Tunable Performance Research Articles

Control of metal-support interaction for tunable CO hydrogenation performance over Ru/TiO2 nanocatalysts.

The catalytic behavior of CO hydrogenation can be modulated by metal-support interactions, while the role of the support remains elusive. Herein, we demonstrate that the presence of strong metal-support interactions (SMSI) depends strongly on the crystal phase of TiO2 (rutile or anatase) and the treatment conditions for the TiO2 support, which could critically control the activity and selectivity of Ru-based nanocatalysts for CO hydrogenation. High CO conversion and olefin selectivity were observed for Ru/rutile-TiO2 (Ru/r-TiO2), while catalysts supported by anatase (a-TiO2) showed almost no activity. Characterization confirmed that the SMSI effect could be neglected for Ru/r-TiO2, while it is dominant on Ru/a-TiO2 after reduction at 300 °C, resulting in the coverage of Ru nanoparticles by TiOx overlayers. Such SMSI could be suppressed by H2 treatment of the a-TiO2 support and the catalytic activity of the as-obtained Ru/a-TiO2(H2) can be greatly elevated from almost inactive to >50% CO conversion with >60% olefin selectivity. Further results indicated that the surface reducibility of the TiO2 support determines the SMSI state and catalytic performance of Ru/TiO2 in the CO hydrogenation reaction. This work offers an effective strategy to design efficient catalysts for the FTO reaction by regulating the crystal phase of the support.

Global Tracking Control With Tunable Transient Performance Under Deferred Time-varying Constraints

Global Tracking Control With Tunable Transient Performance Under Deferred Time-varying Constraints

Ultra-high resistive switching current ratio and improved ferroelectricity and dielectric tunability performance in a BaTiO3/La0.7Sr0.3MnO3 heterostructure by inserting a SrCoO2.5 layer.

A BaTiO3/SrCoO2.5 (BTO/SCO) bilayer and a BTO single film were prepared by radio frequency magnetron sputtering on La0.7Sr0.3MnO3 (LSMO) buffered SrTiO3 (001) substrates. Interestingly, compared with reported BTO-based films, the BTO/SCO/LSMO heterostructure has a maximum ON/OFF current ratio of ∼945. More interestingly, compared with the BTO single layer, a larger Pr (∼18.4 μC cm-2) and larger dielectric tunability (∼71.9%) were achieved in the BTO/SCO bilayer. The improved performance may be attributed to the large tetragonality and improved oxygen vacancy concentrations in the BTO/SCO/LSMO heterostructure. Furthermore, our BTO/SCO/LSMO stacks exhibit potential for flexible electronic informational devices.

Transparent grating-based metamaterials for dynamic infrared radiative regulation smart windows.

Dynamic infrared radiation regulation has been widely explored for smart windows because of its vital importance for comfortable and energy-efficient buildings. However, it remains a great challenge to synchronously achieve high visible transmittance and pronounced infrared tunability. Here, we propose a dynamic infrared tunable metamaterial composed of indium tin oxide (ITO) gratings, an air insulator, and an ITO reflector. The ITO grating-based infrared radiation regulator exhibits a high emissivity tunability of 0.73 at 8-13 μm while maintaining a high visible transmittance of 0.65 and 0.72 before and after actuation, respectively. By adjusting the geometric parameters, the tunable bandwidth can be further extended to 3-30 μm and the ultra-broadband tunability reaches 0.62. The excellent infrared tunable performance arises from the insulator thickness-dependent effect of Fabry-Pérot and propagating surface plasmon resonance coupling and decoupling, which lead to perfect and low absorption, respectively. This work provides potential for the advancement of smart window technology and makes a significant contribution to sustainable buildings.

One-step solvothermal synthesis of full-color fluorescent carbon dots for information encryption and anti-counterfeiting applications.

