Resistivity Anisotropy Research Articles

Interlayer superlubricity of layered Metal-organic frameworks and its heterojunctions enabled by highly oriented crystalline films

Although metal–organic frameworks (MOFs) have shown great potential in superlubricity due to the inorganic–organic hybridization, there is little understanding of their interlayer sliding ability.Simple and convenient testing techniques are also lacking. In this paper, an ingeniousmethod for measuring interlayer friction of layered MOFs and its heterojunctions was developed, namely coating the friction pairs with highly oriented crystalline films assembled by MOFs nanosheets. The overall incommensurability contributed to the robust interlayer superlubricity (µ∼0.0013) that is insensitive to the sliding angle. The interlayer sliding behavior of 2D MOFs differs from that of conventional materials in that the interlayer sliding resistance of heterojunction with lattice mismatch is not necessarily lower than that of homojunction. Theoretical simulation enables us to explore the mechanism of interlaminar sliding resistance of MOFs, which is the energy barrier generated by vertical alignment of the congeneric components between layers. And the key structural factors that determine the strength of frictional resistance and frictional anisotropy between MOFs layers, namely coordination stability and lattice constant, were discovered. Therefore, the structure–function relationship was established to guide the structural design.

Electric current and magnetization distributions’ self-organization features in a magnetoresistive film nanoelement under the influence of an external magnetic field

The new generalized Laplace’s equation for an electric potential is presented, which in the general case, is nonlinear for media with resistance anisotropy caused by the anisotropic magnetoresistance (AMR) effect and determined by the orientation of the magnetization vector relative to the current density vector at an arbitrary point of the sample. The solution to this equation is obtained for an anisotropic medium with a non-uniform distribution of current density and magnetization in the case of an oblique-shaped plate of nanoscale thickness. In addition, the analytical solution was obtained for the current density distribution in such a medium using conformal mapping, which confirms the numerical solution in the case of an isotropic conductor. An analysis of the results showed that the presence of the AMR effect leads to a significant change in the current density distribution in the sample compared to the isotropic case, which is expressed in the deviation of the current density vector in perpendicular to the magnetization vector direction in the plate. It has been established that the presence of an external magnetic field in the film plane, which leads to the emergence of an inhomogeneous magnetization distribution, entails self-organization of the electric current distribution. The graphs of the plate resistance as a function of applied magnetic field demonstrate asymmetry for the cases of the direct and reverse directions of the external magnetic field, which cannot be obtained within the framework of simplified models of current flow in media with the AMR effect.

Resistivity anisotropy from the multiorbital Boltzmann equation in nematic FeSe

We compute the resistivity anisotropy in the nematic phase of FeSe from the static solution of the multiorbital Boltzmann equation. By introducing disorder at the level of the microscopic multiorbital model we show that even elastic scattering by localized impurities may lead to non-trivial anisotropic renormalization of the electronic velocities, challenging the usual understanding of transport based only on cold- and hot-spots effects. Our model takes into account both the $xz/yz$ and the recently proposed $xy$ nematic ordering. We show that the latter one has a crucial role in order to reproduce the experimentally-measured anisotropy, providing a direct fingerprint of the different nematic scenarios on the bulk transport property of FeSe.

Three new Ag-based full-Heusler alloys: Ag2TiGa, Ag2VGa, and Ag2TiTl

There are various new structures with superior performance for Heusler alloy materials that are widely used in spintronic materials, thermoelectric materials, and other fields. In this study, three new Ag-based full-Heusler alloys (Ag2TiGa, Ag2VGa, and Ag2TiTl) are proposed. The stability, mechanical properties, and electronic properties of these three new Ag-based Heusler alloys were studied using first-principles calculations. The results showed that the compression resistance, shear resistance, stiffness, and elastic anisotropy of Ag2VGa were greater than those of Ag2TiGa and Ag2TiTl, whereas the ductility of Ag2TiGa and Ag2TiTl was better than that of Ag2VGa. The spin density of states of Ag2VGa has evident spin splitting near the Fermi level, and the total magnetic moment of the Ag2VGa structure is 2.28 µB, which indicates that Ag2VGa is magnetic. These studies enrich research on Ag-based Heusler alloys and provide theoretical references for subsequent theoretical and experimental research.

