High-performance Functional Devices Research Articles

Controllable antiresonance and low-bias negative differential conductance in T-shaped double dots with electron–phonon interaction

Controlling the quantum interference in nanoscaled systems has potential application for the realization of high-performance functional devices. In this work, the quantum interference of a T-shaped double-quantum-dot system is studied in detail by evaluation of differential conductance by means of nonequilibrium Green’s function method. The factors of Coulomb interaction in Luttinger liquid leads, electron–phonon interaction, interdot tunneling, and dot-lead coupling are taken into account. In the differential conductance curve, there appear a series of antiresonance dips due to phonon-assisted destructive interference when the interdot tunneling is weak, and they can coexist with zero-bias antiresonance dip. When the dot-lead couplings are asymmetric, both the antiresonance dip and Fano line shape dip can occur for strong dot-lead coupling. Our results also show the coexistence of low-bias negative differential conductance and Fano antiresonance, as a manifestation of the interplay between strong intralead Coulomb interaction and weak dot-lead coupling. These interference phenomena emerged in a relatively simple model promises helpful guidance for controlling over the electrical performance of interference-based molecular devices.

Photoluminescence and transport properties of fluorinated graphene via a weak fluorination strategy

The zero-bandgap properties of graphene (Gr) limit its various applications. Fluorination is an alternative strategy to open the bandgap to broaden its applications. However, traditional fluorination methods are detrimental to human health and contribute extensively to environmental pollution. Here, we develop a simple and safe process of weak fluorination that introduces fluorine atoms into Gr, breaking its zero-bandgap structure. This strategy is more environmentally friendly, risk-free, and harmless to humans, making it suitable for large-scale production. Through this highly controllable weak fluorination process, micro-area selective fluorination is achieved and induces excellent photoluminescence characteristics but maintains a high mobility, compared to the pristine Gr with zero bandgap. The degree of fluorination determines the photoelectric and transport properties of Gr. This work provides an experimental foundation for developing materials based on fluorinated graphene and designing high-performance functional devices.

Crystal Self-Assembly under Confinement: Bridging Nanomaterials to Integrated Devices.

ConspectusSelf-assembly, a spontaneous process that organizes disordered constituents into ordered structures, has revolutionized our fundamental understanding of living matter, nanotechnology, and molecular science. From the perspective of nanomaterials, self-assembly serves as a bottom-up method for creating long-range-ordered materials. This is accomplished by tailoring the geometry, chemistry, and interactions of the components, thereby facilitating the efficient fabrication of high-quality materials and high-performance functional devices. Over the past few decades, we have seen controllable organization and diverse phases in self-assembled materials, such as organic crystals, biomolecular structures, and colloidal nanoparticle supercrystals. However, most self-assembled ordered materials and their assembly mechanisms are derived from constituents in a liquid bulk medium, where the effects of boundaries and interfaces are negligible. In the context of nanostructure patterning, self-assembly occurs in confined spaces, with feature sizes ranging from a few to hundreds of nanometers. In such settings, ubiquitous boundaries and interfaces can trap the system in a kinetically favored but metastable state, devoid of long-range order. This makes it extremely difficult to achieve ordered structures in micro/nano-patterning techniques that rely on sessile microdroplets, such as inkjet printing, dip-pen lithography, and contact printing.In stark contrast to sessile droplets, capillary bridges─formed by liquids confined between two solid surfaces─provide unique opportunities for understanding the long-range-ordered self-assembly of crystalline materials under spatial confinement. Because capillary bridges are stabilized by Laplace pressure, which is inversely proportional to the feature size, the confinement and manipulation of solutions or suspensions of functional materials at the nanoscale become accessible through the rational design of surface chemistry and geometry. Although global thermodynamic equilibrium is unattainable in evaporative systems, ordered nucleation and packing of constituent components can be locally realized at the contact line of capillary bridges. This enables the unprecedented fabrication of long-range-ordered micro/nanostructures with deterministic patterns.In this Account, we review the advancements in long-range-ordered self-assembly of crystalline micro/nanostructures under confinement. First, we briefly introduce crystalline materials characterized by strong intramolecular interactions and relatively weak intermolecular forces, analyzing both the opportunities and challenges inherent to self-assembled nanomaterials. Next, we delve into the construction and manipulation of confined liquids, focusing especially on capillary bridges controlled by engineered chemistry and geometry to regulate Laplace pressure. Through this approach, we have achieved capillary bridges with thicknesses on the order of a few nanometers and wafer-scale homogeneity, facilitating the self-assembly of ordered structures. Supported by factors such as local free-volume entropy, electrostatic interactions, curvilinear geometry, directional microfluidics, and nanoconfinement, we have achieved long-range-ordered, deterministic patterning of organic semiconductors, metal-halide perovskites, and colloidal nanocrystal superlattices using this capillary-bridge platform. These long-range microstructures serve as a bridge between nanomaterials and integrated devices, enabling emergent functionalities like intrinsic stretchability, giant photoconductivity, propagating and interacting exciton polaritons, and spin-valley-locked lasing, which are otherwise unattainable in disordered materials. Finally, we discuss potential directions for both the fundamental understanding and practical applications of confined self-assembly.

