Tunable Conductivity Research Articles

Surface Embedded Metal Nanowire-Liquid Metal-Elastomer Hybrid Composites for Stretchable Electronics.

Both liquid metal (LM) and metallic filler-based conductive composites are promising stretchable conductors. LM alloys exhibit intrinsically high deformability but present challenges for patterning on polymeric substrates due to high surface tension. On the other hand, conductive composites comprising metallic fillers undergo considerable decrease in electrical conductivity under mechanical deformation. To address the challenges, we present silver nanowire (AgNW)-LM-elastomer hybrid composite films, where AgNWs and LM are embedded below the surface of an elastomeric matrix, using two fabrication approaches, sequential and mixed. We investigate and understand the process-structure-property relationship of the AgNW-LM-elastomer hybrid composites fabricated using two approaches. Different weight ratios of AgNWs and LM particles provide tunable electrical conductivity. The hybrid composites show more stable electromechanical performance than the composites with AgNWs alone. In particular, 1:2.4 (AgNW:LMP w/w) sequential hybrid composite shows electromechanical stability similar to that of the LM-elastomer composite, with a resistance increase of 2.04% at 90% strain. The sequential approach is found to form AgIn2 intermetallic compounds which along with Ga-In bonds, imparts large deformability to the sequential hybrid composite as well as mechanical robustness against scratching, cutting, peeling, and wiping. To demonstrate the application of the hybrid composite for stretchable electronics, a laser patterned stretchable heater on textile and a stretchable circuit including a light-emitting diode are fabricated.

Carbon-based synergistic catalysis with transition metal dichalcogenides for electrocatalytic oxygen evolution/reduction

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are considered as two of the most critical processes in various renewable energy systems, including multi-electron transfer reactions. However, the kinetics of ORR/OER are usually sluggish, significantly impeding their related applications. This review article summarizes the research advancements in electrocatalytic ORR/OER achieved using traditional noble metals, transition metal dichalcogenides (TMDCs), and carbon-based materials. Exploring diverse engineering strategies, such as defect engineering, strain engineering, and alloying, takes full advantage of the inherent energy band tunability of TMDCs and the advantages of carbon materials, including tunable specific surface area, high conductivity, and good stability. These strategies aim to regulate the intrinsic activity of materials and boost the apparent activity of the electrocatalytic ORR/OER. Finally, the challenges and prospects along this research line are proposed.

Redox-active cerium-based metal–organic layers coordinated on carbon nanotubes as materials for supercapacitors

In this work, the redox-active, two-dimensional (2D), and highly dispersible metal–organic layers (MOLs) constructed from hexa-cerium(IV) clusters, CeBTB (BTB = 1,3,5-benzenetribenzoate), were directly coordinated onto the surface of carboxylic acid-functionalized multi-walled carbon nanotubes (CNTs) by utilizing a post-synthetically grafting approach. Nanocomposites with various MOL-to-CNT ratios can be synthesized. Crystallinity, porosity, morphology, electrical conductivity, and electrochemical behaviors of CeBTB and all nanocomposites as well as the chemical interaction between CeBTB and CNT in the composite are investigated. Thin films of materials with the same mass loading are then fabricated for measuring their capacitive performances in neutral aqueous solutions of Na2SO4. With the electrical conductivity provided by carbon nanotubes and the redox activity of CeBTB between Ce(IV) and Ce(III), the optimal CeBTB-CNT nanocomposite can show a better capacitive performance compared to the pristine CeBTB, pristine CNT, and the physical mixture of both of them with the same MOL-to-CNT ratio. With such a simple post-synthetically grafting approach that can precisely control the ratio between the 2D MOLs and CNTs, the findings here open opportunities for designing numerous composites composed of MOLs and nanocarbons with tunable conductivity, redox activity, and functionality, which are potential candidates for a range of applications.

