Tunable Electrical Properties Research Articles

Resetting the Drift of Oxygen Vacancies in Ultrathin HZO Ferroelectric Memories by Electrical Pulse Engineering

Ferroelectric HfO2‐based films incorporated in nonvolatile memory devices offer a low‐energy, high‐speed alternative to conventional memory systems. Oxygen vacancies have been rigorously cited in literature to be pivotal in stabilizing the polar noncentrosymmetric phase responsible for ferroelectricity in HfO2‐based films. Thus, the ability to regulate and control oxygen vacancy migration in operando in such materials would potentially offer step changing new functionalities, tunable electrical properties, and enhanced device lifespan. Herein, a novel in‐ operando approach to control both wake‐up and fatigue device dynamics is reported. Via clever design of short ad hoc square electrical pulses, both wake‐up can be sped up and both fatigue and leakage inside the film can be reduced, key factors for enhancing the performance of memory devices. Using plasmon‐enhanced photoluminescence and dark‐field spectroscopy (sensitive to <1% vacancy variation), evidence that the electrical pulses give rise to oxygen vacancy redistribution is provided and it is shown that pulse engineering effectively delays wake‐up and reduces fatigue characteristics of the HfO2‐based films. Comprehensive analysis also includes impedance spectroscopy measurements, which exclude any influence of polarization reversal or domain wall movement in interpretation of results.

Highly Porous Particles of Cellulose Derivatives for Advanced Applications.

А chemical modification of cellulose diacetate by phthalate and nitrate was performed to increase solubility in organic solvents and change the electrical properties. The role ofsubstituentson the conductivity, permittivity, and polarizability of cellulose films is revealed. It has been shown that highly porous micro particles can be obtained from cellulose derivatives by a simple and technological freeze-drying method. The resulting micro sized aerogels have a predominantly spherical morphology and amorphous structure. Suspensions of porous particles of nitro- and phthalylated cellulose derivatives in silicone oil have an increased dielectric permittivity compared to cellulose diacetate particles. Produced particles are novel promising material with tunable electrical properties for advanced applications in composites, including for electrorheological fluids.

Crystallographic Pathways to Tailoring Metal-Insulator Transition through Oxygen Transport in VO2.

The metal-insulator (MI) transition of vanadium dioxide (VO2) is effectively modulated by oxygen vacancies, which decrease the transition temperature and insulating resistance. Oxygen vacancies in thin films can be driven by oxygen transport using electrochemical potential. This study delves into the role of crystallographic channels in VO2 in facilitating oxygen transport and the subsequent tuning of electrical properties. A model system is designed with two types of VO2 thin films: (100)- and (001)-oriented, where channels align parallel and perpendicular to the surface, respectively. Growing an oxygen-deficient TiO2 layer on these VO2 films prompted oxygen transport from VO2 to TiO2. Notably, in (001)-VO2 film, where oxygen ions move along the open channels, the oxygen migration deepens the depleted region beyond that in (100)-VO2, leading to more pronounced changes in metal-insulator transition behaviors. The findings emphasize the importance of understanding the intrinsic crystal structure, such as channel pathways, in controlling ionic defects and customizing electrical properties for applications.

Crystallographic Pathways to Tailoring Metal-Insulator Transition through Oxygen Transport in VO2.

The metal-insulator (MI) transition of vanadium dioxide (VO2) is effectively modulated by oxygen vacancies, which decrease the transition temperature and insulating resistance. Oxygen vacancies in thin films can be driven by oxygen transport using electrochemical potential. This study delves into the role of crystallographic channels in VO2 in facilitating oxygen transport and the subsequent tuning of electrical properties. A model system is designed with two types of VO2 thin films: (100)- and (001)-oriented, where channels align parallel and perpendicular to the surface, respectively. Growing an oxygen-deficient TiO2 layer on these VO2 films prompted oxygen transport from VO2 to TiO2. Notably, in (001)-VO2 film, where oxygen ions move along the open channels, the oxygen migration deepens the depleted region beyond that in (100)-VO2, leading to more pronounced changes in metal-insulator transition behaviors. The findings emphasize the importance of understanding the intrinsic crystal structure, such as channel pathways, in controlling ionic defects and customizing electrical properties for applications.