Multicolor fluorescent carbon dots (CDs) have received extensive attention due to their excellent fluorescence tunable performance. In this study, multicolor CDs with color tunable and high fluorescence quantum yields (QYs) were successfully prepared under the same conditions by a one-step solvothermal method using 2-aminoterephthalic acid (ATA) and Nile Blue A (NBA) as reaction reagents, achieving a wide color field coverage. Detailed studies on the relevant mechanisms have been carried out for blue, green and red CDs, indicating that the regulating mechanism of multicolor luminescence is determined by the size of the sp2 conjugated domains, which is due to the increase of particle size that causes an increase in the size of the sp2 conjugated domains, resulting in the narrowing of the band gap and the red-shift of the emission wavelength. It was found that the CDs have the advantages of simple preparation, high photostability and high quantum yield. They were used as fluorescent ink and mixed with polyvinyl alcohol (PVA) to form CD/PVA composites, which were successfully applied in the field of information encryption and anti-counterfeiting. This work provides a new strategy for the synthesis of panchromatic tunable fluorescent CDs and their application in the field of information encryption and anti-counterfeiting.

Structural engineering of rare earth metal-organic frameworks derivatives with high anisotropy for high-efficiency electromagnetic wave absorption

Structural engineering and component design are crucial for conceiving outstanding metal-organic frameworks (MOFs)-based electromagnetic wave (EMW) absorption materials. However, an efficient and direct clarification of the structural influences on the EMW absorption performance of MOF-based absorption materials remains highly challenging and still awaits exploration. To this end, we synthesized a new type of rare earth (RE) MOFs with hexagonal-bipyramidal, snowflake-like, and dendritic structures through facilely controlling the solvent ratios in a scalable coprecipitation approach. The MOF-derived CeO2/Co/C hybrids with the same component content inheriting the morphological structures showcased tunable dielectric property and EMW absorption performance. The dendritic MOF derivatives with the highest anisotropy achieved a superior EMW absorption performance, manifesting a minimum reflection loss value of −71.5 dB at 1.7 mm and an effective absorption bandwidth of 5.2 GHz at 1.6 mm thickness, comparable to those of the best EMW absorbers. This work not only confirmed the high potential of RE MOF derivatives for EMW absorption, but also directly and efficiently unveiled the mechanism of morphological structure on the dielectric property and EMW absorption performance for the MOF-based EMW absorption material.

Imparting anisotropic performance to soft materials via a magnetically-driven programmable templating-deposition strategy

Creating biomimetic aligned structures in soft materials with fast stimuli-responsive ability and tunable performance is of great interest to intelligent material science. However, there is still a technical challenge to balance the relative velocities of polymeric gelation and nano-alignment/accumulation processes in a controllable manner. Herein, a magnetically-driven programmable templating-deposition strategy coupled with an oscillating electrical signal has been developed to impart tunable anisotropic performance to the soft hydrogels. Specifically, the programmable electrophoretic deposition was initiated from a typical self-aggregated chitosan/Fe3O4 nanoclusters in the presence of an external magnetic field, in which case allows magnetically-driven fast templating of chitosan chains to the electrode surface, oriented/enriched nanoclusters into a compact “fiber-like” aligned structure, and then locked by the electric-field induced localized neutralization processes. An oscillating electrical signal has been used for the first time to manipulate the fiber thickness by varying the ON-OFF electrical signal sequences (e.g., each interruption provides extratimes/chances for nano-assembly), resulting in a higher concentration of magnetic particles and tunable aligned structure to the hydrogels with improved multi-functionalities (e.g., mechanical strength, conductivity, magnetic responsiveness, and photothermal activity). The proof-of-concept for potential applications in the controlled drug delivery system and smart magnetic catheter have also been demonstrated. Consequently, this versatile magnetically-driven programmable templating-deposition approach expands the range of stimuli-responsive materials beyond magnetic hydrogels, inspiring the creation of advanced functional soft materials and devices for wide-broad applications.

Tunable Multifunctional Metamaterial Sandwich Panel with Quasi‐Zero Stiffness Lattice Cores: Load‐Bearing, Energy Absorption, and Vibration Isolation

AbstractThe interest in novel mechanical metamaterials that offer advanced functionalities and mechanical tunability for highly compatible multifunctional performance in state‐of‐the‐art engineering applications is growing. Here, a novel tunable multifunctional mechanical metamaterial, also known as a metamaterial sandwich panel, which can achieve load‐bearing, energy absorption, and low‐frequency vibration isolation properties simultaneously, is reported. The designed metamaterial sandwich panel is composed of a quasi‐zero stiffness (QZS) lattice core and two kirigami‐style surfaces, which endow the metamaterial sandwich panel with multi‐function performance and tunable properties. As a proof‐of‐concept, the mechanical properties and tunable multifunctional performance of the proposed metamaterial sandwich panel are demonstrated both in simulations and experiments. This work provides a new alternative for designing novel mechanical metamaterials with tunable multifunctional performance and may have potential applications in a variety of engineering applications, such as medical transportation, marine systems, and aerospace applications.

