Non-planar Electrode Research Articles

Point-of-care diagnostic devices for periodontitis - current trends and urgent need.

Point of care (POC) diagnostic devices provide a method for rapid accurate identification of disease through analysis of biologically relevant substances. This review focuses on the utility of POC testing for early detection of periodontitis, a critical factor in treating the disease. Accessing the oral cavity for biological sampling is less invasive when compared to other internal test sites, and oral fluids contain biomarkers indicative of periodontitis. The ease of access makes the mouth an excellent target location for the development of POC devices. In this review, accepted standards in industry by which these devices must adhere, provided by the World Health Organization such as REASSURED and CLIA, are discussed. An overview is provided for many periodontal biomarkers currently being investigated as a means of predicting periodontal disease and its progression. POC devices currently being investigated for the identification and monitoring of periodontal disease such as paper-based and lab-on-a-chip based devices are outlined. Limitations of current POC devices on the market are provided and future directions in leveraging biomarkers as an adjunctive method for oral diagnosis along with AI-based analysis systems are discussed. Here, we present the ESSENCE sensor platform, which combines a porous non-planar electrode with enhanced shear flow to achieve unprecedented sensitivity and selectivity. The combination of the ESENCE chip with an automated platform allows us to meet the WHO's ASSURED criteria. This platform promises to be an exciting POC candidate for early detection of periodontitis.

A Method of Chemical-Mechanical Polishing of a Thick Silver Layer on Patterned Silicon Wafer

Microfluidics-based biochips for biochemical analysis are receiving much attention nowadays. These composite microsystems, also known as lab-on-a-chip or bio-MEMS, offer a number of advantages over conventional laboratory procedures. They automate highly repetitive laboratory tasks by replacing cumbersome equipment with miniaturized and integrated systems, and they enable the handling of small amounts, e.g., micro- and nano-liters, of fluids. Thus they are able to provide ultra-sensitive detection at significantly lower costs per assay than traditional methods, and in a significantly smaller amount of laboratory space. Advances in microfluidics technology offer exciting possibilities in the realm of enzymatic analysis (e.g., glucose and lactate assays), DNA analysis (e.g., PCR and nucleic acid sequence analysis), proteomic analysis involving proteins and peptides, immuno-assays, and toxicity monitoring.Biochips can be used to detect molecules and/or sequence nucleic acid molecules with aid of an array of electrochemical detector cells containing one or more electrodes per cell where each cell being electrically isolated at a wafer level. For many applications it is beneficial to form a non-planar working electrode using a metal which will corrode during CMP steps.We’ve developed a novel Ag and Cu integration process which a) solves problems of metal corrosion over 3D topography during CMP step and b) prevents metal surface contamination with CMP residual slurry and polishing byproducts not usually removable by brush or megasonic cleaning.Electrochemical studies show corrosion behavior of thick Ag layers in different CMP slurries used in this process. SEM images of cross-sectioned metal lined electrochemical cells (vias) clearly demonstrate advantages of new process (right) without traces of corrosion vs conventional CMP process (left).This process can be used also for polishing of other metals and dielectrics over topography where aggressive cleaning post-CMP steps are not desirable. Figure 1

ESSENCE – A rapid, shear-enhanced, flow-through, capacitive electrochemical platform for rapid detection of biomolecules

The rapid, sensitive, and selective detection of target analytes using electrochemical sensors is challenging. ESSENCE, a new Electrochemical Sensor that uses a Shear-Enhanced, flow-through Nanoporous Capacitive Electrode, overcomes current electrochemical sensors' response limitations, selectivity, and sensitivity limitations. ESSENCE is a microfluidic channel packed with transducer material sandwiched by a top and bottom microelectrode. The room-temperature instrument less integration process allows the switch of the transducer materials to make up the porous electrode without modifying the electrode architecture or device protocol. ESSENCE can be used to detect both biomolecules and small molecules by simply changing the packed transducer material. Electron microscopy results confirm the high porosity. In conjunction with the non-planar interdigitated electrode, the packed transducer material results in a flow-through porous electrode. Electron microscopy results confirm the high porosity. The enhanced shear forces and increased convective fluxes disrupt the electric double layer's (EDL) diffusive process in ESSENCE. This disruption migrates the EDL to high MHz frequency allowing the capture signal to be measured at around 100 kHz, significantly improving device timing (rapid detection) with a low signal-to-noise ratio. The device's unique architecture allows us multiple configuration modes for measuring the impedance signal. This allows us to use highly conductive materials like carbon nanotubes. We show that by combining single-walled carbon nanotubes as transducer material with appropriate capture probes, NP-μIDE has high selectivity and sensitivity for DNA (fM sensitivity, selective against non-target DNA), breast cancer biomarker proteins (p53, pg/L sensitivity, selective against non-target HER2).

