Electrode Contact Research Articles

Molecular dynamics simulation of cathode crater formation in the cathode spot of vacuum arcs

A three-dimensional model based on molecular dynamics has been developed to describe the formation of a single cathode spot in vacuum arcs. The formation of the cathode spot is assumed to be controlled by the plasma ions, the effect of which is simulated in LAMMPS through the process of ion bombardment. The cathode is represented by structured copper atoms, while the ions are continuously injected into the domain with a certain velocity towards the cathode surface. Ion bombardment leads to the appearance of a crater, which is caused by the accumulation of pressure effect against the relaxation of substrate temperature. The size of the crater is found to be determined by the spatial distribution of the injected ions. The formation of the cathode spot is also scrutinised by electron emission from the cathode surface with variable surface temperature during the cathode spot development process. In addition, the evaporated atoms forming the metal vapour are observed. This study provides a description of the formation of the cathode spot at microscale, which shall be helpful to further studies of the arc rooting and arc contact (electrode) erosion in vacuum environment.

Contact holes in vertical electrode structures analyzed by voltage contrast-SEM and conducting AFM

Soaring demands of multi-stacked memory devices request urgent development of backside contact electrode technologies, such as high aspect ratio etching, metallization, and inspection methods. Especially the complex metal contact process should be monitored for each manufacturing step to filter the defective samples and to maintain the high yield of production. Among the inspection methods for detecting the electrical connections, there is voltage contrast (VC)-SEM and conducting AFM (C-AFM). In this report, we investigated the two inspection methods for testing designed samples with different contact hole states. The VC-SEM data shows the contrast variation at the contact holes, from which one may discern the contact status with an optimum voltage. The C-AFM results clearly demonstrate a finite electrical current in the connected contact, while a negligible current in the disconnected one. Finally, we discuss insights of using the two methods for analyzing the contact hole technologies with high aspect ratios.

Altering Mechanical Properties to Improve Electrode Contacts by Organic Modification of Silica-Based Ionogel Electrolytes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are a possible candidate to create safe, sustainable, and cost-effective batteries. Solid sodium-ion conducting organically modified ionogel electrolytes are investigated. Silica-based ionogels typically consist of an ionic liquid electrolyte (ILE) confined within a silica matrix and possess high thermal stability, good ionic conductivity, safety, and good electrochemical stability. However, they readily deteriorate when stress is applied, decreasing the electrolyte's and battery's overall performance. The mechanical characteristics of silica can be improved using organic moieties, creating Ormosils®. Silica-based ionogels with phenyl-modified silanes improve the mechanical characteristics by a reduction of their Young's modulus (from 29 to 6 MPa). This is beneficial to the charge-transfer resistance, which decreases after implementing the electrolyte in half cells, demonstrating the improved interfacial contact. Most importantly, the phenyl groups change the interacting species at the silica interface. Cationic imidazolium species pi-stacked to the phenyl groups of the silica matrix, pushing the anions to the bulk of the ILE, which affects the ionic conductivity and electrochemical stability, and might affect the quality of the SEI in half cells. In essence, the work at hand can be used as a directory to improve mechanical characteristics and modify and control functional properties of ionogel electrolytes.

Safety profile of subdural and depth electrode implantations in invasive EEG exploration of drug-resistant focal epilepsy

