Tunable Electrical Properties Research Articles

Ionic solution-processable Ag nanostructures with tunable optical and electrical properties and strong adhesion to general substrates

We present a solution-processable Ag nanostructure (SPAN) fabrication protocol for thin metallic nanoarchitectures exhibiting tunable optical and electrical properties as well as strong adhesion to general materials, including transparent, flexible, and fabric substrates and graphene-coated surfaces. The SPAN film can be fabricated in a scalable, vacuum-free fashion simply by the coating of an ionic Ag ink with a subsequent thermal annealing process. Here, we systematically analyze and confirm that the Ag nanoclusters are reduced from Ag ions and evolve into the nanostructured film, where its morphology and porosity as well as its optical and electrical properties can be readily controlled by adjusting the initial Ag ink concentration and coating speed as well as the annealing temperature. Compared to the conventional vacuum-deposited Ag layer, the SPAN film shows generally improved adhesion regardless of the substrate material with the aid of additional organic binding. The SPAN architecture can thus be applied to further scalable and pragmatic frameworks such as the transparent and flexible conducting electrodes consisting of micromesh-patterned SPAN structures on transparent, flexible, and/or graphene-coated substrates and SPAN-interwoven electronic textiles. Many diverse material systems and functional architectures can benefit from SPAN, including but not limited to smart sensors, plasmonic structures, and printable and wearable devices.

Nitrogen-doped carbon nanosheets homogeneously embedded with Co nanoparticles via biostructure confinement as highly efficient microwave absorbers

2D/quasi-2D nanomaterial (e.g., graphene, MXene, carbon nanosheet) based composites are efficient absorbers of the ever-growing pollution of electromagnetic wave (EMW) due to their large aspect ratios, ample functional groups, and tunable electric and magnetic properties. However, the nanocomposites' cost-effective and straightforward synthesis process is still elusive. Thus, we demonstrated a simple swelling and carbonization process of exfoliated cellulose fibril to synthesize nitrogen-doped carbon nanosheets with homogeneously embedded Co nanoparticles (Co/NCN). Co/NCN with a carbonization temperature of 800 °C exhibited a minimum reflection loss (RLmin) of −65.7 dB at 13.9 GHz and an effective absorption bandwidth of 5.8 GHz with RL < -10 dB at a thickness of 1.7 mm. In addition, the microwave absorption characteristics of the composite can be further adjusted by the carbonization temperature. Those values are superior to many nanocomposites based on graphene and MXene. The doped nitrogen heteroatoms were essential for maintaining the morphology of carbon nanosheets, increasing the interfacial polarization loss, and improving the impedance matching. The environment-friendly and low-cost process proposed here can be extended to synthesizing many other metal/NCN nanocomposites as high-performance EMW absorbers.

Programmable black phosphorus image sensor for broadband optoelectronic edge computing

Image sensors with internal computing capability enable in-sensor computing that can significantly reduce the communication latency and power consumption for machine vision in distributed systems and robotics. Two-dimensional semiconductors have many advantages in realizing such intelligent vision sensors because of their tunable electrical and optical properties and amenability for heterogeneous integration. Here, we report a multifunctional infrared image sensor based on an array of black phosphorous programmable phototransistors (bP-PPT). By controlling the stored charges in the gate dielectric layers electrically and optically, the bP-PPT’s electrical conductance and photoresponsivity can be locally or remotely programmed with 5-bit precision to implement an in-sensor convolutional neural network (CNN). The sensor array can receive optical images transmitted over a broad spectral range in the infrared and perform inference computation to process and recognize the images with 92% accuracy. The demonstrated bP image sensor array can be scaled up to build a more complex vision-sensory neural network, which will find many promising applications for distributed and remote multispectral sensing.