Dual-band Bandpass Plasmonic Filter Based on Effective Localized Surface Plasmon Resonators

A dual-band bandpass plasmonic filter based on quarter-wavelength effective localized surface plasmon resonators (ELSPRs) is proposed in this work. Compared with conventional microstrip resonators, ELSPRs have a larger unloaded quality factor and compact size, which can be flexibly designed. Since the harmonics of quarter-wavelength ELSPRs are located only at odd times of their dominant mode frequency, we can not only miniaturize the filter but achieve excellent out-of-band rejection performance. For demonstration, we design and fabricate a dual-band bandpass plasmonic filter, whose size is only 0.0396λ2 0 the center frequency is 3.1 GHz and 3.6 GHz, and the relative bandwidth is 10.7% and 7.7% respectively. Measurement results show excellent agreement with the simulations. Our results provide a route for realizing ultra-compact and high-performance functional devices for the fifth generation (5G) applications

Full-space dual-helicity decoupled metasurface for a high-efficiency multi-folded reflective antenna.

The independent tailoring of electromagnetic waves with different circular-polarized (CP) wavefront in both reflection and transmission channels is of broad scientific and technical interest, offering ultimate degrees of freedom in designing advanced devices with the merits of functionality integration and spatial exploitation. However, most metasurfaces only provide dependent wavefront control of dual-helicity in a single channel, restricting their applications to limited practical scenarios. Herein, we propose a full-space dual-helicity decoupled metasurface and apply it to assemble a multi-folded reflective antenna (MFRA) in the microwave regime. A multilayered chiral meta-atom is designed and optimized to reflect a particular helical wave while allowing the orthogonal helical wave to penetrate through, with simultaneous full span of phase modulations in both channels. When a uniform reflection and a hyperbolic transmission phase profile is imposed simultaneously on the metasurface in a polarization-selective manner, it can be engineered to conduct specular reflection for one helical wave and convergent transmission of the other helical wave. Combining the proposed metasurface with a metallic plate as a bottom reflector and an integrated microstrip patch antenna in the center of metasurface as a feed, a MFRA is realized with a low profile, high efficiency, and high polarization purity in a broad frequency band. The proposed design method of the dual-helicity decoupled metasurface and its antenna application provide opportunities for high-performance functional devices, promising more potential in future communication and detection systems.

An Ultra-Broadband Polarization Beam Splitter Based on the Digital Meta-Structure at the 2 µm Waveband

The 2 μm waveband is considered to have great potential in optical communications. Driven by the demands on high-performance functional devices in this spectral band, various integrated photonic components have been demonstrated. In this work, an analog and digital topology optimization method is proposed to design an ultra-broadband polarization beam splitter at the 2 μm waveband. Within an optical bandwidth of 213 nm, the excess losses of TE and TM modes are <0.53 dB and 0.3 dB, respectively. The corresponding polarization extinction ratios are >16.5 dB and 18.1 dB. The device has a very compact footprint of only 2.52 µm × 5.4 µm. According to our best knowledge, this is a benchmark demonstration of an ultra-broadband and ultra-compact polarization beam splitter enabled by the proposed optimization method.

