Cathode Electron Research Articles

Nanoscratch properties of extremely thin diamond-like carbon films

Scratch properties of extremely thin (targeted at 0.03–5.0-nm-thick) diamond-like carbon (DLC) films deposited by the filtered cathodic vacuum arc (FCVA) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) methods are investigated. The difference in profiles and friction coefficients of scratches in both the corn and edge directions are evaluated. The difference of scratch properties between deposition methods is clearly evaluated by the scratching in the corn direction. When scratching in the corn direction, the friction coefficient and wear depth of the FCVA-DLC film increased rapidly at critical load, whereas those of the ECR-CVD-DLC film increased gradually even beyond this critical load. These results are deduced to be caused by the differences in the hardness and brittleness of the films. The dependence of nanoscratch friction force and scratch profile on DLC film thickness can reveal differences in mechanical properties that correspond to atomic-scale thickness.

Electrocatalytic oxidation of methanol on Ru deposited NiZn catalyst at graphite in alkaline medium

The methanol oxidation on C/NiZn-Ru electrode in a 1.00M KOH and 1.00M KOH+1.00M methanol solutions at different scan rates and temperatures was studied by the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. The graphite electrode is coated in a nickel–zinc bath by electrodeposition for use as anode materials for methanol oxidation in alkaline solutions. It is etched in a concentrated alkaline solution to produce a porous and electrocatalytic surface suitable for use in the methanol oxidation (C/NiZn). Ruthenium was electrodeposited on a C/NiZn electrode. The surface morphologies and compositions of electrodes were determined by energy dispersive X-ray (EDX) and scanning electron microscopy (SEM). Kinetic parameters of oxidation such as the anodic electron transfer coefficient (αa), cathodic electron transfer coefficient (αc), charge transfer rate constant (ks) and activation energy values were calculated. The effect of methanol concentration on methanol oxidation were also investigated. It was found that the ruthenium electrodeposited electrode showed higher catalytic activity and stability toward methanol oxidation than the C/NiZn electrode.

Layer-by-Layer All-Transfer-Based Organic Solar Cells

For the first time, we describe a novel cost- and time-effective vacuum-free process to fabricate bulk-heterojunction (BHJ) organic photovoltaics (OPVs) via layer-by-layer selective stamping transfer of all layers. By controlling the surface properties of polyurethane acrylate (PUA) stamping molds with ultraviolet (UV)-ozone (UVO) exposure, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), BHJ layer, and metal cathode were uniformly transferred layer by layer onto each of the bottom layers. Among several interfaces between each layer, we found that the interface between the active layer and metal cathode is a critical factor in obtaining conventional device-like efficiency. To enhance the interfacial connectivity between the BHJ layer and metal cathode and increase electron extraction from the BHJ layer, a titanium oxide (TiOx) interlayer was introduced. Cell performance was optimized by controlling the concentration of TiOx solution. The poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PC60BM) BHJ device fabricated by transferring PEDOT/PSS, TiOx/active layer, and Al cathode showed 2.01% power conversion efficiency. This efficiency is not comparable to those of conventional OPVs, but our approach shows the possibility of fabricating OPVs via the layer-by-layer transfer method for the first time.

Nanotribology properties of extremely thin diamond-like carbon films at high temperatures with and without vibration

Extremely thin diamond-like carbon (DLC) films were deposited by filtered cathodic vacuum arc (FCVA) and electron cyclotron resonance-chemical vapour deposition (ECR-CVD) methods. The nanotribological properties of these films at high temperatures were evaluated using atomic force microscopy. At room temperature (RT), the FCVA-DLC films showed superior nanowear resistance than the ECR-CVD-DLC films. Conversely, at high temperatures in vacuum, the wear increased rapidly. The friction force of the FCVA-DLC films was low at RT in air and vacuum, but it was very high at high temperatures in vacuum. The lubricous adsorbate was removed by sliding at high temperatures. Hard brittle wear debris produced by high friction acted as an abrasive and increased the wear. In contrast, the friction force of the ECR-CVD-DLC films was low at high temperatures, corresponding to a low wear rate. Thus, the lubricous tribochemical products reduced the friction and wear. When the samples were vibrated, the wear depth of the FCVA-DLC films decreased at high temperatures, while that of the ECR-CVD-DLC films increased. Removal of the hard abrasive wear debris from the FCVA-DLC films decreased the wear by vibration, while removal of lubricous tribochemical products of the ECR-CVD-DLC films increased the wear by vibration.