Surface Functional Modification for Boosting Power Density of Hydrovoltaic Devices

AbstractGenerating electricity based on the interaction between water and materials is a new green energy harvesting technology. However, the performance based on streaming potential generation is not sufficient to drive microelectronic devices with high power supply demands. In this work, an asymmetric sandwich structure is designed with adjustable performance of hydrovoltaic devices as a power system for micro‐electronic devices. The flexible hydrovoltaic device structure that only consumes renewable energy is low‐cost, non‐polluting, and highly sustainable, achieving a satisfied output power density exceeding 124.5 µW·cm−2 (2075 µW·cm−3). Both experimental results and theoretical calculations reveal that the working principle of the device depends on the evaporation potential rather than the streaming potential. In addition, the integration of multiple devices makes it easy to drive electronic devices for correct operation and energy storage. For the first time, this integrated hydroelectric photovoltaic device has demonstrated the ability to charge commercial button‐type lithium batteries with great success. The current work combines asymmetric structure and tunable performance, providing an alternative method for high‐efficiency hydrovoltaic devices with high power density.

Fundamental Atomistic Insights into Tunable Tribological Performance of NbC/Nb Films through Thickness and Depth Effects

Ceramic–metal nanolaminates (CMNLs) are promising scratch-resistant coatings, but knowledge gaps remain regarding the interactive effects of individual layer thickness and scratch depth. This study employed molecular dynamics simulations to investigate the tribological performance of NbC/Nb CMNLs, systematically varying ceramic and metal layer thicknesses (0.5–7.5 nm) and scratch depths (3, 5 nm). Models were loaded under displacement-controlled indentation followed by scratching. Mechanical outputs like material removal, friction coefficients, normal, and friction forces quantified scratch resistance. Material removal was even below that for NbC alone, demonstrating the multilayer benefit. Thinner layers showed complete penetration by the indenter, with material rolled in front rather than piled up. Thicker layers resisted penetration, enabling pile-up and lower friction coefficients due to higher normal forces. Excessive material removal decreased normal forces and raised friction coefficients. Peak coefficient occurred around 1.5–3 nm layer thicknesses where substantial top layer volumes were removed, minimizing ceramic under the indenter. Layer thickness corresponding to lowest material removal depended on scratch depth, with 3 nm and 7.5 nm layer thickness for 3 and 5 nm depths, respectively. Metallic layers reduced stiffness and drove material downward over piling up. Quantifying scratch resistance versus geometric parameters elucidates fundamental physics to facilitate superior CMNL coating fabrication.

Stiff, tunable and reprocessable polythiourea supramolecular materials by manipulating hydrogen-bonding and metal-coordinating interactions

Rational strategies manipulating hydrogen-bonding and metal-coordination interactions accelerate the development of supramolecular materials with unprecedented properties, such as adaptability, self-healing, stimuli-responsiveness, reprocessability and recyclability. Herein, supramolecular interactions of thioureas were fully utilized to design new materials with adjusted mechanical performances and robust reprocessability. A series of polythioureas were facilely synthesized by the co-polycondensation of CS2 and two diamines, which was an efficient and economical alternative to the isothiocyanate-based polymerization. Hydrogen-bonded polythiourea materials with tunable mechanical performances were achieved by adjusting the density and regularity of thiourea units in the polymer chains. Further incorporating tiny amount of metal salts (CuCl2, CuCl, CuBr and CuI) resulted in polythiourea materials with enhanced mechanical performances, following the trend determined by the hard-soft acid-base principle. As far as we know, this is the first report of metal-coordinated polythiourea supramolecular materials. The exploration of hard-soft acid-base principle will also provide new inspirations for designing metal-coordinated supramolecular materials.

