Cathode End Research Articles

Voltage Reversal during Stacking Microbial Fuel Cells with or without Diodes

Stacking microbial fuel cells (MFCs) in series can provide higher voltage; however, voltage reversal (VR) adversely affects performance of the stacked MFCs. In this paper, diodes are introduced into three stacked MFCs so as to investigate the VR behavior and offer a diodes-based explanation of the VR. The results show that VR occurs in the different stacked MFCs systems. VR of the stacked MFCs connected with forward diodes (～0.37 V) happens in a similar pattern as that without diodes (～0.80 V). However, it only happens at the end of a cycle. This can be analyzed that the resistance of the diodes consume a part of the flowing electrons and the speed of potential changes of the electrodes slows down. Differently, in the stacked MFCs connected with reverse diodes, the voltages of each unit MFC approximately equal their open circuit voltages (～0.75 V), and VR happens in the unit MFC with reverse diodes at the cathode end only. It implies that the imbalanced consumption of electrons in unit MFCs and the potential changes of specific electrode directly result in VR.

Experimental Study of Effects of Operating Conditions on Water Transport Phenomena in the Cathode of Polymer Electrolyte Membrane Fuel Cell

Water management in polymer electrolyte membrane fuel cells is important because fuel cell performance may be lower when flooding emerges. In addition, the proton conductivity and water transport coefficient in the membrane depend on the hydration of the membrane. In this study a water transport phenomenon in the cathode channels of a polymer electrolyte membrane fuel cell was investigated under various operating conditions. To obtain images of the water the transparent fuel cell had a polycarbonate window installed at the cathode end plate, and gold-coated stainless steel was used for the flow field and current collector of the cathode. The effects of operating conditions on water transport manipulated operating parameters such as cell temperature, cathode flow rate, and cathode backpressure. As the operating time elapsed, it was observed that water droplet formation, growth, coalescence, and removal occurred in the cathode channel. It concluded that a high cathode flow rate prevented flooding by removing water from the cathode flow channel. Also, the quantity of water droplets increased with a high cathode backpressure.

Haemoglobin typing and its variations in Iranian domestic dogs

The study of canine haemoglobin (Hb) components can help to forecast Hb changes during many pathological and physiological processes such as responsive anaemia. The aims of our study were to show canine Hb electrophoretic pattern on cellulose acetate and identify Hb types similar to the human Hb pattern. Blood samples from 78 different canine breeds were randomly collected in tubes containing anticoagulant EDTA. Animals were brought to the Small Animal Teaching Centre for a check-up and vaccination. All blood samples underwent electrophoresis on cellulose acetate paper strips to determine Hb types. Haematocrit and Hb were measured simultaneously. The Hb electrophoresis results showed that Hb A1 was assigned to most of Hb components on cellulose acetate paper. Also, in some blood samples, Hb A2 was detected at the cathode end of cellulose acetate paper similar to human Hb A2, by densitometer. Small amounts of Hb F were detected in some dogs which was not significant. According to our study, Hb A1 composes most of the total Hb percent in canine blood. Two types of Hb, A2 and F, were detected in a few animals, but the majority did not possess Hb F. It seems that Hb F is not significant in these animals. We concluded that one or two Hb types could be seen in dogs. There is no difference in electrophoretic pattern between male and female dogs.

Void dynamics in copper-based interconnects

The electromigration lifetimes of Cu-based interconnects are strongly influenced by whether voids are present before electromigration, and by where fatal voids initially form and grow. Modeling, simulations, and comparisons with in situ experiments are used to establish criteria for void formation away from the cathode end of a copper interconnect. It is shown that observation of voids at locations other than the cathode strongly suggests that the voids grew from pre-existing voids. When pre-existing voids are within a current-density-dependent critical length from the cathode, new voids are unlikely to nucleate at the cathode and failure occurs only when the pre-existing voids grow. As these voids grow, they will either lead directly to open-circuit failure or, once they reach a critical size, they will de-pin from grain boundaries and drift toward the cathode. In the latter case, multiple voids might accumulate and coalesce to cause failure. This mechanism has been observed in both side-view and top-down in situ accelerated life-time testing. It is shown that the relative importance of these various void-induced failure mechanisms depends on the current density, and is different under typical accelerated test conditions from what is expected at service conditions.

