Local Conductivity Measurements Research Articles

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li7La3Zr2O12 garnets

The attractiveness of Li7La3Zr2O12 (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10−4 S cm−1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10−4 S cm−1 and a minimum of 2.6 × 10−4 S cm−1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.

Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry.

Electric energy storage devices such as batteries are complex systems comprised of a variety of materials with each playing separate yet interactive roles, complicated by length scale interactions occurring from the molecular to the mesoscale. Thus, addressing specific battery issues such as functional capacity requires a comprehensive perspective initiating with atomic level concepts. For example, the electroactive materials which contribute to the functional capacity in a battery comprise approximately 30% or less of the total device mass. Thus, the design and implementation of multifunctional materials can conceptually reduce or eliminate the contribution of passive materials to the size and mass of the final system. Material multifunctionality can be achieved through appropriate material design on the atomic level resulting in bimetallic electroactive materials where one metal cation forms mesoscale conductive networks upon discharge while the other metal cations can contribute to atomic level structure and net functional secondary capacity, a device level issue. Specifically, this Account provides insight into the multimechanism electrochemical redox processes of bimetallic cathode materials based on transition metal oxides (MM'O) or phosphorus oxides (MM'PO) where M = Ag and M' = V or Fe. One discharge process can be described as reduction-displacement where Ag(+) is reduced to Ag(0) and displaced from the parent structure. This reduction-displacement reaction in silver-containing bimetallic electrodes allows for the in situ formation of a conductive network, enhancing the electrochemical performance of the electrode and reducing or eliminating the need for conductive additives. A second discharge process occurs through the reduction of the second transition metal, V or Fe, where the oxidation state of the metal center is reduced and lithium cations are inserted into the structure. As both metal centers contribute to the functional capacity, determining the kinetically and thermodynamically preferred reduction processes at various states of discharge is critical to elucidating the mechanism. Specific advanced in situ and ex situ characterization techniques are conducive to gaining insight regarding the electrochemical behavior of these multifunctional materials over multiple length scales. At the material level, optical microscopy, scanning electron microscopy, and local conductivity measurement via a nanoprobe can track the discharge mechanism of an isolated single particle. At the mesoscale electrode level, in situ data from synchrotron based energy dispersive X-ray diffraction (EDXRD) within fully intact steel batteries can be used to spatially map the distribution of silver metal generated through reduction displacement as a function of discharge depth and discharge rate. As illustrated here, appropriate design of materials with multiple electrochemically active metal centers and properties tuned through strategically conceptualized materials synthesis may provide a path toward the next generation of high energy content electroactive materials and systems. Full understanding of the multiple electrochemical mechanisms can be achieved only by utilizing advanced characterization tools over multiple length scales.

Ferromagnetism and Conductivity in Hydrogen Irradiated Co-Doped ZnO Thin Films.

Impressive changes in the transport and ferromagnetic properties of Co-doped ZnO thin films have been obtained by postgrowth hydrogen irradiation at temperatures of 400 °C. Hydrogen incorporation increases the saturation magnetization by one order of magnitude (up to ∼1.50 μB/Co) and increases the carrier density and mobility by about a factor of two. In addition to the magnetic characterization, the transport and structural properties of hydrogenated ZnO:Co have been investigated by Hall effect, local probe conductivity measurements, micro-Raman, and X-ray absorption spectroscopy. Particular care has been given to the detection of Co oxides and metal Co nanophases, whose influence on the increase in the transport and ferromagnetic properties can be excluded on the ground of the achieved results. The enhancement in ferromagnetism is directly related to the dose of H introduced in the samples. On the contrary, despite the shallow donor character of H atoms, the increase in carrier density n is not related to the H dose. These apparently contradictory effects of H are fully accounted for by a mechanism based on a theoretical model involving Co-VO (Co-O vacancy) pairs.