Tailoring Mechanical Properties of a-C:H:Cr Coatings

The development of coatings with tunable performances is critical to meet a wide range of technological applications each one with different requirements. Using the plasma-enhanced chemical vapor deposition (PECVD) process, scientists can create hydrogenated amorphous carbon coatings doped with metal (a-C:H:Me) with a broad range of mechanical properties, varying from those resembling polymers to ones resembling diamond. These diverse properties, without clear relations between the different families, make the material selection and optimization difficult but also very rich. An innovative approach is proposed here based on projected performance indices related to fracture energy, strength, and stiffness in order to classify and optimize a-C:H:Me coatings. Four different a-C:H:Cr coatings deposited by PECVD with Ar/C2H2 discharge under different bias voltage and pressures are investigated. A path is found to produce coatings with a selective critical energy release rate between 5–125 J/m2 without compromising yield strength (1.6–2.7 GPa) and elastic limit (≈0.05). Finally, fine-tuned coatings are categorized to meet desired applications under different testing conditions.

Tunable negative permittivity performance of carbon/silicon dioxide ceramic metacomposites under external DC bias voltage

Metacomposites with negative permittivity have gained increasing momentum in recent years due to their unique electromagnetic characteristics and considerable potential application. However, how to adjust negative permittivity is still a big technical challenge to overcome. In this paper, silicon dioxide (SiO2) ceramic metacomposites consisting of carbon fibers (CFs) were fabricated by vacuum hot press sintering, and their negative permittivity might be modified by adjusting the filler content and applying external direct current (DC) bias voltages. As the CF content increased, the electrical conductivity of composites increased markedly, and the conduction mechanism transformed to a metal-like conductivity from hopping conductivity. The permittivity values of composites with high CF contents were negative at the test frequency range owing to the appearance of a low plasmonic state of unbound electrons in the percolating carbon networks. The conductivity of the composites increased when DC bias voltage was applied, because some of the accumulated local electrons at the CF-SiO2 interface could absorb energy and become free electrons. Larger bias voltages led to increased concentration of free electrons, so the absolute values of the negative permittivity raised according to the Drude model and the frequency band of negative permittivity became wider. This work presents an effective approach for adjusting the negative permittivity value and frequency band, which is advantageous in clarifying the realization and regulation mechanisms of negative permittivity.

Hybrid Modular Redundancy: Exploring Modular Redundancy Approaches in RISC-V Multi-Core Computing Clusters for Reliable Processing in Space

Space Cyber-Physical Systems (S-CPS) such as spacecraft and satellites strongly rely on the reliability of onboard computers to guarantee the success of their missions. Relying solely on radiation-hardened technologies is extremely expensive, and developing inflexible architectural and microarchitectural modifications to introduce modular redundancy within a system leads to significant area increase and performance degradation. To mitigate the overheads of traditional radiation hardening and modular redundancy approaches, we present a novel Hybrid Modular Redundancy (HMR) approach, a redundancy scheme that features a cluster of RISC-V processors with a flexible on-demand dual-core and triple-core lockstep grouping of computing cores with runtime split-lock capabilities. Further, we propose two recovery approaches, software-based and hardware-based, trading off performance and area overhead. Running at 430MHz, our fault-tolerant cluster achieves up to 1160MOPS on a matrix multiplication benchmark when configured in non-redundant mode and 617 and 414 MOPS in dual and triple mode, respectively. A software-based recovery in triple mode requires 363 clock cycles and occupies 0.612 mm 2 , representing a 1.3% area overhead over a non-redundant 12-core RISC-V cluster. As a high-performance alternative, a new hardware-based method provides rapid fault recovery in just 24 clock cycles and occupies 0.660 mm 2 , namely ∼ 9.4% area overhead over the baseline non-redundant RISC-V cluster. The cluster is also enhanced with split-lock capabilities to enter one of the available redundant modes with minimum performance loss, allowing execution of a mission-critical portion of code when in independent mode, or a performance section when in a reliability mode, with <400 clock cycles overhead for entry and exit. The proposed system is the first to integrate these functionalities on an open-source RISC-V-based compute device, enabling finely tunable reliability vs. performance trade-offs.

Tunable Thermoelectric Performance of the Nanocomposites Formed by Diketopyrrolopyrrole/Isoindigo-Based Donor-Acceptor Random Conjugated Copolymers and Carbon Nanotubes.