High-field magnetoresistance of microcrystalline and nanocrystalline Ni metal at 3 K and 300 K

The longitudinal and transverse magnetoresistance curves MR(H) and the magnetization isotherms M(H) were measured at T = 3 K and 300 K up to high magnetic fields for a microcrystalline (µc) Ni foil with grain sizes above 1 µm (corresponding to bulk Ni) and for a nanocrystalline (nc) Ni foil with an average grain size of about 100 nm. At T = 3 K, the field-induced resistivity change was quite different for the two microstructural states of Ni and the evolution of resistivity with magnetic field was also different which could be explained as arising from their very different electron mean free paths. At T = 300 K, the MR(H) curves of both the μc-Ni and nc-Ni samples were very similar to those known for bulk Ni. The MR(H) data were analyzed at both temperatures with the help of Kohler plots from which the resistivity anisotropy splitting (ΔρAMR) and the anisotropic magnetoresistance (AMR) ratio were derived, the latter values being very similar at both temperatures and for both microstructural states of Ni metal. The present high-precision MR(H) data revealed that the available theoretical models do not accurately describe the suppression of thermally induced magnetic disorder at around room temperature in high magnetic fields.

Use of structure-guided 3D controlled-source electromagnetic inversion to map karst features in carbonates in offshore northwest Borneo

Fractured and/or karstic carbonates (FKCs) in the subsurface are commonly associated with significant drilling risk or reservoir effectiveness issues. Understanding the distribution of karsts will help avoid drilling into possible voids and also reassess risks associated with reservoir effectiveness. A 2020 3D seismic acquisition in offshore northwest Borneo provided data for identifying new carbonate prospects and an opportunity to revisit a 2010 marine controlled-source electromagnetic (CSEM) survey that was not designed specifically for FKC mapping but can serve to test new inversion capability for imaging karsted carbonate bodies. A 3D CSEM data were used to detect and characterize the nature (i.e., fractured and/or karsted) of carbonate prospects mapped using 3D seismic data. In one approach, structure tensors computed from these seismic data were used to constrain the 3D CSEM inversion on the Azure cloud platform. In another approach, cross gradients between vertical and horizontal resistivities were used as a structural guide obviating the need for seismic data. The resulting anisotropic resistivity models were validated using resistivity logs from a nearby well; the resistivity results matched the well-logs satisfactorily, providing geologic justification to interpret the presence of karst features in the resistivity volumes. Lateral boundary of the carbonate prospects was mapped based on the resistivity characteristic, in seismic- and nonseismic-guided structure-coupled inversion. Resistivity-depth cross section of the area revealed the presence of resistivity discontinuity at the seismic-inferred boundary of the main carbonate prospect. Also, resistivity depth slices of the models clearly demonstrated that the areal distribution of low and high resistive zones can be mapped and useful deductions such as the presence of FKC and basement characteristics can be made using the 3D inversion of the CSEM data.

Three-Dimensional DC Anisotropic Resistivity Modeling Using a Method in the Mixed Space–Wavenumber Domain

Three-Dimensional DC Anisotropic Resistivity Modeling Using a Method in the Mixed Space–Wavenumber Domain

Nematic Fluctuations in the Non-Superconducting Iron Pnictide BaFe1.9−xNi0.1CrxAs2

The main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe1.9−xNi0.1CrxAs2 by electronic transport, angle-resolved photoemission spectroscopy (ARPES), and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to x = 0.8, with similar Néel temperature TN and structural transition temperature Ts around 32 K, but the charge carriers change from electron type to hole type around x = 0.5. In this study, we have found that the in-plane resistivity anisotropy also highly depends on the Cr dopings and the type of charge carriers. While ARPES measurements suggest possibly weak orbital anisotropy onset near Ts for both x = 0.05 and x = 0.5 compounds, INS experiments reveal clearly different onset temperatures of low-energy spin excitation anisotropy, which is likely related to the energy scale of spin nematicity. These results suggest that the interplay between the local spins on Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the nematic fluctuations of iron pnictides, where the orbital degree of freedom may behave differently from the spin degree of freedom, and the transport properties are intimately related to the spin dynamics.

