Conductivity Mismatch Research Articles

Enhancing Conductivity of Nickel Oxide to Achieve Scalable Preparation for High-Efficiency Perovskite Solar Modules

NiOx, prepared via the sputtering method, exhibits low conductivity and energy level mismatch with the perovskite layer, thereby limiting further enhancements in the performance of perovskite solar modules (PSMs). Unlike traditional methods that enhance the performance of NiOx through reactive sputtering or directly doping NiOx targets with metal ions, both of which incur high costs and low efficiency, we employ an evaporation method using LiF to achieve efficient and low-cost doping of NiOx. Compared to the pristine NiOx, the incorporation of LiF significantly increases the conductivity of NiOx. Additionally, the incorporation of LiF enhances the quality of the deposited perovskite films, as well as the energy level alignment and symmetry between NiOx and the perovskite, effectively improving the hole extraction and transport capabilities between NiOx and the perovskite. As a result, the PSM (active area of 57.30 cm²) fabricated in air achieves an impressive efficiency of 19.54%. Furthermore, the unencapsulated PSM retains 80% of its initial efficiency after 700 h of continuous illumination, whereas the NiOx-based PSM drops to 80% after only 150 h. This study provides a simple and low-cost method for doping NiOx, which is of great significance for the further industrialization of PSMs.

Constructing Metal-Organic Framework Films with Adjustable Electronic Properties on Hematite Photoanode for Boosting Photogenerated Carrier Transport.

Hematite (α-Fe2O3) has become a research hotspot in the field of photoelectrochemical water splitting (PEC-WS), but the low photogenerated carrier separation efficiency limits further application. The electronic structure regulation, such as element doping and organic functional groups with different electrical properties, is applied to alleviate the problems of poor electrical conductivity, interface defects, and band mismatch. Herein, α-Fe2O3 photoanodes are modified to regulate their electric structures and improve photogenerated carrier transport by the bimetallic metal-organic frameworks (MOFs), which are constructed with Fe/Ni and terephthalate (BDC) with 2-substitution of different organic functional groups (─H, ─Br, ─NO2 and ─NH2). The α-Fe2O3 photoanode loaded with FeNi-NH2BDC MOF catalyst exhibits the optimal photocurrent density (2mAcm-2) at 1.23VRHE, which is 2.33 times that of the pure α-Fe2O3 photoanode. The detailed PEC analyses demonstrate that the bimetallic synergistic effect between Fe and Ni can improve the conductivity and inhibit the photogenerated carrier recombination of α-Fe2O3 photoanodes. The ─NH2 group as an electron-donor group can effectively regulate the electron distribution and band structure of α-Fe2O3 photoanodes to prolong the lifetime of photogenerated holes, which facilitates photogenerated carrier transport and further enhances the PEC-WS performance of α-Fe2O3 photoanode.

Highly Efficient Spin Injection and Readout Across Van Der Waals Interface.

Spin injection, transport, and detection across the interface between a ferromagnet and a spin-carrying channel are crucial for energy-efficient spin logic devices. However, interfacial conductance mismatch, spin dephasing, and inefficient spin-to-charge conversion significantly reduce the efficiency of these processes. In this study, it is demonstrated that an all van der Waals heterostructure consisting of a ferromagnet (Fe3GeTe2) and Weyl semimetal enables a large spin readout efficiency. Specifically, a nonlocal spin readout signal of 150mΩ and a local spin readout signal of 7.8Ω is achieved, which reach the signal level useful for practical spintronic devices. The remarkable spin readout signal is attributed to suppressed spin dephasing channels at the vdW interfaces, long spin diffusion, and efficient charge-spin interconversion in Td-MoTe2. These findings highlight the potential of vdW heterostructures for spin Hall effect-enabled spin detection with high efficiency, opening up new possibilities for spin-orbit logic devices using vdW interfaces.

