Bulk Resistivity Research Articles

Unraveling the Effects of Carbon Corrosion on Oxygen Transport Resistance in Low Pt Loading Proton Exchange Membrane Fuel Cells.

Cost and durability have become crucial hurdles for the commercialization of proton exchange membrane fuel cells (PEMFCs). Although a continuous reduction of Pt loading within the cathode catalyst layers (CCLs) can lead to cost savings, it also increases the oxygen transport resistance, which is further compounded by key material degradation. Hence, a further understanding of the mechanism of significant performance loss due to oxygen transport limitations at the triple phase boundaries (TPBs) during the degradation process is critical to the development of low Pt loading PEMFCs. The present study systematically investigates the impact of carbon corrosion in CCLs on the performance and oxygen transport process of low Pt loading PEMFCs through accelerated stress tests (ASTs) that simulate start-up/shutdown cycling. A decline in peak power density from 484.3 to 251.6 mW cm-2 after 1500 AST cycles demonstrates an apparent performance loss, especially at high current densities. The bulk and local oxygen transport resistances (rbulk and Rlocal) of the pristine cell and after 200, 600, 1000, and 1500 AST cycles are quantified by combining the limiting current method with a dual-layer CCL design. The results show that rbulk increased from 1527 to 1679 s cm-2, Rlocal increased from 0.38 to 0.99 s cm-1, and the local oxygen transport resistance with the normalized Pt surface area (rlocal) exhibited an increase from 18.5 to 32.0 s cm-1, indicating a crucial impact on the structure collapse and changes in the chemical properties of the carbon supports in the CCLs. Further, the interaction between the ionomer and carbon supports during the carbon corrosion process is deeply studied via electrochemical quartz crystal microbalance and molecular dynamics simulations. It is concluded that the oxygen-containing functional groups on the carbon surface could impede the adsorption of ionomers on carbon supports by creating an excessively water-rich layer, which in turn aggravates the formation of ionomer agglomerations within the CCLs. This process ultimately leads to the destruction of the TPBs and hinders the transport of oxygen through the ionomer.

Modifying electric and multiferroic properties of lead-free 0.7BFO-0.3BTO ceramics via Sm and Ga co-doping

Polycrystalline lead-free composite ceramics composed of 0.7Bi1-xSmxFe0.95Ga0.05O3−0.3BaTiO3 (BSxFG-BT) with varying doping concentration of x (0.025, 0.05, 0.10, 0.15, and 0.20) were synthesized. This study comprehensively explores the influence of co-doping Samarium (Sm) and Gallium (Ga) on the microstructures, spectral properties, electrical characteristics, and multiferroic behaviour within the 0.7BiFeO3−0.3BaTiO3 system. These composite ceramics exhibited coexistence of R (rhombohedral) and T (tetragonal) phases, characterized by the space groups R3c and P4mm, respectively. The XRD and AFM results show that the Sm and Ga co-doping influenced the crystal structure as well as grain size of BSxFG-BT ceramics. Raman spectroscopy was used to analyze the positions of the phonon modes. High dielectric constant with high Curie temperature of 550 °C were obtained. The impact of grain and grain boundary on the capacitance and resistance in the ceramics was investigated utilizing Z-view software and high magnitude of bulk resistance was obtained for dopant value x = 0.20 at 300 °C. Enhanced multiferroic properties, remanent magnetisation Mr = 0.051 emu g−1 with coercive field (Hc) = 6450 Oe and remanent polarization Pr = 10.98 μC cm−2 with coercive filed Ec = 14.73 kV cm−1 were obtained for x = 0.20.