Soft Liquid Metal Infused Conductive Sponges

AbstractLiquid metal droplets of gallium (Ga) and Ga‐based alloys are traditionally incorporated as deformable additives into soft elastomers to make them conductive. However, such a strategy has not been implemented to develop conductive sponges with real sponge‐like characteristics. Herein, polyurethane‐based sponges with Ga microdroplets embedded inside the polyurethane walls are developed. The liquid phase (at 45 °C) and solid phase (at room temperature) transition of the Ga fillers shows the temperature‐dependent functional variations in the mechanical, thermal, and electrical properties on the prepared composite sponges, which are investigated in detail. Unlike elastomers, the sponge possesses excellent elastic recovery, at ≈90%, and conductivity durability without sacrificing structural integrity. The reversible change of resistivity range is remarkable. When the Ga fillers account for 18% of the total sponge volume, the electrical resistivity varies from infinite values (insulator) under no applied pressure to 39.0 Ω m for the solid phase and 3.8 Ω m for the liquid phase under 386.8 kPa. New opportunities in developing flexible electrically conductive composite sponges with tunable mechanical and electrical properties that can be implemented for a variety of future applications are proposed.

Zinc-metal\u2013organic frameworks with tunable UV diffuse-reflectance as sunscreens

BackgroundUV exposure continues to induce many health issues, though commercial sunscreens are available. Novel UV filters with high safety and efficacy are urgently needed. Metal–organic frameworks (MOFs) could be a suitable platform for UV filter development, due to their tunable optical, electrical, and photoelectric properties by precise controlled synthesis.ResultsHerein, four zinc-based MOFs with various bandgap energies were chose to investigate their optical behaviors and evaluate their possibility as sunscreens. Zeolitic imidazolate framework-8 (ZIF-8) was found to possess the highest and widest UV reflectance, thereby protecting against sunburn and DNA damage on mouse skin and even achieving a comparable or higher anti-UV efficacy relative to the commercially available UV filters, TiO2 or ZnO, on pig skin, a model that correlates well with human skin. Also, ZIF-8 exerted appealing characteristics for topical skin use with low radical production, low skin penetration, low toxicity, high transparency, and high stability.ConclusionThese results confirmed ZIF-8 could potentially be a safe and effective sunscreen surrogate for human, and MOFs could be a novel source to develop more effective and safe UV filters.Graphical

Two-dimensional vanadium sulfide flexible graphite/polymer films for near-infrared photoelectrocatalysis and electrochemical energy storage

Modern wearable electronics require scalable, flexible, and conductive electrodes with tunable properties. Abundant materials such as graphite as a conductive component and polymer as a flexible component forming a composite film (electrode) via simple synthesis technique are particularly captivating. This approach conveniently satisfies the fundamental needs of an ideal electrode yet provides a conductive platform to accommodate a secondary material for various purposes in electrochemical energy conversion and storage. Accordingly, we optimize a graphite-polymer composite film with good conductivity and flexibility to incorporate two-dimensional (2D) VSx (mixed phase predominated by V5S8) as an active material within the film. We exemplify the dual functionalities of the VSx/graphite flexible electrode as i) a photo-electrocatalyst for enhanced hydrogen evolution reaction by visible and near-infrared light irradiation (overpotential ≈500 mV at the current density of −10 mA cm−2), and ii) a conductive electrode for symmetrical solid-state supercapacitor with pseudocapacitive charge storage mechanism (areal capacitance of 123 mF cm−2 and areal capacity of 34 µAh cm−2 at the current density of 0.5 mA cm−2). Our work demonstrates the versatility of graphite films in terms of size, shape, flexibility, and scalability, with tunable physical, optical, and electrical properties by integrating other secondary materials. We combine flexible graphite film and 2D vanadium sulfide with near-infrared photoresponse and pseudocapacitive properties, as an economically feasible avenue for energy harvesting, outer space application, and wearable devices.

Tunable electrical properties of C60·m-xylene and the formation of semiconducting ordered amorphous carbon clusters under pressure

Tunable electrical properties of C60·m-xylene and the formation of semiconducting ordered amorphous carbon clusters under pressure

Two-dimensional ferroelectric MoS2/Ga2O3 heterogeneous bilayers with highly tunable photocatalytic and electrical properties.