マイクロ波原子間力顕微鏡を用いた局所導電率測定に及ぼす試料表面形状の影響

マイクロ波原子間力顕微鏡を用いた局所導電率測定に及ぼす試料表面形状の影響

接点温度法による局所熱伝導率計測の適用条件

The purpose of this study is a development of the local thermal conductivity measurement method by contact temperature method. In this paper, the applicable conditions of this method were examined. First, by the numerical simulation of heat conduction and the measurement test for non-conductive materials coated with gold film, it was found that the proposed method with the platinum wire probe is useful for thermal conductivity of 1 to 100 W/mK. Spatial resolution of this system was also examined. It was noted the resolution for low conductivity sample is approximately 100 μm.

Local measurement of thermal conductivity and diffusivity.

Simultaneous measurement of local thermal diffusivity and conductivity is demonstrated on a range of ceramic samples. This was accomplished by measuring the temperature field spatial profile of samples excited by an amplitude modulated continuous wave laser beam. A thin gold film is applied to the samples to ensure strong optical absorption and to establish a second boundary condition that introduces an expression containing the substrate thermal conductivity. The diffusivity and conductivity are obtained by comparing the measured phase profile of the temperature field to a continuum based model. A sensitivity analysis is used to identify the optimal film thickness for extracting the both substrate conductivity and diffusivity. Proof of principle studies were conducted on a range of samples having thermal properties that are representatives of current and advanced accident tolerant nuclear fuels. It is shown that by including the Kapitza resistance as an additional fitting parameter, the measured conductivity and diffusivity of all the samples considered agreed closely with the literature values. A distinguishing feature of this technique is that it does not require a priori knowledge of the optical spot size which greatly increases measurement reliability and reproducibility.

The role of probe oxide in local surface conductivity measurements

Local probe methods can be used to measure nanoscale surface conductivity, but some techniques including nanoscale four point probe rely on at least two of the probes forming the same low resistivity non-rectifying contact to the sample. Here, the role of probe shank oxide has been examined by carrying out contact and non-contact I V measurements on GaAs when the probe oxide has been controllably reduced, both experimentally and in simulation. In contact, the barrier height is pinned but the barrier shape changes with probe shank oxide dimensions. In non-contact measurements, the oxide modifies the electrostatic interaction inducing a quantum dot that alters the tunneling behavior. For both, the contact resistance change is dependent on polarity, which violates the assumption required for four point probe to remove probe contact resistance from the measured conductivity. This has implications for all nanoscale surface probe measurements and macroscopic four point probe, both in air and vacuum, where the role of probe oxide contamination is not well understood.

ICONE23-2021 INTERGRANULAR OXIDATION WITHIN CREVICE OF AUSTENITIC STAINLESS STEEL IN HIGH TEMPERATURE WATER

Intergranular oxidation (corrosion) occurred within crevice of austenitic low-carbon stainless steel (solution treated, almost no applied stress) after immersion in hightemperature water (288°C, 8.5MPa, dissolved oxygen conc. 32ppm, electrical conductivity: 1.2±0.2 μS・cm^<-1> (measured value at 25℃)) for 500h. The intergranular oxidation occurred at specific position within the crevice that is relatively distant from the crevice mouth with relatively low crevice gap. Both the grain boundary and grain matrix were oxidized. In the oxidized area, Fe and Ni were depleted and Cr was enriched compared to the matrix. Maximum penetration depth of the oxidation was approximately 50μm after 500h. In order to understand potential-pH condition within the crevice, surface oxide layer was microscopically and thermodynamically investigated. Thermodynamic properties of the surface oxides near the intergranular oxidized area indicated lowered pH of approximately 3.2 to 3.4. In-situ measurement of local solution electrical conductivity was carried out using small electrodes (dia. 800μm) imbedded into the crevice former plate. The solution pH was estimated using theoretically calculated pH vs. electrical conductivity relationship. In the area where the intergranular oxidation occurred, the solution electrical conductivity was nearly 100 times higher than that of bulk water and which indicated lowered pH of approximately 3.5. The above results suggested that, in the high temperature and relatively high purity water, acidification occurs within crevice of stainless steels and such aggressive corrosion condition result in the intergranular oxidation.