Electrical conductivity of polyvinyl alcohol/carboxymethyl cellulose doped by zinc oxide and hematite nanoparticles for optoelectronics devices

This research explores polymer nanodielectrics, a category of materials where nanoceramic fillers are incorporated into polymers. These hybrid materials are gaining significant interest due to their tunable optical and electrical properties, making them potentially well-suited for applications in flexible optoelectronic and organic electronic devices. Polyvinyl alcohol (PVA), Carboxymethyl cellulose (CMC), zinc oxide (ZnO), and hematite (Fe2O3) nanoparticles (NPs) have been used to create nanocomposite materials in order to improve their optical and electrical characterization. Physical methods have been used to investigate the effects of varying hematite nanoparticle contents on the optical and electrical characterization of the prepared films. XRD analysis indicated a reduction in the crystalline character of the PVA/CMC blend following the incorporation of ZnO/Fe2O3 nanoparticles (NPs). FTIR data approved the interaction between the PVA/CMC composite and the ZnO/Fe2O3, leading to a decrease in intermolecular interactions within the polymeric matrix and coordination with the ZnO/Fe2O3. Electrical analysis obtained an enhancement in σac values with the rise of ZnO/Fe2O3 NPs content up to 30 min of laser ablation times in the polymeric nanocomposite due to the high content of ZnO/Fe2O3 NPs that were added to the PVA/CMC hybrid polymer matrix. The findings from this study suggest the promise of these materials for applications in high-performance batteries, supercapacitors, or other next-generation energy storage and conversion devices.

Porous PVDF composites with ultralow percolation threshold for wide-range dynamic and static pressure sensing

Porous conductive polymer composites are very attractive for static pressure sensing due to high sensitivity and good elasticity contributed by the porous structure, while they are hard to detect dynamic pressure. Herein, we report a porous conductive poly (vinylidene fluoride) (PVDF) composite capable of detecting static and dynamic pressure over a pressure range of 0–1 MPa, which was fabricated by melt mixing PVDF, polyethylene oxide (PEO) and carbon nanofillers, followed by etching PEO with water. Such porous PVDF composites have a very low percolation threshold (0.035 wt%) of carbon nanostructures (i.e., branched carbon nanotubes) thanks to the selective distribution of conductive fillers in the pore wall after etching. At the same time, the pore size and porosity of the porous PVDF composites can be tuned by the molecular weight (Mw) and blending ratios of two polymers, leading to the kinetically-tailorable blend morphology for tunable mechanical and electrical properties. The as-fabricated porous PVDF composites with a good combination of mechanical properties and electrical conductivities, which can be used as pressure sensors toward wide-range (0–1 MPa) dynamic and static pressure sensing. Such pressure sensors demonstrate potential applications in detecting the degree of finger bending, distinguishing the walking and running, and monitoring a series of technical movements in playing soccer, i.e., static and dynamic exercises.

Macromolecule-Nanoparticle-Based Hybrid Materials for Biosensor Applications.

Biosensors function as sophisticated devices, converting biochemical reactions into electrical signals. Contemporary emphasis on developing biosensor devices with refined sensitivity and selectivity is critical due to their extensive functional capabilities. However, a significant challenge lies in the binding affinity of biosensors to biomolecules, requiring adept conversion and amplification of interactions into various signal modalities like electrical, optical, gravimetric, and electrochemical outputs. Overcoming challenges associated with sensitivity, detection limits, response time, reproducibility, and stability is essential for efficient biosensor creation. The central aspect of the fabrication of any biosensor is focused towards forming an effective interface between the analyte electrode which significantly influences the overall biosensor quality. Polymers and macromolecular systems are favored for their distinct properties and versatile applications. Enhancing the properties and conductivity of these systems can be achieved through incorporating nanoparticles or carbonaceous moieties. Hybrid composite materials, possessing a unique combination of attributes like advanced sensitivity, selectivity, thermal stability, mechanical flexibility, biocompatibility, and tunable electrical properties, emerge as promising candidates for biosensor applications. In addition, this approach enhances the electrochemical response, signal amplification, and stability of fabricated biosensors, contributing to their effectiveness. This review predominantly explores recent advancements in utilizing macrocyclic and macromolecular conjugated systems, such as phthalocyanines, porphyrins, polymers, etc. and their hybrids, with a specific focus on signal amplification in biosensors. It comprehensively covers synthetic strategies, properties, working mechanisms, and the potential of these systems for detecting biomolecules like glucose, hydrogen peroxide, uric acid, ascorbic acid, dopamine, cholesterol, amino acids, and cancer cells. Furthermore, this review delves into the progress made, elucidating the mechanisms responsible for signal amplification. The Conclusion addresses the challenges and future directions of macromolecule-based hybrids in biosensor applications, providing a concise overview of this evolving field. The narrative emphasizes the importance of biosensor technology advancement, illustrating the role of smart design and material enhancement in improving performance across various domains.