Hydrogen Crossover in Anion Exchange Membrane Fuel Cells

In recent years anion exchange membrane fuel cells (AEMFC) have started to draw more attention by potentially allowing catalysts based on more abundant materials, and by showing high performance [1]. One often overlooked parameter in these systems is membrane permeability of hydrogen, often referred to as hydrogen crossover, which directly affects fuel cell stability and efficiency. This undesirable effect creates mixed potential due to the permeated hydrogen reacting with oxygen on the cathode, and not generating useful electric energy, only water and heat [2]. The generated heat creates hotspots of temperatures enough to cause membrane defects or even destruction which further accelerates the degrading process [3].During fuel cell operation relative humidity (RH) and temperature varies in the system, therefore in this study hydrogen crossover is measured at different temperatures (between 50 and 70 ⁰C) and RH (between 30 and 100 %), on Aemion anion exchange membranes (AEMs) with and without reinforcement and with a variety of membrane thicknesses (25 and 50 μm in Figure 1. a). The hydrogen crossover is measured using a mass spectrometer (MS) at the inert gas exhaust. To avoid effects of other components pure membranes and gas diffusion layers (GDLs) were utilized without electrodes.It is shown that AEMs increase in permeability with temperature for all tested while the effect of RH depends on if they are reinforced or not (Figure 1. a). The non-reinforced membranes show a constant decrease in hydrogen crossover with increasing RH, while the reinforced show constant hydrogen crossover until full humidification where it sharply decreases. While the observed trends are different, the quantitative values between reinforced and non-reinforced membranes were relatively similar: at dry conditions, RHs lower than 50 %, crossover is 10 to 30 % lower for reinforced membranes, around 10 % higher at 70 % RH, and at full humidification a non-significant difference compared with non-reinforced (Figure 1. a). It is shown that an increase in the membrane thickness is not proportional to the decrease in hydrogen crossover, suggesting that interface resistance is not negligible. The calculated interface resistance is higher than the bulk resistance for both reinforced and non-reinforced membranes at all RHs (Figure 1. b). However, the bulk resistance is higher for reinforced membranes than for non-reinforced, while interface resistances are relatively similar. Interestingly, the ratio between the interface and the bulk resistance remains constant at all RHs. However, for the membranes without reinforcement the bulk resistance is 20 % of total crossover resistance, while for reinforced it is two times higher, 40 %. Scanning electron microscope (SEM) cross-section analysis shows that the reinforcement is a relatively thin layer of a different polymer in the membrane, which suggests that even a very thin reinforcement could affect membrane permeability properties. Understanding the effects of the reinforcement and their influence on fuel cells will allow for more durable and safer AEMFCs.Figure 1. H2 crossover measured using a MS at the inert gas side. a) At different temperatures, relative humidities and membrane thicknesses. b) H2 crossover resistance at the interface and in the bulk for membranes with and without reinforcement. Measurements are done at 70 °C and at flows 20 ml/min of both hydrogen and the inert gas (Ar).[1] D. R. Dekel, “Review of cell performance in anion exchange membrane fuel cells,” J. Power Sources, vol. 375, pp. 158–169, 2018, doi: 10.1016/j.jpowsour.2017.07.117.[2] S. S. Kocha, J. D. Yang, and J. S. Yi, “Characterization of Gas Crossover and Its Implications in PEM Fuel Cells,” 2006, doi: 10.1002/aic.10780.[3] Q. Tang, B. Li, D. Yang, P. Ming, C. Zhang, and Y. Wang, “Review of hydrogen crossover through the polymer electrolyte membrane,” Int. J. Hydrogen Energy, vol. 46, no. 42, pp. 22040–22061, 2021, doi: 10.1016/j.ijhydene.2021.04.050. Figure 1

Nucleation Behavior and Growth Characteristics of Atomic-Layer Deposited Iridium Thin Films with Ticp and Oxygen

Platinum group elements (Pt, Ru, Pd, Rh, Ag, Au, and Ir) have excellent properties of high thermal and chemical stability, and low electrical resistivity. Due to the attractive characteristics, these materials are also expected for applications in the semiconductor industries. In particular, iridium (Ir) has attracted interests as a potential electrode for memory devices because of its high work function and low resistivity (bulk: 4.7 μΩ cm).Despite the advantages of Ir, the deposition of Ir thin films for the next-generation memory applications faces critical challenges. Since metal has a high surface energy, it is difficult to adsorb on a surface with a lower surface energy. So, formation of metal nuclei is delayed in the initial growth of atomic layer deposition (ALD), and island growth is preferred. During the ALD, sparsely grown nuclei cause an increase in surface roughness which deteriorates the leakage current properties of capacitors.In this study, we attempted ALD of Ir films from newly synthesized tricarbonyl (1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl iridium and oxygen. The growth behavior and film properties of impurity contents and bulk resistivity were investigated in terms of the growth temperature. Also, we examined the changes in the surface morphology of the iridium film with the film thickness. Consequently, we achieved the growth of continuous and smooth Ir films even below 4 nm by forming nucleation-promoting layer at high temperature and followed by ALD of Ir at low temperature. In addition, the capacitor device characteristics were also investigated using Ir as a bottom electrode.