This paper presents the development of thermoelectric properties in nanocomposites comprising donor-acceptor random conjugated copolymers and single-walled carbon nanotubes (SWCNTs). The composition of the conjugated polymers, specifically the ratio of diketopyrrolopyrrole (DPP) to isoindigo (IID), is manipulated to design a series of random conjugated copolymers (DPP0, DPP5, DPP10, DPP30, DPP50, DPP90, DPP95, and DPP100). The objective is to improve the dispersion of SWCNTs into smaller bundles, leading to enhanced thermoelectric properties of the polymer/SWCNT nanocomposite. This dispersion strategy promotes an interconnected conducting network, which plays a critical role in optimizing the thermoelectric performance. Accordingly, the effects of morphologies on the thermoelectric properties of the nanocomposites are systematically investigated. The DPP95/SWCNT nanocomposite exhibits the strongest interaction, resulting in the highest power factor (PF) of 711.1 μW m-1 K-2, derived from the high electrical conductivity of 1690 S cm-1 and Seebeck coefficient of 64.8 μV K-1. The prototype flexible thermoelectric generators assembled with a DPP95/SWCNT film achieve a maximum power output of 20.4 μW m-2 at a temperature difference of 29.3 K. These findings highlight the potential of manipulating the composition of random conjugated copolymers and incorporating SWCNTs to efficiently harvest low-grade waste heat in wearable thermoelectric devices.

A confined self-assembly approach towards chiral photonic materials with circularly polarized structural colors for information storage and encryption

Chiroptical materials with tunable circular polarization performances have gained wide interest because of promising applications in optical devices and information communication. However, limited by their intrinsic chirality, such materials suffer from serious deficiencies in dynamical manipulation on circularly polarized light (CPL). Here, we demonstrate a kinetic trapping approach to capture multi-domain cholesteric mesophases for polarization-dependent structural coloration. The resultant photonic structures depicted by limited solvent evaporation display light control from selective left-handed circularly polarized light reflection to dual reflection, as a result of forming highly tilted and distorted domains with a phase-retardation effect. Notably, a positive linear correlation is established between the circular polarization behavior and structural orientation regulated by the solvent evaporation. The tunable circular polarization structural colors enable the application of the photonic materials for complex encryption in terms of polychromatic coding arrays. The confined-anisotropic-fabrication method of photonic structures paves a foundation toward advanced functional materials with promising applications in light science and technology.

Multi-layer carbon fiber paper @reduced graphene oxide/Co/C composite with adjustable electromagnetic interference shielding properties

Paper-based composite materials exhibit a marked tendency towards thinner and lighter profiles in the context of electromagnetic interference (EMI) shielding. Carbon fiber paper (CFP) has excellent electrical conductivity and Lightweight base characteristics. However, its single electrical loss characteristic and uncontrollable EMI shielding performance are limited in application. Therefore, we prepared CFP@ graphene oxide (GO)/ZIF-67 composites by chemical bonding and in-situ polymerization, and then prepared CFP@rGO/Co/C composites with integrated structure and function by heat treatment. Layer-by-layer assembly technology was employed to develop composite materials with tunable EMI shielding performance. The composite material has excellent high conductivity (2475.86 S/m) and excellent EMI shielding performance (average X-band EMI efficiency (SE)38.46 dB, absolute shielding effectiveness (SSE/t) = 14388.56 dB cm2 g−1). Through the layer-by-layer assembly technology, the EMI SE performance of the 7-layer assembled material reached 85.83 dB, and the EMI SSE/t reached 32110.51 dB cm2 g−1. Through simulation verification, the EMI shielding performance of the materials is compared, and ideas for EMI material design are provided. In addition, the material also has excellent Joule heating performance, fast electrothermal response and good temperature controllability. The material exhibits remarkable resilience against harsh environmental conditions, including strong acids, bases, organic reagents, ultrasonic waves, combustive processes, and extremely low temperatures. Despite these severe treatments, its performance remains above 90 % intact. This study proposes a magnetic-dielectric synergistic, performance-adjustable CFP-based shielding material, which has great application potential in the future wearable, defense, and aerospace fields.