Screening effects in ferroelectric resistive switching of BiFeO3 thin films

We investigate ferroelectric resistive switching in BiFeO3 thin films by performing local conductivity measurements. By comparing conduction characteristics at artificially up-polarized domains with those at as-grown down-polarized domains, the change in resistance is attributed to the modification of the electronic barrier height at the interface with the electrodes, upon the reversal of the electrical polarization. We also study the effect of oxygen vacancies on the observed conduction and we propose the existence of a different screening mechanism for up and down polarized domains.

Enhancing Raman signals with an interferometrically controlled AFM tip

We demonstrate the upgrade of a commercial confocal Raman microscope into a tip-enhanced Raman microscope/spectroscopy system (TERS) by integrating an interferometrically controlled atomic force microscope into the base of an existing upright microscope to provide near-field detection and thus signal enhancement. The feasibility of the system is demonstrated by measuring the Raman near-field enhancement on thin PEDOT:PSS films and on carbon nanotubes within a device geometry. An enhancement factor of 2–3 and of 5–6 is observed, respectively. Moreover, on a nanotube device we show local conductivity measurement and its correlation to Raman and topography recordings. Upgrading an existing upright confocal Raman microscope in the demonstrated way is significantly cheaper than purchasing a complete commercial TERS system.

PTFE Distribution in High-Temperature PEM Electrodes and Its Effect on the Cell Performance

A conventional high-temperature polymer electrolyte membrane (HT-PEM) fuel cell electrode primarily consists of carbon-supported platinum catalyst and nonconductive binder PTFE. Morphology and topography of the electrodes were determined with scanning electron microscopy (SEM), and local surface conductivity measurements of the electrode surfaces were done with atomic force microscopy (AFM). Particle size distribution on the electrode surface was investigated and single PTFE particles in the catalyst layer were resolved. A great influence of the PTFE content in the electrodes on the performance of membrane electrode assemblies (MEA) was observed in single cell experiments. Reducing the PTFE content resulted in a decrease of the internal resistance of the MEA and improvement of the phosphoric acid uptake and its distribution in the cell. Both properties helped enhance the fuel cell performance.

Electrical conductivity of SrBi2Ta2O9 ceramics

Abstract Aurivillius SrBi 2 Ta 2 O 9 (SBT) ceramics were prepared by applying the conventional solid state reaction method. The grain structure and stoichiometry were investigated with the use of a scanning electron microscope with an energy dispersion X-ray spectrometer (EDS). The X-ray diffraction studies revealed an orthorhombic structure with lattice parameters a =5.486 A, b =5.497 A and c =24.91 A in the SBT. Dielectric properties were determined by impedance spectroscopy measurements. It was found that a strong low-frequency dielectric dispersion was present in this material. Its occurrence was ascribed to the presence of ionized space charge carriers such as oxygen vacancies. Dielectric relaxation was defined on the basis of an equivalent circuit. The temperature dependence of various electrical properties is described and discussed. The thermal activation energy for the grain electric conductivity was lower in the high temperature region ( T >328.5 °C, E a−ht =0.23 eV) and higher in the low-temperature region ( T E a−lt =0.78 eV). Moreover local conductivity measurements were performed with the use of the local conductive atomic force microscope method.

Elevated temperature, nano-mechanical testing in situ in the scanning electron microscope