PurposeTo analyze the safety profile of subdural and depth electrode implantation in a large monocentric cohort of patients of all ages undergoing intracranial EEG exploration because of drug resistant focal epilepsy diagnosed and implanted by a constant team of epileptologists and neurosurgeons. MethodsWe retrospectively analyzed data from 452 implantations in 420 patients undergoing invasive presurgical evaluation at the Freiburg Epilepsy Center from 1999 to 2019 (n = 160 subdural electrodes, n = 156 depth electrodes and n = 136 combination of both approaches). Complications were classified as hemorrhage with or without clinical manifestations, infection-associated and other complications. Furthermore, possible risk factors (age, duration of invasive monitoring, number of electrode contacts used) and changes in complication rates during the study period were analyzed. ResultsThe most frequent complications in both implantation groups were hemorrhages. Subdural electrode explorations caused significantly more symptomatic hemorrhages and required more operative interventions (SDE 9.9%, DE 0.3%, p < 0.05). Hemorrhage risk was higher for grids with 64 contacts than for smaller grids (p < 0.05). The infection rate was very low (0,2%). A transient neurological deficit occurred in 8.8% of all implantations and persisted for at least 3 months in 1.3%. Transient, but not persistent neurological deficits were more common in patients with implanted subdural electrodes than in the depth electrode group. ConclusionThe use of subdural electrodes was associated with a higher risk of hemorrhage and transient neurological symptoms. However persistent deficits were rare with either approach, demonstrating that intracranial investigations using either subdural electrodes or depth electrodes carry acceptable risks in patients with drug-resistant focal epilepsy.

Biophysical modeling of the electric field magnitude and distribution induced by electrical stimulation with intracerebral electrodes

Intracranial electrodes are used clinically for diagnostic or therapeutic purposes, notably in drug-refractory epilepsy (DRE) among others. Visualization and quantification of the energy delivered through such electrodes is key to understanding how the resulting electric fields modulate neuronal excitability, i.e. the ratio between excitation and inhibition. Quantifying the electric field induced by electrical stimulation in a patient-specific manner is challenging, because these electric fields depend on a number of factors: electrode trajectory with respect to folded brain anatomy, biophysical (electrical conductivity / permittivity) properties of brain tissue and stimulation parameters such as electrode contacts position and intensity. Here, we aimed to evaluate various biophysical models for characterizing the electric fields induced by electrical stimulation in DRE patients undergoing stereoelectroencephalography (SEEG) recordings in the context of pre-surgical evaluation. This stimulation was performed with multiple-contact intracranial electrodes used in routine clinical practice. We introduced realistic 3D models of electrode geometry and trajectory in the neocortex. For the electrodes, we compared point (0D) and line (1D) sources approximations. For brain tissue, we considered three configurations of increasing complexity: a 6-layer spherical model, a toy model with a sulcus representation, replicating results from previous approaches; and went beyond the state-of-the-art by using a realistic head model geometry. Electrode geometry influenced the electric field distribution at close distances (∼3 mm) from the electrode axis. For larger distances, the volume conductor geometry and electrical conductivity dominated electric field distribution. These results are the first step towards accurate and computationally tractable patient-specific models of electric fields induced by neuromodulation and neurostimulation procedures.

Solid oxide cell electrolytes deposited by atmospheric suspension plasma spraying at high velocity and high temperature

AbstractMetal‐supported solid oxide cells with Yttria‐stabilized zirconia (YSZ) electrolytes fabricated by atmospheric plasma spraying are routinely found to have open‐circuit voltages (OCVs) below the Nernst potential due to gas crossover and combustion resulting from electrolyte defects. To improve splat bonding and reduce coating defects, YSZ electrolytes were fabricated here at &gt;800°C substrate temperatures and torch‐substrate relative velocities of 4 and 12 m/s by atmospheric suspension plasma spraying. Electrolyte microstructures appeared dense, with porosities estimated to be approximately 2.2–3.5 vol%. Minimal segmentation cracking was observed on samples fabricated at 12 m/s. The full cells that were electrochemically tested had permeabilities in the range of 4–6 × 10−19 m2, and the maximum recorded OCV was ∼26 mV below the Nernst potential for 750°C. Potential performance gains from YSZ deposition at substrate temperatures &gt;800°C may have been masked by poor substrate‐fuel electrode contact. Using electrochemical impedance spectroscopy, it was found that the ohmic and polarization resistances decreased and increased, respectively, over time. The calculated distribution of relaxation times of the tested cells, together with observations from the literature, were employed to identify possible cell degradation mechanisms observed during short‐term durability testing.

