Direction Of Electron Flow Research Articles

First-principles prediction of electrochemical polarization and mechanical behavior in Mg based intermetallics

Here the electrochemical and mechanical behavior for different Mg based intermetallics (Mg17Al12, MgZn2, Mg3Nd, Mg2Si, Mg24Y5, Mg2Ca, Mg12Ce, Mg12La, Mg2Cu, and Mg2Sn) was comprehensively quantified. First, a robust thermodynamic framework was developed that utilized first-principles calculations to accurately predict the electrochemical polarization behavior of the Mg based intermetallics. Based on the predicted corrosion potential, apart from Mg2Ca which behaves as an anode to the Mg matrix, the rest of the Mg based intermetallics act as a cathode. The electrochemical polarization behavior of the intermetallics was strongly dependent on surface mediated properties (surface energy and work function) and chemical bonding characteristics. Furthermore, the electrochemical behavior was sensitive to the atomic arrangement on the surface. Based on Bader analysis, it was found that the direction of electron flow between the constituent elements of the intermetallic (towards or away from Mg) strongly influenced the electrochemical behavior. The accurate quantifications of elastic constants for the Mg based intermetallics conclusively clarified the mechanical behavior of Mg2Ca and Mg2Cu. Finally, the computational framework provides an accurate screening tool that can assist in alloy design and development of coatings.

Chirality-dependent spin-transfer torque and current-induced spin rotation in helimagnets

We have built a theory of the spin-transfer torque (STT) effect in a conductive chiral helical magnet (CHM). It is shown that the STT effect induced by a spin current flowing through CHM leads to the rotation of the CHM magnetization spiral around its axis. The frequency of such rotation of the CHM magnetization is found. The former is expressed in terms of the parameters of the quantum-exchange Hamiltonian that specifies helical magnetic ordering in a conductive crystal. We have showcased that both the direction of rotation of the CHM magnetization and the direction of changes in the shape of the magnetic spiral are determined by the electron flow direction and the chirality of the magnet. The theory developed accounts for the generation of an electromagnetic field when rotating the magnetic spiral in the CHM subjected to an electric current flowing through the helimagnet.

Flipping the Switch: Reverse-Demand Voltage-Sensitive Fluorophores.

Fluorescence microscopy with fluorescent reporters that respond to environmental cues is a powerful method for interrogating biochemistry and biophysics in living systems. Photoinduced electron transfer (PeT) is commonly used as a trigger to modulate fluorescence in response to changes in the biological environment. PeT-based indicators rely on PeT either into the excited state (acceptor PeT) or out of the excited state (donor PeT). Our group has been developing voltage-sensitive fluorophores (VF dyes) that respond to changes in biological membrane potential (Vm). We hypothesize that the mechanism of voltage sensitivity arises from acceptor PeT (a-PeT) from an electron-rich aniline-containing molecular wire into the excited-state fluorophore, resulting in decreased fluorescence at negative Vm. In this work, we reversed the direction of electron flow to access donor-excited PeT (d-PeT) VF dyes by introducing electron-withdrawing rather than electron-rich molecular wires. VF dyes containing electron-withdrawing groups show voltage-sensitive fluorescence, but with the opposite polarity: hyperpolarizing Vm now gives fluorescence increases. We used a combination of computation and experiment to design and synthesize five d-PeT VF targets, two of which are voltage-sensitive.

Effect of Grain Structure and Ni/Au-UBM Layer on Electromigration-Induced Failure Mechanism in Sn-3.0Ag-0.5Cu Solder Joints

