Direction Of Electron Flow Research Articles

Guided current-induced skyrmion motion in 1D potential well.

Magnetic skyrmions are particle-like magnetization configurations which can be found in materials with broken inversion symmetry. Their topological nature allows them to circumvent around random pinning sites or impurities as they move within the magnetic layer, which makes them interesting as information carriers in memory devices. However, when the skyrmion is driven by a current, a Magnus force is generated which leads to the skyrmion moving away from the direction of the conduction electron flow. The deflection poses a serious problem to the realization of skyrmion-based devices, as it leads to skyrmion annihilation at the film edges. Here, we show that it is possible to guide the movement of the skyrmion and prevent it from annihilating by surrounding and compressing the skyrmion with strong local potential barriers. The compressed skyrmion receives higher contribution from the spin transfer torque, which results in the significant increase of the skyrmion speed.

Cloaking resonant scatterers and tuning electron flow in graphene

We consider resonant scatterers with large scattering cross sections in graphene that are produced by a gated disk or a vacancy, and show that a gated ring can be engineered to produce an efficient electron cloak. We also demonstrate that this same scheme can be applied to tune the direction of electron flow. Our analysis is based on a partial-wave expansion of the electronic wave functions in the continuum approximation, described by the Dirac equation. Using a symmetrized version of the massless Dirac equation, we derive a general condition for the cloaking of a scatterer by a potential with radial symmetry. We also perform tight-binding calculations to show that our findings are robust against the presence of disorder in the gate potential.

Dominant effects of Sn orientation on serrated cathode dissolution and resulting failure in actual solder joints under electromigration

Excessive metal dissolution is one of the major electromigration-induced degradation mechanisms in interconnects, and it often produces a distinctive serrated cathode interface with most of the serrated teeth inclined toward a specific direction. In this study, actual flip-chip solder joints were systematically analyzed to understand this highly interesting morphology. It was unequivocally established that the Sn grain orientation is a dominant factor that controls the direction of the serrated teeth. When the c-axis of a Sn grain was nearly parallel to the electron flow direction, serrated dissolution occurred, with the serrated teeth inclined toward the c-axis. These observations were rationalized based on the diffusion anisotropy of Cu in Sn.

Flavin Redox Bifurcation as a Mechanism for Controlling the Direction of Electron Flow during Extracellular Electron Transfer

AbstractThe iron‐reducing bacterium Shewanella oneidensis MR‐1 has a dual directional electronic conduit involving 40 heme redox centers in flavin‐binding outer‐membrane c‐type cytochromes (OM c‐Cyts). While the mechanism for electron export from the OM c‐Cyts to an anode is well understood, how the redox centers in OM c‐Cyts take electrons from a cathode has not been elucidated at the molecular level. Electrochemical analysis of live cells during switching from anodic to cathodic conditions showed that altering the direction of electron flow does not require gene expression or protein synthesis, but simply redox potential shift about 300 mV for a flavin cofactor interacting with the OM c‐Cyts. That is, the redox bifurcation of the riboflavin cofactor in OM c‐Cyts switches the direction of electron conduction in the biological conduit at the cell–electrode interface to drive bacterial metabolism as either anode or cathode catalysts.

Flavin redox bifurcation as a mechanism for controlling the direction of electron flow during extracellular electron transfer.

The iron-reducing bacterium Shewanella oneidensis MR-1 has a dual directional electronic conduit involving 40 heme redox centers in flavin-binding outer-membrane c-type cytochromes (OM c-Cyts). While the mechanism for electron export from the OM c-Cyts to an anode is well understood, how the redox centers in OM c-Cyts take electrons from a cathode has not been elucidated at the molecular level. Electrochemical analysis of live cells during switching from anodic to cathodic conditions showed that altering the direction of electron flow does not require gene expression or protein synthesis, but simply redox potential shift about 300 mV for a flavin cofactor interacting with the OM c-Cyts. That is, the redox bifurcation of the riboflavin cofactor in OM c-Cyts switches the direction of electron conduction in the biological conduit at the cell-electrode interface to drive bacterial metabolism as either anode or cathode catalysts.

