. We further discover that as the incident angle increases, the dominant chirality of the proposed metasurface with VO2 in the conducting state can shift from intrinsic to extrinsic chirality. We expect this work will advance the engineering of switchable chiral metasurfaces and promote terahertz applications.