Sheet Resistance Research Articles

Low Temperature Atomic Layer Deposition of (00l)‐Oriented Elemental Bismuth

This study presents the first successful demonstration of growing elemental bismuth (Bi) thin films via thermal atomic layer deposition (ALD) using Bi(NMe2)3 as the precursor and Sb(SiMe3)3 as the co‐reactant. The films were deposited at a relatively low temperature of 100 °C, with a growth per cycle (GPC) of 0.31‐0.34 Å/cycle. Island formation marked the initial growth stages, with surface coverage reaching around 80% after 1000 cycles and full coverage between 2000 and 2500 cycles. Morphological analysis revealed that the Bi grains expanded and became more defined as the number of ALD cycles increased. This coalescence is further supported by X‐ray diffraction (XRD) patterns, which show a preferential shift in growth orientation from the (012) plane to the (003) plane as the film thickness increases. X‐ray photoemission spectroscopy (XPS) confirmed the presence of metallic Bi with minimal surface oxidation. Temperature‐dependent sheet resistance measurements highlight the semimetallic nature of Bi, with a room temperature resistivity of ≈200 µΩcm for the 2500 cycles Bi. Temperature‐dependent sheet resistance was also associated with a transition in carrier‐type dominance from electrons at higher temperatures to holes at lower temperatures.

Low Temperature Atomic Layer Deposition of (00l)-Oriented Elemental Bismuth.

This study presents the first successful demonstration of growing elemental bismuth (Bi) thin films via thermal atomic layer deposition (ALD) using Bi(NMe2)3 as the precursor and Sb(SiMe3)3 as the co-reactant. The films were deposited at a relatively low temperature of 100 °C, with a growth per cycle (GPC) of 0.31-0.34 Å/cycle. Island formation marked the initial growth stages, with surface coverage reaching around 80% after 1000 cycles and full coverage between 2000 and 2500 cycles. Morphological analysis revealed that the Bi grains expanded and became more defined as the number of ALD cycles increased. This coalescence is further supported by X-ray diffraction (XRD) patterns, which show a preferential shift in growth orientation from the (012) plane to the (003) plane as the film thickness increases. X-ray photoemission spectroscopy (XPS) confirmed the presence of metallic Bi with minimal surface oxidation. Temperature-dependent sheet resistance measurements highlight the semimetallic nature of Bi, with a room temperature resistivity of ≈200 µΩcm for the 2500 cycles Bi. Temperature-dependent sheet resistance was also associated with a transition in carrier-type dominance from electrons at higher temperatures to holes at lower temperatures.

Hybrid Liquid Metal/Ionic Nanocomposite Transparent Electrodes for Highly Stretchable Electroluminescent Matrix Displays

AbstractEmerging intrinsically stretchable electroluminescent displays have the potential to transform future smart wearables by seamlessly integrating light‐emitting capabilities with mechanical deformability. A significant challenge in constructing these devices is the lack of compliant transparent electrodes that possess excellent optoelectronic properties. This study presents a design concept for hybrid transparent electrodes that consist of liquid metal frames surrounding transparent ionic nanocomposite fluids. This electrode harnesses the highly conductive liquid metal component, achieving a low sheet resistance of just a few ohms even under extreme uniaxial and biaxial deformations. The central emitting region boasts an impressive optical transmittance of 96.6% at 465 nm thanks to the ionic nanocomposite. As a result, the overall optical transmittance of the entire electrode remains at 81.6% at 465 nm, even when including the opaque liquid metal frame. Stretchable matrix displays have been fabricated through a scalable process, demonstrating uniform luminous intensity, excellent deformability, and exceptional durability. This device can be bent, twisted, stretched, and conformed to curved surfaces, rendering it suitable for diverse applications. The hybrid transparent electrode developed here represents a promising design of mixed electron and ion conductors for advancing stretchable optoelectronic devices.

Flexible and Durable Conducting Fabric Electrodes for Next-Generation Wearable Supercapacitors.