Proton‐conducting hydrogel electrolytes with tight contact to binder‐free MXene electrodes for high‐performance thermally chargeable supercapacitor

AbstractThermally chargeable supercapacitors (TCSCs) have offered exceptional energy‐converting efficiency for absorbing human epidermal heat and generating and storing electrical energy, which then realize continuous power supply to electronic devices, such as sensors and wearable electronic products, in a wide range of practical significance. Here, we proposed a flexible TCSC by attaching binder‐free Ti3C2Tx MXene@PPy electrodes on both ends of the H3PO4@P(AM‐co‐AA‐co‐AYP K+) hydrogel electrolyte, which exhibits a large thermal power of 35.2 mV K−1 at 50% relative humidity and maximum figure of merit of 2.1. The high performances of the fabricated devices can be attributed to the tunable electrical, thermodynamic, thermoelectric, and mechanical properties of the hydrogel electrolyte by adjusting the acid content and the proportion of zwitterionic compound AYP K+ in the hydrogel, and the high photothermal conversion efficiency and electrochemical performance of the electrodes. Moreover, the stable and outstanding thermofvoltage output (∼200 mV) under different time scenarios of the TCSC makes it possible to drive a strain sensor, accomplishing the objectives of a human activity monitor.

Aqueous Topological Synthesis of Au@semiconductor Core-Shell Nanocrystals with Morphology and Composition Engineering.

Core-shell nanocrystals (C-S NCs) are an essential class of materials whose structural engineering has attracted wide attention due to their tunable optical and electrical properties, especially noble metal@semiconductor (NMS) C-S NCs with flexible plasmon-exciton coupling. Due to their diverse critical applications, especially aqueous biological applications, herein we propose an aqueous topological strategy enabled by cation exchange reactions (CER) to synthesize various plasmonic Au@semiconductor C-S NCs, in which environmentally friendly triphenylphosphine (TPP) is used as an initiator instead of inflammable tributyl phosphine (TBP). The introduction of the milder, solid TPP facilitated a new aqueous CER strategy for synthesizing Au@semiconductor NCs with tailored chalcogenide compositions and morphologies. For example, the as-synthesized Au@ZnS C-S NRs had better absorption and biocompatibility and exhibited excellent photodynamic therapy efficacy.

All-Inorganic Halide Perovskites Boost High-Ranged Figure-of-Merit in Bi0.4Sb1.6Te3 for Thermoelectric Cooling and Low-Grade Heat Recovery.

The all-inorganic halide perovskite CsPbX3 (X = Cl, Br, or I) offers various advantages, such as tunable electronic structure and high carrier mobility. However, its potential application in thermoelectric materials remains underexplored. In this study, we propose a simple yet effective method to synthesize a CsPbX3/Bi0.4Sb1.6Te3 (BST) nanocomposite by sintering a uniformly mixed raw powder. The intrinsic excitation of the BST system is suppressed by exploiting the rich phase structure and tunable electrical transport properties of CsPbX3, and the thermoelectric properties were synergistically optimized. Notably, for CsPbI3, its phase-transition-induced dislocation arrays together with low group velocities drastically reduce thermal conductivity. As a result, the composite achieves an ultrahigh average figure-of-merit (ZT) of 1.4 from 298 to 523 K. The two-pair TE module demonstrates a superior conversion efficiency of 7.3%. This study expands the potential applications of inorganic halide perovskites, into thermoelectrics.