Improvement in non‐linear electrical conductivity of silicone rubber by incorporating zinc oxide fillers and grafting small polar molecules

AbstractSilicone rubber (SiR) is commonly used in reinforced insulation parts for high‐voltage direct current (HVDC) cable accessories due to its excellent insulation, elasticity, and high‐temperature resistance. HVDC cable accessories always suffer from the local electric field concentration due to the electrical conductivity mismatch between reinforced insulation and main insulation, which can ultimately lead to electric breakdown. The non‐linear conductive composites based on SiR have the ability to adaptively adjust the distribution of the electric field in cable accessories. This is expected to solve the problem of localised electric field concentration. The zinc oxide (ZnO) and glycidyl methacrylate (GMA) are used as fillers and grafted modifier respectively to improve the non‐linear electrical conductivity of ZnO/SiR‐GMA composites. The results indicate that grafting GMA can increase electrical conductivity of SiR, while doping ZnO filler enables SiR to have non‐linear conductivity characteristics. The combination of doping and grafting modification of the composites achieves excellent non‐linear conductive properties at lower ZnO filler content. Additionally, the mechanical properties of the modified composites are enhanced. The simulation results indicate that ZnO/SiR‐GMA is the most effective material for homogenising the electric field when used as reinforced insulation for cable intermediate joints.

Gate voltage-controlled spin-rectifier diode based on Janus transition metal nitride MXene with spin gapless semiconductor

With the continuous application of spintronics technology, spintronic devices have been expected to become a major direction in the development of next-generation electronic devices. However, for spin rectifier diodes, how to provide a large number of spin-polarized carriers is still a key technical issue. Conventional spin-polarization injection models use ferromagnetic (FM)/semiconductor structures, but because of the conductivity mismatch can limit the injection of their polarization. This makes the search for spin-gapless semiconductor which has the conductivity between metals and semiconductors an effective way to solve this problem. Recently, MXene, a new two-dimensional material with high spin polarization, has been expected to undergo modulation of the electronic structure through external field or proximity effects. Subsequently, we propose a Janus transition metal structure of the MXene which modulates the spin properties by breaking the symmetry of the transition metals. Moreover, we find the band structure of TiCrNO2 can be effectively modulated by an applied electric field, which transforms itself from a magnetic semiconductor to a spin-gapless semiconductor under an electric field strength of 1 V/Å. With this as a basis, we construct a tunable spin rectifier diode and study its spin rectification effect by the first-principle calculations combined with non-equilibrium Green's function. The results show that the rectification ratio of the spin rectification diode can be adjustable by varying the strength of the external electric field, and its rectification rate exceeds the highest value currently available for two-dimensional rectifier devices. Our results provide a reference value for the application of nitride MXene in spintronic devices.

Atomic-Scale Engineering of Grain Boundary Chemistry and Potential for Li-Garnet Solid-State Electrolytes

With increasing demands to replace flammable liquid electrolytes, solid-state electrolytes have sparked interests both in academic and industrial sectors. In particular, Li-garnet LLZO (Li7La3Zr2O12) exhibits outstanding electrical, chemical, and mechanical properties. Despite the promise, LLZO suffers from the formation of lithium (Li) dendrites at high current operations, thereby limiting the safety and performance of garnet-based solid-state batteries. Li metal nucleation and growth reportedly initiate and grow along the locality of grain boundaries (GBs) in such polycrystalline electrolytes, due either to low ionic or high electronic conductivity of the boundaries. However, limited understanding yet exists on the origins of the local GB conductivity mismatch. The mechanistic understanding should be an important prerequisite to develop engineering strategies of the failing GB interfaces. In this work, we first apply grain boundary core-space charge layer model to understand the basis of Li metal nucleation at GBs. Grain boundary core of LLZO is modeled to have excess negative charge potential, leading to the subsequent Li ionic carrier depletion and electronic carrier accumulation in the adjacent space charge layers. The carrier concentration variations then drive the local electronic conductivity surge and detrimental Li metal nucleation at the GBs. Both electrochemical and microscopic characterization techniques are employed to investigate the atomic-level composition and space charge potential at the GBs. This understanding offers us new strategies for controlling Li nucleation. First, sintering atmosphere is selectively chosen to reduce the potential barrier by suppressing intrinsic defect accumulation at the GB core. Second, an aliovalent dopant, with net-positive charge, is introduced to segregate to GB and mitigate the negative core potential. Both approaches are shown effective in lowering the electronic conductivity and to impede Li metal penetration. We successfully achieve critical current densities (CCD) of ~ 1 mA cm-2,a two-fold increase over prior reports. Our theoretical understanding and the engineering approaches will aid in interpreting the failure origin of the garnet electrolytes, and provide a blueprint on how to engineer GBs for improved safety and performance of all-solid-state Li metal batteries.