The development of advanced electronic devices leads to highly miniaturized interconnect circuits (ICs), which significantly increases the electromigration (EM) phenomenon of solder and circuits due to higher current density. The electromigration of solder joints under high current density has become a severe reliability concern in terms of microelectronic product reliability. The microstructure of the solder plays an important role in the electromigration induced degradation. In this study, Sn-3.0Ag-0.5Cu solder bumps with Ni/Au under bump metallization (UBM) layer were fabricated and electromigration acceleration tests were conducted under current density of 1.4 × 104 A/cm2 and 120 °C to investigate the effect of grain structure and Ni/Au-UBM layer on EM-induced failure. Grain structures of solder bumps were determined by utilizing the Electron Backscatter Diffraction (EBSD) technique, and single-crystal solder, single-crystal dominated solder, and polycrystalline solder are observed in different test samples. According to the Scanning Electron Microscope (SEM) images, it is observed that the Ni/Au-UBM layer of the Cu pad can inhibit atom diffusion between solder bump and Cu pad, which reduces the consumption of Cu pad but causes a large void and crack at the interface. The EM lifetime of single crystal solder bumps is lower than that of polycrystalline solder bumps when the c-axis of single crystal solder bumps is perpendicular to the electron flow direction. Additionally, the single crystal structure will increase the brittleness of the solder bump, and cracks are easily generated and expanded under the stress caused by the mismatch of thermal expansion coefficients between the solder bump and Ni/Au-UBM layer near Cu pad. Polycrystalline solder bumps with a higher misorientation angle (15–55°) have a higher atom diffusion rate, which will result in the acceleration of the EM-induced failure.

Synchrotron X-ray study of electromigration, whisker growth, and residual strain evolution in a Sn Blech structure

Synchrotron X-ray analysis of the Sn electromigration behavior and Sn whisker growth in a Blech structure using nano-X-ray fluorescence microscopy and white beam Laue nanodiffraction was conducted. Sn depletion at the cathode and whisker/extrusion formation at the anode were characterized in-situ, and the results obeyed the electromigration kinetics. This electromigration scenario gradually decayed because of the counterbalance between electron wind force and back stress. White beam Laue nanodiffraction analysis showed that a noticeable compressive deviatoric stress in the direction of electron flow built up at the anode of Sn strips, particularly in the roots of Sn whiskers, confirming that electromigration-induced atomic accumulation occurred downstream in a strip and that Sn whiskering was closely related to internal stress resulting from atomic accumulation in confined segments. Finally, a theoretical model based on fundamental electromigration theory revealed that Sn diffused predominately through lattice and grain boundary paths at Sn homologous temperature of 0.6.

Negative nonlocal vicinity resistance of viscous flow in a two-dimensional electron system

We perform a quantum transport study of Hall viscous liquid in multiterminal narrow Hallbar devices of a high-mobility two-dimensional electron system (2DES) in GaAs/AlGaAs heterostructure. In the nonlocal transport measurements of vicinity geometry under magnetic fields $(B)$, we observe that the absolute negative magnetoresistance $({R}_{xx})$ value $({R}_{\text{min}}<0)$ and the corresponding magnetic field $({B}_{\text{min}})$ are both inversely proportional to the adjacent Hallbar arm distance $(L)$. The occurrence of negative resistance is dependent on the characteristic lengths of the devices and the electron flow direction under $B$-fields. The minimal resistance ${R}_{\text{min}}$ occurs when the cyclotron radius ${R}_{C}$ approximates $L$. Multiples of high-order ($n\mathrm{th}$-order) ${R}_{\text{min},n}$'s persist from low to high magnetic fields in a large sample size of $L=5\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$. Our experimental study reveals the transport behaviors in the vicinity regime, where the negative resistances depict viscous electronic flows in the high-mobility 2DES. In addition, the negative and high-order minimal resistances expand to a magnetic field of several kGs.