ID: 221013 Optimizing Spinal Cord Stimulation Using a Novel Green's Function-Based Generalized Activating Function

Prior work has shown that patient-specific computational modeling and optimization of epidural electrical stimulation (EES) of the spine can be used to rapidly restore locomotion in paraplegics [1]. To this end, Rowald et al. describe a pipeline for generating detailed spine models from medical imaging data. For a given model, electromagnetic field distributions are calculated for the activation of each electrode contact and coupled to electrophysiological simulations of axon populations within each root and rootlet. Optimal exposure conditions for the safe and selective activation of target roots may thus be identified.

ID: 211552 Quantification of Lead Sensing Differences Along Rostral-Caudal Axis During Spinal Cord Stimulation

Electrical epidural spinal cord stimulation (EES) has been successfully implemented to relieve chronic pain. Variations in the effect of EES to suppress chronic pain can be attributed to multiple factors such as exact location of the electrode contacts, patient position, and others. Evoked responses triggered during EES, provides a way that may measure and quantify these variations. These evoked responses, including evoked compound action potential (ECAP) from neuronal fiber activation as a major component, still have an enormous number of questions related to the response registration needed to be addressed. This study is focused on evoked response registration related to the latency, amplitude in Area Under the Curve (AUC), and the effect of displacement of the stimulation and recording leads along rostral caudal axis.

Elastic, anisotropic, lattice dynamics and electronic properties of XNiM and XNi2M (X = Ti, Zr, Hf; M = Sn, Ge, Si): DFT comparison study

The ab-initio calculations were performed using density functional theory (DFT) as implemented in the Quantum ESPRESSO (QE) code. Lattice parameter mismatch was minimal (2.5 % - 3 %) in TiNiSn/TiNi2Sn, ZrNiSn/ZrNi2Sn, and HfNiSn/HfNi2Sn compounds. Half-Heusler compounds had shorter bond lengths and smaller bulk moduli than their full-Heusler counterparts. Directional dependencies of the Young’s and shear moduli were investigated using elastic constants. TiNiGe, HfNiSn, and ZrNiSn had a greater universal anisotropy index among the half-Heusler compounds. Half-Heusler, TiNi2Sn, TiNi2Si, ZrNi2Sn, and HfNi2Sn compounds are reported to be dynamically stable. The electronic structure computations show that TiNiSn, ZrNiSn, and HfNiSn compounds have the least indirect energy gaps of 0.4508 eV, 0.5019 eV, and 0.3847 eV respectively. TiNiSn, ZrNiSn, and HfNiSn compounds are good candidates for minimizing the thermal conductivity of thermoelectric devices. TiNi2Sn, ZrNi2Sn, and HfNi2Sn are good candidates as possible contact electrodes for TiNiSn, ZrNiSn, and HfNiSn.

Micromagnetic stimulation (µMS) dose-response of the rat sciatic nerve

Objective. The objective of this study was to investigate the effects of micromagnetic stimuli strength and frequency from the Magnetic Pen (MagPen) on the rat right sciatic nerve. The nerve’s response was measured by recording muscle activity and movement of the right hind limb. Approach. The MagPen was custom-built to be stably held over the sciatic nerve. Rat leg muscle twitches were captured on video, and movements were extracted using image processing algorithms. EMG recordings were also used to measure muscle activity. Main results. The MagPen prototype, when driven by an alternating current, generates a time-varying magnetic field, which, according to Faraday’s law of electromagnetic induction, induces an electric field for neuromodulation. The orientation-dependent spatial contour maps of the induced electric field from the MagPen prototype have been numerically simulated. Furthermore, in this in vivo work on µMS, a dose-response relationship has been reported by experimentally studying how varying the amplitude (Range: 25 mV p-p through 6 V p-p) and frequency (range: 100 Hz through 5 kHz) of the MagPen stimuli alters hind limb movement. The primary highlight of this dose-response relationship (repeated over n rats, where n = 7) is that for a µMS stimuli of higher frequency, significantly smaller amplitudes can trigger hind limb muscle twitch. This frequency-dependent activation can be justified by Faraday’s Law, which states that the magnitude of the induced electric field is directly proportional to the frequency. Significance. This work reports that µMS can successfully activate the sciatic nerve in a dose-dependent manner. The impact of this dose-response curve addresses the controversy in this research community about whether the stimulation from these μcoils arise from a thermal effect or micromagnetic stimulation. MagPen probes do not have a direct electrochemical interface with tissue and therefore do not experience electrode degradation, biofouling, and irreversible redox reactions like traditional direct contact electrodes. Magnetic fields from the μcoils create more precise activation than electrodes because they apply more focused and localized stimulation. Finally, unique features of µMS, such as the orientation dependence, directionality, and spatial specificity, have been discussed.