Thermal conductivity effect on thermophoresis of charged spheroidal colloids in aqueous media.

Thermophoresis of spheroidal colloids in aqueous media under the thermal conductivity effect is analyzed. The thermophoretic velocity and the thermodiffusion coefficient of spheroidal colloids have been formulated for extremely thin electric double layer (EDL) cases. Furthermore, a numerical thermophoretic model is built for arbitrary EDL thickness cases. The parametric studies show that the thermal conductivity mismatch of particle and liquid gives rise to a nonlinear temperature region around the spheroid, with the thickness close to the minor semiaxis. When the EDL region is thin relative to such nonlinear temperature region, the thermal conductivity effect on the thermophoresis of spheroidal colloids is significant, which strongly depends on the ratio of the minor semiaxis to the EDL thickness, the thermal conductivity ratio of particle to liquid, and the particle aspect ratio. Finally, to estimate the thermodiffusion coefficient of spheroidal colloids with arbitrary thermal conductivity, electrolyte concentration, and particle shape, the average dimensionless axial temperature gradient on the spheroidal equator plane in the EDL region is proposed.

In silico study of the effects of cerebral circulation on source localization using a dynamical anatomical atlas of the human head

Objective. This study focuses on the effects of dynamical vascular modeling on source localization errors in electroencephalography (EEG). Our aim of this in silico study is to (a) find out the effects of cerebral circulation on the accuracy of EEG source localization estimates, and (b) evaluate its relevance with respect to measurement noise and interpatient variation. Approach. We employ a four-dimensional (3D + T) statistical atlas of the electrical properties of the human head with a cerebral circulation model to generate virtual patients with different cerebral circulatory conditions for EEG source localization analysis. As source reconstruction techniques, we use the linearly constraint minimum variance (LCMV) beamformer, standardized low-resolution brain electromagnetic tomography (sLORETA), and the dipole scan (DS). Main results. Results indicate that arterial blood flow affects source localization at different depths and with varying significance. The average flow rate plays an important role in source localization performance, while the pulsatility effects are very small. In cases where a personalized model of the head is available, blood circulation mismodeling causes localization errors, especially in the deep structures of the brain where the main cerebral arteries are located. When interpatient variations are considered, the results show differences up to 15 mm for sLORETA and LCMV beamformer and 10 mm for DS in the brainstem and entorhinal cortices regions. In regions far from the main arteries vessels, the discrepancies are smaller than 3 mm. When measurement noise is added and interpatient differences are considered in a deep dipolar source, the results indicate that the effects of conductivity mismatch are detectable even for moderate measurement noise. The signal-to-noise ratio limit for sLORETA and LCMV beamformer is 15 dB, while the limit is under 30 dB for DS. Significance. Localization of the brain activity via EEG constitutes an ill-posed inverse problem, where any modeling uncertainty, e.g. a slight amount of noise in the data or material parameter discrepancies, can lead to a significant deviation of the estimated activity, especially in the deep structures of the brain. Proper modeling of the conductivity distribution is necessary in order to obtain an appropriate source localization. In this study, we show that the conductivity of the deep brain structures is particularly impacted by blood flow-induced changes in conductivity because large arteries and veins access the brain through that region.