Construction of Bi2S3/TiO2/MoS2 S‐Scheme Heterostructure with a Switchable Charge Migration Pathway for Selective CO2 Reduction

Switching between the redox potential of an appropriate semiconductor heterostructure could show critical applications in selective CO2 reduction. Designing a semiconductor photocatalyst with a wavelength‐dependent response is an effective strategy for regulating the direction of electron flow and tuning the redox potential. Herein, the switching mechanism between two charge migration pathways and redox potentials in a Bi2S3/TiO2/MoS2 heterostructure by regulating the light wavelength is achieved. In situ irradiated X‐ray photoelectron spectroscopy (ISI‐XPS), electron spin resonance (ESR), photoluminescence (PL), and experimental scavenger analyses prove that the charge transport follows the S‐scheme approach under UV–vis–NIR irradiation and the heterojunction approach under vis–NIR irradiation, confirming the switchable feature of the Bi2S3/TiO2/MoS2 heterostructure. This switchable feature leads to the reduction of CO2 molecules to CH3OH and C2H5OH under UV–vis–NIR irradiation, while CH4 and CO are produced under Vis–NIR irradiation. Interestingly, the apparent quantum efficiency of the optimal composite at λ = 600 nm is 4.23%. This research work presents an opportunity to develop photocatalysts with switchable charge transport and selective CO2 reduction.

Atomic-Scale Investigation of Electromigration with Different Directions of Electron Flow into High-Density Nanotwinned Copper through In Situ HRTEM

Electromigration (EM) has aroused substantial attention with the shrinkage of modern devices. EM is an interaction between electron carriers and atoms, meaning that it arises from atomic behaviour. Both the number of twin boundaries (TBs) and the direction of electron flow are crucial factors affecting EM behaviour. In this study, EM phenomena with perpendicular and parallel electron flow were investigated by high resolution transmission electron microscopy (HRTEM). Twin planes could limit the growth direction of voids in the parallel case. The evolution of smooth surfaces into step-like surfaces resulting from the triple point retarding EM has been demonstrated. With the measurement of the resistance, it could be concluded that the specimen with electron flow perpendicular to the TBs had better EM restriction. Columnar grains can confine the position of the voids. This study demonstrates the dynamic evolution of the surface structure, providing insight into the fabrication of interconnections in the integrated circuits industry.

Deciphering Single-Bacterium Adhesion Behavior Modulated by Extracellular Electron Transfer.

For bacterial adhesion and biofilm formation, a thorough understanding of the mechanism and effective modulating is lacking due to the complex extracellular electron transfer (EET) at bacteria-surface interfaces. Here, we explore the adhesion behavior of a model electroactive bacteria under various metabolic conditions by an integrated electrochemical single-cell force microscopy system. A nonlinear model between bacterial adhesion force and electric field intensity is established, which provides a theoretical foundation for precise tuning of bacterial adhesion strength by the surface potential and the direction and flux of electron flow. In particular, based on quantitative analyses with equivalent charge distribution modeling and wormlike chain numerical simulations, it is demonstrated that the chain conformation and unfolding events of outer membrane appendages are dominantly impacted by the dynamic bacterial EET processes. This reveals how the anisotropy of bacterial conductive structure can translate into the desired adhesion behavior in different scenarios.

Phase domain boundary motion and memristance in gradient-doped FeRh nanopillars induced by spin injection

The B2-ordered alloy FeRh shows a metamagnetic phase transition, transforming from antiferromagnetic to ferromagnetic order at a temperature Tt∼380 K in bulk. In addition to temperature, the phase transition can be triggered by many means such as strain, chemical doping, or magnetic or electric fields. Its first-order nature means that phase coexistence is possible. Here, we show that a phase boundary in a 300-nm-diameter nanopillar, controlled by a doping gradient during film growth, is moved by an electrical current in the direction of electron flow. We attribute this to spin injection from one magnetically ordered phase region into the other driving the phase transition in a region just next to the phase boundary. The associated change in resistance of the nanopillar shows memristive properties, suggesting potential applications as memory cells or artificial synapses in neuromorphic computing schemes.