A graphene-based THz selective absorber with absorptivity 95 % and wide-range electrical tunability

A growing adoption of Terahertz (THz) frequency across various applications is witnessed in the recent years. This specific frequency range is said to yield a breakthrough in high-speed electronics and communications, besides its significant role in the medical field regarding scanning and treatment. As frequency absorbers are one of the common blocks in the mentioned applications, they were the focus of many research work. In this paper, we present a theoretical model for a selective THz frequency absorber that has more than 90 % absorptivity and can reach 95 % and near unity absorptivity at some frequencies. The structure is based on monolayers of nanoribbons of graphene, MoS2, and phosphorene. The utilization of the surface plasmon oscillations of these two-dimensional (2D) materials, in addition to the impedance matching, is employed to achieve maximum absorptivity. The structure has an electrically tunable selective frequency from 1.3 THz to 10 THz that nearly covers the whole THz range, and a bandwidth ranging from 0.9 THz to 1.3 THz. Electrical tunability is done through varying the applied voltage on the MoS2/graphene heterostructure (0.2 V ∼ 5 V) based on the tunable conductivity of graphene. In addition to the voltage tunability of the design, the absorption frequency is also swept by varying the nanoribbons widths (20 nm ∼ 160 nm). The proposed design surpasses previous ones by its simple structure and high absorption through the entire THz range, besides its low cost of fabrication. The structure is ultrathin (∼10 nm) that it can fit in ultrathin electronics. It has a relatively small bandwidth compared to previous work, that represents the basis for narrowband absorbers. The structure is simulated using the finite element method (FEM) and verified using the transmission line circuit theory which demonstrated the validity of the structure for higher frequency ranges. The possibility of future synthesis is also discussed.

High thermoelectric performance near the Mott–Ioffe–Regel limit in CuxS0.6Te0.4 meta-phases

The meta-phase, characterized by crystal-amorphicity duality in the extremely special case, has garnered considerable interests due to its glass-like thermal conductivity and tunable conduction mechanisms for carriers. However, the impact of crystal-amorphicity duality on the electrical and thermal transports remains elusive, and the carrier concentration in the meta-phase is rarely tuned in a wide range for optimized thermoelectric properties. Herein, through a combination of molecular dynamic simulations, chemical bonding analysis, and structural characterization, we reveal the glass-like distribution of Cu cations modulated by the mismatched S/Te anions in CuxS0.6Te0.4 meta-phase. Such unique atomic structure leads to hopping conduction of carriers and extremely low thermal conductivity. The carrier concentration is effectively optimized by tuning the Cu content in CuxS0.6Te0.4. Finally, we achieve a high zT of 1.4 at 900 K for Cu2.01S0.6Te0.4 sample, which is three times larger than those of Cu2S and Cu2Te matrixes. Remarkably, the high zT value is attained near the Mott–Ioffe–Regel Limit where the carrier mean free path is close to the average atomic distance. Our findings shed light on a new route to discovering high-performance thermoelectric materials.

Resurrected and Tunable Conductivity and Ferromagnetism in the Secondary Growth La0.7Ca0.3MnO3 on Transferred SrTiO3 Membranes.

To avoid the epitaxy dilemma in various thin films, such as complex oxide, silicon, organic, metal/alloy, etc., their stacking at an atomic level and secondary growth are highly desired to maximize the functionality of a promising electronic device. The ceramic nature of complex oxides and the demand for accurate and long-range-ordered stoichiometry face severe challenges. Here, the transport and magnetic properties of the La0.7Ca0.3MnO3 (LCMO) secondary growth on single-crystal freestanding SrTiO3 (STO) membranes are demonstrated. It has been experimentally found that on an only 10 nm thick STO membrane, the LCMO can offer a bulk-like Curie temperature (TC) of 253 K and negative magnetoresistance of -64%, with a weak dependence on the thickness. The resurrected conductivity and ferromagnetism in LCMO confirm the advantages of secondary growth, which benefits from the excellent flexibility and transferability. Additionally, this study explores the integration strategy of complex oxides with other functional materials.