Thermoelastic fields for a heat exchanger of arbitrary shape in a bi-material infinite plane

When a bi-material with two jointed dissimilar half-planes containing an arbitrarily shaped polygonal inclusion is subjected to heat flow, the thermoelastic fields, including temperature and displacement, can be derived by the Green’s function technique with the integral of the source over the inclusion. Using Hadamard’s regularization, the two-dimensional (2D) thermal, elastic, and thermoelastic Green’s functions of two-jointed dissimilar half-planes are firstly derived from the 3D Green’s functions as the corresponding fundamental solutions. The fundamental solutions for semi-infinite and infinite domains can be recovered by adjusting the material constants. Eshelby’s tensors are derived in terms of the biharmonic, harmonic, and two Boussinesq’s displacement potential functions. When a heat exchanger of arbitrary shape is embedded in a matrix with different thermal and mechanical properties, combining a continuously distributed eigen-temperature gradient and eigenstrain field, the dual equivalent inclusion method (DEIM) is applied to handle the material mismatch of thermal conductivity, stiffness, and thermal expansion coefficient, respectively. Therefore, the full thermoelastic fields can be obtained by the integral over the heat exchanger only. The eigen-fields are expanded in the Taylor series referred to the center of the particle, which exhibits tailorable accuracy with uniform, linear or quadratic terms in comparison with the analytical solution for a circular inhomogeneity in the infinite domain. An exact thermoelastic solution of a circular inhomogeneity embedded within the infinite domain is present. The case study of an electric heat cable in the concrete block demonstrates the capability and exactness of the model. The method can be used for a thin film containing a heat exchanger of arbitrary shape as either a heat sink or source.

The Green’s function based thermoelastic analysis of spherical geothermal tanks in a semi-infinite domain

When an underground heat exchanger is subjected to a surface load on the ground and temperature change inside, the stress transfer between the thermal tank and the earth may cause the deformation and destruction of the tank. The bi-material thermoelastic fundamental solution of two-jointed dissimilar half-spaces is applied to elastic and thermal analysis of spherical heat storage tanks, where the continuity equations at the bi-material interface are satisfied. Using Hadamard’s regularization in the x3 direction, the two-dimensional bi-material thermoelastic fundamental solution can be obtained. By changing the material constants, the fundamental solution for a semi-infinite domain or an infinite domain with a single material can be recovered. In general, the storage tanks and soil exhibits different thermal and mechanical properties. A dual equivalent inclusion method (DEIM) is proposed to simulate the material mismatch of thermal conductivity and elasticity with continuously distributed eigen-temperature-gradients and inelastic eigenstrains on the tanks, respectively. Using the analytical domain integrals, no mesh is required for inhomogeneities. Due to the boundary effects and inhomogeneity interactions, the eigen-fields are expanded at the center of each inhomogeneity using the Taylor series with tailorable accuracy. The DEIM is verified by the finite element method and demonstrated by the geothermal applications using uniform, linear, or quadratic orders of eigen-fields. For a spherical heat exchanger in an infinite homogeneous domain, DEIM provides the exact solutions of the thermoelastic fields for a uniform heat source and a uniform far-field heat flux field.

Alumina tunnel contact based lateral spin-Field effect transistor

In the present work, modified Datta and Das Type silicon based lateral spin-Field Effect Transistor (MDD Type s-FET) is presented with alumina as tunnel contact. The insertion of alumina enhances the spin injection ability of Co-Graphene nanosheets based ferromagnetic electrode (FM) and also resolves the conductivity mismatch problem. The main accomplishment of present work is that fabricated MDD Type s-FET with alumina as tunnel contact exhibits the non-rectifying current–voltage characteristic with sufficiently large value of MR which is an indispensable requirement of spintronics devices. Also, in present work 2-dimensional electron gas was used as a channel which can control MR through gate voltage. Similarly, the control on MR through gate voltage enables the switching action in s-FET.