Field induced shape and work function modification for the ZrO/W(100) Schottky cathode

The origin of the frequently observed long and short term current drifts after a change in the extractor voltage for the ZrO/W(100) Schottky cathode has been investigated. It has been found that a reversible, field dependent change in the equilibrium work function and shape of the cathode end form occurs at the typical operating temperature of 1800 K. The shape change results in three distinct geometric end form shapes. Although these end forms have been observed previously [L. W. Swanson and G. A. Schwind, in Handbook of Charged Particle Optics, 2nd ed., edited by J. Orloff (CRC, New York, 2008), Chap. 1, p. 1; S. Fujita, T. R. Wells, W. Ushio, H. Sato, and M. M. El-Gomati, J. Microsc. 235, 215 (2010); M. S. Bronsgeest and P. Kruit, J. Vac. Sci. Technol. B 27, 2524 (2009)], the purpose of this study is to elucidate the operating conditions under which these changes occur and the associated changes in emission properties. Emitters in the radii range 200–900 nm were investigated over the typical current density operating range employed in most electron probe forming systems. A correlation between work function and electric field has been found, which can be explained by a reversible, field induced change in the ZrO equilibrium coverage in the high field region of the emitter, thereby causing a change in the work function. It is believed that these field induced changes in the equilibrium work function and emitter shape at 1800 K explain the short and long term drifts observed after a change in extractor voltage.

Analysis of DNA complexes with small solutes by CE with LIF detection

In this article, we describe the analysis of aptamers for Hg(2+) ions through CE with LIF (CE-LIF) detection using 2% poly(ethylene oxide) solutions containing OliGreen (fluorophore). In the presence of an EOF, DNA strands migrating against the EOF were detected at the cathode end. Four DNA strands - T(33), T(5)C(28), T(5)C(5)T(23), and T(15)C(5)T(13) - could not be separated through CE-LIF in the absence of Hg(2+). At 0.3 mM Hg(2+), however, all four were partially separated within 20 min, with SDs of the migration times all being less than 2.5%. From the CE, fluorescence, and ellipticity data, we concluded that the conformations of these four DNA strands all changed from random-coil to folded structures as a result of T-Hg(2+)-T bonding. In addition, we found that this CE approach provided different electropherograms patterns for T(7), T(15), and T(33) in the absence and presence of Hg(2+), indicating various interactions of the DNA strands with Hg(2+). Using this simple, high-resolution CE approach, we also demonstrated that adenosine triphosphate has a stronger interaction with the adenosine triphosphate aptamer than with either the platelet-derived growth factor aptamer or T(33). This CE approach holds great potential for screening aptamers for small solutes, studying the catalytic activity of DNAzymes, and evaluating the biological functions of microRNA.

Numerical Analysis of Vacancy Transport by Residual Stress in Electromigration on LSI Interconnects

The Li multiplication method for the driving force induced particle migration equation was proposed to solve numerically the stress and electric fields induced vacancy migration equation. On the basis of this method, vacancy migration behaviors were found to be predicted under the competitive relationship between stress and electric field. When a residual stress is dominant, vacancies concentrate around the maximum hydrostatic stress region, such as elastic–plastic boundary. On the other hand, when the electric field is dominant, vacancies do not concentrate around the maximum hydrostatic stress region, but move from the cathode end to the anode end. An in situ observation of electromigration on AlCuSi interconnect was conducted to verify the simulation results. A void nucleated and grew at the tip of a notch on an AlCuSi line without passivation film, while many voids appeared and grew in cathode side in a line with passivation film. Greater hydrostatic stress gradient is considered to occur in the line without passivation film, owing to a small scale of yielding, and this leads to concentrate void formation at the tip of the notch. These results indicate that numerical analysis of electromigration is valid to represent the experimental result. Based on results mentioned above, various failure modes in interconnects cased by electromigration are predictable by the proposed Li multiplication method.