Two-dimensional van der Waals heterostructures with strong intrinsic ferroelectrics are highly promising for novel devices with designed electronic properties. The polarization reversal transition of the 2D ferroelectric Ga2O3 monolayer offers a new approach to tune the photocatalytic and electrical properties of MoS2/Ga2O3 heterogeneous bilayers. In this work, we study MoS2/Ga2O3 heterogeneous bilayers with different intrinsic polarization using hybrid-functional calculations. We closely investigate the structural, electronic and optical properties of two stable stacking configurations with opposite polarization. The results reveal a distinct switch from type-I to type-II heterostructures owing to polarization reversal transition of the 2D ferroelectric Ga2O3 monolayer. Biaxial strain engineering leads to type-I-to-II and type-II-to-III transitions in the two polarized models, respectively. Intriguingly, one of the MoS2/Ga2O3 heterolayers has a larger spatial separation of the valence and conduction band edges and excellent optical absorption ranging from infrared to ultraviolet region under biaxial strain, thus ensuring promising novel applications such as flexible electrical and optical devices. Based on the highly tunable physical properties of the bilayer heterostructures, we further explore their potential applications, such as photocatalytic water splitting and field-controlled switch channel in MOSFET devices.

Memristive and biological synaptic behavior in transition metal dichalcogenide-WS2 nanostructures: A review

Recently, two dimensional (2D) layered materials are being identified as potential candidates for different device applications such as memristors and brain inspired computing. These materials exhibit unusual physical properties such as atomic thickness, mechanically robust, tunable electrical and optical properties. These fascinating properties of 2D materials are very difficult to achieve with traditional materials used for different electronic purposes. The 2D materials are promising for high performance synapses and artificial neurons because of their high energy efficiency, excellent scalability, and high integration density. The present article gives an overview on the properties of 2D transition metal dichalcogenides (WS2) based electronic devices for memristive switching and biological synaptic behavior. Moreover, its integration into large-scale devices and associated challenges are being summarized along with the future prospective.

A Flexible, Mechanically Strong, and Anti‐Corrosion Electromagnetic Wave Absorption Composite Film with Periodic Electroconductive Patterns

AbstractDemand for high‐efficiency electromagnetic wave (EMW) absorption composite films continues to increase with technical advances in 5G telecommunications, wearable electronics, portable devices, and deployable military applications. However, realizing flexible ultra‐thin single‐layer EMW absorption composite films with multifunctionality, rather than using traditional particle absorbents, is a known challenge. In this study, the authors propose a series of polyimide (PI) reinforced composite films with periodic copper‐based electroconductive units that possess tunable electrical properties for specific applications. These periodic units optimize the electric field distribution of the films in an alternating electromagnetic field, resulting in stronger power loss. Furthermore, the hierarchical structure and abundant heterogeneous interfaces of each unit contribute to multiple scattering and polarization loss. The obtained copper mesh@Cu2−xS@PI (CCP) film shows excellent EM shielding performance (63.7 dB), while the Air@Cu2−xS@PI (ACP) film delivers a superior specific absorbency value of 391.43% mm–1 in the X‐band. Furthermore, owing to their mechanical properties, thermal conduction/dissipation performance, and excellent environmental stability characteristics, these films offer significant potential as high‐performance EMW response materials with resistance to harsh conditions.

Colorful Conducting Polymer Nanocomposites Brighten up Silicon Solar Cells

Multi-functional films with tunable electrical and optical properties are key to developing efficient and visually attractive silicon solar panels. Yet, a single-component material has not been able to address the challenge. Researchers now have found a means to blend multiple polymers and inorganic components in nanocomposite films. The optical and electrical properties of the nanocomposite films can be easily tailored to meet the requirement of rendering silicon solar cells of any designer color whilst maintaining efficient power conversion efficiencies. Cells with vivid colors offer the promise of the otherwise dull silicon solar panels as decorative structural materials.