Schottky barrier height engineering on MoS2 field-effect transistors using a polymer surface modifier on a contact electrode

Two-dimensional (2D) materials are highly sought after for their superior semiconducting properties, making them promising candidates for next-generation electronic and optoelectronic devices. Transition-metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2), are promising alternative 2D materials. However, the devices based on these materials experience performance deterioration due to the formation of a Schottky barrier between metal contacts and semiconducting TMDCs. Here, we performed experiments to reduce the Schottky barrier height of MoS2 field-effect transistors (FETs) by lowering the work function (Фm = Evacuum − EF,metal) of the contact metal. We chose polyethylenimine (PEI), a polymer containing simple aliphatic amine groups (–NH2), as a surface modifier of the Au (ФAu = 5.10 eV) contact metal. PEI is a well-known surface modifier that lowers the work function of various conductors such as metals and conducting polymers. Such surface modifiers have thus far been utilized in organic-based devices, including organic light-emitting diodes, organic solar cells, and organic thin-film transistors. In this study, we used the simple PEI coating to tune the work function of the contact electrodes of MoS2 FETs. The proposed method is rapid, easy to implement under ambient conditions, and effectively reduces the Schottky barrier height. We expect this simple and effective method to be widely used in large-area electronics and optoelectronics due to its numerous advantages.

Investigating the Electromechanical Sensitivity of Carbon-Nanotube-Coated Microfibers.

The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30-60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5-30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors.

Self‐Driven Narrow‐Band Photodetector based on FAPbBr2.5I0.5 Single Crystal for Yellow Light Intensity Meter Application

AbstractAccurate and quantifiable detection of the specific wavelength is vital in different application scenarios. Herein, a novel self‐driven narrowband photodetector (NB‐PD) based on CH(NH2)2PbBr2.5I0.5 crystal film is employed for building a yellow light intensity meter. By taking advantage of the carrier collection narrowing mechanism, a sensitive NB‐PD with peak response at 580 nm and the full‐width at half‐maximum of 23 nm are successfully achieved. The asymmetric contact electrodes of Ag/Pt allow the device to work without bias. The optoelectronic analysis demonstrates that the NB‐PD achieves a maximum responsivity of 59.89 mA W−1, a fast response speed of 202/331 µs, and a high on/off ratio of 636 at zero bias. Then, through introducing the back‐end circuit, a yellow light intensity meter is constructed with the NB‐PD. The absolute error and relative error of the light meter are estimated to be lower than 0.08 mW cm−2 and 4.22%, respectively, indicating the good capability for the yellow light monitoring. Given the simple device geometry and good performance, the achieved yellow light intensity meter can also be extended to other narrowband light detection system.

In silico development and validation of Bayesian methods for optimizing deep brain stimulation to enhance cognitive control

Objective. deep brain stimulation (DBS) of the ventral internal capsule/striatum (VCVS) is a potentially effective treatment for several mental health disorders when conventional therapeutics fail. Its effectiveness, however, depends on correct programming to engage VCVS sub-circuits. VCVS programming is currently an iterative, time-consuming process, with weeks between setting changes and reliance on noisy, subjective self-reports. An objective measure of circuit engagement might allow individual settings to be tested in seconds to minutes, reducing the time to response and increasing patient and clinician confidence in the chosen settings. Here, we present an approach to measuring and optimizing that circuit engagement. Approach. we leverage prior results showing that effective VCVS DBS engages cognitive control circuitry and improves performance on the multi-source interference task, that this engagement depends primarily on which contact(s) are activated, and that circuit engagement can be tracked through a state space modeling framework. We develop a simulation framework based on those empirical results, then combine this framework with an adaptive optimizer to simulate a principled exploration of electrode contacts and identify the contacts that maximally improve cognitive control. We explore multiple optimization options (algorithms, number of inputs, speed of stimulation parameter changes) and compare them on problems of varying difficulty. Main results. we show that an upper confidence bound algorithm outperforms other optimizers, with roughly 80% probability of convergence to a global optimum when used in a majority-vote ensemble. Significance. we show that the optimization can converge even with lag between stimulation and effect, and that a complete optimization can be done in a clinically feasible timespan (a few hours). Further, the approach requires no specialized recording or imaging hardware, and thus could be a scalable path to expand the use of DBS in psychiatric and other non-motor applications.