Manual shaking exfoliation of large‐size two‐dimensional LiInP2S6 nanosheets with exponential change in ionic conductivity for water detection

AbstractLarge‐sized and atomically thin two‐dimensional metal thiophosphate materials have been widely exploited in detectors due to their rich physical/chemical properties of high surface area and massive adjustable sites. However, existing production methods are limited in terms of meeting the demanding challenges in achieving the scalable fabrication of high‐quality nanomaterials under mild conditions. Here, we develop a facile intercalation–exfoliation method that can fabricate large lateral size (>23 μm) and few‐layer LiInP2S6 nanosheets with high crystalline quality fast. Due to the advantage of hydrophilicity of lithium, swelled interlayer spacing can be obtained, which enables the rapid exfoliation by only slight manual shaking within tens of seconds. Concomitantly, the inorganic LiInP2S6 film manufactured by nanosheets has inter‐connected ionic channels, which can be adjusted on the basis of the water content, enabling tunable ionic conductivity. As a result, ionic conductor films using ions as charge carriers can achieve high water response with good repeatability and excellent long‐term stability in a wide moisture range. Moreover, the as‐prepared detector has excellent capability in real‐time noncontact human–machine interfacing. This study, not only is a powerful strategy for the fabrication of large‐sized and high‐quality nanosheets presented but also proof for the promising development of iontronic devices in new applications.

Practical applications of copper-based enzymes: synthesis of sulfonated polyaniline through laccase-catalyzed oxidation.

Known for its tunable conductivity and stability, Polyaniline (PANI) is a valuable polymer for electronics and sensing devices. Challenges in solubility have been addressed by creating sulfonated PANI (SPANI), enhancing its practical use. Synthesizing SPANI from sulfonated aniline is intricate, but laccase biocatalysis offers an eco-conscious solution, effective even against high redox potential obstacles. This research monitored the Trametes versicolor laccase-induced oxidation of 3-ABSa via UV-vis spectroscopy, with a notable peak at 565nm signifying SPANI synthesis, effective even at suboptimal pH. Mediators further boost this process. Moreover, NMR and spectroelectrochemistry confirm the green synthesis of SPANI by laccase, hinting that pH fine-tuning could improve yields, alongside the concurrent creation of azobenzene derivatives.

Graphene Used for Energy Conversion and Storage by Electrochemistry: A Brief Global Overview

Background: Graphene and its derivatives have been widely used in modern electrochemical- related technologies due to their versatile structure, tunable conductivity, and large specific surface area. However, there is a need to provide the latest global literature overview in this field. Methods: In this study, we reported a literature overview of current developments in the applications of graphene in energy conversion and storage by electrochemistry. In this overview, 1285 pieces of literature were retrieved and analyzed based on the web of science core database using bibliometric tools. Results: The major contributing countries are China and the United States. The most widespread fields are the development of novel nanomaterials and catalysts and approaches to improve the electrocatalytic performance of batteries and supercapacitors. The hotspots of current research include sodium-ion batteries, lithium-sulfur batteries, sulfur-doped electrodes, and the study of high-efficiency electrocatalysts for oxygen and evolution reactions. Conclusion: With the continuous development in this field, scientists are committed to continuously improving the performance of energy equipment. The applications of graphene-based materials for electrochemical energy conversion and storage are briefly summarized. The challenges and prospects for future research in this field are also discussed.

Multiple physical crosslinked highly adhesive and conductive hydrogels for human motion and electrophysiological signal monitoring.

