Electrode Height Research Articles

Towards Acoustic Radiation Free Lamb Wave Resonators for High-Resolution Gravimetric Biosensing

A novel Lamb wave resonator with fully suppressed acoustic radiation in water is proposed for high-resolution mass-sensitive detection of biomolecules. The elimination of acoustic radiation is achieved by slowing down the Lamb wave to a velocity lower than the sound speed in water. This enables high-quality-factor resonance in water and reduces the sensing frequency noise. High aspect ratio electrodes (HAREs) are used to slow down the Lamb wave. The elastic resonance and large surface area of the HAREs can also enhance the mass sensitivity of the device. The improved mass sensitivity together with the low frequency noise substantially improves the overall sensing resolution. Although reducing the plate thickness can also slow down the Lamb wave, it makes the device very fragile and not practical to use. In contrast, slowing down the Lamb wave by increasing electrode height allows the use of thick plates which is robust. In this article, the behavior and performance of the proposed high aspect ratio electrode Lamb wave resonator (HARE-LWR) are theoretically analyzed using finite element method simulations. Optimum design parameters were found through the simulations. Reported results show that a significant figure of merit improvement was achieved by the proposed HARE-LWR design.

The Link between Ag‐Paste Rheology and Screen‐Printed Solar Cell Metallization

AbstractToday's photovoltaic production chain is moving into a material crisis as the use of silver for front‐side metallization of passivated emitter and rear contact solar cells remains a crucial requirement. The shared effort of the scientific and industrial community to further reduce Ag‐consumption as much as possible without compromising cell efficiency has become more challenging in recent years. Further improvements require a deep understanding on the paste‐screen interaction at narrow line widths. This study presents the impact of Ag‐paste rheology on fine line screen printing for screen openings between 15 and 24 µm at industrial printing speeds of up to 600 mm s−1. A clear trade‐off is there between maintaining a sufficient reproducibility of the screen printing process and achieving an optimized printed Ag‐electrode geometry, thus optimal Ag‐consumption. Further, a correlation between the work of adhesion at the paste–wire interface and the resulting deviation of the printed electrode height is discovered, highlighting the importance of an advanced screen optimization for the future of fine line screen printing. Finally, an easy to use method for analyzing the reproducibility of printed Ag‐electrode geometries even for lab‐scale data sets is presented.

Electrical Performances of a Surface Acoustic Wave Device With Inter-Digital Transducers Electrodes in Local Resonances

Abstract In this paper, we investigate numerically the coupling of the Rayleigh mode with the micro-wall resonance modes in inter-digital transducers (IDTs) electrodes of surface acoustic wave (SAW) devices. We perform a finite element analysis (FEA) of the SAW features using an implemented model using comsol Multiphysics® software. The SAW structure comprises identical transmitter and receiver IDTs electrodes, with different electrode heights (he). The proposed FEA study is based on the extraction of reflection (S11) and transmission (S21) coefficients of the SAW device. The IDTs are considered to be a micro-wall phononic crystal acting as local resonators at frequencies inside the SAW passband. The locally resonance gap is strongly dependent on the he value, and S11 and S21 parameters are affected by the SAW energy absorption in the IDTs system. We have chosen two he values (0.5 and 3 µm) to study low and high aspect ratios of micro-walls, corresponding respectively to Bragg-type and resonance-type bandgaps appearing near the SAW central frequency. At the SAW resonance frequency, the return (S11) and the insertion (S21) losses are reduced. S21 is reduced by 12.73 and 18.49 dB for he = 0.5 and 3 µm, respectively, accompanied by an increase in the quality factor, and S11 parameter is reduced by 1.357 and 4.98 dB for he = 0.5 and 3 µm, respectively.