Controlled caging, flat band and thermoelectric response in a quasi-one dimensional kagomé ribbon

A quasi-one dimensional kagomé ribbon geometry is studied in respect of its band spectrum, electronic transport as well as the thermopower within the tight-binding formalism. Analytic proposition of Bloch bands along with the dispersionless flat band states is seen to be consistent with the numerical evaluation of density of states, transmission and band dispersion. A uniform magnetic flux can act as an external agency to tune the spectral landscape and the transport at will. Flux sensitive band engineering leads to an interesting proposal of tunable thermoelectric performance of an identical model device. The tunable behavior can be explored by the calculation of Seebeck co-efficient. The external magnetic perturbation plays the key role in this demonstration and it is an easily adjustable parameter. We have critically investigated all the characteristic features using the Sommerfeld expansion within a tight-binding framework based on Green’s function formalism. The present analysis may provide useful directive for constructing efficient thermoelectric devices at the nanoscale level.

Chlorinated benzothiadiazole-based donor-acceptor polymers with tunable optoelectronic performances

Chlorinated benzo[c][1,2,5]thiadiazole, a new analogue of benzo[c][1,2,5]thiadiazole (BT), exhibits strong electron-withdrawing ability nature, while also offering advantages of lower cost and easier accessibility compared to its fluorinated analogues. This inspires us to investigate donor-acceptor-type (D-A) conjugated polymers based on chlorinated BT. Therefore, in this work, three D-A-D type monomers (0Cl, 1Cl, and 2Cl) were successfully synthesized with BT and chlorinated BT as acceptor units and EDOT as donor units by Stille coupling reaction. Subsequently, the corresponding D-A polymers (P0Cl, P1Cl, and P2Cl) were obtained via electrochemical polymerization. The results show that the two chlorinated monomers have higher initial oxidation potentials of 1.08 V (1Cl) and 1.09 V (2Cl), which are significantly higher than their non-chlorinated analogue (0.72 V). The two chlorinated polymers demonstrate good redox activity but with relatively poor stability (only 65.7 % and 20.7 % electroactivity are preserved after 100 cycles). Due to the decreased effective conjugation length caused by the deviations from planarity, both absorption spectra of the chlorinated polymers were blue-shifted when compared with P0Cl, leading to an increase in the optical band gap (1.64–1.68 eV). Introducing the Cl atom substitution on the BT unit resulted in the improvement of both the switching time and coloration efficiency. Specifically, the monochlorinated polymer (P1Cl) showed light gray in the neutral state and obvious electrochromic properties in the near-infrared region (optical contrast: 24 %, coloration efficiency: 195.6 cm2 C−1, and quick response time: 0.4 s). This study further expands the selection of chlorinated BT-based acceptor units and the application prospect of D-A electrochromic polymers.

Ferroelectric Layer‐Assisted Asymmetric Heterojunction Boosts Power Output in Silicon Hydrovoltaic Device

AbstractHydrovoltaic devices (HDs) that convert ubiquitous environmental energy via water evaporation serves as a prospective technology for renewable power schemes. However, it remains a grand challenge to perform controllable and stable modulation of hydrovoltaic power generation for multi‐scenario practical applications. Here, a ferroelectric‐field assisted silicon HD is proposed, which sandwiches an ultrathin polarizable polymer between nanostructured silicon and the top electrode, constituting an asymmetric heterojunction designed to clinch well‐regulated and robust electrical signal output. Tunable modulation of the internal electric field at the silicon/top electrode interface can be realized by facilely aligning the polarization orientation of the ferroelectric domains, thus dominating the silicon energy band bending and controlling the ultimate electrical signal. Upon effective forward polarization, the interfacial dipoles can build a stronger asymmetric electric field, which allows an efficient sweep of the charges out of the heterojunction. Accordingly, the resulting device clinches to yield a considerably modulated voltage of 1.04 V, nearly three‐fold modulation over the reverse polarization one. As prospective applications, multifunctional sensing platforms including the self‐sufficient environmental temperature detector, intelligent water‐level alarm system, and automatic‐manual dual‐mode irrigation control system are demonstrated. This work exhibits the unique characteristics of ferroelectric HDs with tunable electrical performance.