Hydrogel-based flexible electronic devices serve as a next-generation bridge for human-machine interaction and find extensive applications in clinical therapy, military equipment, and wearable devices. However, the mechanical mismatch between hydrogels and human tissues, coupled with the failure of conformal interfaces, hinders the transmission of information between living organisms and flexible devices, which resulted in the instability and low fidelity of signals, especially in the acquisition of electromyographic (EMG) and electrocardiographic (ECG) signals. In this study, we designed an ion-conductive hydrogel (ICHgel) utilizing multiple physical interactions, successfully applied for human motion monitoring and the collection of epidermal physiological signals. By incorporating fumed silica (F-SiO2) nanoparticles and calcium chloride into an interpenetrating network (IPN) composed of polyvinyl alcohol (PVA) and polyacrylamide (AAm)/acrylic acid (AA) chains, the ICHgel exhibited exceptional tunable stretchability (>1450% strain) and conductivity (10.58 ± 0.85 S m-1). Additionally, the outstanding adhesion of the ICHgel proved to be a critical factor for effective communication between epidermal tissues and flexible devices. Demonstrating its capability to acquire stable electromechanical signals, the ICHgel was attached to different parts of the human body. More importantly, as a flexible electrode, the ICHgel outperformed commercial Ag/AgCl electrodes in the collection of ECG and EMG signals. In summary, the synthesized ICHgel with its outstanding conformal interface capabilities and mechanical adaptability paves the way for enhanced human-machine interaction, fostering the development of flexible electronic devices.

Single-crystalline oligomer-based conductors modeling the doped poly(3,4-ethylenedioxythiophene) family.

Conductive polymers with highly conjugated systems, such as the doped poly(3,4-ethylenedioxythiophene) (PEDOT) family, are commonly used in organic electronics. However, their structural inhomogeneity with various chain lengths makes it difficult to control their conductivities and structural details. On the other hand, low-molecular-weight materials have well-defined structures but relatively narrow conjugate areas with a limited range of Coulomb repulsion between carriers (Ueff), which hamper the flexible control of conductivities. To bridge this gap, we developed oligomer-based conductors, which are intermediate materials between polymers and low-molecular-weight materials. Using a library of single-crystal charge-transfer salts of oligo(3,4-ethylenedioxythiophene) (oligoEDOT) analogs that model the doped PEDOT family, we have investigated the structure-determining factors affecting their conductivities, such as counter anion variations, lengths of oligomer donor, and band fillings. Through the screening study, we developed oligoEDOT analogs with tunable room temperature conductivities by several orders of magnitude, including a metallic state above room temperature. In this study, we consistently evaluated the electronic structural insights by first-principles calculations and revealed that Ueff is the dominant factor that determines the relationship between the structures and conductivities. The unique features of oligoEDOT conductor systems with widely variable Ueff can differentiate these systems from strongly electron-correlated systems.

Tunable long-range spin transport in a van der Waals Fe3GeTe2/WSe2/Fe3GeTe2 spin valve.

The seamless integration of two-dimensional (2D) ferromagnetic materials with similar or dissimilar materials can widen the scope of low-power spintronics. In this regard, a vertical van der Waals (vdW) heterostructure of 2D ferromagnets with semiconducting transition metal dichalcogenides (TMDCs) forms magnetic junctions with exceptional stability and electrical control. Interestingly, 2D metallic Fe3GeTe2 (FGT) reveals above room temperature Curie temperatures and has large magneto anisotropy due to spin-orbit coupling. In addition, it also possesses topological states and a large Berry curvature. Herein, we designed the FGT/WSe2/FGT vdW heterostructure with a uniform and sharp interface so that FGT could maintain its inherent electronic properties. Also, the uniform thickness of the barrier provides a smooth flow of spins through the junctions as tunneling exponentially decays with an increasing barrier thickness. However, strong energy-dependent spin polarization is crucial for achieving optimum spin valve properties, such as large tunneling magnetoresistance (TMR) along with the manipulation of the magnitude and sign reversal. We have observed a shifting of high-energy localized minority spin states toward low-energy regions, which causes spin polarization fluctuation between -42.5% and 41% over a wide range of bias voltage. This leads to a negative TMR% of ∼-100% at 0.1 V Å-1 and also a large positive TMR% at 0.2 V Å-1 and -0.4 V Å-1. Besides, the system exhibits a highly tunable large anomalous Hall conductivity (AHC) of 626 S cm-1. Interestingly, such unprecedented electronic behaviour with large and switchable spin polarization, anomalous Hall conductivity and TMR can be incorporated into MTJ devices, which provide electrical control and long-range spin transport. Additionally, the system emerges as a standout candidate in low-power spintronic devices (e.g., MRAM and magnetic sensors) owing to its distinctive energy-dependent electronic structure with a wide range of external bias.