Atomic-Scale Investigation of Electromigration with Different Directions of Electron Flow into High-Density Nanotwinned Copper Through In Situ HRTEM

Electromigration (EM) has aroused substantial attention with the shrinkage of modern devices. EM is an interaction between electron carriers and atoms, meaning that it arises from atomic behaviour. Both the number of twin boundaries (TBs) and the direction of electron flow are crucial factors affecting EM behaviour. In this study, EM phenomena with perpendicular and parallel electron flow were investigated by high resolution transmission electron microscopy (HRTEM). Twin planes could limit the growth direction of voids in the parallel case. The evolution of smooth surfaces into step-like surfaces resulting from the triple point retarding EM has been demonstrated. With the measurement of the resistance, it could be concluded that the specimen with electron flow perpendicular to the TBs had better EM restriction. Columnar grains can confine the position of the voids. This study demonstrates the dynamic evolution of the surface structure, providing insight into the fabrication of interconnections in the integrated circuits industry.

Modulation of mitochondrial site-specific hydrogen peroxide efflux by exogenous stressors

Oxygen (O2) deprivation and metals are common environmental stressors and their exposure to aquatic organisms can induce oxidative stress by disrupting cellular reactive oxygen species (ROS) homeostasis. Mitochondria are a major source of ROS in the cell wherein a dozen sites located on enzymes of the electron transport system (ETS) and substrate oxidation produce superoxide anion radicals (O2˙‾) or hydrogen peroxide (H2O2). Sites located on ETS enzymes can generate ROS by forward electron transfer (FET) and reverse electron transfer (RET) reactions; however, knowledge of how exogenous stressors modulate site-specific ROS production is limited. We investigated the effects of anoxia-reoxygenation and cadmium (Cd) on H2O2 emission in fish liver mitochondria oxidizing glutamate-malate, succinate or palmitoylcarnitine-malate. We find that anoxia-reoxygenation attenuates H2O2 emission while the effect of Cd depends on the substrate, with monotonic responses for glutamate-malate and palmitoylcarnitine-malate, and a biphasic response for succinate. Anoxia-reoxygenation exerts a substrate-dependent inhibition of mitochondrial respiration which is more severe with palmitoylcarnitine-malate compared with succinate or glutamate-malate. Additionally, specific mitochondrial ROS-emitting sites were sequestered using blockers of electron transfer and the effects of anoxia-reoxygenation and Cd on H2O2 emission were evaluated. Here, we find that site-specific H2O2 emission capacities depend on the substrate and the direction of electron flow. Moreover, anoxia-reoxygenation alters site-specific H2O2 emission rates during succinate and glutamate-malate oxidation whereas Cd imposes monotonic or biphasic H2O2 emission responses depending on the substrate and site. Contrary to our expectation, anoxia-reoxygenation blunts the effect of Cd. These results suggest that the effect of exogenous stressors on mitochondrial oxidant production is governed by their impact on energy conversion reactions and mitochondrial redox poise. Moreover, direct increased ROS production seemingly does not explain the increased adverse effects associated with combined exposure of aquatic organisms to Cd and low dissolved oxygen levels.

Surface Plasmon-Induced Hot Electrons as the Racemate to Regulate Ionization

Plasmon-assisted reactions have different reaction mechanisms than conventional chemical reactions occurring in solutions, and the hot electrons produced by plasmon decay play an irreplaceable role in plasmon-assisted coupling reactions. Here, we use p-mercaptobenzoic acid (pMBA) to illustrate this point from different aspects. In a typical chemical reaction, a base is added to deprotonate the carboxylic acid group in pMBA. In this system, however, there is no alkali or external charge to remove the hydrogen, but it is obvious that this system is a dynamic process. Here, although a Lewis base (Ag NPs) was used as the base, the generated hot electrons were trapped by hydrogen ions in an acidic environment, which reduced the efficiency of the ionization reaction. We used SERS to study the ionization of pMBA and to propose a method to regulate its ionization by adjusting its substituents. Furthermore, in contrast to previous studies, the direction of electron flow is clearly defined in this reaction system.

The In-Situ Observation of Grain Rotation and Microstructure Evolution Induced by Electromigration in Sn-3.0Ag-0.5Cu Solder Joints.