Real-Time Intent Sensing for Assistive Devices with Implications for Minimising Maintenance

Intent sensing is a growing field within medical device control, with major potential applications for assistive devices, such as prosthetics. As many sensors as possible should be utilised to maximise accuracy. The availability of sensors may change over time due to changing surroundings or activities, sensors failing, and electrode contact being lost. The sensor network should be dynamic and modular in nature, continuing to function even when some sensors are unavailable. The management of sensor unavailability may help to reduce the need for device maintenance, particularly in developing nations with limited availability of these services. An algorithm is proposed to classify intent using networked sensors in real time. Data are gathered using human participants wearing four surface electromyography sensors and performing a pseudo-random sequence of grasps. The relationship between time offset and prediction accuracy is investigated, with the algorithm predicting future intent actions up to half a second in advance. Sensor dropout is simulated by randomly replacing sensor readings with recorded noise. The new algorithm is compared to existing algorithms and shown to be more accurate in situations of sensor dropout, with the difference increasing as more sensors become unavailable. This suggests that when reductions in sensing capabilities are likely to occur over time, the modular method is more appropriate for control.

Enhanced Interlayer Charge Injection Efficiency in 2D Multilayer ReS2 via Vertical Double-Side Contacts.

Two-dimensional (2D) van der Waals (vdW) layered materials have provided novel opportunities to explore interesting physical properties such as thickness-dependent bandgap, moiré excitons, superconductivity, and superfluidity. However, the presence of interlayer resistance along the thickness and Schottky barrier in metal-to-2D vdW semiconducting materials causes a limited interlayer charge injection efficiency, perturbing various intrinsic properties of 2D vdW multilayers. Herein, we report a simple but powerful contact electrode design to enhance interlayer carrier injection efficiency along the thickness by constructing vertical double-side contact (VDC) electrodes. A 2-fold extended contact area of VDC not only strongly limits an interlayer resistance contribution to the field-effect mobility and current density at the metal-to-2D semiconductor interface but also significantly suppresses both current transfer length (≤1 μm) and specific contact resistivity (≤1 mΩ·cm2), manifesting clear benefits of VDC in comparison with those in conventional top-contact and bottom-contact configurations. Our layout for contact electrode configuration may suggest an advanced electronic device platform for high-performing 2D optoelectronic devices.

Electrical performance of monolayer MoS2 transistor with MoS2 nanobelt metallic edges as electrodes

The contact electrodes have great influence on the performance of monolayer MoS2 devices. In this paper, monolayer MoS2 and MoS2 nanobelts were synthesized on SiO2/Si substrates via the chemical vapor deposition method. By using wet and dry transfer process, MoS2 nanobelt metallic edges were designed as the source/drain contact electrodes of monolayer MoS2 field effect transistor. The ‘nanobelt metallic edges’ refers to the top surface of the nanobelt being metallic. Because the base planes of MoS2 nanobelt vertically stand on the substrate, which makes the layer edges form the top surface of the nanobelt. The nonlinear I ds–V ds characteristics of the device indicates that the contact between the monolayer MoS2 and MoS2 metallic edges displays a Schottky-like behavior. The back-gated transfer characteristics indicate that monolayer MoS2 device with MoS2 nanobelt metallic edges as electrodes shows an n-type behavior with a mobility of ∼0.44 cm2 V−1·s−1, a carrier concentration of ∼7.31 × 1011 cm−2, and an on/off ratio of ∼103. The results enrich the electrode materials of two-dimensional material devices and exhibit potential for future application of MoS2 metallic edges in electronic devices.