Mathematical Model Based on Staircase Structure for Impedance Analysis of Non-Ideal and Non-Uniform Processes in Porous Electrodes

Electrochemical impedance spectroscopy analysis for porous electrodes in energy conversion and storage, described as resistance and capacitance, is widely used to understand their electrochemical processes. These processes include: (i) electronic resistance inside the electrode (R e), (ii) ionic resistance in the electrolyte bulk and inside the porous electrode (R ion), (iii) electrical double layer formation (C dl) and charge transfer resistance at the electrode electrolyte interface (R ct) , and (iv) diffusion for charge compensation.As one of the mathematical models in electrochemical impedance spectroscopy for porous electrodes, a transmission line model is known, in which the pore structure is described as a cylinder geometry.1 We have proposed an analytical method that combines the transmission line model with electrochemical impedance spectroscopy using a symmetric cell,2 and have investigated resistance separation in lithium-ion batteries and its effect on battery performances.3-5 Due to mathematical constraints, the transmission line model is limited to a representation of an ideal, uniform process model. Here we propose a mathematical model based on a network model consisting of a staircase structure for electrochemical impedance spectroscopy at porous electrodes that can describe not only ideal and uniform processes but also non-ideal and non-uniform processes (Fig. 1), and aims to help elucidate their borderline behavior.6 The proposed staircase model (Z SCM) gives a series equivalent circuit consisting of Z 0, which is a series circuit of electrode/electrolyte interface impedance (Z int0) and electronic resistance (R e0), and electrolyte resistance (R ion0) as an initial step without pores (Z SCM0 = R ion(0) + Z 0). The one-step model (Z SCM1) is then given a series equivalent circuit consisting of the parallel circuit of Z SCM0 and Z 1 and the electrolyte resistance R ion(1) in series (Z SCM1 = R ion(1) + (Z SCM0 −1+Z1 −1)−1). The staircase model is calculated by incorporating the 1 prior step (Fig. 2). Thus, the model with n steps (Z SCM(n)) is composed of a series equivalent circuit of the parallel circuit of Z SCM(n−1) and Z n and the electrolyte resistance R ion(n) (Z SCM(n) = R ion(n) + (Z SCM(n−1) −1 +Z n −1)−1).Fig. 3 shows Nyquist plots computed for each input parameter at 50 steps for non-Faradic and Faradic processes in the staircase model. The results are in good agreement with the profiles calculated for the transmission electric model.2 The presentation will further show examples of the calculated results using the staircase model for non-ideal and inhomogeneous processes and discuss the analysis of impedance behavior using real electrodes reflecting non-uniform processes. References R. de Levie, Electrochim. Acta, 9, 1231-1245 (1964). N. Ogihara, S. Kawauchi, C. Okuda, Y. Itou, Y. Takeuchi and Y. Ukyo, J. Electrochem. Soc., 159, A1034-A1039 (2012). N. Ogihara, Y. Itou, T. Sasaki and Y. Takeuchi, J. Phys. Chem. C, 119, 4612-4619 (2015). N. Ogihara, Y. Itou and S. Kawauchi, J. Phys. Chem. Lett., 10, 5013-5018 (2019). Y. Itou, N. Ogihara and S. Kawauchi, J. Phys. Chem. C, 124, 5559-5564 (2020). N. Ogihara and Y. Itou, Phys. Chem. Chem. Phys., 24, 21863-21871 (2022). Figure 1