The in-situ observation of Sn-3.0Ag-0.5Cu solder joints under electromigration was conducted to investigate the microstructure and grain orientation evolution. It was observed that there was a grain rotation phenomenon during current stressing by in-situ electron backscattered diffraction (EBSD). The rotation angle was calculated, which indicated that the grain reorientation led to the decrease of the resistance of solder joints. On the other hand, the orientation of β-Sn played a critical role in determining the migration of Cu atoms in solder joints under current stressing migration. When the angle between the electron flow direction and the c-axis of Sn (defined as α) was close to 0°, massive Cu6Sn5 intermetallic compounds were observed in the solder bulk; however, when α was close to 90°, the migration of the intermetallic compound (IMC) was blocked but many Sn hillocks grew in the anode. Moreover, the low angle boundaries were the fast diffusion channel of Cu atoms while the high grain boundaries in the range of 55°–65° were not favorable to the fast diffusion of Cu atoms.

Modelling stress evolution and voiding in advanced copper nano-interconnects under thermal gradients

As the chip power densities increase radically with scaling, thermal gradients are predicted to become a major reliability concern in interconnects compatible with the 3 nm technology node and beyond. In this study, the impact of temperature gradients on the reliability of Cu nano-interconnects with highly scaled linewidth of 10 nm is simulated using a Korhonen-type modelling framework previously calibrated for electromigration predictions. ∆T dictates the stress distribution at steady state while dT/dx along the interconnect governs the stress evolution rate. It is shown that a linear temperature profile with a ∆T of >25 °C can generate voiding by thermomigration alone in these narrow lines. The adverse impact of thermal gradients by thermomigration and also by thermally induced flux divergence points are explored, showing a 20% drop of jmax in the presence of a ∆T of 10 °C and secondary nucleation sites along the line depending on temperature distribution. Immortality of Cu nano-interconnects to electromigration in the presence of thermal gradients was assessed whereby a thermally adjusted jLc is found relevant depending on the direction of electron flow with respect to temperature gradient.

Controlling βSn grain orientations in electronic interconnects with single-crystal Cobalt substrates

The reliability of electronic solder joints is strongly influenced by βSn grain orientations. Single-crystal Cobalt substrates were used to control βSn nucleation and grain orientations in solder joints. On (0001)Co, (112¯0)Co, (101¯0)Co, and (11¯02)Co, interfacial αCoSn3 crystals that are potent to catalyze βSn nucleation exhibited strong textures with 2–5 symmetric orientations featuring reproducible orientation relationships (ORs) with the Co. Preferred ORs and orientation selections of αCoSn3 were examined by exploring i) thermodynamic stabilities of interfaces represented by interfacial atomic matches and work of adhesion and interfacial energies calculated based on density functional theory (DFT) and ii) crystal growth kinetics indicated by the angle between (100)CoSn3 and the substrate plane. In sharp contrast to the innumerable grain orientations in joints on commonly used substrates, dramatically reduced orientations are attributed to the strongly textured αCoSn3, on which βSn grains nucleated by fixed ORs. On (112¯0)Co, the total number of orientations including twinned grains were reduced to 20. On (101¯0)Co, none of the βSn orientations exhibit the c-axis perpendicular to the substrate (i.e. parallel to the electron flow direction), which should reduce fast diffusion paths across the joint and improve the reliability of solder joints.

Effect of Sn Grain c-Axis on Cu Atomic Motion in Cu Reinforced Composite Solder Joints Under Electromigration

Because of its tetragonal structure, β-Sn exhibits anisotropy in electromigration behavior. The diffusivity of Cu atoms along the c-axis of Sn is much faster than that along the a-axis; therefore, the orientation of the c-axis exerts a strong influence on Cu atomic motion. In this work, the effect of Sn grain c-axis on Cu atomic motion was investigated by using Cu reinforced Sn3.5Ag composite solder joints. The microstructure and morphology of the solder joints were characterized by scanning electron microscopy (SEM) equipped with a backscattered electron (BSE) detector. It was found that intermetallic compounds (IMCs) in the solder matrix were formed due to the migration of Cu atoms to the surface of the solder joint under current stressing. There was a large amount of IMCs on the solder matrix which protruded from the solder matrix. By changing the direction of electron flow, i.e. changing the anode and the cathode side, the IMCs which formed after current stressing in the solder matrix disappeared and the protruding Sn remained unchanged. The results revealed that the growth of IMCs was closely related to the migration of Cu atoms, while Cu atomic motion depended on the orientation of the Sn grain c-axis.