Suitable contacting scheme for evaluating electrical properties of GaN-based p-type layers

A suitable contacting scheme for p-(Al)GaN facilitating quick feedback and accurate measurements is proposed in this study. 22 nm p+-GaN followed by 2 nm p-In0.2Ga0.8N was grown on p-type layers by metal-organic chemical vapor deposition. Samples were then cut into squares after annealing and contact electrodes using In balls were put at the corners of the squares. Good linearity between all the electrodes was confirmed in I–V curves during Hall measurements even with In metal. Serval samples taken from the same wafer showed small standard deviation of ~ 4% for resistivity, Hall mobility and hole concentration. The influence of contact layer on the electrical characteristics of bulk p-type layers was then investigated by step etching technique using inductively coupled plasma etching and subsequent Hall-effect measurements. Identical values could be obtained consistently when a 28 nm non-conductive layer thickness at the surface was taken into account. Therefore, the procedures for evaluating the electrical properties of GaN-based p-type layers just using In balls proposed in this study are shown to be quick and useful as for the other conventional III–V materials.

Self‐Folding Graphene‐Based Interface for Brain‐Like Modular 3D Tissue

AbstractElectrophysiology of 3D neuronal cultures is of rapidly growing importance for revealing cellular communications associated with neurodevelopment and neurological diseases in their brain‐like 3D environment. Despite that the brain also exhibits an inherent modular architecture that is essential for cortical processing, it remains challenging to interface a modular network consisting of multiple 3D neuronal tissues. Here, a self‐folding graphene‐based electrode array is proposed that enables to reconstruct modular 3D neuronal tissue and investigate firing dynamics among moduli. A graphene‐sandwiched parylene‐C film self‐folds into a cylindrical structure within which living cells can be encapsulated. Culture of encapsulated cells inside the folded graphene enables to spontaneously construct 3D cell aggregates and ensure firm contact between the graphene surface and encapsulated cells. As the inner graphene surface can be utilized as an electrode, the reliable cell–electrode contact allows for long‐term electrical recording from multiple 3D aggregates. Additionally, the modular network consisting of multiple 3D aggregates exhibits richer firing patterns than a conventional homogenous 2D network, which demonstrates that the approach enables measurements of firing dynamics in complex 3D neuronal networks. The deformable graphene electrode will be a powerful platform for investigating complex cellular communications in brain‐like 3D cultures.

Extraction and analysis of TCO coated glass from waste amorphous silicon thin film solar module

Considering the fast pace of the development of the Photovoltaic (PV) market and the installations in last two decades and also the increasing scarcity of resources for semiconductor materials, recycling waste PV modules including thin film is very important. Transparent conducting oxides (TCOs) are extensively used as front contact electrodes in thin-film photovoltaic devices. The paper presents, the new strategies developed to extract TCO coated glass from thin film amorphous silicon PV end-of-life modules. The recycling of thin film PV modules is based on a very simple approach that includes chemical, thermal and mechanical treatments. Optimised solutions of 1 M NaOH and 1 M KOH were used to extract TCO coated glass. The feasibility of the processing steps was demonstrated on laboratory scale size module and the etching rate for P, I, and N-layers of amorphous silicon is also studied. The extracted TCO was identified as fluorine-doped tin oxide (FTO) using X-ray diffraction and UV–visible spectroscopy techniques. The laser scribed FTO glass was successfully extracted without damaging the properties of the material. The extracted FTO has very low resistivity and sheet resistance in the range of 10−4 Ω-cm and 11.74 Ω/sq. respectively, has uniform transmission throughout the measured film surface of 2 cm2 in the visible region having bandgap ∼3.8eV. The recycling cost and current market value of the recycled FTO are also estimated for all the installed capacities of amorphous silicon. Considering the TCO properties, extracted FTO has the potential for its reuse in the fabrication of new thin film PV modules and other optoelectronic device applications as well.