Effects of temperature and ferrous sulfate concentrations on the performance of microbial fuel cell

The two-chambered microbial fuel cell (MFC) was operated in a batch mode, using enriched hydrogen-producing mixed bacteria as the anodic inoculum, artificial sucrose wastewater as the substrate (sucrose concentration 10.0 g/L) and potassium ferricyanide as cathodic electron acceptor. The performance of the MFC was analyzed under five different temperatures of 40, 35, 25, 20, and 15 °C, respectively. The microbial fuel cells (MFCs) which were operated at high operating temperatures (35 and 40 °C) had greater power generation than the other MFCs at start-up. However, only the MFC operated at 35 °C exhibiting stable and high power output over a long period. As for the effect of ferrous sulfate concentration on performance of the MFC, ferrous sulfate had efficiently accelerated influence on power generation during the initial operation period (0–9 d), but had inhibitive influence on power generation after 9 days of operation when the concentration increment of 50–400 mg/L in anolyte. The maximum increase was observed at the concentration increment of 50 mg/L in anolyte.

Growth of single-crystal diamonds in microwave plasma

A microwave plasma (2.45 GHz) was used for depositing single crystal diamond layers at the deposition rate up to 40 μm/h in hydrogen-methane mixtures on the substrates from natural and synthetic diamond with the (100) deposition surface and with the size up to 5 × 5 mm. The structure and the defect-impurity composition of the fabricated single crystals with the thickness up to 600 μm have been investigated using Raman spectroscopy, photoluminescence spectroscopy, cathode luminescence spectroscopy, and electron and optical microscopy. A high quality and purity of the diamond layers deposited from a plasma was confirmed.

Electron heat transport through the plasma-electrode boundary in weakly ionized plasma

The average electron thermal energies in the emission flux from the electrode into the plasma, Ė1, and from the plasma toward the electrode, Ė2, are determined for the cases of large and small values of the coefficient of kinetic reflection. It is shown that these energies vary within the ranges 0.5kBTc < Ė1 < 2kBTc and 0.5kBTe < Ė2 < 2kBTe, where Tc and Te are the temperatures of the cathode and plasma electrons, respectively. The obtained values can be used to formulate the boundary conditions for the hydrodynamic equations at the electrode or a dielectric wall.

Investigation of the Temporal Evolution of X-Ray Emission From a Copper Vacuum Spark Plasma

The temporal evolution of the X-ray pulses generated by the vacuum spark device was investigated by using five channels of p-i-n diodes, which were mounted at the end-on position along the axis of the electrode system. A time-integrated X-ray spectrometer was used to record the spectral distribution of the X-ray emission. Two types of X-ray emission mechanisms can be identified from our experiments. The first mechanism is due to an electron beam accelerated to bombard at the anode tip, which produces a Cu-Kα-dominated spectrum. The second mechanism of X-ray emission is due to the formation of hot plasma during the vacuum spark discharge. There can be two possible sources of energetic electron beams. One is the transient hollow cathode electron beam that is used to trigger the main discharge of the vacuum spark, and the second one is due to plasma instability. The plasma emission during the vacuum spark discharge may be contaminated by electron beam-target emission toward the end of the pinching action. From discharges with clear evidence of the formation of hot plasma and insignificant Cu-Kα contamination, electron temperatures in the range of 4-8 keV for the copper plasma had been deduced.