Analysis of misconceptions by four tier tests in electrochemistry, case study on students of the chemistry education study program UIN Antasari Banjarmasin

This study aims to determine misconceptions on electrochemistry on the students of Chemistry Education Study Program UIN Antasari. The qualitative descriptive approach in this study was used to identify student misconceptions using the four-tier test. There are four (4) test levels which include: (1) multiple-choice with C2-C6 level, (2) confidence rating of the answer beliefs, (3) reasons for the answers, and (4) confidence rating of the reasoning beliefs for the answers. The three criteria used in the level of misconception consist of high, medium and low criteria. The results show that the students of the Chemistry Education Study Program of UIN Antasari experience misconception with moderate criteria on all electrochemical concepts which include the concepts of species undergoing oxidation and reduction in both Voltaic and electrolysis cells. Student’s misconception about the direction of electron flow, the condition of electron flow during electrolysis, and cathodic protection of iron.

Spin-dependent electron transmission across the corrugated graphene

We study various mechanisms of electron transmission across the corrugations in the graphene sheet. The spin dependence of the electron transmission probability in the rippled graphene is found. The electrons mean free path and transmission probabilities are analysed for different distributions of ripples in the graphene sheet as well. We demonstrate that the periodically repeated rippled graphene structure (the superlattice) leads to the suppression of the transmission of the ballistic electrons with one spin orientation in contrast to the other, depending on the direction of the incoming electron flow.

Molecular hydrogen suppresses superoxide generation in the mitochondrial complex I and reduced mitochondrial membrane potential

Molecular hydrogen (H2) is recognized as a medical gas applicable to numerous diseases including neurodegenerative diseases, metabolic disorders, and rheumatoid arthritis. Although the efficacy of H2 is reportedly attributed to its scavenging capability against the hydroxyl radical, the mechanisms underlying its therapeutic efficacy are not fully understood. Herein, we estimated the role of H2 in the energy converting system of the mitochondria, the source of reactive oxygen species.To investigate the effects of H2 on mitochondrial function, direction of electron flow, superoxide generation, and mitochondrial membrane potential were investigated. Forward electron transport (FET) or reverse electron transport (RET) was assessed by monitoring the decrease or increase of β-nicotinamide adenine dinucleotide hydrate (NADH, - or +, μM, respectively) in the presence of β-nicotinamide adenine dinucleotide (NAD+) and/or succinate in the isolated mitochondria. H2O2 converted from superoxide by superoxide dismutase (SOD) was measured to estimate electron leakage in the mitochondria. The effects of H2 on mitochondrial membrane potential were observed by staining cells with the fluorescence probe, teramethylrhodamine ethyl ester (TMRE).Despite the absence of succinate, a distinct RET was observed (from +0.0313 ± 0.0106 μM to +1.20 ± 0.302 μM) by adding 25 μM H2. In the presence of 5 μM NADH, RET by succinate inverted to FET from +1.62 ± 0.358 μM to −1.83 ± 0.191 μM, accompanied by a suppression of superoxide generated predominantly from complex I by 51.1%. H2 solely reduced mitochondrial membrane potential of the cultured cells by 11.3% as assessed by TMRE. The direction of electron flow was altered by H2 depending on the NAD+/NADH ratio, accompanied by suppression of superoxide generationH2 could suppress superoxide generation in complex I in vitro and reduce membrane potential in vivo. H2 may also neutralize semiquinone radicals to reduce superoxide produced in complex III. H2 may function as a rectifier of the electron flow affecting the mitochondrial membrane potential to suppress oxidative damage in mitochondria.