Reduction in the interface-states density of metal-oxide-semiconductor field-effect transistors fabricated on high-index Si (114) surfaces by using an external magnetic field

After fabrication of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices on high-index silicon (114) surfaces, their threshold voltage (Vth) and interface-states density (Dit) characteristics were measured under the influence of an externally applied magnetic field of B = 6 μT at room temperature. The electron flow of the MOSFET's channel presents high anisotropy on Si (114), and this effect is enhanced by using an external magnetic field B, applied parallel to the Si (114) surface but perpendicular to the electron flow direction. This special configuration results in the channel electrons experiencing a Lorentzian force which pushes the electrons closer to the Si (114)-SiO2 interface and therefore to the special morphology of the Si (114) surface. Interestingly, Dit evaluation of n-type MOSFETs fabricated on Si (114) surfaces shows that the Si (114)-SiO2 interface is of high quality so that Dit as low as ∼1010 cm−2·eV−1 are obtained for MOSFETs with channels aligned at specific orientations. Additionally, using both a small positive Vds ≤ 100 mV and B = 6 μT, the former Dit is reduced by 35% in MOSFETs whose channels are aligned parallel to row-like nanostructures formed atop Si (114) surfaces (channels having a 90° rotation), whereas Dit is increased by 25% in MOSFETs whose channels are aligned perpendicular to these nanostructures (channels having a 0° rotation). From these results, the special morphology of a high-index Si (114) plane having nanochannels on its surface opens the possibility to reduce the electron-trapping characteristics of MOSFET devices having deep-submicron features and operating at very high frequencies.

Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation

Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =de=c/ωpe), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheets (half thickness ∼5 de), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.

Operating principle of a three-terminal domain wall device with perpendicularly magnetized Ta/CoFeB/MgO free layer and underlying hard magnets

The behavior of a three-terminal domain wall (DW) device with a perpendicularly magnetized CoFeB free layer and underlying hard magnets was investigated. In a Ta/CoFeB/MgO free layer without hard magnets, a current-induced DW motion in the direction of electron flow was observed. In a device having a hard magnet under each end of the free layer, we found that a DW nucleated by injecting current played an important role in the switching of magnetization. We concluded that the switching of magnetization in our device is due to the displacement in the direction of electron flow of the DW created by current. After deriving the principle of operation through experiments, we describe a way to reduce the current required for writing by increasing the thickness of the hard magnets.

Effect of isothermal aging and low density current on intermetallic compound growth rate in lead-free solder interface

This study investigated the effects of isothermal aging and low density current on intermetallic compound (IMC) growth rate and microstructural evolution of lead-free solder interface at a temperature of 398K. The results showed that the morphology of IMC layers under high temperature aging and current stressing was basically same. The growth rate of IMC at the anode was the fastest. That was because chemical diffusion force and electronic wind acted together to drive the growth of IMC at the anode. The current density was not high enough for obvious polarization effects and crack along the electron flow direction to be observed. Next the mean-time-to-failure analysis was used to calculate the lifetime of ball grid array solder joints stressed electrically. However, the calculated value was much shorter than the true value. Indicating that perhaps the equation needs to be modified when applied to Cu interconnects and flip chip solder joints.