High-density and low-density gas diffusion layers for proton exchange membrane fuel cells: Comparison of mechanical and transport properties

Gas diffusion layers (GDL) play multi-roles in proton exchange membrane fuel cells, including gas-water transport, thermal-electron conduction and mechanical support. Mechanical strength and transport properties are essential for GDLs. In this work, high-density (paper-type) and low density (felt-type) GDLs are scanned and reconstructed using X-ray computed tomography. Porosities under different compression ratios are compared and discussed. Effective diffusivity and liquid water permeability are calculated using pore-scale modeling and lattice Boltzmann method. Mechanical strength, anisotropic thermal-electrical resistivity for two types of GDLs are obtained using compression tests and thermal-electrical conductivity measurements. Results show that the porosity, diffusivity, permeability, and through-plane thermal-electrical conductivity of felt-type GDL are significantly higher than that of paper-type GDL owing to the higher porosity and fiber-clusters oriented along the through-plane direction. The in-plane electrical resistivity of paper-type GDL is lower than that of felt-type GDL. The mechanical strength of felt-type GDL is much lower, but the fibers of paper-type GDL are more easily to be broken because of its lower elasticity. The results obtained may guide microstructure optimization and performance improvement of GDLs.

Resistivity anisotropy analysis of Longmaxi shale by resistivity measurements, scanning electron microscope, and resistivity simulation

The resistivity anisotropy of shale has a non-negligible effect on resistivity logs. Many studies have shown that the macroscale factors of shale anisotropy are depositional environment, compaction process, and diagenesis process, and the microscale factors mainly include lamination, orientation of clay minerals, and microfractures. However, the mechanism of laminations, pores, organic matters, pyrite and clay minerals driving resistivity anisotropy remains unclear. In this research, experiments and simulations were performed to investigate the characteristics and mechanism of the resistivity anisotropy of shale. Two sets of shale samples were collected at different inclination angles from the Lower Silurian Longmaxi Formation in the Pengshui area, southeastern Sichuan Basin, China. Core sample resistivities were measured in several water saturation states established using imbibition, pressurized saturation and centrifuge methods. Scanning electron microscopy, thin sections, X-ray diffraction, the mercury injection capillary method, and N2 adsorption were also performed. Resistivity simulations were applied to three-dimensional models derived from the microimages. The results of the experiments and simulations show that Longmaxi shale has strong resistivity anisotropy. The resistivity anisotropy coefficient (λ) of Longmaxi shale ranged from 1.3699 to 2.1623. Longmaxi shale has a strong lamination structure. In the submillimeter scale, strawberry-like pyrite (3.8%–10.2%, v/v) aggregates in elongated strips with an extension direction consistent with the horizontal direction. Due to the differential compaction, the clay minerals (21.1%–26.4%, v/v) also tend to be parallel to the formation bedding. The most obvious directional distribution of pores occured in the organic pores. Most interparticle pores between detrital minerals did not exhibit anisotropic characteristics. Because of the horizontal distribution of lamination, pyrite, clay minerals and organic pores, a higher resistivity is measured in the vertical direction than in the horizontal direction.

Directional ballistic transport in the two-dimensional metal PdCoO2

In an idealized infinite crystal, the material properties are constrained by the symmetries of the unit cell. The point-group symmetry is broken by the sample shape of any finite crystal, but this is commonly unobservable in macroscopic metals. To sense the shape-induced symmetry lowering in such metals, long-lived bulk states originating from an anisotropic Fermi surface are needed. Here we show how a strongly facetted Fermi surface and the long quasiparticle mean free path present in microstructures of PdCoO2 yield an in-plane resistivity anisotropy that is forbidden by symmetry on an infinite hexagonal lattice. We fabricate bar-shaped transport devices narrower than the mean free path from single crystals using focused ion beam milling, such that the ballistic charge carriers at low temperatures frequently collide with both of the side walls that define the channel. Two symmetry-forbidden transport signatures appear: the in-plane resistivity anisotropy exceeds a factor of 2, and a transverse voltage appears in zero magnetic field. Using ballistic Monte Carlo simulations and a numerical solution of the Boltzmann equation, we identify the orientation of the narrow channel as the source of symmetry breaking.