Synthesis, optical characterization and electrical behavior of chitosan/MgO/Cr2O3 nanocomposite for electrical applications

Magnesium oxide nanoparticles (MgO NPs) are straightforward, cheap, biocompatible, and biodegradable, making them one of the most popular inexpensive and non-toxic nanoparticles. In addition, Nanosized chromic oxide (Cr2O3) is a significant transition metal oxide due to its numerous exceptional attributes, it finds application in several domains. It has good electrical conductivity, excellent thermal and chemical stability. It is utilized in several industries for its ability to resist oxidation at high temperatures, as well as its application in refractory materials and catalysts. In this study, we utilized a laser ablation approach to synthesize a ternary nanocomposite composed of MgO and Cr2O3 nanoparticles as it is considered a clean method for the preparation of nanoparticles. Subsequently, these nanoparticles were integrated into Chitosan (CS) solution to create polymer nanocomposite via casting route. XRD confirmed the formation of Cr2O3 nanocrystals with size of 61 nm dispersed in chitosan/MgO matrix. FTIR verified the interactions between chitosan, MgO, and Cr2O3 nanoparticles. The broadening and shifting of the OH and NH bands with increasing Cr2O3 content confirms the interaction and complexation between Cr2O3 and Chitosan/MgO. UV–Vis analysis revealed that incorporating 7 wt% Cr2O3 reduced optical band gap from 5.59 eV for chitosan to 3.91 eV. The band gap values decreased with increasing Cr2O3 content due to polaronic defects. TGA showed improved thermal stability, with the 7 wt% Cr2O3 nanocomposite exhibiting a residual mass of 47 % at 700 °C compared to 28 % for chitosan. Dielectric studies demonstrated high dielectric constant and conductivity (10−5 S/cm at 10 Hz) values for the 7 wt% Cr2O3 nanocomposite, attributed to interfacial polarization effects and nanocapacitor formation by the conductive nanofillers. The ternary chitosan/MgO/Cr2O3 nanocomposites with tunable optical, thermal and electrical properties show promising potential for electronic applications.

Optical and electronic properties of BCN films deposited by magnetron sputtering.

Boron carbonitride (BCN) films containing hybridized bonds involving B, C, and N over wide compositional ranges enable an abundant variety of new materials, properties, and applications; however, their electronic performance is still limited by the presence of structural and electronic defects, yielding sluggish mobility and electrical conductivity. This work reports on mechanically stable BCN films and their corresponding optical and electronic properties. The ternary BCN films consisting of hybridized B-C-N bonds have been achieved by varying N2 flow by the radio frequency magnetron sputtering method. The BCN films show a bandgap value ranging from 3.32 to 3.82eV. Hall effect measurements reveal an n-type conductivity with an improved hall mobility of 226cm2/V s at room temperature for the optimal film. The n-BCN/p-Si heterojunctions exhibit a nonlinear rectifying characteristic, where the tunneling behavior dominates the injection regimes due to the density of defects, i.e., structural disorder and impurities. Our work demonstrates the tunable electrical properties of BCN/Si p-n diodes and, thus, is beneficial for the potential application in the fields of optics, optoelectronics, and electrics.

Tongue-inspired gelatin/poly(acrylate-co-acrylamide)-Fe3+ organic hydrogel with tunable mechanical, electrical, and sensory properties

Conductive hydrogels have emerged as one of the most promising candidates for the next generation of wearable soft electronics. However, they face limitations during practical implementation owing to their unbalanced overall properties. In this study, we present a dynamic cross-linked gelatin/poly(acrylic acid-co-acrylamide) (GxPyFez) hydrogel with tunable mechanical strength, self-healing, freezing resistance, electrical conductivity, and high sensitivity, which was prepared by incorporating Fe3+ ions. The hydrogel was prepared based on the tongue, in which gelatin/poly(acrylic acid-co-acrylamide) and Fe3+ ions mimic the connective tissue and receptor cells of the human tongue. The synergistic effect of reversible crosslinking, along with the modulation of rigid and flexible components enabled tunable flexible structures that exhibit excellent mechanical properties such as elongation at break (569 %) and toughness (8.82 MJ m−3). Notably, the G2P3Fe0.1 hydrogel exhibited remarkable self-healing ability, even at room temperature, while maintaining a good freezing resistance. Furthermore, the G2P3Fe0.1 demonstrated fast response characteristics along with a high sensitivity (GF = 2.75). Consequently, it could be assembled into sensors capable of effectively detecting various movements of the human body; it serves as an electronic skin that responds to diverse external stimuli and monitors underwater motion signals. This study provides new insights into the design of conductive hydrogels with tunable overall properties that can be modified to suit specific application scenarios.