Fundamental properties of field emission-driven direct current microdischarges

For half a century, it has been known that the onset of field emission in direct current microdischarges with gap sizes less than 10 μm can lead to breakdown at applied voltages far less than predicted by Paschen's law. It is still unclear how field emission affects other fundamental plasma properties at this scale. In this work, a one-dimensional fluid model is used to predict basic scaling laws for fundamental properties including ion density, electric field due to space charge, and current-voltage relations in the pre-breakdown regime. Computational results are compared with approximate analytic solutions. It is shown that field emission provides an abundance of cathode electrons, which in turn create large ion concentrations through ionizing collisions well before Paschen's criterion for breakdown is met. Breakdown due to ion-enhanced field emission occurs when the electric field due to space charge becomes comparable to the applied electric field. Simple scaling analysis of the 1D Poisson equation demonstrates that an ion density of n+ ≈ 0.1VAε0/qd2 is necessary to significantly distort the electric field. Defining breakdown in terms of this critical ion density leads analytically to a simple, effective secondary emission coefficient γ′ of the same mathematical form initially suggested by Boyle and Kisliuk [Phys. Rev. 97, 255 (1955)].

Experimental Investigation of Pseudospark generated electron beam

The pseudospark (PS) discharge is, however, more recently recognized as a different type of discharge which is capable of generating electron beams with the highest combined current density and brightness of any known type of electron source. PS discharge is a specific type of gas discharge, which operates on the left-hand side of the hollow cathode analogy to the Paschen curve with axially symmetric parallel electrodes and central holes on the electrodes. The PS discharge generated electron beam has tremendous applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been carried out experimentally for different applied voltages. The investigation has been done at different axial and radial location inside the drift tube in argon atmosphere. This paper represents experimentally derived axial and radial variation of the beam current inside the plasma filled drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed. It has been further confirmed the successful propagation of electron beam in confined manner without any assistance of external magnetic field.

A novel carboxymethylcellulose–gelatin–titanium dioxide–superoxide dismutase biosensor; electrochemical properties of carboxymethylcellulose–gelatin–titanium dioxide–superoxide dismutase

A novel highly sensitive electrochemical carboxymethylcellulose–gelatin–TiO2–superoxide dismutase biosensor for the determination of O2•− was developed. The biosensor exhibits high analytical performance with a wide linear range (1.5nM to 2mM), low detection limit (1.5nM), high sensitivity and low response time (1.8s). The electron transfer of superoxide dismutase was first accomplished at the carboxymethylcellulose–gelatin–Pt and carboxymethylcellulose–gelatin–TiO2–Pt surface. The electron transfer between superoxide dismutase and the carboxymethylcellulose–gelatin–Pt wihout Fe(CN)64−/3− and carboxymethylcellulose–gelatin–Pt, carboxymethylcellulose–gelatin–TiO2–Pt with Fe(CN)64−/3− is quasireversible with a formal potential of 200mV, 207mV, and 200mV vs Ag|AgCl respectively. The anodic (ksa) and cathodic (ksc) electron transfer rate constants and the anodic (αa) and cathodic (αc) transfer coefficients were evaluated: ksa=6.15s−1, αa=0.79, and ksc=1.48s−1αc=0.19 for carboxymethylcellulose–superoxide dismutase without Fe(CN)64−/3−, ksa=6.77s−1, αa=0.87, and ksc=1s−1αc=0.13 for carboxymethylcellulose–superoxide dismutase with Fe(CN)64−/3−, ksa=6.85s−1, αa=0.88, and ksc=0.76s−1αc=0.1 carboxymethylcellulose–gelatin–TiO2–superoxide dismutase. The electron transfer rate between superoxide dismutase and the Pt electrode is remarkably enhanced due to immobilizing superoxide dismutase in carboxymethylcellulose–gelatin and TiO2 nanoparticles tend to act like nanoscale electrodes.

Direct Electrochemistry of Artificial Peroxidase Based on Self-Assembled Cytochrome c-SDS-Nano-Micelle