Cherenkov masers with two-dimensional distributed feedback

The possibility of using a two-dimensional (2D) distributed feedback to generate spatially coherent radiation by straight sheet and annular electron beams is studied. The schemes of sectional Cherenkov masers with the transverse synchronization of radiation performed in a 2D Bragg structure, which is arranged at the cathode end of the interaction space and conjugates the longitudinal and transverse (azimuthal) wave flows, is analyzed. By introducing dissipation into this structure, it is possible to increase the transverse dimensions of masers to a level on the order of 103 wavelengths with the corresponding increase in the total output radiation power without changing spectral characteristics and decreasing the energy conversion efficiency.

Soldered contact and current risetime effects on negative polarity wire array Z pinches

The experimental results described in this paper were motivated by earlier, low current, single wire experiments. In these experiments, single 10–25 μm diameter wires were driven by 1–5 kA current pulses with variable dI/dt from 5 to 60 A/ns. The amount of energy deposited in the wires, the expansion rate, and expansion uniformity that occurred before a plasma induced voltage collapse were found to depend on the polarity, dI/dt, and the quality of the contacts between the wires and the electrodes. This paper reports the results of experiments with cylindrical wire arrays driven by Cornell Beam Research Accelerator (COBRA) [J. B. Greenly, J. D. Douglas, D. A. Hammer et al., Rev. Sci. Instrum. 79, 073501 (2008)] current pulses that reached 1 MA. The pulse lengths were varied from 100 to 200 ns. These larger current pulses drove the wires of the array through the initiation phase studied in the single wire experiments and through ablation and Z-pinch implosion to stagnation on the cylindrical axis of the array. Regardless of the current pulse length, the COBRA dI/dt per wire during initiation reached approximately 175 A/ns and resistive voltage breakdown occurred at ∼13 ns. Wire-electrode contacts were modified by soldering the cathode ends of the wires to the brass electrode. With the 100 ns COBRA pulse, voltage monitor data suggested that soldering produced a smaller radius pinch, but bolometer data showed that this did not affect the total energy emitted from the array compared to nonsoldered contacts. With the 200 ns COBRA pulse and soldered contacts, the bolometer data showed an average of 69% increase in time integrated x-ray emission and the photoconducting detector data showed an increase in x-ray power and yield compared with nonsoldered contacts. Under these same conditions the four-frame extreme ultraviolet images showed a more pronounced “Christmas tree” effect at the cathode.

In situ measurement of electromigration-induced transient stress in Pb-free Sn–Cu solder joints by synchrotron radiation based x-ray polychromatic microdiffraction

Electromigration-induced hydrostatic elastic stress in Pb-free SnCu solder joints was studied by in situ synchrotron x-ray white beam microdiffraction. The elastic stresses in two different grains with similar crystallographic orientation, one located at the anode end and the other at the cathode end, were analyzed based on the elastic anisotropy of the β-Sn crystal structure. The stress in the grain at the cathode end remained constant except for temperature fluctuations, while the compressive stress in the grain at the anode end was builtup as a function of time during electromigration until a steady state was reached. The measured compressive stress gradient between the cathode and the anode is much larger than what is needed to initiate Sn whisker growth. The effective charge number of β-Sn derived from the electromigration data is in good agreement with the calculated value.

Analysis of electromigration induced early failures in Cu interconnects for 45 nm node

Bi-directional current stressing was used for monitoring electromigration (EM) lifetime evolution in 45 nm node interconnects. Experimental results show that an initial bimodal distribution of lifetimes can be modified into a more robust mono-modal distribution. Since the bi-directional tests provide successive void nucleation and void healing phases, the Cu microstructure is thought to evolve once the formed void is filled thanks to EM induced matter displacement. FEM modeling is used to compare the predicted location of void nucleation for given microstructures at the cathode end: a multigrain structure is compared to a perfect bamboo microstructure. Experimental and modeling results let us assume that small grains (<linewidth or via diameter) at the cathode end present a risk of EM induced early fails. Indeed at this location void nucleates and grows nearby the via opening it shortly. On the contrary, the bamboo microstructure is thought to provide more robust lifetime because voids nucleate a few hundred nanometers in the line and grow down reaching the bottom diffusion barrier of the line. This latter case provides larger void size before circuit opening.