Spin injection by spin–charge coupling in proximity induced magnetic graphene

Within the field of spintronics major efforts are directed towards developing applications for spin-based transport devices made fully out of two-dimensional materials. In this work we present an experimental realization of a spin-valve device where the generation of the spin signal is exclusively attributed to the spin-dependent conductivity of the magnetic graphene resulting from the proximity of an interlayer antiferromagnet, chromium sulfide bromide (CrSBr). We clearly demonstrate that the usage of the conventional air-sensitive 3D magnetic contacts can be fully avoided when graphene/CrSBr heterostructures are employed. Moreover, apart from providing exceptionally long spin relaxation length, the usage of graphene for both generation and transport of the spin allows to automatically avoid the conductivity mismatch between the source and the channel circuits that has to be considered when using conventional low-resistive contacts. Our results address a necessary step in the engineering of spintronic circuitry out of layered materials and precede further developments in the area of complex spin-logic devices. Moreover, we introduce a fabrication procedure where we designed and implemented a recipe for the preparation of electrodes via a damage-free technique that offers an immediate advantage in the fields of air-sensitive and delicate organic materials.

The Green’s Function-Based Thermal Analysis of a Spherical Geothermal Tank in a Semi-Infinite Domain

Abstract The Green’s function of a bimaterial infinite domain with a plane interface is applied to thermal analysis of a spherical underground heat storage tank. The heat transfer from a spherical source is derived from the integral of the Green’s function over the spherical domain. Because the thermal conductivity of the tank is generally different from soil, the Eshelby’s equivalent inclusion method (EIM) is used to simulate the thermal conductivity mismatch of the tank from the soil. For simplicity, the ground with an approximately uniform temperature on the surface is simulated by a bimaterial infinite domain, which is perfectly conductive above the ground. The heat conduction in the ground is investigated for two scenarios: First, a steady-state uniform heat flux from surface into the ground is considered, and the heat flux is disturbed by the existence of the tank due to the conductivity mismatch. A prescribed temperature gradient, or an eigen-temperature gradient, is introduced to investigate the local temperature field in the neighborhood of the tank. Second, when a temperature difference exists between the water in the tank and soil, the heat transfer between the tank and soil depends on the tank size, conductivity, and temperature difference, which provide a guideline for heat exchange design for the tank size. The modeling framework can be extended to two-dimensional cases, periodic, or transient heat transfer problems for geothermal well operations. The corresponding Green’s functions are provided for those applications.

Solution-processed Cu-doped SnO2 as an effective electron transporting layer for High-Performance planar perovskite solar cells

A high-quality electron transport layer (ETL) is indispensable for effective and stable planar perovskite solar cells (PSCs). Tin oxide (SnO2) is considered the most promising alternative to TiO2 as ETL due to its excellent optical and electrical properties. However, some of improvements need to be carried out for intrinsic SnO2, such as conductivity, energy loss, and lattice mismatch in the SnO2/perovskite interface. Herein, the Cu-doped SnO2 (Cu: SnO2) as ETL has been made through mixing the copper salt precursor solution with SnO2 colloidal solution in room-temperature solution-processed. The Cu incorporated into SnO2 increases the conductivity of ETL and uplifts the conduction band to obtain a more suitable band alignment in SnO2/perovskite interface for relieving the energy barrier in the charge transporting. Moreover, it further improves the quality of perovskite films with the enhanced crystallinity, enlarged grain size, which have an impact on light absorption and reduction of defect states for the perovskite layer. The power conversion efficiency (PCE) of the prepared planar PSCs with Cu:SnO2 ETL exceeds 21%, compared with the SnO2-based PSCs (19.63%), and the long-term stability was improved.

Performance-Enhancing Sulfur-Doped TiO2 Photoanodes for Perovskite Solar Cells

High-performance electron transport layer (ETL) anode generally needs to form a uniform dense layer with suitable conduction band position and good electron transport properties. The TiO2 photoanode is primarily applied as the ETL because it is low-cost, has diverse thin-film preparation methods and has good chemical stability. However, pure TiO2 is not an ideal ETL because it lacks several important criteria, such as low conductivity and conduction band mismatch with compositional-tailored perovskite. Thus, TiO2 is an inefficient photo-anode or ETL for high-performance perovskite devices. In this study, sulfur as dopant in the TiO2 photo-anode thin film is used to fabricate solid-state planar perovskite solar cells in relatively high humidity (40–50%). The deposited S-doped thin film improves the power conversion efficiency (PCE) of the device to 6.0%, with the un-doped TiO2 producing a PCE of 5.1% in the best device. Improvement in PCE is due to lower recombination and higher photocurrent density, resulting in 18% increase in PCE (5.1–6.0%).