This study presents the fabrication of highly conducting Au fabric electrodes using a layer-by-layer (LBL) approach and its application toward energy storage. Through the ligand-exchange mechanism, the alternating layers of tris(2-aminoethyl)amine (TREN) and gold nanoparticles (Au NPs) encapsulated with tetraoctylammonium bromide (TOABr) ligands (Au-TOABr) were deposited onto the fabric to achieve a highly conducting Au fabric (0.12 Ω/□) at room temperature in just two LBL cycles. In contrast to several existing techniques, the current study realizes highly conducting Au fabric (7-15 Ω/□) in a layer-by-layer coating. The obtained Au fabrics demonstrate excellent stability against various deformations and abrasions, and its sheet resistance remained unaltered even after multiple cycles of bending, twisting, scotch tape adhesions, and sandpaper abrasions. In addition, the prepared Au fabrics exhibit high robustness toward various chemical media, highlighting their anticorrosive properties. Although Au fabrics showed a slight increase in sheet resistance postwashing and ultrasonication tests, it was got ridden by coating a thin layer of a biocompatible polydimethylsiloxane (PDMS) polymer. Besides enhancing the adhesion of Au NPs, PDMS coating offered a hydrophobic surface to fabrics rendering their use toward self-cleaning applications. High-performing energy storage devices integrated with wearable technologies are in great demand. In this context, here, electropolymerized polyaniline (PANI)-coated Au fabrics were employed to develop supercapacitors with remarkable energy-storing capability. In a symmetric two-electrode configuration, the device offered a maximum areal capacitance of 660 mF/cm2 with high areal energy and power densities of 58.64 μWh/cm2 and 22.86 mW/cm2, respectively. The solid-state supercapacitor device (SSD) fabricated using Au/PANI-30 electrodes exhibited an areal capacitance of 495 mF/cm2 with energy and power densities of 33 μWh/cm2 and 10,660 μW/cm2, respectively. This LBL method offers a significant advantage over existing techniques by offering simple room-temperature fabrication with excellent conductivity and adaptability to various substrates and with ease of scalability.

Improved area scaling of radio-frequency patch antenna by highly intercalated multilayer graphene / nickel hybrid structure

Abstract Using a novel hybrid conductor with intercalated multilayer graphene (I-MLG) and Ni, it was demonstrated that the area of a radio frequency (RF) patch antenna at around 18 GHz can be reduced by one-third. Improved intercalation doping of MLG was realized by a novel split-CVD method for improved MLG crystallinity and uniformity and higher intercalation doping to MLG. With the process improvement, the sheet resistance of I-MLG layer was reduced and the current was considered to flow preferentially in the I-MLG layer by skin effect at high frequencies, and a kinetic inductance was induced by the current in the I-MLG layer. In addition, the Ni layer served as a magnetic core to enhance the magnetic inductance induced by the current. It is considered that the area reduction effect was obtained by the higher inductance density with the kinetic inductance and the enhanced magnetic inductance.

THz Shielding Properties of Optically Transparent PEDOT:PSS/AgNW Composite Films and Their Sandwich Structures

The modern pace of scientific and technological development dictates unprecedented requirements for the speed of information transfer. The THz range is considered one of the most promising and has been actively developing in recent years. Along with the need to develop transmitting devices, the demand for shielding materials in this range, including transparent ones, is also growing. In this work, we present two types of composite films based on silver nanowires and PEDOT:PSS. We characterized these composite films in terms of optoelectrical parameters, as well as shielding characteristics in the THz range. We found that our composite films have a sheet resistance (R□) of about 8.6 ± 1.2 Ω/□ with a transparency of about 83.41 % and shielding efficiency is 25.85 dB in the THz region, which makes them excellent candidates for transparent shielding materials. We also made a bilayer sandwich structure from these composite films, which showed a shielding efficiency of about 49.34 dB in the range of 0.2–0.8 THz with a transparency of 66.33%. In addition, we assessed the possibility of real application of the structures in terms of stability to external conditions. Our composite films sustain atmospheric corrosion and maintain stable sheet resistance for 30 days.