A Two-Step Fabrication Method for 3D Printed Microactuators: Characterization and Actuated Mechanisms

The fabrication and integration of microactuators with 3D micromechanisms are necessary to develop microrobots with higher capability and complexity. In this work, a two-step fabrication method combining 3D printing with two-photon polymerization (TPP) and aluminum sputtering is demonstrated. Actuators using two different transduction mechanisms (thermal and electrostatic) were fabricated in this process, and a thermal actuator was printed with a mechanism in three-dimensional space without additional assembly steps. This work also provides parameterized characterizations which can be used as design guidelines for building actuators and mechanisms. A design approach to electrically isolate the actuators from the substrate is introduced so that the device can be functional after two fabrication steps without patterning the metal layer. Metal coverage on the sidewalls of trenches are characterized, which provides a design space for deciding electrode gaps and heights in electrostatic actuators. Using these guidelines, 500 $\mu \text{m}$ long thermal actuators showed a maximum displacement of 18.0 $\mu \text{m}$ at 8.31mW and reliably actuated up to 8,500 cycles. An interdigitated electrostatic comb-drive actuator was also successfully demonstrated, displacing 12.7 $\mu \text{m}$ when 160V was applied. Finally, a 3D actuated mechanism was designed by incorporating a thermal actuator with 3D compliant mechanisms to flap 250 $\mu \text{m}$ long wings. Flapping motion was successfully demonstrated. [2020-0010]

Interdigital electrodes of air@NiO porous nanoshells for high performance microsupercapacitors by thermally-assisted 3D printing

Microsupercapacitors of air@NiO porous nanoshells are manufactured by a novel thermally-assisted 3D printing process. It entails the use of printing inks of the moderate solid content of CNT-PS@Ni-precursor-nanoparticle mixture, a real-time heating substrate to print 3D interdigital electrodes, and subsequent thermal annealing to convert PS@Ni-precursor particles into air@NiO porous nanoshells. The microstructure of 3D printed electrodes is characterized by air@NiO porous nanoshells being well dispersed in the CNT network. The CNT network provides a fast electronic migration path and meanwhile ensures the mechanical integrity of electrodes to prevent the fracture and/or collapsing of electrode structures during 3D printing manufacturing and charging/discharging cycles. The air@NiO porous nanoshells, manufactured in our labs, consist of randomly oriented nanosheets and offer superb charge storage via redox reactions. The metal layer is sputtered indiscriminately on the surface of interdigital electrodes and substrate before it is peeled off with electrolyte film and electrodes. The proposed tactic resolves problems connected with the tedious courses of traditional lithography and the delamination at the interface of active materials and collectors from mechanical stress. Experiments were conducted to study the performance of the microsupercapacitors (i.e. areal capacitances, energy and power densities) as a function of printing parameters, such as electrode heights, embedded amount of air@NiO porous nanoshells and the thickness of the metal layer on the electrochemical characteristics. The thickness of as-printed electrodes reaches up to 117 μm, which is vital in ensuring high energy density and is beyond the reach of any other technology. Moreover, the 3D printedmicrosupercapacitors of air@NiO porous nanoshells show excellent cycle stability and deliver an excellent areal capacitance of 56.7 mF cm−2, about a magnitude or two higher than that of C-based counterparts.

Penetrating glassy carbon neural electrode arrays for brain-machine interfaces.

This paper presents a fabrication method for glassy carbon neural electrode arrays that combines 3D printing and chemical pyrolysis technology. The carbon electrodes have excellent biological compatibility and can be used in neural signal recording. A pretreated Si wafer is used as the substrate for 3D printing, and then, stereolithography 3D printing technology is employed to print photosensitive resin into a cone shape. Next, chemical pyrolysis is applied to convert the 3D prints into glassy carbon electrodes and modify the electrochemical performance of the carbon electrodes. Finally, the glassy carbon electrodes are packed with conductive wires and PDMS. The proposed fabrication method simplifies the manufacturing process of carbon materials, and electrodes can be fabricated without the need of deep reactive ion etching (DRIE). The height of the carbon electrodes is 1.5mm, and the exposure area of the tips is 0.78mm2, which is convenient for the implantation procedure. The specific capacitance of the glassy carbon arrays is higher than that of a platinum electrode (9.18 mF/cm2 vs 3.32 mF/cm2, respectively), and the impedance at 1kHz is lower (7.1 kΩ vs 8.8 kΩ). The carbon electrodes were tested in vivo, and they showed excellent performance in neural signal recording. The signal-to-noise ratio of the carbon electrodes is 50.73 ± 6.11, which is higher than that of the Pt electrode (20.15 ± 5.32) under the same testing conditions. The proposed fabrication method of glassy carbon electrodes provides a novel approach to manufacture penetrating electrodes for nerve interfaces in biomedical engineering and microelectromechanical systems.