Thermally-stable graphene metamaterial absorber with excellent tunability for high-performance refractive index sensing in the terahertz band

Graphene plasmons have attracted great interest for constructing high-performance functional metamaterial devices, among which graphene-based narrowband metamaterial absorbers are valuable in numerous applications. In this paper, a graphene-dielectric-metal hybrid structure is proposed to achieve dual-band excellent absorption and high-performance refractive index sensing. Numerical simulations show that the designed structure exhibits a high Q factor of 277.8 at 1.945 THz, which is higher than most previously-reported results. The sensitivity of the proposed structure can be up to 1.84 THz/RIU when the analyte thickness is 80 μm, and it exhibits promise for sensing thin-film biomolecule and thick biologic tissues. The electromagnetic field distributions show that the electromagnetic energy is highly confined in the structure at the higher order plasmon resonance, which plays an important role in achieving the excellent characteristics of the proposed structure. The tunability of the proposed structure is realized via changing the gate voltage applied to the graphene and the angles of the incident THz wave. In addition, we reveal that the proposed structure can be switched between single-band, dual-band, and 3-band absorption by tuning the incident angle under TM and TE polarization. Further results demonstrate that the proposed device possesses good thermal stability, polarization insensitivity, and outstanding fabrication tolerance. We believe that the proposed dual-band narrowband absorber can serve as a good example for other devices based on plasmons, such as selective sensors, modulators, and optical detectors.

Biomimicry-Gradient-Based Algorithm as Applied to Photonic Devices Design: Inverse Design of Flat Plasmonic Metalenses

The classical adjoint-based topology optimization (TO) method, based on the use of a random continuous dielectric function as design variable distribution is known to be one of the timely efficient and fast optimization methods enable a very high performance functional optical devices. It relies on the computation of the gradient of a figure of merit (FOM) with respect to the design parameters. The gradient of the figure of merit (FOM) may then be used to update the design vector element in several senarios. One of the most common use scenario consists of updating simultaneously all the design parameter vector elements. In a linear problem case involving a simply convex FOM-function shape, using the gradient information, it is a relatively easy to reach an optimal solution. In the case of constrained and non linear problems stated in an infinite and indeterminate design space, the conventional TO, a local optimizer, may require multiple restarts, with multiple initial points and multiple runs. The algorithm strongly depends on the initial conditions. In this paper, we report a global-like optimizer inspired by a wolf pack hunting, enabling efficient design of metasurfaces through their geometrical parameters. We apply the method to design a non periodic metasurface consisting of plasmonic metalenses, enabling a high energy flow focusing on a well-defined 2D focus spot. Numerical results show that the proposed inverse design method has a low sensitivity to initial conditions. In our design method of metalens, we optimize the full micro device at once, and demonstrate that the proposed method may provide both symmetric and more creative unexpected asymmetric on-axis metalenses even though under a normal illumination.

Ultracompact Effective Localized Surface Plasmonic Bandpass Filter for 5G Applications

In this article, we present a novel ultracompact plasmonic bandpass filter (BPF) based on a recently proposed concept of effective localized surface plasmons (ELSPs). By virtue of the insensitiveness of the ELSPs resonator's dipolar mode resonance frequency to the variations of its cross-sectional area and shape, we can significantly miniaturize the occupied area of the filter. Moreover, the unloaded quality factor of the ELSPs resonator can be flexibly tuned and adjusted to be much larger than that of conventional microstrip and substrate integrated waveguide (SIW) resonators. For demonstration, we design and implement two Sub-6G BPFs centered at 3.3 and 3.4 GHz with the size of only 0.006 and 0.021λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured in-band insertion loss (IL) and fractional bandwidth are 0.8 dB and 5.6% for the third-order BPF, and 0.7 dB and 5.9% for the fourth-order BPF, respectively. Excellent agreements between the measured and simulated results verify our design. The proposed ELSPs BPFs pave the way to realize ultracompact and high-performance functional devices for fifth-generation (5G) applications.