Exsolution Synthesis of Nanocomposite Perovskites with Tunable Electrical and Magnetic Properties

AbstractNanostructured functional oxides play an important role in enabling clean energy technologies and novel memory and processor devices. Using thin‐film La0.6Sr0.4FeO3 (LSF) as a model system, the novel utility of exsolution in fabricating self‐assembled metal oxide nanocomposites with tunable functionalities is shown. Exsolution triggers the formation of metallic iron (Fe0) nanoparticles, Ruddlesden–Popper domains, and nm‐scale percolated Fe‐deficient channels in LSF. Combining multimodal characterization with numerical modeling, the chemical, magnetic, and electrical properties of the exsolution‐synthesized nanocomposite at different stages of Fe0 exsolution as well as during redox cycling are assessed. After exsolution, the electronic conductivity of the nanocomposite LSF increased by more than two orders of magnitude. Based on numerical analysis representing all the constituents, it is expected that this increase in conductivity originates mainly from the Fe‐deficient percolating channels formed during exsolution. Moreover, the exsolved nanocomposite is redox‐active even at moderate temperatures. Such redox capabilities can enable dynamic control of the nanocomposite functionality by tailoring the oxygen non‐stoichiometry. This concept is demonstrated with a continuous modulation of magnetization between 0 and 110 emu cm−3. These findings point out that exsolution may serve as a platform for scalable fabrication of complex metal oxide nanocomposites for electrochemical and electronic applications.

Optically photoactive Cu–In–S@ZnS core-shell quantum dots/biopolymer sensitized TiO2 nanostructures for sunlight energy harvesting

Colloidal semiconductor quantum dots (QDs) have been intensively investigated because of their remarkable tunable optical and electrical properties for potential clean energy production through solar photoconversion devices. Herein, we present for the first time the design and development of a hybrid nanostructure for applications in sunlight energy photoconversion, relying on a “safe and sustainable by design (SSD)” strategy, as follows: a) “Cadmium-free” (non-Cd-containing) inorganic semiconductor quantum dots (QDs), as optically active nanomaterials composed of quaternary Cu–In–S/ZnS systems (ZCIS); b) carboxylic-functionalized cellulose derivative (CMC) as biopolymer ligand and macromolecular stabilizing agent; c) A green chemistry approach based on an aqueous synthesis at mild conditions (e.g., pH, temperature, “organic-free”, nontoxic precursors) for creating water-soluble supramolecular colloidal core-shell nanostructures (i.e., [email protected], core: ZCIS; shell: CMC); d) As a proof-of-concept, the fabrication of a photoelectrochemical cell (PEC-cell) based on a solid-liquid heterojunction using the photoanode composed of TiO2 sensitized by [email protected] nanohybrids. Regarding optical properties, the results demonstrated that the [email protected] nanohybrids presented absorption/emission characteristics with maxima responses within the visible range of the light spectrum, which is prospectively appropriate for sunlight photoconversion applications. The solid-liquid junction photoelectrochemical cells (PEC-cell) fabricated using TiO2 films deposited onto ITO glass slides sensitized by ZCIS QDs evidenced photoactivity under visible light illumination using “dark” (“OFF”) and “light” (“ON”) cycles. Moreover, the PEC-cells confirmed the significant enhancement of photoinduced current density (over 150%) upon illumination when the relative sensitization density associated with the ZCIS QDs/TiO2 ratio was increased, and ethanol was used as the co-solvent. The results were credited to better contact between ZCIS QDs and TiO2 nanoparticles, tailoring a more favorable energy level alignment at the heterojunction interfaces, promoting the formation of a cascade of conduction band edges. Thus, these quantum dot-sensitized nanostructures developed through a sustainable and biocompatible approach produced strictly via green chemistry process can be anticipated as a sustainable alternative to the existing heavy metal-based sunlight photoactive optical nanomaterials after further optimization of conversion efficiency parameters.