전자전달증대기를 이용한 고효율 태양전지 시스템에서 전자전달증대기 입력 교류 전압 변화에 따른 태양전지 효율 향상에 대한 연구

본 연구에서는 기존의 상업용 태양전지에서 전자-정공 재결합을 최소화하여 태양전지의 효율을 향상시키는 부가장치인 전자전달증대기(Electron Relay Enhancer: ERE)를 소개한다. 전자전달증대기는 교류 전력 공급 장치와 연결된 두 개의 캐패시터와 전자의 흐름 방향을 제어하는 브릿지 다이오드 시스템으로 구성되어 있다. 두 개의 캐패시터는 브릿지 다이오드 시스템을 통하여 태양전지로부터 전자를 포집하고 포집된 전자를 로드저항이나 인버터쪽으로 펌핑하는 것을 반복한다. 양으로 대전된 한 개의 캐패시터가 전자를 포집하는 동안 음으로 대전된 다른 캐패시터는 전자를 펌핑한다. 태양전지에서 여기된 전자가 정공에 재결합되기 전에 양으로 대전된 캐패시터는 태양전지로부터 더 많은 여기된 전자를 끌어온다. 이러한 까닭에 ERE 시스템은 태양전지의 효율을 증대시킨다. 연구결과로 ERE 활성 시 태양전지의 증가된 전력은 각각의 실험조건에서 5.9 W에서 25.6 W사이였고, 가장 높은 태양전지전력증가율은 ERE 비활성 시 태양전지 전력의 30.8%였다. In this paper, we would like to introduce Electron Relay Enhancer (ERE), a supplementary device, which improves commercial solar cell efficiency minimizing electron-hole recombination of solar cell. The ERE in this study is mainly composed of two capacitors which are connected to AC power source and bridge diode system which controls electron flow direction. Two capacitors repeat collecting electrons from solar cell and pumping the collected electrons to load resistance or inverter through the bridge diode system. While one positively charged capacitor collect electrons, the other negatively charged one pumps electrons. A positively charged capacitor pulls the more exited electrons from the solar cell, before the exited electrons recombine the holes in solar cell. That is why the ERE system enhances solar cell efficiency. As a result, the measured power increase of the solar cell with the ERE is varied from 5.9 W to 25.6 W in each experimental condition. Maximal increase rate of the solar cell power with ERE is 30.8% of solar cell power without ERE.

Reverse Engineering To Suggest Biologically Relevant Redox Activities of Phenolic Materials

Phenolics are among the most abundant redox-active organics in nature, but the intractability of phenolic materials (e.g., melanin) has precluded study of their biological activities and functions. Previous studies demonstrated that a model abiotic catecholic matrix can rapidly exchange electrons with biological oxidants and reductants without the need for enzymes. Here, a novel electrochemically based reverse engineering approach was employed to probe redox interactions between this model matrix and a population of bacteria. Specifically, this method employs redox-active natural products (e.g., pyocyanin) to shuttle electrons between the bacteria and the abiotic matrix, and imposed oscillating potential inputs to engage redox-cycling mechanisms that switch the matrix's redox state. The oscillating output currents were observed to be amplified, gated, and partially rectified, while the overall magnitude and direction of electron flow across the matrix depended on the biological and environmental context. These response characteristics support hypotheses that natural phenolic materials may be integral to extracellular electron transport for processes that include anaerobic respiration, redox signaling, and redox-effector action.

Current-induced motion of a transverse magnetic domain wall in the presence of spin Hall effect

We theoretically study current-induced dynamics of a transverse magnetic domain wall in bi-layer nanowires consisting of a ferromagnetic layer on top of a nonmagnetic layer with strong spin-orbit coupling. Domain wall dynamics is characterized by two threshold current densities, JthWB and JthREV, where JthWB is a threshold for the chirality switching of the domain wall and JthREV is another threshold for the reversed domain wall motion caused by spin Hall effect. Domain walls with a certain chirality may move opposite to the electron-flow direction with high speed in the current range JthREV<J<JthWB for the system designed to satisfy the conditions JthWB>JthREV and α>β, where α is the Gilbert damping constant and β is the nonadiabaticity of spin torque. Micromagnetic simulations confirm the validity of analytical results.