Dilute magnetic semiconductor electrode based all semiconductor magnetic tunnel junction for high-temperature applications

In this paper, the spin-transport properties of Gallium Nitride/Indium Phosphide/Gallium Nitride (GaN/InP/GaN) all semiconductor magnetic tunnel junction (MTJ) has been investigated. To induce ferromagnetic properties in the electrodes made of GaN, the electrodes are doped with Manganese (Mn). The central region is made of InP, which is a large bandgap material, thereby improving the zero-bias magnetoresistance. The electrodes used in the proposed device show ferromagnetic behavior beyond room temperature without the conductivity mismatch problem. Finally, a comparison based on the proposed device's performance parameters with the devices reported in the open literature is carried out in this work. The comparison clearly shows the pre-eminence of the proposed device over the previously reported devices as it has high TMR (1.97 × 104%) and works over a wide range of temperature.

Electrical Spin Injection into the 2D Electron Gas in AlN/GaN Heterostructures with Ultrathin AlN Tunnel Barrier

AbstractThe spin injection into 2D electron gas (2DEG) in AlN/GaN heterostructures is studied by magneto‐transport measurements. An ultrathin AlN layer at the hetero‐interface acts as a barrier to form high‐quality 2DEG in the triangular quantum well and a tunneling barrier for the spin injection to overcome the conductance mismatch issue. In this study, Hanle signals and inversed Hanle signals are observed, proving that the spin injection is achieved in the 2DEG in the AlN/GaN heterostructure rather than in the interfacial states. The spin‐relaxation time in 2DEG at 8 K is found to be as long as 860 ps, which almost keeps constant with bias and decreases with increasing temperature. The spin‐relaxation process is illustrated as Rashba spin‐orbit coupling dominated D'yakonov Perel’ mechanisms above 8 K. These results show the promising potential of 2DEG in AlN/GaN heterostructures for spin field‐effect transistor applications.

Fabrication of Graphene-Inserted Tunneling Device (GiTD) for Emerging Spin Devices