Act in contravention: a non-planar coupled electrode design utilizing “tip effect” for ultra-high areal capacity, long cycle life zinc-based batteries

Aqueous zinc-based batteries (ZBBs) have great potential as commercial energy storage devices. However, the poor cycling stability of zinc anode under high areal capacity limits their further application. Herein, a coupled non-planar electrode design achieved by the tailored flat-top pyramid carbon felt (TCF) is proposed for ZBBs, which can effectively increase the zinc deposition sites, adjust the deposition morphology, optimize the current and electrolyte flow velocity distribution and provide necessary space for zinc plating. Interestingly, by utilizing “tip effect”, the coupled TCFs enable precise control of the zinc dendrite growth position, effectively reducing the risk of short circuit. Based on such coupled TCFs, zinc-iodine flow batteries can deliver an ultra-high areal capacity of 240 mAh cm−2 and a superb cycling stability over 300 cycles (areal capacity of 160 mAh cm−2) at a high current density of 40 mA cm−2. Therefore, we provide an effective strategy for high areal capacity zinc anode design, which may promote the development of high energy density and long cycle life ZBBs.

Mesoscale Electrochemical-Mechanical Analyses of Solid-State Non-Planar Conversion Cathodes

In the quest for high performing battery technologies, conversion cathode materials often stand out for producing high energy densities. Combined with non-planar electrode geometries, such as 3D/2.5D battery architectures, conversion cathodes can achieve both high power and energy densities. However, electrochemical conversion processes are often mechanically abusive at the mesoscale, with significant changes in particle volumes leading to high stresses within the electrode. While previous studies have investigated mesoscale stress impacts for a variety of planar cathode materials, the added complication of non-planar electrode geometries complicates our previous understanding, particularly when the geometric features are on the same size as a mesoscale representative volume element.In this paper, we demonstrate a coupled electrochemical-mechanical model of a 2.5D pillar conversion cathode system. The mesoscale geometry is generated using discrete element models. The electrochemical model consists of species and electrical transport coupled by Butler-Volmer interfacial reaction kinetics. A moving mesh technique is implemented to track the conversion reaction front and separate reacted from unreacted materials. The impact of the electrochemical reaction leads to the generation of mechanical stresses within the electrode structure. We demonstrate how the mechanical response differs between planar and non-planar electrode geometries and explore the role of the geometric feature sizes on stress localization.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Effects of non‐planar interface and electrode parameters on the residual stress of solid oxide fuel cell

The thermomechanical response of solid oxide fuel cell will endanger its structural reliability. In this study, the effects of non-planar interface and electrode parameters are investigated by building a cosine anode-electrolyte interface with amplitude A and wavelength λ. Results show that the planar interface model cannot completely reflect the stress state of solid oxide fuel cells. Non-planar interface can stimulate high normal stress Sn and shear stress St at the interface, but these stresses are zero at the planar interface. Cosine interface causes approximately cosinoidal Sn and sinusoidal St. The bigger the ratio of amplitude to wavelength A/λ is, the more serious the Sn fluctuates. Electrode parameter analysis shows that increasing initial porosity of oxidized anode can reduce the maximum Sn but increases the maximum St and the cell deflection. Parameter study show that initial porosity between 0.15 and 0.25 is suitable. The effect of anode thickness on the maximum Sn and St is weak, while the electrolyte thickness has a relatively strong effect when the electrolyte thickness is less than 12 μm. A NiO volume fraction between 0.52 to 0.58 is recommended to avoid overlarge Sn, St, and deflection.