Influence of Cu column under-bump-metallizations on current crowding and Joule heating effects of electromigration in flip-chip solder joints

The electromigration behavior of SnAg solder bumps with and without Cu column under-bump-metallizations (UBMs) has been investigated under a current density of 2.16 × 104 A/cm2 at 150 °C. Different failure modes were observed for the two types of samples. In those without Cu column UBMs, when SnAg solder bumps that had implemented 2 μm Ni UBMs were current stressed at 2.16 × 104 A/cm2, open failure occurred in the bump that had an electron flow direction from the chip side to the substrate side. However, in those with Cu column UBMs, cracks formed along the interface of Cu6Sn5 intermetallic compounds and the solder on the substrate side in the Sn-3.0Ag–0.5Cu solder bump that had an electron flow direction from the substrate side to the chip side. A three-dimensional simulation of the current density distribution was performed in order to obtain a better understanding of the current crowding behavior in solder bumps. The current crowding effect was found to account for the void formation on both the chip and the substrate side for the two kinds of solder bumps. One more important finding, as confirmed by infrared microscopy, is that the alleviation of current crowding by Cu column UBMs also helped decrease the Joule heating effect in solder bumps during current stressing. Therefore, the measured failure time for the solder joints with Cu column UBMs appears to be much longer than that of the ones with the 2 μm Ni UBMs.

Effect of electromigration on interfacial reaction in Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P flip chip solder joints

The effect of electromigration (EM) on the interfacial reaction in the Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P flip chip solder joint is investigated under a current density of 1.0× 104 A/cm2 at 150℃. The (Cu,Ni)6Sn5 intermetallic compounds (IMCs) form at both solder/Ni and solder/Ni-P interfaces in the as-reflowed state. During aging at 150℃, the (Cu,Ni)6Sn5 interfacial IMCs grow thicker and transform into (Ni,Cu)3Sn4 type after 200 h at solder/Ni interface and 600 h at solder/Ni-P interface, respectively. During EM, the current direction plays an important role in Ni-P layer consumption. When electrons flow from Ni-P to Ni, EM enhances the consumption of Ni-P, i.e., the Ni-P s completely consumed and transforms into Ni2SnP after EM for 600 h. There is no Cu-Sn-Ni ternary IMC at the solder/Ni-P interface (cathode). Crack forms at the Ni2SnP/Cu interface due to the weak bonding force between Ni2SnP and Cu. When electrons flow from Ni to Ni-P, no obvious consumption of Ni-P is observed during EM; the current crowding effect induces a rapid and localized dissolution of Ni UBM and Cu pad at the chip side (cathode). The dissolved Ni and Cu atoms are driven along the flowing direction of electrons and form a large number of IMC particles in the solder matrix. During EM, the (Au,Pd,Ni)Sn4 phase prefers to be redistributed only at the anode interface, regardless of the direction of electron flow.

Analysis and design of a double-anode magnetron injection gun for 1THz gyrotron

Based on the electron optics theory, through a massive numerical calculation by programming, a double-anode magnetron injection gun (MIG) for a 1THz gyrotron is designed. The method of calculation and design of MIG is expounded, and the problem that high magnetic compression ratio in THz gyrotron(compression ratio of 125 in electron gun for 1THz gyrotron in this paper)could lead to the reversal of direction of electron flow is also detailedly analyzed and simulated. Through simulation and optimization, an MIG with a modest velocity ratio of the beam (=1.3) and a low velocity spread (8%) is designed.

On the complementarity of comprehensive decomposition analysis of stabilization energy (CDASE) – Scheme and supermolecular approach

Complementarity of the recently proposed comprehensive decomposition analysis of stabilization energy (CDASE) – scheme [34] and the conventional ‘supermolecular approach’ is studied in the present article. While supermolecular approach complements the CDASE scheme by providing geometries of the individual components in the supermolecular environment, the CDASE scheme complements supermolecular approach by providing the direction of electron flow through reliable energetic parameters. The qualitative trend of stabilization energy values, generated by the CDASE scheme and derived from the conceptual density functional theory (DFT) based reactivity descriptors of the individual components in the overall geometry of the molecular complex, fully agrees with the trend of interaction energy values generated from supermolecular approach. Geometrical and the electronic parameters (i.e., bond distances, charges, etc.) also support the above results which are also as observed experimentally.