A Large-Scale, Wireless Electrochemical Bipolar Electrode Microarray

We report a microelectrochemical array composed of 1000 individual bipolar electrodes that are controlled with just two driving electrodes and a simple power supply. The system is configured so that faradaic processes occurring at the cathode end of each electrode are correlated to light emission via electrogenerated chemiluminescence (ECL) at the anode end. This makes it possible to read out the state of each electrode simultaneously. The significant advance is that the electrode array is fabricated on a glass microscope slide and is operated in a simple electrochemical cell. This eliminates the need for microfluidic channels, provides a fabrication route to arbitrarily large electrode arrays, and will make it possible to place sensing chemistries onto each electrode using a robotic spotter.

An in situ investigation of electromigration in Cu nanowires

Electromigration in copper (Cu) nanowires deposited by electron beam evaporation hasbeen investigated using both resistance measurement and the in situ scanning electronmicroscopy technique. During electromigration, voids formed at the cathode end whilehillocks (or extrusions) grew close to the anode end. The failure lifetimes were measured forvarious applied current densities and the mean temperature in the wire was estimated.Electromigration activation energies of 1.06 eV and 0.94 eV were found for the wire widthsof 90 nm and 141 nm, respectively. These results suggest that the mass transport of Cuduring electromigration mainly occurs along the wire surfaces. Further investigations of theAuger electron spectrum show that both Cu atoms and the surface contaminants ofcarbon and oxygen migrate from cathode to anode under the electrical stressing.

In-situ observation of electromigration failure in AlCuSi interconnects with a passivation film

In-situ observation with an optical microscope of electromigration in a widely used Al-0.5wt%Cu-1wt%Si inter- connects was conducted to study the mechanism of void formation and transportation. In the case of an interconnect covered with a passivation film, generation of voids occurred in the cathode side around a triangle shaped notch, which was introduced to be able to detect void formation. The voids accumulated in the cathode side and moved toward the cathode end. Rupture occurred in the cathode side, which was damaged by electromigration. On the other hand, in the case of an interconnect without a passivation film, generation and accumulation of voids was observed at the tip of the notch. Growth of voids was found at the tip of the notch and the rupture occurred at this damaged region. The authors analyzed the theory of void transport by electromi- gration and stress. The experimental results are in good agreement with the theoretical results and show that electromigration is significantly influenced by the stress in the interconnection. Moreover, the mechanism of void growth was discussed to consider nucleation theory.

Fraction collection in capillary electrophoresis for various stand-alone mass spectrometers

A procedure for collecting fractions during capillary electrophoresis for their analysis using various stand-alone instruments is described. The results of a systematic study of the optimization and application of capillary electrophoresis (CE) in conjunction with a reverse-phase high-performance liquid chromatography electrospray ionization quadrupole time of flight-tandem mass spectrometry (RP-HPLC-ESI-Q-TOF-MS/MS) and inductively-coupled mass spectrometry (ICP-MS) to the analysis of the seed extract of the Japanese Pagoda Tree ( Sophora japonica) are presented. The off-line coupling of CE to the matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) for the proteins mixture was applied. The cathode end of the capillary was placed inside a stainless steel needle using a coaxial liquid-sheath-flow configuration. The optimization of experimental parameters resulted in an efficient methodology for MS analysis of fractions. Several components contained in the extract of S. japonica were identified, some not previously known. It was demonstrated that low sensitivity, which is a real problem in off-line CE–MS analysis, could be tolerated because of a more flexible optimization of the CE separation conditions and the choice of independent stand-alone instruments for analysis of separated fractions. The estimated limit of detection for CE-RP-HPLC-ESI-Q-TOF-MS was 50 μM of polyphenols and for CE-ICP-MS, 1–100 μg/l.