Transparent OLED displays for selective bidirectional viewing using ZnO/Yb:Ag cathode with highly smooth and low-barrier surface

Transparent organic light-emitting diode (TrOLED) displays represent cutting-edge technology posed to significantly enhance user experience. This study addresses two pivotal challenges in TrOLED development. Firstly, we focus on the innovation of transparent cathodes, a fundamental component in TrOLEDs, by introducing a ZnO/Yb:Ag cathode. This cathode employs a combination of seed layer and metal doping techniques to achieve a highly uniform surface morphology and a low surface energy barrier. The optimized Yb:Ag cathode on ZnO, with a mere thickness of 15 nm, exhibits remarkable properties: an extremely low surface roughness of 0.52 nm, sheet resistance of 11.6 Ω ϒ−1, an optical transmittance of 86.7% at 510 nm, and tunable work function (here, optimized to be 3.86 eV), ensuring superior electron injection capability. Secondly, we propose a novel TrOLED pixel structure that features selective bidirectional viewing, allowing different types of information to be selectively displayed on each side while preserving overall transparency and minimizing pixel complexity. This design innovation distinguishes itself from conventional TrOLEDs that display images on only one side. The bidirectional TrOLED design not only enhances openness and esthetic appeal but also holds promise for diverse applications across various user environments.

Innovative Method for Reliable Measurement of PEM Water Electrolyzer Component Resistances.

Understanding the sheet resistance of porous electrodes is essential for improving the performance of polymer electrolyte membrane (PEM) water electrolyzers and related technologies. Despite its importance, existing methods often fail to provide reliable and comprehensive data, especially for porous materials with complex morphologies and non-uniform thicknesses. This study introduces a robust and straightforward method for determining the sheet resistance of porous electrodes using a novel probe concept based on industrial printed circuit board (PCB) technology. This probe measures resistance across ten distances, ranging from 250 µm to 2500µm, enabling local mapping of resistance. The study focuses on the sheet resistance of key components in PEM water electrolyzers, including the gas diffusion layer (GDL), porous transport layer (PTL), and catalyst layers deposited on a membrane. Additionally, an image-processing-based method is presented to obtain the thickness distribution of the studied catalyst layers, facilitating a detailed analysis of the electrical in-plane resistivity with thickness variations. Overall, this methodology has the potential to expedite material integration and bridge the gap between electrode engineering and single-cell testing, thereby advancing the development of PEM water electrolyzers.

Preparation and Optoelectrical Property of Silver Nanowire Transparent Conductive Film via Slot Die Coating

Silver nanowire transparent conductive films (AgNW TCFs), as the novel transparent electrode materials replacing ITO, are anticipated to be applied in numerous optoelectronic devices, and slot-die coating is currently acknowledged as the most suitable method for the mass production of large-sized AgNW TCFs. In this study, sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA), as film-forming aids, and AgNWs, as conductive materials, were utilized to prepare a specialized AgNW ink, and a slot-die coating is employed to print and prepare AgNW TCFs. The optoelectrical properties of AgNW TCFs are optimized by adjusting the compositions of AgNW ink and the process parameters of slot-die coating. The suitable compositions of AgNW ink and the optimal parameters of slot-die coating are a CMC type of V, a PVA volume of 1 mL, a AgNW volume of 1.5 mL, a volume ratio of 30 and 45 nm AgNWs (2:1), and a coating height of 400 μm. The resultant AgNW TCFs achieve excellent comprehensive optoelectronic performance, with a sheet resistance of less than 50 Ω/sq, a visible light transmittance exceeding 92%, and a haze below 1.8%. This research provides a valuable approach to producing AgNW TCFs on a large scale via the slot-die coating.

Fully Inkjet-Printed Flexible Graphene-Prussian Blue Platform for Electrochemical Biosensing.