Comparison of Electrochemical Characteristics of in Film on Cu and Ru Surfaces

Indium is a potential superconducting interconnect material in a quantum computer, becoming superconducting at 3.37 K [1]. In particular, Indium has good ductility in cryogenic environments, making Indium bonding advantageous for 3D quantum systems. Many researchers have used the ECD method to fabricate Indium micro-bumps because of the requirement of low temperature and achieving a high aspect ratio with a high deposition rate. There have been some studies on the formation of micro-bump of Indium on Copper surfaces using the ECD technique, however, Copper is not a superconducting material. Cobalt and Nickel are materials with electromagnetic properties that affect the conductivity of the quantum system. Ruthenium is considered a suitable underlayer for direct deposition owing to its low resistivity (bulk resistivity of 7.1 μΩ.cm) [2, 3] and transition temperature of 0.47 K [4]. To the best of our knowledge, the deposition of an In film on the Ru surface has not been studied. Therefore, this study aims to evaluate the formation of In thin films on the Ru surface as well as compare the characteristics of In on Cu and Ru surfaces to develop the superconducting Indium micro-bump technology.Indium deposition was studied in a standard three-electrode cell using a potentiostat-galvanostat system. Before deposition, the ruthenium surface was cleaned for 180s at a fixed current of -10 mA/cm2 in 1.2 mol/L H2SO4 [5]. The primary electrolyte was an indium solution (MicroFAB In4950) with an additive (MicroFAB Uniformer).In Fig. 1, the electrochemical behavior of In solution on Cu and Ru surfaces was investigated. Indium metal begins to deposit at -0.87 V and dissolve at -0.25 V on the Cu surface. Meanwhile, the peak currents of In on the Ru surface at the cathode and anode are -1.75 V and 1.17 V, respectively. The electrochemical reaction of Indium is on Cu and Ru surfaces by the following reaction (1):In3+ + 3e- ↔ In (1)SEM micrographs observations of both surfaces at each stage show that island growth occurs when the potential is applied, specifically that the nanoparticles coated on the Ru surface have a porous morphology. The formation of the porous structure upon increasing the voltage on the Ru surface is due to the generation of H2 bubbles, so this study further clarifies the mechanism of In film formation on the Ru substrate. In addition, the change in current is evaluated to determine the effect of current on the structure of the In film. The roughness, thickness, and crystal structure of In film layer have all been thoroughly investigated. To evaluate the bonding ability in low temperatures, the micro-bump formation on both Cu and Ru substrates is demonstrated.In conclusion, the properties and deposition mechanism of In films on Cu and Ru are investigated using the ECD technique. The surface properties of Ru influenced nucleation and In film properties, suggesting a potential study to elucidate the mechanism of In deposition on Ru. Figure 1

Correlating Solid-Electrolyte Interface Composition to Charge Transfer Resistance for Improved Low-Temperature Performance of Lithium-Ion Batteries

The adverse impact of low temperatures on Li-ion batteries (LIBs) is a well known challenge. Currently, at subfreezing temperatures, the efficiency of conventional LIBs greatly decreases compared to their room temperature performance, which of course severely limits the performance of applications using LIBs in the colder regions on the planet. From a fundamental perspective, the causes of such performance decreases are yet to be fully understood, but are believed to be related to the ability of ions to move through the various phases (as well as move across phase interfaces) that exist in the battery.Several studies have been conducted to improve the low-temperature performance of LIBs, most of them focusing on using solvents with lower viscosity and higher dielectric constant to promote transport through the electrolyte at the lower temperatures so as to achieve lower bulk resistance (Rbulk) of the cell. However, our Electrochemical Impedance Spectroscopy (EIS) studies at low temperatures have indicated that it is the charge transfer resistance (Rct) that grows exponentially as we go to sub-zero Celsius temperatures and is responsible for the increase in the total resistance of the cell. EIS on 3-electrode cells have shown that the anode side (Gr) is predominantly responsible for the poor cell performance, necessitating our focus on the charge transfer process in the Gr-electrolyte interface. We observe that the Rct is not only related to the Li-solvation shell but also to the composition of the Solid Electrolyte Interface (SEI). By modifying the electrolyte, such as by changing the salt concentration, adding additives, and changing the solvent, significant changes in the interface and hence in the RSEI and Rct of the cell have been observed. By combining EIS with various techniques like mass spectrometry, differential capacity analysis and SEM, we have been able to better understand the SEI composition and its impact on interfacial resistances. We specifically focus on the influence of SEI composition on the charge-transfer resistance of the cell, correlating the effect of amounts of LiF and carbonates in the SEI with the interfacial performance of the cell. Through these relations, we aim to facilitate the development of electrolytes by having a better understanding of the solvation shells and the SEI composition for low temperature performance.

Evaluation of geohydraulic response properties of hydrogeological units in Littoral hydro-lithofacies in Uyo, Southern Nigeria

Aquifer geohydraulic response properties are important parameters in groundwater resource management and exploitation. However, geohydraulic properties in the study area is sketchy and due to wildcat drilling. This practice, which leads to inadequate inventory of groundwater parameters, deprived the area of efficient exploitation, monitoring and management of groundwater resources. This study is aimed at evaluating the geo-hydraulic response properties of hydrogeological units in littoral hydro-lithofacies in Uyo, Southern Nigeria. Vertical electrical sounding (VES) technique was carried out, and a total of fifteen geoelectric soundings were obtained using IGIS Resistivity metre model SSR-MP-ATS and its accessories employing Schlumberger electrode configuration. The interpreted data give sets of geoelectric curves from which the aquifer resistivity and thickness were determined. The results reveal the aquifer bulk resistivity ranging from 23.4 to 1306.2 Ωm with an average of 347.99 Ωm, while aquifer thickness spanned from 7.4 to 56.3 m. The formation factor, fractional porosity and transmissivity ranged from 2.41 to 12.52, 0.20 to 0.46, and 0.001 to 0.037m2/s, respectively. The formation tortuosity also ranged from 1.05 to 1.58; longitudinal conductance ranged from 0.020 to 1.004 Ω−1; and transverse resistance ranged from 549.90 to 69,097.98 Ωm2. These parameters were contoured, and their variations are displayed on the contour maps generated. The graphs plotted showed strong correlation coefficient and earth response function that can be used in modelling the aquifer repositories in areas with similar geomaterials. The results of this study indicate that the survey area has a good prospect for groundwater accumulation, and the results can be useful in installing matching hydraulic pumps in boreholes in the survey area.