Automatic recognition and control of welding arc morphology as a function of the welding current and the tungsten electrode height

Automatic recognition and control of welding arc morphology as a function of the welding current and the tungsten electrode height

Arsenite removal from groundwater by aerated electrocoagulation reactor with Al ball electrodes: Human health risk assessment

The application of conventional electrocoagulation (EC) process for removal of As(III) from groundwater suffers from the need of external oxidation agent for oxidation of As(III) to As(V). To tackle this limitation, an aerated EC reactor for the removal of As(III) from groundwater was evaluated in this study. The effect of initial pHi, air flow rate, applied current, and electrode height in the EC reactor was examined. The experimental results showed that removal of arsenic mostly dependent on the applied current, electrode height in EC reactor, and air flow rate. The As(III) removal efficiency (99.2%) was maximum at pHi of 7.5, air flow rate of 6 L min−1, applied current of 0.30 A, and electrode height in EC reactor of 5 cm, with an total operating cost of 0.583 $ m−3. Furthermore, the carcinogenic risk (CR) and non-carcinogenic risk of arsenic (As) was in the range of tolerable limits at all operating conditions except applied current of 0.075 A at the end of the aerated EC process to remove As from groundwater. The present EC reactor process is able to remove As(III) from groundwater to below 10 μg L−1, which is maximum contaminant level of arsenic in drinking water according to the World Health Organization (WHO).

Significantly enhanced energy storage density of epitaxial Ba0.53Sr0.47TiO3 thin films by optimizing bottom electrode material

Electrode materials of dielectric thin-film capacitors have significant effect on their energy storage properties. In this work, Ba0.53Sr0.47TiO3 thin films were successfully deposited on LaNiO3 or La0.7Sr0.3MnO3 buffered (001) SrTiO3 substrates by pulsed laser deposition method (abbreviated as BST/LNO/STO and BST/LSMO/STO, respectively). The effect of LNO or LSMO bottom electrode on energy storage properties of BST films was systematically studied. It was found that the recoverable energy density of BST/LSMO/STO films is 36.1 J/cm3 at 3400 kV/cm, which is 59.1% higher than that of BST/LNO/STO thin films, i.e., 22.7 J/cm3 at 2765 kV/cm. Besides, the breakdown strength of the BST/LSMO/STO thin films is 22.9% higher than that of the BST/LNO/STO films. Both films show the good thermal stability from 20 °C to 160 °C as well as excellent fatigue resistance after up to 109 electrical cycles. The results show that the lattice mismatch strain of the film, surface roughness of the electrode and Schottky barrier height at the electrode-dielectric interface greatly affect the energy storage properties of BST thin-film capacitors. Our work offers a practical methodology to enhance the energy storage performances of thin-film capacitors by optimizing bottom electrode materials.

Scalability and stacking of self-stratifying microbial fuel cells treating urine

The scalability of Microbial fuel cells (MFCs) is key to the development of stacks. A recent study has shown that self-stratifying membraneless MFCs (S-MFCs) could be scaled down to 2 cm without performance deterioration. However, the scaling-up limit of S-MFC is yet unknown. Here the study evaluates the scale-up height of S-MFCs treating urine, from 2 cm, 4 cm to 12 cm high electrodes. The electrochemical properties of the S-MFCs were investigated after steady-states were established, following a 70-days longevity study. The electrochemical properties of the 2 cm and 4 cm conditions were similar (5.45 ± 0.32 mW per cascade). Conversely, the 12 cm conditions had much lower power output (1.48 ± 0.15 mW). The biofilm on the 12 cm cathodes only developed on the upper 5–6 cm of the immersed part of the electrode suggesting that the cathodic reactions were the limiting factor. This hypothesis was confirmed by the cathode polarisations showing that the 12 cm S-MFC had low current density (1.64 ± 9.53 µA cm−2, at 0 mV) compared to the other two conditions taht had similar current densities (192.73 ± 20.35 µA cm−2, at 0 mV). These results indicate that S-MFC treating urine can only be scaled-up to an electrode height of around 5–6 cm before the performance is negatively affected.