Effect of exogenous electron shuttles on growth and fermentative metabolism in Clostridium sp. BC1

In this study, the influence exogenous electron shuttles on the growth and glucose fermentative metabolism of Clostridium sp. BC1 was investigated. Bicarbonate addition to mineral salts (MS) medium accelerated growth and glucose fermentation which shifted acidogenesis (acetic- and butyric-acids) towards solventogenesis (ethanol and butanol). Addition of ferrihydrite, anthraquinone disulfonate, and nicotinamide adenine dinucleotide in bicarbonate to growing culture showed no significant influence on fermentative metabolism. In contrast, methyl viologen (MV) enhanced ethanol- and butanol-production by 28- and 12-fold, respectively with concomitant decrease in hydrogen, acetic- and butyric-acids compared to MS medium. The results show that MV addition affects hydrogenase activity with a significant reduction in hydrogen production and a shift in the direction of electron flow towards enhanced production of ethanol and butanol.

Interfacial Effects During Thermal Cycling of Cu-Filled Through-Silicon Vias (TSV)

Large shear stresses may develop at interfaces between dissimilar materials during thermal excursions when there is a significant difference in their coefficients of thermal expansion. The shear stress may cause interfaces to slide via diffusional process, thereby accommodating the relative dimensional changes between the two materials. This phenomenon presents a significant reliability issue in three-dimensional (3-D) interconnect structures involving through-silicon vias (TSVs), which are subjected not only to continuous thermal cycling but also to large electric current densities during service. This paper reports experimental evidence of interfacial sliding between Cu and Si in Cu-filled TSVs during thermal cycling conditions, and in the presence of electric current. Two different thermal cycling conditions were used: (i) small ΔT thermal cycling (−25°C to 135°C) and (ii) large ΔT thermal cycling (25°C to 425°C). Prior to thermal cycling, a few Cu-filled TSV samples were annealed for 30 min at 425°C. Cu intruded inside Si in nonannealed samples during small ΔT thermal cycling, whereas protrusion of Cu relative to Si occurred during all other thermal excursions. Application of electric current biased the net displacement of the Cu in the direction of electron flow, leading to enhanced protrusion (or intrusion) of Cu relative to the thermal cycling only (i.e., without electric current) condition. A simple one-dimensional analytical model and associated numerical simulations are utilized to rationalize the experimental observations.

Influence of crystallographic orientation of Sn–Ag–Cu on electromigration in flip-chip joint

The influence of the crystallographic orientation of Sn–3.0 wt%Ag–0.5 wt%Cu flip-chip joints and underfill on electromigration was investigated. The current density applied in our tests was 15 kA/cm 2 at 160 °C. Various times to failure of the test samples show a clear dependence of the electromigration behavior on the Sn grain orientations. Different microstructural evolutions were observed in all solder bumps in correlation with the crystallographic orientations of the Sn grains after an electromigration test. The primary failure of the solder joints was caused by dissolution of the Cu electrode at the cathode interface. Rapid dissolution of the Cu electrode occurred when the c-axis of the Sn grains was parallel to the direction of electron flow. On the other hand, slight dissolution of the Cu electrode was observed when the c-axis of the Sn grains was perpendicular to the direction of electron flow. Some grain boundaries interrupt the migration of Cu and the trapped Cu atoms form new grains of intermetallic compounds at the grain boundaries. In addition, underfill inhibits serious deformation of solder bumps during current stressing.

Effects of the crystallographic orientation of Sn on the electromigration of Cu/Sn–Ag–Cu/Cu ball joints

Abstract