Hydrogel-Gated FETs in Neuromorphic Computing to Mimic Biological Signal: A Review.

Hydrogel-gated synaptic transistors offer unique advantages, including biocompatibility, tunable electrical properties, being biodegradable, and having an ability to mimic biological synaptic plasticity. For processing massive data with ultralow power consumption due to high parallelism and human brain-like processing abilities, synaptic transistors have been widely considered for replacing von Neumann architecture-based traditional computers due to the parting of memory and control units. The crucial components mimic the complex biological signal, synaptic, and sensing systems. Hydrogel, as a gate dielectric, is the key factor for ionotropic devices owing to the excellent stability, ultra-high linearity, and extremely low operating voltage of the biodegradable and biocompatible polymers. Moreover, hydrogel exhibits ionotronic functions through a hybrid circuit of mobile ions and mobile electrons that can easily interface between machines and humans. To determine the high-efficiency neuromorphic chips, the development of synaptic devices based on organic field effect transistors (OFETs) with ultra-low power dissipation and very large-scale integration, including bio-friendly devices, is needed. This review highlights the latest advancements in neuromorphic computing by exploring synaptic transistor developments. Here, we focus on hydrogel-based ionic-gated three-terminal (3T) synaptic devices, their essential components, and their working principle, and summarize the essential neurodegenerative applications published recently. In addition, because hydrogel-gated FETs are the crucial members of neuromorphic devices in terms of cutting-edge synaptic progress and performances, the review will also summarize the biodegradable and biocompatible polymers with which such devices can be implemented. It is expected that neuromorphic devices might provide potential solutions for the future generation of interactive sensation, memory, and computation to facilitate the development of multimodal, large-scale, ultralow-power intelligent systems.

Topologically Tunable Conjugated Metal–Organic Frameworks for Modulating Conductivity and Chemiresistive Properties for NH3 Sensing

AbstractElectrically conductive metal–organic frameworks (cMOFs) have garnered significant attention in materials science due to their potential applications in modern electrical devices. However, achieving effective modulation of their conductivity has proven to be a major challenge. In this study, we have successfully prepared cMOFs with high conductivity by incorporating electron‐donating fused thiophen rings in the frameworks and extending their π‐conjugated systems through ring‐closing reactions. The conductivity of cMOFs can be precisely modulated ranging from 10−3 to 102 S m−1 by regulating their dimensions and topologies. Furthermore, leveraging the inherent tunable electrical properties based on topology, we successfully demonstrated the potential of these materials as chemiresistive gas sensors with an outstanding response toward 100 ppm NH3 at room temperature. This work not only provides valuable insights into the design of functional cMOFs with different topologies but also enriches the cMOF family with exceptional conductivity properties.

Topologically Tunable Conjugated Metal-Organic Frameworks for Modulating Conductivity and Chemiresistive Properties for NH3 Sensing.

Electrically conductive metal-organic frameworks (cMOFs) have garnered significant attention in materials science due to their potential applications in modern electrical devices. However, achieving effective modulation of their conductivity has proven to be a major challenge. In this study, we have successfully prepared cMOFs with high conductivity by incorporating electron-donating fused thiophen rings in the frameworks and extending their π-conjugated systems through ring-closing reactions. The conductivity of cMOFs can be precisely modulated ranging from 10-3 to 102 S m-1 by regulating their dimensions and topologies. Furthermore, leveraging the inherent tunable electrical properties based on topology, we successfully demonstrated the potential of these materials as chemiresistive gas sensors with an outstanding response toward 100 ppm NH3 at room temperature. This work not only provides valuable insights into the design of functional cMOFs with different topologies but also enriches the cMOF family with exceptional conductivity properties.