Modulation Asymmetry Suppression of Multifunction Integrated Optic Circuit by Sinking Electrode

The modulation asymmetry of a multifunction integrated optic circuit (MIOC) indicates the difference in the phase response to modulation electric fields with the same magnitude but different directions, and is partly caused by the vertical component of the modulation signal. This introduces a nonlinear phase error that is difficult to compensate in fiber optic gyroscopes (FOGs), which needs to be suppressed. In this paper, a sinking-electrode MIOC design to suppress the modulation asymmetry is proposed and verified through numerical simulations. Optimal parameters of the gap, height, side-wall angle, and center position error of the sinking electrodes are obtained on the basis of the simulation results. With the proposed method, the modulation asymmetry of MIOC can be reduced from 5 × 10 -4 rad to 1 × 10 -6 rad, thus facilitating the development of high-performance FOGs. Furthermore, compared with the traditional electrode design, the sinking-electrode design can increase the tolerance for the manufacturing process, and the design configuration can be obtained through the general process method.

Direct Hydroxylation of Benzene to Phenol by Dielectric Barrier Discharge Plasma

Direct synthesis of phenol from benzene was realized using atmospheric dielectric barrier discharge (DBD) plasma. In the process, various experimental parameters such as irradiation time, electrode height, and discharge power were found to play crucial roles in determining the yield and selectivity of phenol. Also, serious carbonization phenomenon was observed at the surface of used electrode due to the extensive interaction between benzene and electrode, which greatly inhibited the hydroxylation of benzene to phenol. To resolve this issue, silica coated electrode was employed, and significant improvement of conversion efficiency was obtained. The yield of phenol as high as 19.5% could be obtained in the optimal condition, and its selectivity was 83.3% based on the analysis of gas chromatography-mass spectrometry.

Rotational plating process design with computational fluid analysis

During the semiconductor manufacturing process and equipment development, we designed a face-up type electro-plating process and equipment including technologies of single wafer processing, wafer handling, and cyclic fluid delivery. In this study, with the help of computational fluid dynamics, we presented the flow effect on the wafer from the viewpoint of the coating uniformity. Process and hardware parameters, such as the electrode rotating speed, the gap between the electrode and the wafer, and the electrode shape were considered. The electrode height of 10 mm exhibited the best results, and this may be caused by the shoulder gap location to the outlet duct. A rotating speed of 5 rpm was shown to produce better results than those at other speeds. The butterfly wing and the meshed disk electrode showed a similar tendency in terms of the rotating speed and the gap. However, the butterfly-wing-type might show less uniform results than those of the meshed disk due to its original non-uniformity in the circumferential direction in case of lower rotating speed.

Three-Dimensional Electrohydrodynamic Enhanced Water Evaporation Using Needle-Arrayed Electrodes

A study was made of the electrohydrodynamic (EHD) effect on the water evaporation rate of a channel flow with a needle-arrayed electrode system using both numerical and experimental methods. The local charged density, flow, and concentration distributions and their growth along the flow stream of a rectangular channel were described in detail. The results showed that the EHD effect on the evaporation rate increased with increases in applied voltage and electrode pitch and decreased in electrode height. For example, at an applied voltage of 16 kV, the mass transfer enhancement was 1.5 times than that of the electrode pitch from 50 to 100 mm at an electrode height of 20 mm. The mass transfer enhancement was twice as great for electrode height from 20 to 15 mm at an applied voltage of 12 kV and pitch of 100 mm. The present needle-arrayed electrode system results were compared with a five-wire electrode system based on the same geometric model and boundary conditions. It was concluded that the needle electrode cases achieved better mass transfer gains than the wire electrode cases for the present evaluated cases. Finally, the numerical results obtained satisfactory consistency with experimental data with a maximum error of 25%.

On the impedance response of interdigitated electrodes

Finite-element impedance simulations were used to provide a relationship between the characteristic dimension and the physical dimensions of the interdigitated electrodes. Inclusion of electric and displacement currents allowed simulation of the capacitive loop associated with the geometric capacitance. An error analysis was used to quantify the influence of mesh and domain sizes on the numerical accuracy of the simulations. The interdigitated electrode geometry is shown to induce a frequency dispersion, dependent on electrode digit width, height, and separation, that can be characterized in terms of a complex ohmic impedance with real asymptotic limits for ohmic resistance at high and low frequencies. Characteristic dimensions, calculated from the primary ohmic resistance, the geometric capacitance, and the high-frequency ohmic resistance were in agreement for all geometries considered. The characteristic dimension calculated from the low-frequency ohmic resistance deviated under conditions that led to frequency dispersion. The Havriliak-Negami equation is shown to provide a good representation of the complex ohmic impedance. The present work is applicable to the analysis and interpretation of experimental data obtained using interdigitated electrodes.