Carrier density and delocalization signatures in doped carbon nanotubes from quantitative magnetic resonance.

High-performance semiconductor materials and devices are needed to supply the growing energy and computing demand. Organic semiconductors (OSCs) are attractive options for opto-electronic devices, due to their low cost, extensive tunability, easy fabrication, and flexibility. Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been extensively studied due to their high carrier mobility, stability and opto-electronic tunability. Although molecular charge transfer doping affords widely tunable carrier density and conductivity in s-SWCNTs (and OSCs in general), a pervasive challenge for such systems is reliable measurement of charge carrier density and mobility. In this work we demonstrate a direct quantification of charge carrier density, and by extension carrier mobility, in chemically doped s-SWCNTs by a nuclear magnetic resonance approach. The experimental results are verified by a phase-space filling doping model, and we suggest this approach should be broadly applicable for OSCs. Our results show that hole mobility in doped s-SWCNT networks increases with increasing charge carrier density, a finding that is contrary to that expected for mobility limited by ionized impurity scattering. We discuss the implications of this important finding for additional tunability and applicability of s-SWCNT and OSC devices.

A wheel-shaped Zr-substituted phosphotungstate [{Zr(C2O4)2}3 (PO4)(P6W39O150)]39- with tunable proton conduction properties.

A wheel-shaped Zr-substituted phosphotungstate, [N(CH3)4]2K16Na10.5H10.5[{Zr(C2O4)2}3(PO4)(P6W39O150)]·45H2O (1), was synthesised from a hexavacant Dawson-type precursor [H2P2W12O48]12-via a conventional solution method. Compound 1 features a wheel-shaped polyanion comprising an annular [P6W39O150]36- cluster supported by a turbine-shaped [{Zr(C2O4)2}3(PO4)]3- fragment, with three oxalate groups covalently anchored to W atoms. Compound 1 was systematically characterized by IR, UV, PXRD, TGA and 31P NMR spectra. The 31P NMR spectra over time were monitored to verify the stability of 1 in aqueous solution. This compound possesses remarkable proton conductive behavior with a high conductivity of 1.18 × 10-2 S cm-1 at 368 K.

Aluminum-based ceramic/metal composites with tailored thermal expansion fabricated by spark plasma sintering.

We have devised a moderate temperature spark plasma sintering route for preparing aluminum matrix composites which possess tailored coefficients of thermal expansion (CTEs) in combination with tunable electrical and thermal conductivities. Due to its isotropic negative thermal expansion over a wide temperature range, cubic-phase ZrW2-xMoxO8 (x = 0.0, 1.0) is an ideal secondary phase for metal matrix composites with suitable CTEs. In this study, high-density ZrW2O8/Al and ZrWMoO8/Al composites containing 30-70 vol% Al were fabricated using spark plasma sintering. X-ray diffraction analysis indicated that the composites were composed of a thermally-stable cubic phase at temperatures as high as 873 K for ZrW2O8 and 773 K for ZrWMoO8, without any orthorhombic high-pressure phase derived from the large thermal mismatch between the ceramic and metal during sintering. The thermal expansion curves of the ZrW2-xMoxO8/Al composites were consistent with the predictions made using the Rule-of-Mixtures. The CTEs could be controlled from negative to positive and even close to zero by simply varying the volume fraction of aluminum. Similarly, the thermal and electrical conductivity of the ZrW2-xMoxO8/Al composites increases with increasing Al content, which is thought to be mainly related to the contribution of the free electron conduction path of Al in the composites.