Inter- to intra-layer resistivity anisotropy of NdFeAs(O,H) with various hydrogen concentrations

With molecular beam epitaxy and a topotactic chemical reaction, we prepared NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on 5\ifmmode^\circ\else\textdegree\fi{} vicinal-cut MgO substrates. By measuring the resistivities along the longitudinal and transversal directions, the $ab$-plane and the $c$-axis resistivities (${\ensuremath{\rho}}_{ab}$ and ${\ensuremath{\rho}}_{c}$) were obtained. The resistivity anisotropy ${\ensuremath{\gamma}}_{\ensuremath{\rho}}\ensuremath{\equiv}{\ensuremath{\rho}}_{c}/{\ensuremath{\rho}}_{ab}$ of NdFeAs(O,H) with various hydrogen concentrations was compared with that of NdFeAs(O,F). At the H concentrations which led to superconducting transition temperatures ${T}_{\mathrm{c}}$ over 40 K, ${\ensuremath{\gamma}}_{\ensuremath{\rho}}$ recorded $\ensuremath{\sim}100--150$ at 50 K. On the other hand, a low ${\ensuremath{\gamma}}_{\ensuremath{\rho}}$ value of 9 was observed with the highest-doped sample. The exponent \ensuremath{\beta} of the $ab$-plane resistivity obtained by fitting a power-law expression ${\ensuremath{\rho}}_{ab}(T)={\ensuremath{\rho}}_{0}+A{T}^{\ensuremath{\beta}}$ to the data was close to unity down to a low temperature in the vicinity where the second antiferromagnetic phase locates, which may be related to the quantum critical point discussed at the overdoped side of the phase diagram.

Easy and computer-time-saving implementation of the van der Pauw method including anisotropy and probe positioning correction factors using approximate closed-form analytical functions.

Measurements in a van der Pauw configuration often require the use of complicated mathematical expressions or implicit relations, which may be computer-time-consuming or tedious to implement in a given software. Thus, a closed-form expression is often desirable. We propose to approximate these relations by closed-form analytical functions using only basic operators that can be easily implemented. We present explicitly the functions and the numerical values of their parameters for the cases of standard van der Pauw measurement, anisotropic resistivities, and the probe position correction factor. The discrepancy with the exact values is smaller than 10-5, which is sufficient for practical purposes.

Elucidating the signal for contact guidance contained in aligned fibrils with a microstructural-mechanical model.

Despite its importance in physiological processes and tissue engineering, the mechanism underlying cell contact guidance in an aligned fibrillar network has defied elucidation due to multiple interdependent signals that such a network presents to cells, namely, anisotropy of adhesion, porosity and mechanical behaviour. A microstructural-mechanical model of fibril networks was used to assess the relative magnitudes of these competing signals in networks of varied alignment strength based on idealized cylindrical pseudopods projected into the aligned and orthogonal directions and computing the anisotropy of metrics chosen for adhesion, porosity and mechanical behaviour: cylinder-fibre contact area for adhesion, persistence length of pores for porosity and total force to displace fibres from the cylindrical volume as well as network stiffness experienced upon cylinder retraction for mechanical behaviour. The signals related to mechanical anisotropy are substantially higher than adhesion and porosity anisotropy, especially at stronger network alignments, although their signal to noise (S/N) values are substantially lower. The former finding is consistent with a recent report that fibroblasts can sense fibril alignment via anisotropy of network mechanical resistance, and the model reveals this can be due to either mechanical resistance to pseudopod protrusion or retraction given their signal and S/N values are similar.