Lithium‐Sulfur Batteries with Triethylsulfonium Bis(trifluoromethane sulfonyl)imide Ionic Liquid During First Charge‐Discharge Cycling: EIS & DFT Study

AbstractWith high theoretical capacity and energy density, lithium‐sulfur batteries (Li−S) have the potential to meet future energy demands including electric vehicles. Various strategies have been developed to address the challenges of Li−S batteries such as polysulfide shuttling, capacity fading, and lithium dendrite formation. By using suitable electrolyte additives, it is possible to enhance the interfacial properties of Li−S batteries and mitigate polysulfide shuttling. In the present work, an aprotic ionic liquid Triethylsulfonium bis(trifluoromethane sulfonyl)imide ([S222][TFSI]) has been used as an electrolyte additive, and the physico‐electrochemical and interfacial properties are investigated. The Li||Li cell with hybrid electrolyte shows stable interfacial resistance and the EIS study during the first discharge and charge of Li−S cell demonstrates stable charge transfer and bulk resistances which indicate the enhanced interfacial properties and the inhibition of polysulfide shuttling. The first‐principles calculations were conducted to investigate the nature of the interaction between the lithium polysulfides (LiPSs) and the [S222][TFSI] molecule. Long chain LiPSs (Li2Sx, 4<x<8) interact with [S222][TFSI] molecule via Li‐bond and hyperconjugation effect. [S222][TFSI] shows the ability to dissolve Li2S and Li2S2 precipitation at the cathode surface which can result in increased utilization of active sulfur and reduced capacity fading.

Surfactants effect on the electrochemical properties of FeSe2 electrode for supercapacitor with first principles insights into quantum capacitance

Nanostructured material like FeSe2 has been synthesized through a simple and cost-effective hydrothermal method. The effect of cationic, non-ionic, and anionic surfactants has been studied on the structural, morphological, and electrochemical properties of FeSe2 electrode material. The FeSe2 electrode material prepared with the assistance of CTAB surfactant displayed a superior specific capacitance value of 401 F g −1 at a scan rate of 10 mV s −1 and 337 F g −1 at a current density of 3.3 A g −1, respectively. The maximum energy density of the symmetric supercapacitor cell fabricated with the same material is evaluated to be 47 Wh kg−1 at a power density of 1667 W kg−1. The addition of the surfactant cetyltrimethylammonium bromide (CTAB) during the synthesis process is found to have a significant impact on the charge storage capability of the material, which is attributed to an increase in active surface area, porosity, reduced crystallite size, and reduced bulk resistance, etc. The real-time use of CTAB-based FeSe2 symmetric cells has been verified via illuminating different voltage light-emitting diodes. Further, the electronic properties and the quantum capacitance of FeSe2 material synthesized without the assistance of any surfactant have been analyzed theoretically using first-principles density functional theory calculations. Acquired results unveil the potential growth of FeSe2 electrode material in energy storage applications.

Use of Recycled Polyethylene in Asphalt Mixture

Abstract Plastics and plastic products have become part of our lives extremely quickly. Although, they make our lives easier in many aspects, at the end of their useful life, especially thanks to the thoughtless actions of people, they are becoming a serious environmental problem. Even though the laws and legislation are still forcing limits of using the plastic products and thus prevent waste, the concept of plastic-free living is probably not going to be reached easily and quickly. Using the recycling technology, we can prepare the recycled material, which represents a new raw material resource. With the right choice of physical-chemical parameters of recycled materials and using a suitable reaction condition we can incorporate them into the asphalt mixtures. Since their introduction the polymer-modified asphalt mixtures have gained in importance during the second half of the twentieth century, and they now play a fundamental role in the field of road paving. Moreover, the use of recycled plastic in such a product will contribute to the technical and economic recovery of secondary raw materials. The use of various recycled material in paving industry is a common practice but needs further research work. Thus, this study aims to the incorporation of recycled plastics into asphalt mixture. The main objective of our work was to find a suitable recycled plastic, which with its physico-chemical and technical parameters is suitable for incorporation into the asphalt mixture. In our study the recycled low-density polyethylene granulate was used, taken from films and various packaging materials. Our preliminary laboratory experiments were based on the possibilities to prepare and characterized the asphalt mixtures containing recycled plastic at different percentage, i.e., 4 %, 6 %, 8 % and 10 % by weight of bitumen. The experimental tests performed in the study were bitumen content, intergranularity, maximum bulk density, water sensitivity and resistance to permanent deformations. The results showed that the mix containing 6 % by weight of recycled plastic has ideal properties and meets most of the criteria that have been set for asphalt mixes. A commercially available polymer of similar chemical composition to the recycled material was used as a reference sample.