Rare Guest-Induced Electrical Conductivity of Zn-Porphyrin Metallacage Inclusion Complexes Featuring π-Donor/Acceptor/Donor Stacks.

Charge-transfer (CT) interactions between co-facially aligned π-donor/acceptor (π-D/A) arrays engender unique optical and electronic properties that could benefit (supra)molecular electronics and energy technologies. Herein, we demonstrate that a tetragonal prismatic metal-organic cage (MOC18+) having two parallel π-donor tetrakis(4-carboxyphenyl)-Zn-porphyrin (ZnTCPP) faces selectively intercalate planar π-acceptor guests, such as hexaazatriphenylene hexacarbonitrile (HATHCN), hexacyanotriphenylene (HCTP), and napthanelediimide (NDI) derivatives, forming 1:1 πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads. The π-acidity of intercalated π-acceptors (HATHCN ≫ HCTP ≈ NDIs) dictated the nature and strength of their interactions with the ZnTCPP faces, which in turn influenced the binding affinities (Ka) and optical and electronic properties of corresponding πA@MOC18+ inclusion complexes. Owing to its strongest CT interaction with ZnTCPP faces, the most π-acidic HATHCN guest enjoyed the largest Ka (5 × 106 M-1), competitively displaced weaker π-acceptors from the MOC18+ cavity, and generated the highest electrical conductivity (2.1 × 10-6 S/m) among the πA@MOC18+ inclusion complexes. This work demonstrates a unique through-space charge transport capability of πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads, which generated tunable electrical conductivity, which is a rare but much coveted electronic property of such supramolecular assemblies that could further expand their utility in future technologies.

Structural, electronic, optical, and thermoelectric properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds: First-principle study

BackgroundAmong photovoltaic materials, halide-based perovskites, such as CsPbI3, have been the subject of many research papers due to their suitable and direct bandgap, very good optical properties, and remarkable thermoelectric properties. Enhancing optoelectronic and thermoelectric properties can be achieved by combining halide atoms intelligently. The purpose of this article is to examine the physical properties of Br substitution at different concentrations in CsPbI3 perovskite. MethodsThe structural, electrical, and optical properties of CsPbI3-yBry (y = 0.5, 1.5, 2.5) compounds have been investigated by using the QUANTUM-ESPRESSO/PWSCF computational package which is based on the density functional theory and the pseudo-potential technique. The thermoelectric properties of CsPbI3-yBry perovskites were calculated by solving the Boltzmann transport equations within the constant relaxation time approximation as employed in the BoltzTraP package. Significant findingsThe structural investigation reveals that when the I atom is substituted by Br, the lattice constant decreases, increasing the bulk modulus and stiffness of compounds. The calculated negative formation energy confirmed the thermodynamic stability of CsPbI3-yBry compounds, and the stability improved with an increase in Br concentration. The electronic investigation indicates the semiconductor nature of compounds with a direct band gap, with a slight increase in electronic band gap as Br concentration increases. The noticeable optical absorption coefficient in the visible range of the electromagnetic spectrum, along with high and tunable optical conductivity, confirms the capability of the compounds for use in optoelectronic devices. The positive value of the Seebeck coefficient revealed the p-type semiconducting nature of CsPbI3-yBry perovskites. Lattice thermal conductivity calculation reveals that this quantity is decreased because of the increase in phonon-phonon interaction due to rising temperature. Thermoelectric investigation indicates that a precise mixture of halide I and Br atoms significantly enhances the electrical and thermal conductivity of perovskites. Also, the substitution of halide I atoms by Br can improve the figure of merit (ZT). The maximum value of ZT at room temperature is equal to 0.99, justifying the brilliant thermoelectric properties of the studied compounds.