Prussian Blue (PB) is commonly incorporated into screen-printed enzymatic devices since it enables the determination of the enzymatically produced hydrogen peroxide at low potentials. Inkjet printing is gaining popularity in the development of electrochemical sensors as a substitute for screen printing. This work presents a fully inkjet-printed graphene-Prussian Blue platform, which can be paired with oxidase enzymes to prepare a biosensor of choice. The graphene electrode was inkjet-printed on a flexible polyimide substrate and then thermally and photonically treated with intense pulsed light, followed by inkjet printing of a PB nanoparticle suspension. The optimization of post-printing treatment and electrode deposition conditions was performed to yield a platform with minimal sheet resistance and peak potential differences. A thorough study of PB deposition was conducted: the fully inkjet-printed system was compared against sensors with PB deposited chemically or by drop casting the PB suspension on different kinds of carbon electrodes (glassy carbon, commercial screen-printed, and in-house inkjet-printed electrodes). For hydrogen peroxide detection, the fully inkjet-printed platform exhibits excellent sensitivity, a wider linear range, better linearity, and greater stability towards higher concentrations of peroxide than the other tested electrodes. Finally, lactate oxidase was immobilized in a chitosan matrix, and the prepared biosensor exhibited analytical performance comparable to other lactate sensors found in the literature in a wide, physiologically relevant linear range for measuring lactate concentration in sweat. The development of mediator-modified electrodes with a single fabrication technology, as demonstrated here, paves the way for the scalable production of low-cost, wearable, and flexible biosensors.

Excellent Mechanical Performance of Cellulose Composite Papers for Flexible Self-Powered Photodetectors Using the ZnO/PbS Heterojunction.

Cellulose is attracting considerable attention in the field of flexible electronics due to its unique properties and environmental sustainability, particularly as a substrate for flexible devices. Flexible photodetectors are an integral part of cellulose-based devices and have become essential in optical communication, heart rate monitoring, and imaging systems. The performance and adaptability of these photodetectors depend significantly on the quality of the flexible substrates. However, poor bonding with conductive materials results in poor conductivity stability, and limited thermal stability makes cellulose unsuitable for many preparation processes. This study designed polyvinylpyrrolidone (PVP)-coated silver nanowires (AgNWs) as conductive materials, integrating them with cellulose nanofibers (CNFs). The resulting AgNW/CNF composite paper demonstrated high tensile strength (183.9 MPa), low sheet resistance (2.38 Ohm sq-1), and excellent bending durability. Spin-coated PbS colloidal quantum dots (CQDs) films and low-temperature magnetron-sputtered ZnO films were used as functional layers to create a flexible self-powered photodetector. This device features low dark current density (2.35 × 10-9 mA cm-2 @0 V), fast photoresponse (40/24 ms), and stability under bending (up to 180°, 1 mm radius). It shows potential for applications in infrared optical communication and real-time heart rate monitoring, demonstrating the promise of cellulose substrate photodetectors for flexible electronics.

High-Mobility All-Transparent TFTs with Dual-Functional Amorphous IZTO for Channel and Transparent Conductive Electrodes.

The increasing demand for advanced transparent and flexible display technologies has led to significant research in thin-film transistors (TFTs) with high mobility, transparency, and mechanical robustness. In this study, we fabricated all-transparent TFTs (AT-TFTs) utilizing amorphous indium-zinc-tin-oxide (a-IZTO) as a dual-functional material for both the channel layer and transparent conductive electrodes (TCEs). The a-IZTO was deposited using radio-frequency magnetron sputtering, with its composition adjusted for both channel and electrode functionality. XRD analysis confirmed the amorphous nature of the a-IZTO layers, ensuring structural stability post-thermal annealing. The a-IZTO TCEs demonstrated high optical transparency (89.57% in the visible range) and excellent flexibility, maintaining a low sheet resistance with minimal degradation even after 100,000 bending cycles. The fabricated AT-TFTs exhibit superior field-effect mobility (30.12 cm2/V·s), an on/off current ratio exceeding 108, and a subthreshold swing of 0.36 V/dec. The AT-TFT device demonstrated a minimum transmittance of 75.46% in the visible light range, confirming its suitability for next-generation flexible and transparent displays.

Multilayer Graphene Stacked with Silver Nanowire Networks for Transparent Conductor.