Liquid Metal Motor

As an emerging soft material, liquid metal has demonstrated enormous potential for developing high performance functional devices and machines. However, current liquid metal enabled machines suffer from several issues, such as the requirement of a liquid environment, generation of weak actuating forces, and insufficient maneuverability. These restrictions limit the application of liquid metal in constructing more complex, flexible and powerful actuating systems. Here, a motor is developed based on the electrical actuation of liquid metal droplets without the need for conventional electromagnets. The approach is distinguished by (1) the encapsulation of electrolyte and multiple liquid metal droplets within an enclosed system, and (2) the creation of stable and continuous torque outside a liquid environment. In addition, an electrical brush is introduced to contact liquid metal with solid electrodes and operate the motor with low friction. The parameters affecting the actuation behavior are further investigated. Moreover, the versatility and maneuverability of the motor is demonstrated by applying it to drive untethered vehicles and boats. The unique driving mechanism endows the liquid metal motor with several advantages, including low friction, no sparking, low noise, versatile working environment, and being built from soft materials that could offer new opportunities for developing soft robotics.

Crossing interfacial conduction in nanometer-sized graphitic carbon layers.

Graphitic carbon layers (GCLs), exemplified by graphene, have been proposed for potential application in high-performance functional devices due to superior electrical properties, e.g., high electron mobility. In state-of-the-art electronics, it is required that GCLs are miniaturized to nanometer scales and incorporated into the integrated circuits to exhibit novel functions at nanometer scales. However, the implementation of nanometer-scale GCLs is suspended; the function in devices is deteriorated by increasing contact resistance in miniaturized GCL/electrode interfaces. In this study, nanometer-sized GCL/gold (Au) interfaces were fabricated via atomistic visualization of nanomanipulation, and simultaneously their contact resistance was measured. We showed that the contact resistivity of the interfaces was decreased to the order of 10-10Ω cm2, which was 104 times smaller than that of micrometer-sized or larger GCL/metal interfaces. In addition, it was revealed that peculiar electrical conduction at the nanometer-sized GCL/Au interfaces emerged; current flows throughout the entire area of the interfaces unlike micrometer-sized or larger GCL/metal interfaces. These results directly contribute to actual application of GCLs in advanced nanodevices.

Enhanced optoelectronic performance of 2D organic-inorganic hybrid perovskite through light-illumination.

Improving the optoelectronic characteristics of organic-inorganic perovskites is crucial for fabrication of functional devices. Herein, we demonstrate that the optoelectronic properties of 2D organic-inorganic perovskites can be greatly improved by UV-light illumination during growth. The photoluminescence emission of the 2D perovskite exhibits a 3.1-folds increase in intensity, with a decreased trap-assisted recombination. The improved optoelectronic characteristics can be attributed to the high-quality crystallization and lattice expansion induced by the UV-light illumination. Moreover, the optimized 2D perovskites enable the fabrication of photoconductive devices with improved optoelectronic responses. This work indicates that light illumination is a novel and convenient approach for engineering the fabrication of 2D organic-inorganic hybrid perovskites, which advocates great promise for achieving high-performance functional devices.

Anti-resonance features of destructive quantum interference in single-molecule thiophene junctions achieved by electrochemical gating.

Controlling the electrical conductance and in particular the occurrence of quantum interference in single-molecule junctions through gating effects has potential for the realization of high-performance functional molecular devices. In this work we used an electrochemically gated, mechanically controllable break junction technique to tune the electronic behaviour of thiophene-based molecular junctions that show destructive quantum interference features. By varying the voltage applied to the electrochemical gate at room temperature, we reached a conductance minimum that provides direct evidence of charge transport controlled by an anti-resonance arising from destructive quantum interference. Our molecular system enables conductance tuning close to two orders of magnitude within the non-faradaic potential region, which is significantly higher than that achieved with molecules not showing destructive quantum interference. Our experimental results, interpreted using quantum transport theory, demonstrate that electrochemical gating is a promising strategy for obtaining improved in situ control over the electrical performance of interference-based molecular devices.