Two-dimensional cobalt ferrite through direct chemical vapor deposition for efficient oxygen evolution reaction

Two-dimensional (2D) transition metal oxides (TMOs) are promising electrocatalysts for the new energy industry, owing to their earth-abundancy, excellent performance, and unique physicochemical properties. However, microscopic electrochemical study for 2D TMOs is still lacking to provide detailed electrocatalytic mechanisms due to the challenges in synthesizing 2D TMOs with high quality and controlled thickness, which is indispensable for the microscopic studies. In this study, we report the direct synthesis of 2D cobalt ferrite (CoFeO) using a chemical vapor deposition (CVD) method. The as-synthesized 2D CoFeO possesses a well-crystallized spinel structure with an ultrathin thickness of 6.8 nm. Its oxygen evolution reaction (OER) properties under alkaline conditions were accurately assessed using an ultra-microelectrode testing platform. The (111) facet of the 2D CoFeO exhibits a low overpotential of 330 mV at a current density of 10 mA cm–2 and a high current density of ~142 mA cm–2 at an overpotential of 570 mV. The OER mechanism of the 2D CoFeO was analyzed using density functional theory (DFT) calculations, which reveal the bimetallic sites on the surface reduce the energy barrier and facilitate the reaction. Moreover, we demonstrate the reduced thickness of 2D CoFeO improves the OER activity by lowering the bulk resistance and improving the utilization of active sites, which was confirmed by the thickness-activity dependency (6.8 to 35 nm) tests using the ultra-microelectrode platform. Furthermore, the practical values of the as-prepared 2D CoFeO was demonstrated by synthesizing a large-area continuous film and collecting high OER activity and superb durability from macro-electrochemical experiments. Our study provides new solutions for the controlled synthesis of 2D TMOs electrocatalysts and uncovers the electrocatalytic mechanisms with the ultra-microelectrode platform, which provides new insights for exploring the inherent properties and applications of 2D materials in electrocatalysis.

On non-local electrical transport in anisotropic metals

We discuss various aspects of nonlocal electrical transport in anisotropic metals. For a metal with circular Fermi surface, the scattering rates entering the local conductivity and viscosity tensors are well-defined, corresponding to eigenfrequencies of the linearized collision operator. For anisotropic metals, we provide generalized formulas for these scattering rates and use a variational approximation to show how they relate to microscopic transition probabilities. We develop a simple model of a collision operator for a metal of arbitrary Fermi surface with finite number of quasi-conserved quantities, and derive expressions for the wavevector-dependent conductivity σ(q) and the spatially-varying conductivity σ(x) for a long, narrow channel. We apply this to the case of different rates for momentum-conserving and momentum-relaxing scattering, deriving closed-form expressions for σ(q) and σ(x) — beyond generalizing from circular to arbitrary Fermi surface geometry, this represents an improvement over existing methods which solve the relevant differential equation numerically rather than in closed form. For the specific case of a diamond Fermi surface, we show that, if transport signatures were interpreted via a model for a circular Fermi surface, the diagnosis of the underlying transport regime would differ based on experimental orientation and based on whether σ(q) or σ(x) was considered. Finally, we discuss the bulk conductivity. While the common lore is that “momentum”-conserving scattering does not affect bulk resistivity, we show that crystal momentum-conserving scattering — such as normal electron-electron scattering — can affect the bulk resistivity for an anisotropic Fermi surface. We derive a simple formula for this contribution.