On the Reversibility and Fragility of Sodium Metal Electrodes

AbstractMetallic sodium is receiving renewed interest as a battery anode material because the metal is earth‐abundant, inexpensive, and offers a high specific storage capacity (1166 mAh g−1 at −2.71 V vs the standard hydrogen potential). Unlike metallic lithium, the case for Na as the anode in rechargeable batteries has already been demonstrated on a commercial scale in high‐temperature Na||S and Na||NiCl2 secondary batteries, which increases interest. The reversibility of room temperature sodium anodes is investigated in galvanostatic plating/stripping reactions using in situ optical visualization and galvanostatic polarization measurements. It is discovered that electronic disconnection of mossy metallic Na deposits (“orphaning”) is a dominant source of anode irreversibility in liquid electrolytes. The disconnection is shown by means of direct visualization studies to be triggered by a root‐breakage process during the stripping cycle. As a further step toward electrode designs that are able to accommodate the fragile Na deposits, electrodeposition of Na is demonstrated in nonplanar electrode architectures, which provide continuous and morphology agnostic access to the metal at all stages of electrochemical cycling. On this basis, nonplanar Na electrodes are reported, which exhibit exceptionally high levels of reversibility (Coulombic efficiency >99.6% for 1 mAh cm−2 Na throughput) in room‐temperature, liquid electrolytes.

Physical Orphaning versus Chemical Instability: Is Dendritic Electrodeposition of Li Fatal?

The dendritic electrodeposition of lithium, leading to physical orphaning and chemical instability, is considered responsible for the poor reversibility and premature failure of electrochemical cells that utilize Li metal anodes. Herein we critically assess the roles of physical orphaning and chemical instability of electrodeposited Li on electrode reversibility using planar and nonplanar electrode architectures. The nonplanar electrodes allow the morphology of electrodeposited Li to be interrogated in detail and in the absence of complications associated with cell stacking pressure. We find that physical orphaning is a key determinant of the poor reversibility of Li. We report further that fiber-like, dendritic electrodeposition is an intrinsic characteristic of Li, irrespective of the electrolyte solvent chemistry. With guaranteed electronic access to prevent physical loss, we finally show that a Li metal electrode exhibits high levels of reversibility (99.4% CE), even when the metal electrodeposits are in obvious, dendritic morphologies. We take advantage of these findings to create high-loading (7−8 mAh/cm2) Li||LFP full cells with a nearly unity N:P ratio and demonstrate that these cells exhibit good reversibility.

Nonplanar Electrode Architectures for Ultrahigh Areal Capacity Batteries

We report on the design of a battery electrode architecture in which ion and electronic transport pathways are contiguous and span the entire volume of a thick, nonplanar electrode. It is shown tha...

Transfer Printing of Sub-5 μm Graphene Electrodes for Flexible Microsupercapacitors.

Printed graphene microsupercapacitors (MSCs) are attractive for scalable and low-cost on-chip energy storage for distributed electronic devices. Although electronic devices have experienced significant scaling to smaller formats, the corresponding miniaturization of energy storage components has been limited, with a typical resolution of ∼30 μm for printed graphene patterns to date. Transfer printing is demonstrated here for patterning graphene electrodes with fine line and spacing resolution less than 5 μm. The resulting devices exhibit an exceptionally small footprint (∼0.0067 mm2), which provides, to the best of our knowledge, the smallest printed graphene MSCs. Despite this, the devices retain excellent performance with a high areal capacitance of ∼6.63 mF/cm2 along with excellent electrochemical stability and mechanical flexibility, resulting from an efficient nonplanar electrode structure and an optimized two-step photoannealing method. As a result, this miniaturization strategy facilitates the on-chip integration of printed graphene MSCs to power emerging electronic devices.

Ultra-fast AC electro-osmotic micropump with arrays of asymmetric ring electrode pairs in 3D cylindrical microchannel

AC electro-osmotic (ACEO) micropumps presently involve the planar or nonplanar electrode pair array in the rectangular microchannel. However, this paper presented a theoretical model of an ultra-fast 3D ring ACEO micropump with arrays of asymmetric ring electrode pairs in the cylindrical microchannel. The theory is on the basis of the interaction between the nonuniform electric field and ions of an electric double layer (EDL) on the surface of ring electrodes. Therefore, we first established the equivalent hollow cylinder capacitance of EDL for ring ACEO micropumps. Then, the 3D Poisson-Boltzmann model by solving the electric field and fluidic flow field with the charge conservation and the slip velocity boundary conditions was numerically calculated. For a dilute strong electrolyte solution, the conductivity as a function of the electrolyte concentration can be obtained by the modified Kohlrausch's dilution empirical equation with the molar conductivity. The results revealed that the flow rate of ring ACEO was higher than the planar ACEO, which agreed well with the experiment. The dependences of the time-averaged pumping velocity on the frequency and concentration have similar bell profiles with a maximal value. Moreover, the optimal velocity with proper geometric parameters was obtained at a given frequency, voltage, concentration, and radius. The high-speed ring ACEO micropump will be significant for the experimental studies to further improve the flow rate and be hopeful for applications of microfluidic mixing, particle manipulation, and so on.