A peroxidase activity nano-artificial enzyme (AP) was designed by feeding cytochrome c (Cty c) in sodium dodecyl sulfate (SDS) nano-micelle in 50 mM, pH 10.5 sodium phosphate buffer solution (PBS), and 30% catalytic efficiency of native HRP was achieved. The UV-Vis, Circular Dichroism (CD) specropolarimetry, Surface Tension and Isothermal titration calorimetric (ITC) methods were utilized for additional characterization of the AP. Direct electron transfer between AP and electrode was achieved by immobilizing the monolayer of AP on a glassy carbon electrode using the electro-deposition method. CMCs of Cyt-SDS micelle and SDS micelle were determined to be 4.68 mM and 4.83 mM, respectively, in 50 mM PBS at pH 10.5. The aggregation number of SDS in Cyt c-SDS-nano-micelle was calculated to be 116. The immobilized AP modified electrodes showed quasi-reversible electrochemical redox behaviors with a formal potential of −38 ± 5 mV (vs. Ag/AgCl) at a scan rate of 50 mV/s. The cathodic transfer coefficient and electron transfer rate constant were evaluated to be 0.51 and 0.72 s−1, respectively. The apparent Michaelis-Menten constant () was calculated to be 0.14 mM.

Efficiency of photon enhanced thermionic emission solar converters

Photon Enhanced Thermionic Emission (PETE) is a recently proposed novel concept in solar energy conversion, combining thermal and photovoltaic carrier excitation with thermionic emission. A recent study has shown that PETE conversion efficiencies can theoretically rise above 40% at concentration of 1000 suns. We analyze two major aspects missing from previous treatment of PETE conversion efficiency: changes in the cathode's conduction band carrier concentration with the electrical operating point; and determination of the cathode temperature from a full thermal energy balance. The results show that the conversion efficiency is a monotonically increasing function of temperature, and a monotonically decreasing function of the cathode electron affinity. It is shown that PETE converter efficiency according to the modified model is higher than previously reported, but achieving very high efficiencies of over 40% requires high temperatures that may be difficult in practical implementation.

Model of the stabilized distribution function for oscillating electrons in a hollow cathode

The form of the velocity distribution function of oscillating electrons in a low-pressure discharge with a hollow cathode is determined using the simple model of mathematical billiards. The distribution function is nonequilibrium and permits the development of instability of the plasma beam type.

Effects of cathodic electron acceptors and potassium ferricyanide concentrations on the performance of microbial fuel cell

The effects of different cathodic electron acceptors and potassium ferricyanide concentrations on performance of a two-chambered microbial fuel cell (MFC) were studied. The MFC was operated in a batch mode, using enriched hydrogen-producing mixed bacteria as the anodic inoculum and artificial sucrose wastewater as the substrate. To find out the excellent electron acceptor for the two-chambered MFC, three MFCs using potassium ferricyanide catholyte sparged with air (M1), aerated catholyte (M2) and potassium ferricyanide catholyte (M3) were operated separately to elucidate the difference in power generation under similar anodic operating conditions (sucrose concentration 10.0 g/L). The results show that the power generation in M3 was slightly higher than that in M1, while both were much higher than that in M2. The effect of potassium ferricyanide concentrations in catholyte (pH 7.0, 100 mM phosphate buffer solution) on electricity generation characteristics was studied under constant anodic operational conditions. The maximum resultant MFC output power density (181.48 mW/m3) was produced using a potassium ferricyanide concentration of 0.1 M in the catholyte.

Investigations of a Double-Gap Vircator at Submicrosecond Pulse Durations

The results of investigations of a double-gap vircator driven by a 20 Ω and 500-ns generator operating in the output voltage range 400-600 kV are presented. The vircator generated microwave pulses with a peak power of up to 200 MW at ~5% efficiency and the frequency varied from 2.0 to 2.3 GHz depending on the cavity geometry. The limitations on the microwave pulse duration not related to the cathode plasma expansion are addressed. On the one hand, the microwave generation is terminated because of the plasma formation at the foil separating the cavity sections, so that the virtual cathode (VC) electron space charge is neutralized by the plasma ion flux. On the other hand, if the electron beam energy deposition into the foil is reduced, a substantial delay in the start time of the microwave generation appears, which has been studied in detail. With these limiting factors, the microwave pulse full duration varied from 100 to 350 ns; the maximal full width at half maximum duration achieved in the experiments was ~180 ns. Measurements of the current transmitted through the vircator cavity indicated the existence of a VC in spite of the absence of microwave generation during the delay. The experimental dependence of the microwave generation starting current on the diode voltage is presented, and possible mechanisms behind the generation delay are discussed. Simplified numerical simulations emphasize the role of the portion of electrons that are reflected from the VC, the number of which must be sufficient for the microwave generation to occur.