A general nano-mechanical test platform capable of performing variable temperature and variable strain rate testing in situ in the scanning electron microscope is described. A variety of test geometries are possible in combination with focused ion beam machining or other fabrication techniques: indentation, micro-compression, cantilever bending, and scratch testing. The system is intrinsically displacement-controlled, which allows it to function directly as a micro-scale thermomechanical test frame. Stable, elevated temperature indentation∕micro-compression requires the indenter tip and the sample to be in thermal equilibrium to prevent thermal displacement drift due to thermal expansion. This is achieved through independent heating and temperature monitoring of both the indenter tip and sample. Furthermore, the apex temperature of the indenter tip is calibrated, which allows it to act as a referenced surface temperature probe during contact. A full description of the system is provided, and the effects of indenter geometry and of radiation on imaging conditions are discussed. The stabilization time and temperature distribution throughout the system as a function of temperature is characterized. The advantages of temperature monitoring and thermal calibration of the indenter tip are illustrated, which include the possibility of local thermal conductivity measurement. Finally, validation results using nanoindentation on fused silica and micro-compression of [100] silicon micro-pillars as a function of temperature up to 500 °C are presented, and procedures and considerations taken for these measurements are discussed. A brittle to ductile transition from fracture to splitting then plastic deformation is directly observed in the SEM for silicon as a function of temperature.

Reduction in Radiation (Fluoroscopy) While Maintaining Safe Placement of Pedicle Screws During Lumbar Spine Fusion

Prospective, randomized, controlled study. To report the results of using the PediGuard (SpineGuard, Inc., San Francisco, CA), a local electrical conductivity measurement device, to reduce radiation exposure while drilling the pilot hole for pedicle screw placement. Reports of pedicle screw placement in the lumbar spine have shown medial pedicle perforations with nerve root impingement in addition to lateral pedicle and vertebral body perforations that can impinge the nerve root within the psoas. Routine use of fluoroscopy (fluoro) is thought to reduce the risk of perforations but is associated with increased radiation. A new pedicle-drilling device (PediGuard) which uses electrical conductivity differentiation at the tip for assessing bone versus soft tissue, has been developed to improve the safe positioning of pedicle screws. This device not only warns of an impending medial breach but also is the only device available to, in real time, nonradiographically detect a lateral breach. METHODS.: Eighteen patients with a diagnosis of lumbar degenerative spine who had a posterior spinal fusion were enrolled. The average age of the patients was 55 ± 12 years. Postoperative computed tomographic scans were reviewed by an independent reviewer. Screws were considered "in" (<2 mm of breach) or "out" (≥ 2 mm of breach). In a randomized fashion, the surgeon placed a pilot hole either with a standard technique (manual probe) or the PediGuard, and used fluoro for each drilling as a guidance assist as necessary. Electromyographic testing was not done by the surgeon. A total of 78 screws (39 via standard probe and 39 with PediGuard assist) were analyzed. There was no significant difference in breach rate of 2 mm or more by either of the 2 methods (P = 1.000), with 1 screw out in each group. Fluoro shots averaged 5.2 (range, 0-15) per screw in the PediGuard group versus 7.5 (range, 2-17) in the standard group (P < 0.001). This represents an average decrease of 2.3 (30%) fluoro shots per screw with the PediGuard. There were 202 total fluoro shots used in the PediGuard group versus 293 in the standard group. In this prospective, randomized trial of a pedicle drilling device that uses electrical conductivity differentiation at the tip for assessing bone versus soft tissue, the number of fluoro shots was reduced by 30% compared with a standard drilling probe while maintaining a 97.5% accurate, safe screw placement.

Development and Application of Multiple‐Probe Scanning Probe Microscopes

In the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

TEM Study of Local Conduction Mechanisms in Model Specimens of Ag-Based Conductive Adhesive

The conduction mechanisms of silver (Ag)-based conductive adhesives, which consist of metallic Ag particles and an epoxy resin, are discussed on the basis of transmission electron microscopy (TEM) studies and local conductivity measurements of model specimens. A small electrical current was observed in the model specimens, in which a thin epoxy layer was sandwiched between Ag electrodes. TEM observations demonstrated that the irreversible changes in the current versus voltage characteristics occurred along with microstructural changes in the Ag electrode, which was subjected to a large electrical current. Calculated equipotential lines indicated a considerable change in the electric field distribution near a small horn that was formed in the surface of the Ag electrode. The results provide useful information for understanding local conduction in the cured adhesive.