Printed 3D Electrode Arrays with Micrometer‐Scale Lateral Resolution for Extracellular Recording of Action Potentials

AbstractCurrent investigations on neuronal or cardiac tissues call for systems that can electrically monitor cellular activity in three dimensions as opposed to classical planar approaches. Typically the fabrication of such 3D microelectrode arrays (3D MEAs) relies on advanced cleanroom fabrication techniques. However, additive manufacturing is becoming an ever versatile alternative for rapid prototyping of novel sensor designs due to its low cost and material expense. Here, the possibility of fabricating high‐resolution 3D MEAs is demonstrated by using electrohydrodynamic inkjet printing. The height and aspect ratio of the 3D electrodes can be readily tuned by adjusting the printing conditions and number of deposited ink droplets per electrode. The fabrication of pillar electrode arrays with electrode diameters of sintered structures below 3 µm is shown. The functionality of the array is confirmed using impedance spectroscopy and extracellular recordings of action potentials from HL‐1 cells.

3D Printed MXene Micro-Supercapacitors with Ultra-High Energy Density

Small scale energy storage devices are expected to play a significant role in the future advances of portable electronics, wireless sensors, and multifunctional micro/nanosystems. A crucial requirement for the fabrication of energy storage devices with high energy and power densities is using electrode materials with superior electrochemical properties. Another important requirement is the assembly of the electrode materials into structures that promote high ionic and electronic conductivities. In this talk, we report a scalable printing method for fabrication of on-chip three-dimensional (3D) micro-supercapacitors based on a class of 2D transition metal carbides called MXenes as electrode materials. MXenes offer high electronic conductivity and high specific capacitance and therefore, have attracted much interest as high-performance electrode materials for supercapacitors. In our work, the fabrication of MXene electrodes and device assembly is achieved using an extrusion-based 3D printing process that uses viscoelastic water-based MXene ink. A programmable printing machine was used in the printing process which involved layer-by-layer deposition of the MXene ink to fabricate the 3D electrodes. The developed printing method allows rapid fabrication of micro-supercapacitors on a variety of substrates, while electrode height can be controlled by the number of deposited layers. All-solid-state devices printed on flexible substrates showed excellent electrochemical performances under different bending conditions and delivered extremely high areal capacitances (over 1035 mF cm-2). Our study suggests that due to its high electronic conductivity and electrochemical properties, MXene is an excellent electrode material for the fabrication of 3D energy storage devices

The Influence of Geometry-Induced Frequency Dispersion on the Impedance Response of Interdigitated Electrodes

Interdigitated electrodes consist of interlaced electrode and counterelectrode fingers deposited on a non-conductive substrate. The electrode digits typically have a length on the order of millimeters, a width on the order of micrometers, and a separation distance on the order of micrometers. The diminutive dimensions of the electrochemical cell allow for low-noise impedance measurements and allow for the extraction of the electrical properties of the media in contact with the electrodes. Interdigitated electrodes are commonly utilized in measurements employing electrochemical impedance spectroscopy. Applications for interdigitated electrodes include the detection of contaminants, anti-corrosion coatings, and label-less detection of cells and viruses. Previous modeling of interdigitated electrodes was achieved by conformal mapping and finite-element methods and yielded estimates of the high-frequency ohmic resistance. The objective of our work was to determine the influence of geometry-induced frequency dispersion on the impedance response of interdigitated electrodes. Three aspects of the interdigitated electrode geometry were analyzed using finite-element simulations: the working-electrode width, the counterelectrode proximity to the working electrode, and the working electrode height. The meshing and domain size followed that developed for a disk-electrode geometry, for which ohmic resistances were obtained within 0.0009% of the analytic solution for an isolated disk electrode.1 The observations of the simulated impedance responses provided insight into the interpretation and analysis of data obtained using an interdigitated-electrode geometry. The ohmic response of the electrolyte may best be described as a complex frequency-dependent ohmic impedance with asymptotic real values of ohmic resistance in the high- and low-frequency limits.2 For an isolated flat embedded rectangular electrode, the geometry-induced frequency dispersion yielded a low-frequency ohmic resistance that was 1.29% larger than the high-frequency ohmic resistance. The high-frequency ohmic resistance was equal to that obtained for a primary current distribution. In the presence of a mirror-image counterelectrode, the ohmic resistances at high and low frequency were reduced up to an order of magnitude in comparison to an isolated electrode. The ratio of the low-frequency and high-frequency ohmic resistance ranged from 1.014 to 1.951 and was a function of the distance between the electrodes. Simulations were also performed that accounted for a finite electrode height for equal electrode width and spacing. Two characteristic frequencies were identified in the simulations; one that corresponded to the geometric capacitance of the interdigitated electrochemical cell, and one that corresponded to onset of low-frequency geometry-induced frequency dispersion. References Newman, “Resistance for Flow of Current to a Disk,” Journal of the Electrochemical Society, 113(5) (1966), 501-501.Huang, V. Vivier, M. E. Orazem, N. Pébère, and B. Tribollet, “The Apparent Constant-Phase-Element Behavior of an Ideally Polarized Blocking Electrode: A Global and Local Impedance Analysis,” Journal of The Electrochemical Society, 154 (2007), C81-C88.