Two-dimensional superconductivity in a bulk superlattice van der Waals material Ba6Nb11Se28

The observation of clean 2D superconductivity and bosonic Landau levels below 0.85 K in superlattice van der Waals material ${\mathrm{Ba}}_{6}{\mathrm{Nb}}_{11}{\mathrm{S}}_{28}$ have received much interest. Here we report the crystal structure, Hall resistivity, and 2D superconductivity of its sister compound, ${\mathrm{Ba}}_{6}{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$. The atomic-resolution transmission electron microscopy images reveal an alternate stacking of $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$ with a 3 \ifmmode\times\else\texttimes\fi{} 3 commensurate block layer, which is isostructural to ${\mathrm{Ba}}_{6}{\mathrm{Nb}}_{11}{\mathrm{S}}_{28}$ and with a larger $\mathrm{Nb}{X}_{2}$ ($X=\mathrm{S}$, Se) interlayer distance (12.8 \AA{}). Transport property measurements demonstrate a twofold enhancement in superconducting temperature $({{T}_{\mathrm{c}}}^{0}=2.2\phantom{\rule{0.16em}{0ex}}\mathrm{K})$, meanwhile the anisotropy in resistivity and carrier mobility in ${\mathrm{Ba}}_{6}{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$ decrease drastically compared to its sulfur counterpart, driving the superconductor towards the dirty limit. Further measurements of angular-dependent upper critical field suggest the superconductivity in ${\mathrm{Ba}}_{6}{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$ be Pauli-limit breaking (2 times the ${\ensuremath{\mu}}_{0}{H}_{P}$), and can be well described by the 2D Tinkham form. Our findings offer a valuable platform to investigate 2D superconductivity in bulk superlattice materials based on the transition-metal dichalcogenides.

Highly Conductive Polymer Composite Based on Graphite-Filled Immiscible Polyolefin/Epoxy Blends

Conductive polymer composites (CPCs) based on polypropylene (PP)/epoxy (EP) and high-density polyethylene (HDPE)/EP blends filled with synthetic graphite (SG) were produced and characterized to explore their potential for high electrical conductivity applications. The polymer blends were chosen as matrices due to their immiscibility and potential to enable co-continuous morphology formation and preferential distribution of filler, which allows formation of maximized conducting networks. In-plane and through-plane resistivities of PP/EP/SG composites decreased from 0.083 Ω.cm to 0.015 Ω.cm and 10.16 Ω.cm to 0.31 Ω.cm, respectively, while for HDPE/EP/SG composites, in-plane and through-plane resistivities decreased from 0.086 Ω.cm to 0.014 Ω.cm and 5.02 Ω.cm to 0.24 Ω.cm, respectively, when SG content was increased from 30 to 80 wt%. The immiscible blend-based composites produced in this study have the potential to achieve significantly higher conductivity than filled single polymers due to concentration of filler in one of the polymer phases and the co-continuous structure of the blends. Also, resistivity anisotropy of the PP/EP/SG and HDPE/EP/SG composites generally decreased with increase in SG content, with HDPE/EP/SG composites showing lower resistivity anisotropy than PP/EP/SG composites at the same SG content.

Physical properties of superconducting Ca10(Pt4As8)((Fe0.92Pt0.08)2As2)5 crystal and comprehensive cognition on the transition temperature for Ca10-3(4)-8

Superconducting single crystal of Ca10(Pt4As8)((Fe0.92Pt0.08)2As2)5 has been prepared using flux method, and the physical properties of which are careful examined. Resistivity anisotropy between ab plane and c-axis is observed, T −0.5 term originated from the interlayer Josephson coupling is essential to be added to the formula used to describe the out-of-plane resistivity. The density of state (DOS) value at Fermi level derived from the fitting of specific heat data is consistent with the calculation results. Both direct and indirect platinum doping effect have influences on the superconducting transition temperature (Tc) of Ca 10-3(4)-8 system, the Tc of our sample falls well into the trend strip formed by the data reported previously.