Sequential Infiltration Synthesis of Nano-porous and Electrically Conductive In2O3 for Water Remediation

Sequential infiltration synthesis (SIS) is derivative of atomic layer deposition (ALD) that expands the morphological palate of materials to enable an even greater variety of applications. During SIS, a vapor phase precursor reversibly and selectively adducts with a polymer matrix. By controlling the polymer moieties, precursor chemistry, and reaction parameters such as time, temperature, and pressure, the process can yield precise deposition and high growth rates (equivalent to > 30 nm/cycle) in complex matrices that are 100s of nanometers thick. In our work, we leverage those parameters to deposit nano-porous In2O3 electrodes for water remediation. Electrified water treatment has the potential to greatly improve energy and cost efficiency over current methods. SIS has been used previously to create well-defined nano-porous structures, yet there has not been a report of an electrode developed via SIS. Our work describes how amorphous InOHx clusters deposited by SIS combine to form an interconnected and electrically conductive network of crystalline In2O3. Changes in optical parameters, probed by spectroscopic ellipsometry, reveal that the oxygen annealing burns off the polymer and leads to partial densification of the film. XRD and TEM further demonstrate the development of a crystalline network of In2O3 with grain sizes of approximately 20 nm. Additional annealing in forming gas yields resistivity values on the order of 10-3 Ω*m. Aside from the annealing conditions, the microstructure of the In2O3 network also influences electrical properties. Using SIS to control the volume fraction of In2O3 in PMMA, annealed samples were prepared with porosity ranging from 30-80% In2O3. As the amount of In2O3 increases, Hall measurements reveal that the resistivity decreases and the mobility increases, which suggests that the prevalence of charge conduction pathways within the In2O3 film can be controlled. We demonstrate nano-porous In2O3 films with tunable electrical properties and further highlight the opportunity to precisely control properties of In2O3 for applications such as water remediation.

Multicolor Patterning of 2D Semiconductor Nanoplatelets.

Nanocrystal micro/nanoarrays with multiplexed functionalities are of broad interest in the field of nanophotonics, cellular dynamics, and biosensing due to their tunable electrical and optical properties. This work focuses on the multicolor patterning of two-dimensional nanoplatelets (NPLs) via two sequential self-assembly and direct electron-beam lithography steps. By using scanning electron microscopy, atomic force microscopy, and fluorescence microscopy, we demonstrate the successful fabrication of fluorescent nanoarrays with a thickness of only two or three monolayers (7-11 nm) and a feature line width of ∼40 nm, which is three to four NPLs wide. To this end, first, large-area thin films of red-emitting CdSe/ZnyCd1-yS and green-emitting CdSe1-xSx/ZnyCd1-yS core/shell NPLs are fabricated based on Langmuir-type self-assembly at the liquid/air interface. By varying the concentration of ligands in the subphase, we investigate the effect of interaction potential on the film's final characteristics to prepare thin superlattices suitable for the patterning step. Equipped with the ability to fabricate a uniform superlattice with a controlled thickness, we next perform nanopatterning on a thin film of NPLs utilizing a direct electron-beam lithography (EBL) technique. The effect of acceleration voltage, aperture size, and e-beam dosage on the nanopattern's resolution and fidelity is investigated for both of the presented NPLs. After successfully optimizing EBL parameters to fabricate single-color nanopatterns, we finally focus on fabricating multicolor patterns. The obtained micro/nanoarrays provide us with an innovative experimental platform to investigate biological interactions as well as Förster resonance energy transfer.

Biomaterial‐Based Solid‐Electrolyte Organic Electrochemical Transistors for Electronic and Neuromorphic Applications

AbstractA systematic study of biomaterial‐based solid‐state organic electrochemical transistors (OECTs) is presented in which biogels consisting of gelatin and glycerol, two food‐grade materials, are chosen as the model solid electrolyte. Such gels are fundamentally attractive for bioelectronics and wearable applications due to their superior and tunable electrical and mechanical properties, which allow one to fabricate solid‐state organic transistors with high ON/OFF ratio and transconductance, possible millisecond‐switching speed, and 6‐month stability in ambient air. Next, the authors show a good control of the state‐retention property of biogel OECTs, demonstrated herein by employing them as artificial synapses with various synaptic functions, such as frequency‐based short‐term plasticity. This study herein paves the way for the development of biomaterial‐based electronics by providing guiding principles for future works that employ biomaterials in OECTs.

Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines.

Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines’ detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection.

Tunable ferroelectric properties in (K0.5Na0.5)NbO3 ceramics fabricated by a simple modification of the conventional sintering technique

ABSTRACT In this work, a modified sintering method, i.e. the three-step sintering technology, has been applied to fabricate the K0.5Na0.5NbO3 ceramics. The impact of the detailed sintering conditions on the sinterability, dielectric and ferroelectric properties of K0.5Na0.5NbO3 is systematically investigated. Attributed to the three-step sintering, the highest density of 4.07 g cm−3 can be observed, which is strongly improved compared with that of the single-step sintering technique and is increased up to 90% of the theoretical density. Furthermore, through the analysis on the tunability of the dielectric and ferroelectric performances, it is found that the maxima of permittivity and polarisation can be obtained in K0.5Na0.5NbO3 sintering at 1160–1220–1120°C. These results illustrate that both the dielectric and ferroelectric behaviours can be effectively modulated through the simple modification of sintering technique, which would provide a novel route to achieve tunable electrical properties in ferroelectrics.

Tunable Electric and Magnetic Properties of Transition Metal@Nx Cy -Graphene Materials by Different Metal and Defect Types.

Transition metal@Nx Cy -graphene (TM@Nx Cy -GR) materials have been widely used as redox reaction catalysts in the field of fuel cells due to their low cost and high performance. In the present work, we systematically investigate the effect of different metal and defect types on the electro-magnetic properties of TM@Nx Cy -GR materials using first principles calculations. Our simulations show that TM@N3 -GR (the minimum defect size) and TM@N7 -GR (the maximum defect size) materials always possess metallic property regardless the metal type. However, doping different TM can regulate the medium defects (TM@N2 C2 -GR-I and TM@N2 C2 -GR-II) among metallicity, half-metallicity and semi-conductivity. In addition, we found that different TM and defect type largely affects the magnetic moment. The spin density and projected density of state calculations show that the net charges of the defect structure are mainly located near the hole, and the magnetic regulation comes from the coupling of TM-d orbital with carbon (nitrogen)-s(p) orbitals. The present study provides abundant valuable information for the TM@Nx Cy -GR materials designs and applicants in the future.

Photocatalytic degradation of methylene blue over N-doped MnWO4 under visible light irradiation

In recent years, the transition-metal tungstate materials with formula MWO4 have attracted much attention in photocatalytic environmental purification due to their interesting structural and optical properties. Among the others, manganese tungstate (MnWO4) has attracted particular attention because of its appropriate bandgap energy (2.67 ​eV) with tunable optical and electrical properties, chemical stability, and low cost which makes a suitable photocatalyst. Nevertheless, the manganese tungstate (MnWO4) based materials are less explored as visible light responsive photocatalysts for wastewater purification. Hence, both parent and N-doped MnWO4 are synthesized by a hydrothermal method with different nitrogen contents (5, 10, and 15 ​mol%). The as-prepared photocatalysts were characterized by XRD, SEM-EDS, TEM-SAED, FT-IR, UV–Vis DRS, XPS and PL techniques. The photocatalytic activities of the synthesized samples were evaluated by degradation of methylene blue (MB) dye under the visible light irradiation. All the N-doped MnWO4 samples exhibited enhanced visible-light photocatalytic activity compared to the parent MnWO4, and the optimal dopant amount of nitrogen was 15 mol% for the best photocatalytic activity. The active species generated during the process of MB degradation are investigated by scavenging experiments. Further, the reusability of the 15 ​mol% N-doped MnWO4 photocatalyst was examined in three consecutive catalytic runs.