A mechanically robust flexible transparent conductor with high thermal and chemical stability was fabricated from welded silver nanowire networks (w-Ag-NWs) sandwiched between multilayer graphene (MLG) and polyimide (PI) films. By modifying the gas flow dynamics and surface chemistry of the Cu surface during graphene growth, a highly crystalline and uniform MLG film was obtained on the Cu foil, which was then directly coated on the Ag-NW networks to serve as a barrier material. It was found that the highly crystalline layers in the MLG film compensate for structural defects, thus forming a perfect barrier film to shield Ag NWs from oxidation and sulfurization. MLG/w-Ag-NW composites were then embedded into the surface of a transparent and colorless PI thin film by spin-coating. This allowed the MLG/w-Ag-NW/PI composite to retain its original structural integrity due to the intrinsic physical and chemical properties of PI, which also served effectively as a binder. In view of its unique sandwich structure and the chemical welding of the Ag NWs, the flexible substrate-cum-electrode had an average sheet resistance of ≈34 Ω/sq and a transmittance of ≈91% in the visible range, and also showed excellent stability against high-temperature annealing and sulfurization.

Communication─A High-Efficiency and Low-Damage Treatment for Pressure Less Sintering of Ag Micro-Nano Particles at Low Temperature

Pressure-free and low-damage interconnections are essential for high-density packaging of high-power devices. Here, a novel and high-efficient plasma treatment method to sinter micro-nano particles at low temperature without pressure is discussed. The silver paste was exposed to Ar/H2 plasma for only 10 s, followed by sintering at 200 ℃ for 15 min. The shear strength increased to 2.6 times that of the untreated sample. Improvements in the sheet resistivity and thermal conductivity were observed. Ar/H2 plasma treatment is a viable approach for enhancing the sintering performance of commercially available silver pastes, thereby contributing to advancements in packaging technology.

Regulable crack patterns for the fabrication of high-performance transparent EMI shielding windows.

Crack pattern-based metal grid film is an ideal candidate material for transparent electromagnetic interference shielding optical windows. However, achieving crack patterns with narrow grid spacing, small wire width, and high connectivity remains challenging. Herein, an aqueous acrylic colloidal dispersion was developed as a crack precursor for preparing crack patterns. The ratio of hard monomers in the precursor, the coating thickness, and the drying mediation strategy were systematically varied to control the spacing and width of the crack patterns. The resulting dense and narrow crack patterns served as sacrificial templates for the fabrication of patterning metal grid films on transparent substrates, intended for optoelectronic applications. These films demonstrated excellent optoelectronic properties (82.7% transmission at 550nm visible light, sheet resistance 4.1Ω/sq) and strong EMI shielding effectiveness (average shielding effectiveness 33.6 dB at 1-18 GHz), showcasing their potential as a scalable and effective transparent EMI shielding solution.

A Low-profile Half-Mode Substrate Integrated Waveguide-based Sensor for Contactless Sheet Resistance Characterization

A Low-profile Half-Mode Substrate Integrated Waveguide-based Sensor for Contactless Sheet Resistance Characterization

Chemical Reduction of Cu(OH)2/Cu(O,S) Bilayers Fabricated by Chemical Bath Deposition to Form Adhesive and Low-Resistive Metallic Cu Layers on Glass Substrates

Chemical reductions of Cu(OH)2/Cu(O,S) and Cu(O,S)/Cu(O,S) bilayers fabricated on glass substrates by chemical bath deposition (CBD) was investigated through electrochemical measurements, X-ray diffraction, and evaluations of the electrical properties and adhesion strength by a tape-peeling test. The potential change during the chemical reduction in NaBH4 aqueous solutions was measured and discussed based on a mixed potential theory using the equilibrium potential calculated with chemical thermodynamics. The sheet resistance decreased from over 1 × 108 W/□ to 0.24 W/□, mainly due to the increase in the thickness, with the resistivity estimated to be 4.8 × 10–6 W cm. The metallic Cu layer showed adhesion strengths of 6.4 and 4.4 N cm−1 for maximum and average values respectively by tape-peeling test, without any detachment, but the Cu sheet peeled off from the glass substrate after the complete chemical reduction of the Cu(OH)2/Cu(O,S) bilayer. The Cu fragments formed by the chemical reduction of the Cu(O,S)/Cu(O,S) bilayer peeled off from the glass substrate, but the Cu(O,S)/Cu(O,S) bilayer showed the adhesion strengths of 6.7 and 4.0 N cm−1 for maximum and average values, respectively, by the tape-peeling test. Both the Cu(OH)2 and Cu(O,S) layers were indispensable to secure the Cu layer on the glass substrate.