Defining the light emitting area for displays in the unipolar regime of highly efficient light emitting transistors.

Light-emitting field effect transistors (LEFETs) are an emerging class of multifunctional optoelectronic devices. It combines the light emitting function of an OLED with the switching function of a transistor in a single device architecture. The dual functionality of LEFETs has the potential applications in active matrix displays. However, the key problem of existing LEFETs thus far has been their low EQEs at high brightness, poor ON/OFF and poorly defined light emitting area - a thin emissive zone at the edge of the electrodes. Here we report heterostructure LEFETs based on solution processed unipolar charge transport and an emissive polymer that have an EQE of up to 1% at a brightness of 1350 cd/m2, ON/OFF ratio > 104 and a well-defined light emitting zone suitable for display pixel design. We show that a non-planar hole-injecting electrode combined with a semi-transparent electron-injecting electrode enables to achieve high EQE at high brightness and high ON/OFF ratio. Furthermore, we demonstrate that heterostructure LEFETs have a better frequency response (fcut-off = 2.6 kHz) compared to single layer LEFETs. The results presented here therefore are a major step along the pathway towards the realization of LEFETs for display applications.

Conformal growth of anodic nanotubes for dye-sensitized solar cells: part II. Nonplanar electrode.

Anodic titania nanotube array features highly ordered alignment as well as porous nature, and exhibits intriguing properties when employed in a variety of applications. All these profit from the continuous efforts on controlling the nanotube configurations. Recently, nonplanar electrodes have also been used to grow the nanotubes besides the conventional planar counterparts. As such, it is of great interest and significance to complete a picture to link the nanotubes grown on planar and various nonplanar electrodes for a comprehensive understanding of nanotube growing manners, in an attempt to boost their future applications. In the first part of this review, planar electrodes are focused with regard to nanotube growth and application in dye-sensitized solar cells. In this part, the nanotubes grown on patterned or curved surfaces are discussed first with reference to a similar structure of alumina nanopores, which are subsequently used to mirror the growth of nanotubes on cylindrical electrodes (i.e., titanium wires or meshes). The last section focuses on titanium tubular electrodes which are attractive for thermal fluids in view of the drastically reduced thermal conductivity in the presence of anodic nanotubes. As a recent hot topic, wire-shaped dye-sensitized solar cells are deliberated in terms of cell structure, efficiency calculation, merits, challenges and outlook.

Effect of structured electrodes on heating and plasma uniformity in capacitive discharges

The effect of various structured (non-planar) electrode topologies, e.g. rectangular, rounded and triangular trenches, on the electron heating dynamics and ion density profile in capacitively coupled radio frequency plasmas is investigated experimentally and by an analytical model. The measurements are carried out in neon. 2D Phase resolved optical emission spectroscopy is utilized to study the dynamics of energetic electrons inside and outside these structures at the kinetic level. In the presence of structured electrodes, non-planar RF sheaths form and affect the electron heating dynamics. We observe a local agglomeration of energetic electrons above the structures. These electrons originate from sheath expansion heating. Inside the structures, opposite vertical sheaths cause a temporal confinement of electrons. Non-planar sheaths at the trench orifice cause convergent fluxes of energetic electrons. Also, the ionization and, as a consequence, the plasma density are modified by these effects. This is characterized by radially resolved Langmuir probe measurements and described by a diffusion model with localized sources. Subsequently, the control of the radial plasma density profile is demonstrated. Via customized electrode topologies, high plasma uniformity at specific pressures and heights above the electrode is achieved with the additional benefit of strong enhancement of the plasma density.

Electrodeposition of Pt Nanoparticle Catalysts from H2Pt(OH)6 and Their Application in PEM Fuel Cells

We report the electrochemical deposition of Pt nanoparticles from platinic acid H2[Pt(OH)6] using pulse potential deposition (PPD). We are able to control the size, morphology, and loading of platinum nanoparticles from H2[Pt(OH)6] by controlling the deposition parameters such as the pH of the plating solution, the pulse potential, the pulse width, and the duty cycle of the pulse sequence. We show that a high density of Pt nanoparticles electrodeposited can be produced on both planar and nonplanar electrode supports with high surface area and high catalytic activity. Finally, we show that fuel cell electrodes can be produced using H2[Pt(OH)6] as the source of Pt via our optimized PPD technique. The fuel cells produced from these electrodes are highly efficient with less than half the Pt content of commercially available fuel cells, which results in a gravimetric power more than twice that of fuel cells produced by using commercially available electrodes.