High -yield Fabrication of Thin Glass Interposers

Thin glass substrates with through vias (TGV) have excellent properties for a new generation of interposers. Glass has a large bulk resistance and low loss at high frequency (RF, mmWave). Physically, it is moisture insensitive, highly dimensionally stable, and has a thermal expansion coefficient that can be tailored to match silicon. The surface of as-received glass has roughness below 1 nm, like silicon wafers, and thus supports fine line/space patterning and advanced processes like damascene. A key focus of our current work involves metallizing thin glass interposers with TGVs, including both copper electroplating of TGVs and patterning of redistribution layers. We demonstrate void-free fill for vias ranging from in aspect ratio from 2:1 to 8:1, in a bottoms-up process like that used for through silicon vias. The vias are hermetic by helium leak detection, even after annealing in some cases to 450C. Since thin (≤ 200 micron) free-standing glass substrates are difficult to handle in current fabs, we discuss an advanced temporary bond approach using silicon or glass handles which enables high-yield processing. The bond is robust to temperatures exceeding 400 °C, and creates handle/glass stacks with total thickness variation (TTV) similar to that of a silicon wafer. The end result is a bonded pair that can be processed like a silicon wafer, with a simple mechanical debond to yield the processed thin glass. We discuss the bond and debond processes, showing the ability to control the bond strength. Data on the bonded glass stack resistance to various processing steps will also be shown.

Fabrication and conductivity of zirconium doped Li2TiO3 tritium breeder

The tritium diffusion rate of the tritium breeder is one of the main factors affecting the Deuterium–Tritium (DT) nuclear fusion. In the paper, the zirconium ion (Zr4+)-doped Li2TiO3 tritium breeder with a small grain size of 0.66 μm was successfully prepared at a high temperature of 950 °C. Zr4+-doping could inhibit grain growth of Li2TiO3, which benefited from the effect of segregating, pinning, and dragging to the Li2TiO3 grain boundary. Then, the conductivity was innovatively used to indirectly and rapidly evaluate the tritium release property of Zr4+-doped Li2TiO3. The results show that the short lithium-ion diffusion distance for the small-grained Zr4+-doped Li2TiO3 decreases bulk resistance, and the abundant interfaces enhance grain boundary conductivity. Besides, the zirconium (Zr) dopant increases the cell volume of Li2TiO3, which provides a broader channel for the diffusion of lithium ion. It indirectly illustrates that the Zr4+-doped Li2TiO3 with small grains has better tritium release performance than the Li2TiO3 with large grains. The results would provide new insights into the Zr doping to accelerate tritium diffusion on the Li2TiO3 surface.

In-situ polymerization of the electrolyte on the electrode surface: A novel process to eliminate interfacial impedance in flexible Zn-air batteries

Flexible rechargeable quasi-solid-state metal air/O2 batteries are advanced energy sources for wearable and flexible electronic devices. This study proposes an in-situ polymerization of gel electrolyte on the electrode surface (IPEES) technique for the Zn-air battery. The utilization of the IPEES technique for batteries results in superior battery performance as compared to conventional layer-by-layer batteries. The enhanced performance can be credited to several factors, including a reduction in charge transfer resistance and bulk resistance, an increase in ion conductivity, improved water retention, and the establishment of a robust and stable interface between the electrolyte and cathode. The battery with the poly(acrylic acid) gel using the IPEES technique results in a charge-discharge process of 171 h at 1 mA cm−2, while the specific capacity (SC) and power density (PD) of the battery are 72.86 mAh cm−2 and 88.88 mW cm−2, respectively. The novel IPEES method yields an increase of up to 78.6 % in specific capacity compared to the conventional method. At a current density of 10 mA cm−2, the highest values of SC and PD are attained, reaching 83.85 mAh cm−2 and 90.6 mW cm−2, respectively. The novel method exhibits exceptional electrochemical performances and offers additional benefits such as affordability and high mechanical stability.

Negative temperature co-efficient of resistance behaviour of Cr doped ZnO nanoceramics

Here, High Energy Ball Milling (HEBM) is used to prepare Cr doped ZnO (Zn1-xCrxO, x = 0–0.04) nanoceramics and their electrical behaviour is studied in detail. The X-ray diffraction suggests a hexagonal wurtzite structure. The Rietveld refinement XRD pattern of the sample calcined at 900 °C suggests that up to 4 at% of Cr can be doped into the ZnO structure. After sintering, the growth in the particle size was observed for Cr doped ZnO samples. The complex impedance behaviour of samples suggests a decrease in resistance with temperature. This shows the Negative Temperature Coefficient of Resistance (NTCR) characteristic of the Cr doped ZnO sample in the studied temperature range (300–500 °C). At higher temperature, the electrical relaxation behaviour is of the non-Debye type as observed from the relaxation time distribution. The equivalent electrical circuit of ZnO and Cr doped ZnO ceramic samples are a parallel arrangement of bulk capacitance (Cb) and bulk resistance (Rb).