Comparison between conventional and high-resolution measurements for unlocking the thin laminated potential reservoir, a case study

In Low resistivity low contrast (LRLC), also known as low resistivity pay (LRP), one of the factors is, the existence of alternating thin sedimentary layers of various rock types in hydrocarbon reservoirs, commonly consist of sandstone, siltstone and claystone and have been widely reported today. This phenomenon causes the potential intervals to be misinterpreted as non-hydrocarbon bearing zone due to its ability to reduce the measured apparent resistivity which result in overestimated water saturation calculation and due to its low contrast, in comparison with water bearing interval, this phenomenon always make well analyst to by passed this interval. As a result, from falsified measured resistivity, the final reserves volume tends to be underestimated. A huge number of studies have proven this kind of interval able to produce oil with very low water-cut therefore this paper would like to present the case study of solving this complex lithology by using sophisticated petrophysical modeling with a combination of Thomas-Stieber plot. Measured vertical (Rv) and horizontal (Rh) resistivity is available for this study and will be used as comparison. In general, this paper will present two case studies for final saturation computation, a) The sand resistivity will be estimated through inversion using measured resistivity anisotropy (Rv - Rh), b) The sand resistivity is reconstruct based on identified volume fraction of clay, whereas the shale resistivity estimated from conventional resistivity (RDEEP). Both of the cases will be calibrated using measured saturation from core by using Dean-Stark technique. Selected interval in this study (X1 zone) is a proven oil interval with a standard volume production rate 698 bbl/day. The final comparison of saturation computed using measured resistivity anisotropy yield a high correlation in contrast, the inversion using conventional resistivity yields less correlation with saturation from core. Nonetheless, by comparing with conventional computed saturation i.e. Waxman Smith, the final saturation of these two cases is significantly increased and unmasked the hydrocarbon-bearing interval. Therefore, case b indicates the best approach to be used whenever the advance measured resistivity anisotropy is unavailable.

Stochastic aspects of crack deflection and crack path prediction in short fiber reinforced polymer matrix composites

Owing to the production process, short fiber reinforced composites exhibit a pronounced anisotropy of both elastic properties and crack growth resistance. In particular the latter issue has a major impact on crack deflection and inevitably has to be taken into account for the sake of an accurate prediction of crack paths. The perpendicular axes of transverse isotropy are associated with the fiber orientations, whereupon a crack in transverse direction encounters the largest fracture toughness. While the local mean fiber orientations in polymer matrix composites are determined by the injection molding process, their statistical fluctuations can approximately be described in terms of Gaussian random field models. Furthermore, statistical variations of the volume fraction of fibers and the fiber–matrix adhesion give rise to stochasticity of the local ratio of fracture toughness anisotropy. Influencing factors of prediction regions of crack paths obtained from finite element simulations with an adapted J-integral deflection criterion are investigated, just as stochastic aspects of bifurcation phenomena of crack deflection observed under mode-I loading.

An orthogonal dual-regulation strategy for sensitive biosensing applications.

ABSTRACTBiosensing systems based on controllable motion behaviors of droplets have attracted extensive attention, but still face challenges of insufficient sensitivity and uncontrollable dynamic range due to imprecise manipulation of droplet motion on the surfaces. Here, we report an orthogonal dual-regulation strategy for precise motion control of droplets and we demonstrate its utility as a sensitive sensing system with controllable dynamic ranges of sensing for adenosine triphosphate, miRNA, thrombin and kanamycin, as well as discrimination of five kinds of DNA. We endowed a DNA-contained bio-droplet sliding on a lubricant-infused structural surface with micro-grooves to separately adjust the resistance from liquid phase and solid phase. The resistance from liquid phase mainly depended on hydrophobic interaction between DNA and lubricant, which can be finely tuned by different DNA’s average chain length. Meanwhile, the resistance from solid surface was determined by the energy barrier from the periodic micro-grooves, which can be adjusted by varying the droplet's sliding direction on the surface. The hydrophobic interaction is conformed to be orthogonal to the micro-grooves’ anisotropic resistance by three different methods. This orthogonal dual-regulation strategy thus demonstrated its ability to precisely control bio-droplets’ motion behaviors and sensitive detection with adjustable dynamic ranges for various bio-targets. The dual-regulation strategy will provide significant insights for super-wettable biosensors, visual inspection and beyond.