Investigation of electron beam parameters inside the drift region of plasma cathode electron gun

This paper presents experimental studies for the production and propagation of an electron beam from a single gap pseudospark discharge based plasma cathode electron (PCE) gun. The generated electron beam has been successfully propagated for more than 25 cm in a gaseous environment without application of external guiding magnetic field at different operating conditions. The electron beam losses due to recombination with ions and collision with walls of drift space have been estimated. The electron beam profile has also been analyzed in the drift region of the gun.

Comparative simulation studies of plasma cathode electron (PCE) gun

Pseudospark discharge based plasma cathode has capability to provide high current density electron beam during discharge process. In this paper an effort has been made to simulate the breakdown processes in the pseudospark discharge based plasma cathode electron gun. The two-dimensional plasma simulation codes VORPAL and OOPIC-Pro have been used and results are compared. The peak discharge current in the plasma cathode electron gun is found to be dependent on aperture size, hollow cathode dimensions, anode voltage and seed electrons energy. The effect of these design parameters on the peak anode current has been analysed by both the codes and results matches well within 10% variation. For the seed electron generation an electron beam trigger source is used to control the discharge process in the hollow cathode cavity. The time span of trigger source has been varied from 1-100 ns to analyze the effect on the peak anode current.

Butyrate production enhancement by Clostridium tyrobutyricum using electron mediators and a cathodic electron donor

Electron mediators and electron supply through a cathode were examined to enhance the reducing power for butyrate production by an acidogenic clostridium strain, Clostridium tyrobutyricum BAS 7. Among the tested electron mediators, methyl viologen (MV)-amended cultures showed an increase of butyrate productivity (1.3 times), final concentration (1.4 times), and yield (1.3 times). The electron flow altered by MV addition from the ferredoxin pool to the NADH pool was shown by one electron model, implying that more available NADH increased butyrate production. In the cathode compartment poised at -400 mV versus the Ag/AgCl electrode, the neutral red (NR)-amended cultures of Clostridium tyrobutyricum BAS 7 increased butyrate concentration (from 5 to 8.8 g/L) and yield (from 0.33 up to 0.44 g/g) with no acetate production at all. Given that electrically reduced NR (NR(red) , yellow) by the cathode was re-oxidized (NR(ox) , red) in the cells on the basis of color change, electron flow from NR(red) to NAD(+) (i.e., NADH generation) induced an increase in butyrate production. This is the first report to show the increase of butyric acid production by electrically driven acidogenesis. These results show that the electron flow altered NADH formation by electron mediators and by the cathodic electron donor, increasing the yield and selectivity of reduced end-products like butyrate.

Enhanced electricity generation from whey wastewater using combinational cathodic electron acceptor in a two-chamber microbial fuel cell

While energy consumption is increasing worldwide due to population growth, the fossil fuels are unstable and exhaustible resources for establishing sustainable life. Using biodegradable compounds present in the wastewater produced in industrial process as a renewable source is an enchanting approach followed by scientists for maintaining a sustainable energy production to vanquish this problem for ulterior generations. In this research, bioelectricity generation with whey degradation was investigated in a two-chamber microbial fuel cell with humic acid as anodic electron mediator and a cathode compartment including combinational electron acceptor. Escherichia coli was able to use the carbohydrate originated from whey to generate bioelectricity. The open-circuit potential in absence of mediator was 751.5 mV at room temperature. The voltage was stable for more than 24 h. Humic acid was used as a suitable mediator. In addition, some mixed chemicals were employed as catholyte. Based on polarization curve, the power and current values in the presence of a mixed solution of potassium iodide (KI), ferric chloride [FeCl3 (Ш)] and manganese chloride tetrahydride (MnCl2·4H2O) with doubling of oxidant (oxygen) concentration using agitation with magnet stirrer in cathode compartment without any buffer solution were boosted to 562.9 μW and 1906.1 μA, respectively, and demonstrated the best result for power generation.