Precisely controllable n-type doping in MoTe2 field effect transistors by hydrazine treatment

An accurate and controllable n-type doping method for MoTe2 field effect transistors is developed by hydrazine treatment. It is shown that hydrazine molecules are absorbed physically without a new substance being formed, as determined by X-ray photoelectron spectroscopy measurements. The conduction type, electron concentrations, and minimum conductivity points in the transfer characteristics could be modulated precisely for a wide range by varying the concentration of hydrazine solution. Compared to pristine MoTe2 control devices, the electron concentrations are changed from 9.67 × 1011 cm−2 to 3.46 × 1012 cm−2 in the n-type regime, while the electron current on/off ratio is increased from 104 to 106 after 5 wt. % of hydrazine treatment. It is also interesting to observe that the ambipolar window increases almost linearly as the device temperature is reduced from 260 K to 5 K. The effective Schottky barrier heights for electrons in hydrazine treated MoTe2 field-effect transistors are extracted and found to be lower than 0.024 eV, indicating that the thermionic emission is not dominated. Furthermore, a lateral MoTe2 p–n junction with a rectification ratio higher than 103 and an ideality factor of around 1.66 is demonstrated through selective doping. This developed unique method of n-type doping and p-n junction creates an opportunity to fabricate high performance functional devices based on 2D layered materials.

Coalescence and epitaxial self-assembly of Cu nanoparticles on graphene surface: A molecular dynamics study

A detailed understanding of surface decoration and interconnecting technologies is essential in realizing high-performance functional devices incorporating metal nanoparticle/graphene nanohybrids. This study employs classical molecular dynamics (MD) simulations to investigate the formation of amorphous copper (Cu) layers on a graphene surface via the collision, coalescence and nucleation of individual Cu nanoparticles (NPs) at temperatures in the range of 300–1300 K. The results indicate that the coalescence and melting temperatures are both sensitive to the particle size and the presence of the substrate. Moreover, an epitaxial interaction is found between the Cu NPs and the graphene substrate, in which mobile Cu atoms are captured and dragged to the graphene surface to produce self-assembled NP layers via a nucleation process. A series of structural evolutions and phase transitions are revealed during thethermalization process of the NPs. Finally, the results show that the presence of the substrate and associated contact epitaxy phenomenon play a key role in governing the structural morphology and thermal behavior of the Cu NP-based thin film.

Large-area plastic nanogap electronics enabled by adhesion lithography

Large-area manufacturing of flexible nanoscale electronics has long been sought by the printed electronics industry. However, the lack of a robust, reliable, high throughput and low-cost technique that is capable of delivering high-performance functional devices has hitherto hindered commercial exploitation. Herein we report on the extensive range of capabilities presented by adhesion lithography (a-Lith), an innovative patterning technique for the fabrication of coplanar nanogap electrodes with arbitrarily large aspect ratio. We use this technique to fabricate a plethora of nanoscale electronic devices based on symmetric and asymmetric coplanar electrodes separated by a nanogap < 15 nm. We show that functional devices including self-aligned-gate transistors, radio frequency diodes and rectifying circuits, multi-colour organic light-emitting nanodiodes and multilevel non-volatile memory devices, can be fabricated in a facile manner with minimum process complexity on a range of substrates. The compatibility of the formed nanogap electrodes with a wide range of solution processable semiconductors and substrate materials renders a-Lith highly attractive for the manufacturing of large-area nanoscale opto/electronics on arbitrary size and shape substrates.

Poly(vinyl alcohol)-Assisted Fabrication of Hollow Carbon Spheres/Reduced Graphene Oxide Nanocomposites for High-Performance Lithium-Ion Battery Anodes.

Three-dimensional hollow carbon spheres/reduced graphene oxide (DHCSs/RGO) nanocomposites with high-level heteroatom doping and hierarchical pores are fabricated via a versatile method. Poly(vinyl alcohol) (PVA) that serves as a dispersant and nucleating agent is used as the nonremoval template for synthesizing melamine resin (MR) spheres with abundant heteroatoms, which are subsequently composited with graphene oxide (GO). Use of PVA and implementation of freezing treatment prevent agglomeration of MR spheres within the GO network. Molten KOH is used to achieve the one-step carbonization/activation/reduction for the synthesis of DHCSs/RGO. DHCSs/RGO annealed at 700 °C shows superior discharge capacity of 1395 mA h/g at 0.1 A/g and 606 mA h/g at 5 A/g as well as excellent retentive capacity of 755 mA h/g after 600 cycles at a current density of 2 A/g. An extra CO2 activation leads to further enhancement of electrochemical performance with outstanding discharge capacity of 1709 mA h/g at 0.1 A/g and 835 mA h/g at 2 A/g after 600 cycles. This work may improve our understanding of the synthesis of graphene-like nanocomposites with hollow and porous carbon architectures and fabrication of high-performance functional devices.