Objective:Spintronics, which utilizes the spin degree of freedom of elementary particles, holds the promise for many attractive applications including non-volatile logic and storage. However, the main challenge is to achieve spin manipulation (spin injection, transport and detection) with high efficiencies. Here in this work, we focus on spin injection from the nanomagnet to another layer, which is typically degraded by any conductivity mismatch and/or interfacial imperfections. Inserting a tunnel barrier between the ferromagnetic and channel layers has shown to relieve this problem.The best way to quantitatively study spin polarization of a ferromagnetic thin film that is modified by any spin flipping at the interfaces is to directly measure the tunneling spin polarization across the ferromagnet and the tunnel barrier using superconducting tunneling spectroscopy (STS) [1]. One practical challenge in using this technique to investigate a role of any specific material of interest (any insertion layer other than the ferromagnet itself) in terms of spin polarization is to fabricate such a multi-layered device structure. The difficulty mainly arises from oxidation of underlying metallic layers.Recently, graphene has been considered as a promising material for spintronic applications. Advantages of graphene include weak spin-orbit coupling and low lattice mismatch with conventional ferromagnets such as Permalloy (Ni80Fe20). This leads researchers to re-think graphene as the long-range spin transport channel or the efficient tunnel barrier material(or both) [2]. The primary objective of this work is to demonstrate the graphene-inserted tunneling device (GiTD) that enables subsequent STS measurements to study how graphene impacts tunneling spin polarization and ultimately use it to enhance the spin injection efficiency in spin devices.New results:Fig. 1 illustrates a schematic device structure (GiTD) investigated in this work. Initially, a superconducting thin layer (5 nm) of Al was deposited by sputtering. A CVD-grown monolayer graphene was then transferred on top, which was followed by deposition of Permalloy (Py). Because a thin tunnel barrier of AlOx is easily formed by exposing the sample to ambient air, we study the role of graphene in the F/I/S device stack (F: ferromagnet, I: insulator, S: superconductor) with a native thin oxide formed at the graphene/S-layer interface. We patterned the graphene layer by photolithography and O2-plasma etching to avoid an electrical short between the top and bottom layers in the cross-bar geometry. Details of the process flow are depicted in Fig. 2, and a micrograph image of the fabricated GiTD structure (mounted on the STS holder) is shown in Fig. 3. Raman spectroscopy [3] was also conducted to confirm both the presence and absence of graphene in respective regions (Fig. 4).One important piece of innovation introduced in this work is an “offset contact” method that was developed to ensure any unnecessary oxidation of contact electrodes does not adversely impact the electrical testing. Since the STS measurement requires the sample to be mounted on a chip carrier wire-bonded to separate contact pads on the substrate, deposition of any additional metallic layer (known to facilitate the wire bonding process) may result in oxide formation on the underlying contact layer unless all constituent layers are deposited in-situ. As seen in Fig. 2 (steps (2) through (7)), we deposited first a thin film of Py and then put the S-layer (Al) with a slight offset to Py. By depositing another Py layer on top, a direct link between the top Py and bottom Py was established to bypass the oxidized Al layer in between. Fig. 5 shows the current-voltage (I-V) characteristic of the fabricated control device (Py/AlOx/Al) measured at room temperature, clearly demonstrating that (1) current flows well through the multi-layered contact pads and (2) memristor-like switching behavior is observed due to formation of a thin metal oxide (AlOx).Significance:By conducting the STS measurements that compare the control device with the graphene-inserted device (GiTD), the role of graphene in terms of tunneling spin polarization will be quantitatively studied. This will enable us to develop the novel tunnel barrier material, possibly consisting of 2D graphitic nanostructures. It will be best interfaced with both the ferromagnetic contact (spin injector or detector) and the graphene-based spin transport channel. Ultimately, this study will greatly impact the development of active spin devices such as spin FET where achieving the high spin injection still remains the biggest challenge.

Fabrication of Graphene-Inserted Tunneling Device (GiTD) for Emerging Spin Devices

Spintronic nanostructures such as magnetic tunnel junctions possess great potential for advancing a future computing paradigm requiring high speed and low power consumption. One great challenge limiting their widespread application is the conductivity mismatch between the ferromagnet and the channel material, resulting in low spin injection efficiency. The possible use of graphene as an atomically-thin tunnel barrier has been widely discussed because it could be readily interfaced with the ferromagnet to mitigate the conductivity mismatch problem. However, it still remains relatively unexplored to quantitatively understand how graphene will impact the spin polarization of tunneling currents. Here we present the experimental process to design and fabricate a graphene-inserted tunneling device, which will serve as the useful platform to study the fundamentals required for developing emerging spin devices. Further follow-up studies such as superconducting tunneling spectroscopy can be applied to the device structure developed in this work.

Objects interacting with solidification fronts: Thermal and solute effects

Objects, such as droplets, bubbles, or particles, interact with a moving solidification front in several material processing routes. The consequences of this confrontation, varying from instantaneous engulfment to complete rejection of suspended objects, regulates the solidified microstructure and thus, the functional properties of the material. In this study, we utilize in situ cryo-confocal microscopy to investigate the interplay between thermal conductivity mismatch (of the object and the melt) and the role of solute, which both impact the geometry of the ice-water solidification front in different manners. First, we experimentally validate the theoretical predictions of physical models on the distortion of thermal fields in the presence of foreign objects. Subsequently, we report on the dominating effect of solute on the front curvature with the dynamic evolution of premelted films. In the case of cellular front morphology, we depict that particles with a lower thermal conductivity than water induce a distortion of the encircling ice crystals, thereby modifying the final microstructure of the solid. Finally, our results demonstrate that to successfully predict and control the solidification microstructure, in the presence of objects, physical models incorporating both thermal and long-range solute effects are required.