Insights into dynamic molecular intercalation mechanism for Al[sbnd]C battery by operando synchrotron X-ray techniques

Recently, a novel rechargeable Al ion battery (AIB) with high performance has been developed. Owing to its low cost, high-rate capability, excellent cyclability, and non-flammability, AIB provides a safe alternative to many commercial batteries used in the energy storage system. To improve its performance, identifying molecular structure and arrangement of chloroaluminate anion (AlCl4−) intercalated in the graphite layer remains a great challenge. In this work, operando analysis of X-ray diffraction (XRD) measurement and X-ray absorption (XAS) spectroscopy were performed to investigate the intercalation of AlCl4− anion and related molecular arrangement in the graphite layers. The intercalated stage and intercalant gallery height of graphite cathode electrode during AIB battery operation were observed to be stage 3 and 9.22 Å, respectively. Furthermore, the spectral evolution from ex-situ XAS at the Al and Cl K-edge was associated with closely packed intercalation of AlCl4− molecules. With density functional theory (DFT) calculation, three simulated models of intercalated AlCl4− molecules in the graphite layer were revealed successfully, which explained possible molecular structures at different charging states. This analytical methodology paves the way for better understanding the structural transformation of molecular ions de-/intercalation in graphite layers.

(Invited) Multiscale Image-Based Control and Characterization of Lithium-Ion Batteries

Lithium-ion batteries (LIB) are today the main energy storage devices from portable electronics devices to electric vehicles. LIB have a high energy density, low self-discharge, and low memory effect allowing for large number of charging cycle without degrading storage capacity. Performance, cost and safety are the main factors driving research and different chemistry are investigated in order to achieve better performance at a lower cost and increase safety. Research, development and quality control of LIB can benefit much from X-ray Computed Tomography (CT) and Focused-Ion Beam – Scanning Electron Microscopy (FIB-SEM). MicroCT allows for complete non-destructive acquisition of a complete battery cell, allowing to control the production process and to monitor the changes occurring in the structure during multiple charging cycles. Different visualization techniques are proposed on a 7µm microCT acquisition of a Lithium Nickel Manganese Cobalt Oxide cell 18650 (NMC) which allow for a visual inspection of the internal structure of the cell, including techniques of unfolding to look at rolled electrodes and measurement such as electrode thickness, height, or length. Macroscopic properties of a battery, including mechanical, thermal and electrical, find their origins at a nano-scale. Using FIB-SEM, high resolution images can be acquired which can reveal the structure of the electrodes or the separator. Besides the volume fraction or surface areas of the different phases, the connectivity of pores and/or particles, their surface of contacts, path tortuosity or constrictivity, permeability or molecular diffusivity, become accessible. We will present simulation results on permeability and tortuosity on this sample. We will also present correlative experiment, performing first a microCT scan of a cathode foil sample on its aluminium collector, spotting sites of interest in it, and acquiring those volumes with FIB-SEM.