Characterization of Microstructured Multiwalled Carbon Nanotube/Polydimethylsiloxane Composites for Piezoresistive Sensing Applications

Technological advancements in the field of flexible and printed electronics are creating a need for large‐area sensors that can be embedded over different types of surfaces. Such sensors can be used to monitor physical signals over flexible, curved, or soft devices. Hence, it is herein proposed, a formulation to produce piezoresistive multiwalled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) composites with tunable electric properties for pressure sensing purposes. The composite is obtained through few manufacturing steps, avoiding the use of hazardous solvents. Different weight percentages of MWCNT dispersed in PDMS are evaluated and the results evidence that using 3.0 wt% of infill is sufficient to obtain highly sensitive sensors. To enhance the dispersion of the MWCNT and add microstructure to the composite, a system composed of a surfactant and foaming agent is used. Finally, pressure sensing units and arrays are printed and tested. The sensors present fast response, low hysteresis, repeatability, and a sensing range of 0–160 kPa. The composite is more sensitive to lower pressure and a maximum sensitivity of 8.0% kPa−1 is achieved for porous composites at pressure <10 kPa. Thanks to these characteristics, the sensors are successfully used in the development of a pressure sensing array and heartbeat sensor for proof of concept.

Tunable electrical and magnetic properties of 2D SiC via adsorption and doping of atmospheric elements (H, C, N, and O)

The direct bandgap nonmagnetic semiconductor two-dimensional SiC has attracted extensive research attention recently due to its unique physical and chemical properties. The synthesis of materials is inevitably affected by atmospheric elements. In this paper, the effects of adsorption and doping of atmospheric elements (H, C, N, and O) on the structure, electronic, and magnetic properties of SiC were studied based on first-principles calculations. It was found that O-doped SiC is unstable. O-adsorbed SiC and C-doped SiC exhibit non-magnetic semiconductor properties with reduced bandgap. In contrast, a semi-metallic state emerges in H- and N-adsorbed, as well as H- and N-doped SiC. In addition, C-adsorbed SiC displays a magnetic semiconductor state, which may have significant potential for application in spintronics due to the high Curie temperature of 441 K. These findings demonstrate that the electronic and magnetic properties of SiC could be effectively tuned by doping or adsorbing atoms of atmospheric elements.

Defects and Defect Engineering of Two-Dimensional Transition Metal Dichalcogenide (2D TMDC) Materials.

As layered materials, transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) materials. Interestingly, the characteristics of these materials are transformed from bulk to monolayer. The atomically thin TMDC materials can be a good alternative to group III-V and graphene because of their emerging tunable electrical, optical, and magnetic properties. Although 2D monolayers from natural TMDC materials exhibit the purest form, they have intrinsic defects that limit their application. However, the synthesis of TMDC materials using the existing fabrication tools and techniques is also not immune to defects. Additionally, it is difficult to synthesize wafer-scale TMDC materials for a multitude of factors influencing grain growth mechanisms. While defect engineering techniques may reduce the percentage of defects, the available methods have constraints for healing defects at the desired level. Thus, this holistic review of 2D TMDC materials encapsulates the fundamental structure of TMDC materials, including different types of defects, named zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D). Moreover, the existing defect engineering methods that relate to both formation of and reduction in defects have been discussed. Finally, an attempt has been made to correlate the impact of defects and the properties of these TMDC materials.

Designing State-of-the-Art Gas Sensors: From Fundamentals to Applications.

Gas sensors are crucial in environmental monitoring, industrial safety, and medical diagnostics. Due to the rising demand for precise and reliable gas detection, there is a rising demand for cutting-edge gas sensors that possess exceptional sensitivity, selectivity, and stability. Due to their tunable electrical properties, high-density surface-active sites, and significant surface-to-volume ratio, nanomaterials have been extensively investigated in this regard. The traditional gas sensors utilize homogeneous material for sensing where the adsorbed surface oxygen species play a vital role in their sensing activity. However, their performance for selective gas sensing is still unsatisfactory because the employed high temperature leads to the poor stability. The heterostructures nanomaterials can easily tune sensing performance and their different energy band structures, work functions, charge carrier concentration and polarity, and interfacial band alignments can be precisely designed for high-performance selective gas sensing at low temperature. In this review article, we discuss in detail the fundamentals of semiconductor gas sensing along with their mechanisms. Further, we highlight the existed challenges in semiconductor gas sensing. In addition, we review the recent advancements in semiconductor gas sensor design for applications from different perspective. Finally, the conclusion and future perspectives for improvement of the gas sensing performance are discussed.