Bio‐Nanotechnology in High‐Performance Supercapacitors

AbstractThe use of bio‐nanotechnology for the fabrication of diverse functional nanomaterials with precisely controlled morphologies and microstructures is attracting considerable attention due to its sustainability and renewability. As one of the key energy storage devices, supercapacitor (SC) requires the active electrode material to have high specific surface area, interconnected porous structure, excellent electronic conductivity, and appropriate heteroatom doping for promoting the transfer of electrons and electrolyte ions. The combination of bio‐technology and SC will open up a new avenue for the large‐scale fabrication of high performance functional energy storage devices. In this review, the most state‐of‐the‐art research progress in bio‐nanotechnological fabrication of different nanomaterials, including carbon materials, metal oxides, conducting polymers, and their corresponding composites are reviewed with the following three bio‐nanotechnical approaches covered: (1) biomass carbonization technologies; (2) bio‐template methods; and (3) bio‐complex technologies, while also highlighting their applications as functional SC electrodes.

Single-crystal perovskites prepared by simple solution process: Cast-capping method

We investigated the formation of single-crystal CH3NH3PbCl3 and CH3NH3PbI3 perovskites by cast-capping method. This very simple but high efficiency technique based on modified solution process was successful to grow large-domain single crystals up to a millimeter size. Their X-ray diffraction patterns revealed that both crystals grew in the cubic form. The (100) planes of both crystals grew predominantly in contact with the substrate surface. The present technique helps further studies as an alternative method to fabricate high performance functional devices.

Tin Oxides with Nano and Micron-Sized Pores for Functional Electrochemical Devices

Metal oxides with one-dimensional (1-D) nano-channels have drawn much attention as potential electrode materials for high performance functional electrochemical devices. This is mainly because the large surface area of nanostructures and the 1-D pathway of reactants/products in channels result in low activation and concentration polarizations, respectively. In spite of such advantages, the expected high rate and high efficient operation of the devices adopting the electrodes with nano-channeled structure might not be quite sustainable particularly when the rate of surface reaction far exceeds that of mass transport through the channels. That is, the reactants/products would be seriously depleted/accumulated in the channel at the very high rate of surface reaction, possibly leading to the significant decrease in total reaction rate. One way to solve this problem is to prepare the hybrid porous structure composed of both nano-sized and micron-sized pores, where the latter efficiently provides the reactants to or receives the products from the nano-channels. It has been known that an anodic oxidation process is a quite effective way to create the metal oxide films with well-defined 1-D nano-channeled structure. Among the anodic metal oxides with 1-D structure, tin oxide is worthy of attention due to its widespread use in various applications, such as catalysis, gas sensing and energy storage. In this work, meso- and macro- hybrid porous structure is created without a template by an anodic oxidation process. From the experimental results, it is suggested that the substrate, the anodizing time, the thickness of the pre-anodized tin have an important effect on the size and density of macro-pores in hybrid porous structure. For example, the well-defined meso/macro hybrid porous tin oxides can be created when silicon was used as a substrate to anodize tin thin film. On the basis of the mechanical analysis of the different substrates and different thicknesses of tin film on them, it is suggested that the substrate with high elastic modulus might result in high compressive stress to the anodic tin oxide and generate local cracks in the initial stage of anodizing process, which grow to macro-pores with semispherical shape in the later stage. From two step anodizing process including the intervening selective etching of tin oxide, highly-open meso/macro hybrid porous tin oxide is successfully prepared. Anodic tin oxide formed under the macro-pores has meso-porous structure with radial shape, ideally suited for high rate and high efficient functional electrochemical devices.