Multifunctional transparent conductive films via Langmuir-Blodgett assembly of large MXene flakes.

The rapid development of information technology has put forward new requirements for multifunctional properties of transparent conductive films (TCFs) beyond their excellent optoelectrical performance. Despite the recent progress in the preparation of multifunctional films composed of Ti3C2Tx MXenes, achieving highly uniform single-layer Ti3C2Tx MXene films (SLMFs) with continuous and dense conductive pathways to realize multifunctional TCFs (M-TCFs) remains a significant challenge. Here, the Langmuir-Blodgett (LB) technique is employed to assemble large Ti3C2Tx MXene (LM) flakes (∼52 μm2) into SLMFs with controlled stacking density and morphology, enabling the fabrication of M-TCFs with high conductivity and transparency simultaneously. The SLMFs assembled from LM flakes (L-SLMFs) not only exhibit balanced optical and electrical properties with a figure of merit of 9.67 (sheet resistance Rs = 318 Ω sq-1 at transmittance T = 88%) due to the close-packed morphology with significantly reduced inter-flake junctions, but also demonstrate excellent electrothermal conversion capability (105.5 °C within 40 s at 20 V when T = 75%) and remarkable absolute shielding effectiveness (up to 7.86 × 105 dB cm2 g-1 at T = 89%). The LB assembly approach provides a straightforward way to produce high-performance M-TCFs for next-generation electronic devices.

Synergistic role of Cl- and Br- ions in growth control and mechanistic insights of high aspect ratio silver nanowires for flexible transparent conductive films.

Silver nanowires (AgNWs) with high aspect ratios are pivotal for the production of flexible transparent conductive films (TCFs). The growth of AgNWs is significantly influenced by the strong affinity of halogen ions for silver ions. This affinity plays a crucial role in the controlled deposition of silver along the nanowire axis. By precisely controlling the concentrations of Cl- and Br- ions, we have successfully synthesized AgNWs with remarkable lengths of 96 μm and diameters of 40 nm, achieving an impressive aspect ratio of 2400. Utilizing density functional theory and molecular dynamics simulations, we investigate the impact of these ions on the growth of AgNWs. Our findings reveal that halogen ions strongly adsorb onto the Ag (100) plane in the radial direction, with Cl- ions promoting anisotropic growth and Br- ions effectively limiting the nanowire diameter, thus achieving high aspect ratio AgNWs. The resulting TCFs exhibit a high transmittance of 95.0% at 550 nm and a low sheet resistance of 14.7 Ω sq-1. Moreover, when integrated into a flexible transparent heater, these TCFs demonstrate a high heating rate of 12.1 °C s-1. The development of AgNWs is poised to significantly enhance the performance and versatility of flexible TCFs.

Continuous and Extremely Flat Ag Electrode by Tailoring Surface Energy for Organic Light‐Emitting Diodes

AbstractThe exploration of alternative transparent electrodes to indium tin oxide (ITO) in organic light‐emitting diodes (OLEDs) has been a topic of interest. Among various candidates, ultrathin and continuous metal films have garnered significant interest for their ability to offer both transparency and conductivity. However, due to the higher surface energy of metals compared to substrates, metal films tend to grow in a discrete island shape, resulting in poor conductivity and even low transparency due to a localized surface plasmon by metal islands. In this work, a way to produce homogeneous ultrathin and continuous Ag film (UCAF) achieved through primary NF3 plasma treatment on a glass substrate is proposed. This treatment introduces F bonds on the surface, enhancing the hydrophilicity of the glass surface and facilitating the formation of UCAF with high optical transmittance (>70%) and low sheet resistance (<10 Ω/ϒ). By incorporating UCAF into OLEDs as a bottom electrode, the current efficiency showed an 86% enhancement compared to an ITO bottom electrode at an operating current density of 10 mA cm−2. Numerical simulation results elucidated superior light extraction efficiency in OLED with UCAF compared to that with ITO, attributed to both cavity effect and reduced waveguide mode at the organic/electrode interface.