Investigation of an X-band magnetically insulated transmission line oscillator

An X-band magnetically insulated transmission line oscillator (MILO) is designed and investigated numerically and experimentally for the first time. The X-band MILO is optimized in detail with KARAT code. In simulation, the X-band MILO, driven by a 720 kV, 53kA electron beam, comes to a nonlinear steady state in 4.0 ns. High-power microwaves (HPM) of TEM mode is generated with an average power of 4.1 GW, a frequency of 9.3 GHz, and power conversion efficiency of 10.8% in durations of 0–40 ns. The device is fabricated according to the simulation results. In experiments, when the voltage is 400kV and the current is 50kA, the radiated microwave power reaches about 110 MW and the dominating frequency is 9.7 GHz. Because the surfaces of the cathode end and the beam dump are destroyed, the diode voltage cannot increase continuously. However, when the diode voltage is 400kV, the average power output is obtained to be 700 MW in simulation. The impedance of the device is clearly smaller than the simulation prediction. Moreover, the duration of the microwave pulse is obviously shorter than that of the current pulse. The experimental results are greatly different from the simulation predictions. The preliminary analyses show that the generations of the anode plasma, the cathode flare and the anode flare are the essential cause for the remarkable deviation of the experimental results from the simulation predictions.

Effects of microstructure on the formation, shape, and motion of voids during electromigration in passivated copper interconnects

In situ scanning electron microscope observations have been performed on passivated damascene Cu interconnect segments of different widths during accelerated electromigration tests. In some cases, voids form and grow at the cathode. However, an alternative failure mode is also observed, during which voids form distant from the cathode end of the interconnect segment and drift toward the cathode, where they eventually lead to failure. The number of observations of this failure mode increased with increasing linewidth. During void motion, the shape and the velocity of the drifting voids varied significantly. Postmortem electron backscattered diffraction (EBSD) analysis was performed after in situ testing, and a correlation of EBSD data with the in situ observations reveals that locations at which voids form, their shape evolution, and their motion all strongly depend on the locations of grain boundaries and the crystallographic orientations of neighboring grains.

Vacuum-Breakdown-Induced Needle-Shaped Ends of Multiwalled Carbon Nanotube Yarns and Their Field Emission Applications

The Joule-heating-induced vacuum breakdown of the carbon nanotube (CNT) yarns was studied. Wall-by-wall breakdown and superplastic deformation of CNTs are the main physical processes at the hottest location before breakdown. The two ends at the breaking point are needle-shaped with surfaces rich in tightly compacted conelike CNT bundles with a single CNT at the tips. Both of the ends can provide emission currents of over 150 μA within an area 5 μm in diameter; the cathode ends start field emission at a lower voltage. Laser irradiation was introduced to control the breaking location making the methodology more practical. Small pixels were constructed with the yarn emitter cathodes, which are potentially building blocks of large outdoor displays.

Activation energy and prefactor for surface electromigration and void drift in Cu interconnects

Surface electromigration rates on oxide-free surfaces of unpassivated damascene Cu interconnect segments have been determined through electromigration testing under vacuum. Electromigration-induced voids grew at the cathode end of the segments due to a flux divergence at refractory-metal-lined vias to the lead lines below the test segment. Copper diffusivity on a clean Cu surface was determined by measuring the size of the voids as a function of time and test temperature at a fixed current. An activation energy of 0.45±0.11eV and a prefactor of 3.35×10−12m2∕s were found for the product of the effective charge z* and the surface diffusivity Ds. This result is shown to be consistent with void drift rates measured in passivated interconnects.

Information Entropy Measure for Evaluation of Image Quality

This paper presents a simple and straightforward method for synthetically evaluating digital radiographic images by a single parameter in terms of transmitted information (TI). The features of our proposed method are (1) simplicity of computation, (2) simplicity of experimentation, and (3) combined assessment of image noise and resolution (blur). Two acrylic step wedges with 0-1-2-3-4-5 and 0-2-4-6-8-10 mm in thickness were used as phantoms for experiments. In the present study, three experiments were conducted. First, to investigate the relation between the value of TI and image noise, various radiation doses by changing exposure time were employed. Second, we examined the relation between the value of TI and image blurring by shifting the phantoms away from the center of the X-ray beam area toward the cathode end when imaging was performed. Third, we analyzed the combined effect of deteriorated blur and noise on the images by employing three smoothing filters. Experimental results show that the amount of TI is closely related to both image noise and image blurring. The results demonstrate the usefulness of our method for evaluation of physical image quality in medical imaging.