Intelligent fluid flow management for enhanced geothermal system in fractured horizontal wells

The presence of thermal short-circuiting impedes the further development of enhanced geothermal systems (EGSs) with horizontal wells. The objective of this research is to explore the effectiveness of a new technique, i.e., tunable fracture conductivity, in the control of thermal short-circuiting in EGSs with horizontal wells. The core idea of tunable fracture conductivity is to adjust the hydraulic conductivity of fractures according to the surrounding temperature at any point and seal any dominant flow path with a low temperature that may short-circuit the fluid flow. By utilizing this technique, thermal shortcuts between the wells can be effectively suppressed, and uniform heat extraction from each flow path can be expected. The performance of tunable fracture conductivity is investigated based on numerical simulations. According to the simulation results, tunable fracture conductivity can significantly improve heat sweeping between the injection and production well. After 50 years of operation, this technique increases production temperature by approximately 50 K, from 358.71 K to 410.32 K, which significantly elongates the effective period of operation in an EGS. Furthermore, using temperature-adaptive fracture conductivity improves heat extraction efficiency by 113.2 % which can be translated as an extra reduction in greenhouse gas (GHG) emission for 1.15 – 3.21 Mt with only one pair of wells. Besides, smaller fracture half-length and fracture spacing can also help the tunable fracture conductivity to better control the thermal short-circuiting and maintain the high-efficient EGS operation. This study provides a new method to achieve cleaner, more profitable, and highly efficient geothermal systems in the future.

Tunable Crystallinity and Electron Conduction in Wavy 2D Conjugated Metal-Organic Frameworks via Halogen Substitution.

Currently, most reported 2D conjugated metal-organic frameworks (2D c-MOFs) are based on planar polycyclic aromatic hydrocarbons (PAHs) with symmetrical functional groups, limiting the possibility of introducing additional substituents to fine-tune the crystallinity and electrical properties. Herein, a novel class of wavy 2D c-MOFs with highly substituted, core-twisted hexahydroxy-hexa-cata-benzocoronenes (HH-cHBCs) as ligands is reported. By tailoring the substitution of the c-HBC ligands with electron-withdrawing groups (EWGs), such as fluorine, chlorine, and bromine, it is demonstrated that the crystallinity and electrical conductivity at the molecular level can be tuned. The theoretical calculations demonstrate that F-substitution leads to a more reversible coordination bonding between HH-cHBCs and copper metal center, due to smaller atomic size and stronger electron-withdrawing effect. As a result, the achieved F-substituted 2D c-MOF exhibits superior crystallinity, comprising ribbon-like single crystals up to tens of micrometers in length. Moreover, the F-substituted 2D c-MOF displays higher electrical conductivity (two orders of magnitude) and higher charge carrier mobility (almost three times) than the Cl-substituted one. This work provides a new molecular design strategy for the development of wavy 2D c-MOFs and opens a new route for tailoring the coordination reversibility by ligand substitution toward increased crystallinity and superior electric conductivity.

Multiscale Heterogeneous Polymer Composites for High Stiffness 4D Printed Electrically Controllable Multifunctional Structures.

4D printing is an emerging field where 3D printing techniques are used to pattern stimuli-responsive materials to create morphing structures, with time serving as the fourth dimension. However, current materials utilized for 4D printing are typically soft, exhibiting an elastic modulus (E) range of 10-4 to 10MPa during shape change. This restricts the scalability, actuation stress, and load-bearing capabilities of the resulting structures. To overcome these limitations, multiscale heterogeneous polymer composites are introduced as a novel category of stiff, thermally responsive 4D printed materials. These inks exhibit an E that is four orders of magnitude greater than that of existing 4D printed materials and offer tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, a flat geometry that morphs into a 3D self-standing lifting robot is designed and printed, setting new records for weight-normalized load lifted and actuation stress when compared to other 3D printed actuators. Furthermore, this ink palette is employed to create and print planar lattice structures that transform into various self-supporting complex 3D shapes. Finally these inks are integrated into a 4D printed electrically controlled multigait crawling robotic lattice structure that can carry 144 times its own weight.