Self-sensing nano-engineered ultra-high performance concrete (UHPC) under tension

With the addition of electrically conductive steel or carbon fibers, Ultra-High-Performance Concrete (UHPC) possesses an intrinsic self-sensing capability. This opens up the possibility of combining the resilience and sustainability of UHPC with the development of self-sensing solutions for structural applications. In this study, the self-sensing behaviour of a proprietary nano-engineered UHPC material subjected to tension was investigated. To assess the self-sensing performance of the material, bulk resistivity measurements were used on direct tension and pure flexure tests, while a novel wireless approach that operates on was used on out-of-plane bending tests. The wireless approach used alternate current (AC) measurements while the bulk resistivity methods were performed through direct current (DC) and the four-probe method. In both methods, the fractional change in resistance was correlated to the state of deformation. The disposition of the actual strain field was evaluated using Digital Image Correlation (DIC). It was found that in the case of direct tension and pure flexure, the fractional change of resistance was initially decreased up to the onset of strain localization, while it gradually increased in the post-peak range, where the separation of the localized crack gradually increased. In the case of the wireless approach using AC, the onset of cracking was successfully predicted with an abrupt increase in resistivity. The wireless strain-sensing approach also captured the Poisson’s effect due to the loading.

Temperature effects on electrical resistivity of selected ceramics for high‐temperature packaging applications

AbstractWe report the results of the characterization of the electrical resistivity of selected ceramic materials, namely aluminum nitride (AlN), silicon nitride (Si₃N₄), beryllium oxide (BeO), yttrium oxide (Y₂O₃), and non‐ceramic silicon dioxide (SiO2), which are candidates for packaging silicon carbide (SiC) sensors and electronics that can operate at temperatures beyond 800°C. Samples of these materials were thermally cycled twice to 1200°C in nitrogen while the bulk and surface resistivities were measured in situ. Although the resistivity values of all samples dropped with increasing temperature, BeO maintained the relatively highest bulk and surface resistivity values at 1200°C of 28 and 34 kΩ cm, respectively, while AlN had the lowest values at 6.8 and 0.64 kΩ cm. In terms of viability for packaging SiC sensors for >800°C operation, AlN and Si₃N₄ are the choice candidates due to their lowest mismatches in the coefficient of thermal expansion with SiC. However, the relative resistivity stability of Si₃N₄ over AlN makes it a promising candidate, even with its lower thermal conductivity relative to AlN.

STEM-16. PROMOTING THE CANCER STEM CELL SUBPOPULATION AND PHENOTYPE IN GLIOBLASTOMA VIA EXTRACELLULAR VESICLE CROSS-TALK

Abstract INTRODUCTION Extracellular vesicles (EVs) released from cancer cells contain bioactive molecules that have been long implicated in tumorigenesis. In glioblastoma (GBM), there is mounting evidence that EVs play a role in critical processes including angiogenesis, immune suppression, and invasion. GBM secreted EVs have also been demonstrated to promote a cancer stem cell (CSC) phenotype by transporting stemness markers and proteins (I.e. Notch-1) involved in stem-cell activating pathways. Understanding the maintenance of CSCs, which contributes to tumor proliferation, treatment resistance, and re-expansion of the tumor bulk, can offer insight into new therapeutic drug targets that can disrupt this subpopulation. METHODS EVs were isolated from patient-derived primary GBM cell lines maintained as adherent cultures and free floating spheres (n = 3) using a staged ultracentrifugation technique. Normal astrocytes were used as the control group (n = 1). Protein expression profiles were then generated via high-throughput mass spectrometry for both EVs and whole cell lysate samples from the same cell line and compared against each other. RESULTS EGF-containing fibulin extracellular matrix protein 1 (EFEMP1) was shown to be upregulated in GBM derived EVs compared to control. Further analysis shows that EFEMP1 is enhanced in adherent cultures compared to free floating sphere cultures. CONCLUSION EFEMP1 is an extracellular matrix protein that has been identified as an oncogenic protein in GBM by activating Notch-1, Akt, and NF-Kb signaling pathways resulting in increased Temozolomide resistance, cellular proliferation, and invasion, all of which are hallmark characteristics of CSCs. EFEMP1 is also a downstream effector in the HIF-1 pathway, which has been strongly correlated in the maintenance of CSCs. Our results therefore demonstrate a possible EV mediated mechanism for the maintenance of the CSC population and phenotype in GBM.