Simultaneous Enhancement of Brightness, Efficiency, and Switching in RGB Organic Light Emitting Transistors

An innovative design strategy for light emitting field effect transistors (LEFETs) to harvest higher luminance and switching is presented. The strategy uses a non-planar electrode geometry in tri-layer LEFETs for simultaneous enhancement of the key parameters of quantum efficiency, brightness, switching, and mobility across the RGB color gamut.

Induced-charge electrokinetic phenomena

Abstract The field of nonlinear “induced-charge” electrokinetics is rapidly advancing, motivated by potential applications in microfluidics as well as by the unique opportunities it provides for probing fundamental scientific issues in electrokinetics. Over the past few years, several surprising theoretical predictions have been observed in experiments: (i) induced-charge electrophoresis of half-metallic Janus particles, perpendicular to a uniform AC field; (ii) microfluidic mixing around metallic structures by induced-charge electro-osmosis, and (iii) fast, high-pressure AC electro-osmotic pumping by non-planar electrode arrays, and ICEK effects upon the collective behavior of polarizable particle suspensions has been studied theoretically and computationally. A new experimental system enables a clean and direct comparison between theoretical predictions and measured ICEK flows, providing a route to fundamental studies of particular surfaces and high-throughput searches for optimal ICEK systems. Systematic discrepancies between theory and experiment have engendered the search for mechanisms, including new theories that account for electrochemical surface reactions, surface contamination, roughness, and the crowding of ions at high voltage. Promising directions for further research, both fundamental and applied, are discussed.

MPSA effects on copper electrodeposition investigated by molecular dynamics simulations

In superconformal filling of copper-chip interconnects, organic additives are used to fill high-aspect-ratio trenches or vias from the bottom up. In this study we report on the development of intermolecular potentials and use molecular dynamics simulations to provide insight into the molecular function of an organic additive (3-mercaptopropanesulfonic acid or MPSA) important in superconformal electrodeposition. We also investigate how the presence of sodium chloride affects the surface adsorption and surface action of MPSA as well as the charge distribution in the system. We find that NaCl addition decreases the adsorption strength of MPSA at a simulated copper surface and attenuates the copper-ion association with MPSA. The model also was used to simulate induced-charge effects and adsorption on a nonplanar electrode surface.

Geometric effects on surface roughness in electrodeposition

Our aim is to understand the early stages of roughness growth in electrodeposition. We present a study of the branching of steady planar electrode surfaces to steady non-planar electrode surfaces as the voltage imposed at a cathode is decreased through its critical value. We aim to discover the type of branching and to learn whether or not the new branches can be detected by measuring the current. The cross-sectional shape of the electrode makes a difference. Circular electrodes lead to transcritical branching; ordinarily, rectangular electrodes lead to a pitchfork, sometimes forward and sometimes backward.

Fabrication and Characterization of an Active Matrix Thin Film Transistor Array for Intracellular Probing

AbstractIn order to achieve multiple intracellular stimulation and recording devices with high electrode density and low manufacturing cost, we have fabricated and characterized an active matrix thin film transistor array with integrated vertically aligned carbon nanofibers. This device has the potential for cell probing and screening that provides great potential to execute direct cell sensing/probing and recording with a high electrode density. Each unit pixel in the array is individually addressed by a thin film transistor (TFT) and the vertically aligned carbon nanofibers (VACNF) used to impale the cell are fabricated on the drain electrode of the TFT. The VACNF is grown by direct current plasma enhanced chemical vapor deposition (DCPECVD) using a nickel catalyst. Electroanalysis or impedance differences between the cell probing site and a reference electrode are recorded with a potentiostat or a semiconductor analyzer connected to the output terminals. Additionally, the impedance change with frequency of the intracellular probe can be measured by applying a frame signal input and the signal can be recorded in storage capacitors after the frame scan of the TFTs. Consequently, actively addressed nanofiber arrays enable bidirectional interfacing with tissue matrices in a format that provides intercellular positioning of electrode elements as well as the potential for intracellular residence of probes within individual cells. In our research, we exploit these non-planar electrode systems for efficient coupling with excitable cell matrices as well as for intracellular biochemical manipulation and sensing of and delivery to single cells. In this paper, we will discuss the fabrication sequence of the inverted metal-oxide-semiconductor (MOS) TFT, and will elaborate the materials issues related to integrating the carbon nanofibers with the TFT.