Direct Mapping of Ionic Transport in a Si Anode on the Nanoscale: Time Domain Electrochemical Strain Spectroscopy Study

Local Li-ion transport in amorphous silicon is studied on the nanometer scale using time domain electrochemical strain microscopy (ESM). A strong variability of ionic transport controlled by the anode surface morphology is observed. The observed relaxing and nonrelaxing response components are discussed in terms of local and global ionic transport mechanisms, thus establishing the signal formation mechanisms in ESM. This behavior is further correlated with local conductivity measurements. The implications of these studies for Si-anode batteries are discussed. The universal presence of concentration-strain coupling suggests that ESM and associated time and voltage spectroscopies can be applied to a broad range of electrochemical systems ranging from batteries to fuel cells.

Planar sensors for local conductivity measurements in biological objects—Design, modelling, sensitivity maps

The paper focuses on the realisation of the idea of local electrical conductivity measurement in biological objects. In particular, it presents a set of planar electrode sensors that can be used in such measurements. Properties and parameters essential for local conductivity measurements have been analysed and compared for proposed electrode arrangements. The analyses were performed using the Finite Elements Method. The correctness of the results obtained using this method was verified by comparison with the results obtained experimentally and calculated analytically. The influence of the sample volume and its environment conductivity on the measurement result has been analysed for the presented electrode configurations. These parameters determine which of the proposed sensors are preferable in local conductivity measurements and can help to increase credibility and repeatability of the result. The outcome of these analyses also determines requirements that have to be met to perform correct conductivity measurement. Alternatively, if these requirements cannot be met, at least the error of the measurement result can be estimated. Biological objects are usually heterogeneous so the knowledge of sensitivity maps of the sensor can be very useful. Therefore, the modelling procedure for sensitivity map calculations of any four-electrode planar conductivity sensor was proposed and described in this paper. This procedure has been used to calculate and present sensitivity maps of the sensors. The results of these calculations allow the sensitivity of the sensor for the selected area of the sample to be estimated and indicate which part of the measured object has the greatest influence on the measurement result.

Combination of Wirebound and Microwave Measurements for In Situ Characterization of Automotive Three-Way Catalysts

Recently, a novel approach for the characterization of the state of automotive catalysts has been proposed, viz., the direct electrical characterization of the catalyst material itself. This direct approach has the potential to do away with the complex models needed by indirect measurement methods to infer the catalyst state, for instance from the oxygen partial pressure outside of the catalyst determined by lambda probes. In this work, we compare two ways of directly observing the catalyst state. Firstly, the electrical conductivity of the catalyst material is determined by wirebound sensors mounted inside of the catalyst and fabricated from catalyst-formulation coated planar interdigital electrodes. Secondly, we employ a contactless method based on the perturbation of the partially filled microwave cavity resonator formed by the catalyst and its metallic housing. For a better understanding of the observed effects, the data obtained at microwave frequencies from engine tests are compared with the local electrical conductivity measurements. It is shown that both methods give a coherent picture of the oxygen loading state of an automotive three-way catalyst and that both methods enable one to follow the progress of reaction fronts inside the catalyst. Furthermore, it is demonstrated that the resonance frequency is strongly correlated with the oxygen load.

Methodology for Measurement of Submicron Metallic Wire's Local Electrical Conductivity by Applying Four-points AFM Probe Technique

The quantitative measurement of electrical conductivity plays a key role in ensuring material performance,improving yield and fabrication process.The four-points AFM probe technique is applied for the purpose of quantitatively measuring local conductivities of the 99.999% aluminum wires and 350 nm thickness and different widths of 600 nm,2.0 μm,5.0 μm,25.0 μm and 50.0 μm.As position the width and thickness of the specimen is very close to the minimum distance of the electrodes,we consider the factors that affect the measurement accuracy,such as size,diversity of parameter and precision in processing and position error of the four-points AFM probe,modify the calculation model of conductivity and extend the traditional four-electrode conductivity measurements to the sub-micron level.The repeatability of conductivity measurements indicates that this four-point AFM probe technique could be used for fast in situ characterization of local electrical properties of nanocircuits and nanodevices.