Anode-cathode Distance Research Articles

Model calculation for the field enhancement factor of carbon nanotube

To estimate the apex field enhancement factor associated with carbon nanotube on a planar cathode surface, the simple model of floated sphere between parallel anode and cathode plates was studied. When the anode-cathode distance d is much larger than the height h of carbon nanotube, the field enhancement factor of carbon nanotube was given as the following expression β0=h∕ρ+3.5 with the image method, which is a little than the early work of Miller. Finally, the influence of the anode-cathode distance on the enhancement factor was also discussed and the expression of enhancement factor of carbon nanotube should be modified to be β=h∕ρ+3.5+A(h∕d)3, where A is the constant. This shows a much weaker influence of the relatively smaller anode-cathode distance on the field enhancement factor of carbon nanotube than that estimated earlier. Thus, we can lower the threshold voltage to some extent by the decrease of the anode-cathode distance. The higher aspect ratio of carbon nanotube and the lower anode-cathode distance (still larger than a few times of the height of carbon nanotube) are the main factors leading to the stronger field at the apex.

Current–voltage characterization and temporal stability of the emission current of silicon tip arrays

We report an investigation of current–voltage ( I– V) characteristics of silicon tip arrays, presenting a discussion of the electrical phenomena with respect to the field emission current. The samples were fabricated on silicon substrates using reactive ion etching SF 6 plasma and sharpened by thermal oxidation. Current–voltage measurements were performed using anode–cathode distances of 30 and 50 μm, and followed a Fowler–Nordheim behavior. No significant changes in the field enhancement factor were found for the different anode–cathode spacings. However, a rise in threshold voltage was detected as anode–cathode separation increased. We also studied the histeresis behavior of the silicon tips for a fixed distance and found differences in the threshold voltage for ascending and descending ramps, possibly caused by a variation in the “effective” work function. Finally, we investigated the short-term current emission stability and found the behavior to be consistent with evidence from the literature, which correlates the instability in electron emission to localized interface traps and gas desorption events.

Techniques developed for the ATLAS thin gap chambers mass production in Japan

The thin gap chambers (TGCs) are used for the muon trigger system in the end-cap regions of the ATLAS detector. The TGC mass production phase at High Energy Accelerator Research Organization (KEK) started in January 2001. As the anode-cathode distance is small, 1.4 mm, chamber flatness is essential to achieve a uniform gas gain over the chamber. In order to perform a stable production with high quality we developed a chamber closing system. When we glue two half-chambers together, we sandwich them between a granite table and an aluminum honeycomb panel to keep the chamber flat from both sides. By using silk screens, we control the quantity of epoxy adhesive that affects the chamber thickness. Due to these developments, we can achieve the flatness of less than 100 /spl mu/m. Uniformity of detection efficiency of the TGC is measured with a cosmic-ray test bench at Kobe University. So far we have tested 300 TGCs. Position dependence of the efficiency is measured with a granularity of 5 mm /spl times/ 5 mm. The average efficiency over the tested chambers is achieved to be 99% excluding the wire supports and spacers.

Enhanced cold field emission from 〈100〉 oriented β–W nanoemitters

Well-aligned β-phase W(100) nanorods having square-base pyramidal apexes were grown on oxidized Si(100) substrate using glancing angle deposition technique with substrate rotation. The field emission characteristics of nanorods were measured using scanning tunneling microscope (STM) tip as an extraction anode. A highly confined emission current of about 23 μA was obtained at a low extraction voltage of ∼260 V at ∼280 nm anode-cathode distance with <3% fluctuations over ∼2 h. The Fowler–Nordheim plot of the field emission characteristics of nanorods is nonlinear compared with the linear behavior from a conventional W film. The STM topography after the field emission showed a type of nanolips structure grown over the pyramidal apex, which was suggested to enhance and stabilize the emission current.

Approach curve method for large anode–cathode distances

An important technique used to characterize field emission is the measurement of the emitted current against electric field (I×E). In this work we discuss a procedure for obtaining I×E data based on multiple approach curves. We show that the simulated features obtained for an idealized uniform surface matches available experimental data for small anode–cathode distances, while for large distances the simulation predicts a departure from the linear regime. We also discuss the shape of the approach curves for large anode–cathode distances for a cathode made of carbon nanotubes.

Effect of geometrical parameters on the field-emission properties of single-walled carbon nanotube ropes

Aligned single-walled carbon nanotube (SWNT) ropes show excellent field-emission performance due to their high aspect ratio and sound alignment. In this study, the effect of geometrical parameters, such as cathode-anode distance and the height of SWNT ropes on the field-emission properties of SWNT ropes was investigated. It was found that the cathode-anode distance influences the emission properties, such as the turn-on fieldFtoand threshold fieldFthr, of SWNT ropes, and the turn-on and threshold fields are marginally decreased at relatively larger gaps between the SWNT emitter tip and the anode plane. It was also found that the emission properties of SWNT ropes are improved by increasing the rope length, at least in the present experimental range. A possible two-step field amplification model was proposed to explain this length effect of SWNT ropes. The estimated results show that the local field at the tip of SWNT ropes, which causes a certain emission-current density, seems not to change with the cathode-anode distance, and the effective emission area of the SWNT rope is much smaller than the apparent cross-sectional area of the SWNT rope. The results obtained suggest that it is possible to optimize the performance of SWNT rope-based cold cathode by adjusting geometrical parameters of SWNT rope emitters.

Synthesis and characterization of well-aligned quantum silicon nanowires arrays

Abstract Quantum silicon nanowires (SiNWs) arrays have been synthesized by chemical vapor deposition template method without catalyst. The results of SEM and TEM reveal clear alignment of the SiNWs and each nanowire with perfect lattices is a single crystal. The growth mechanism of SiNWs without catalyst is discussed based on VLS mechanism. The unusual pattern in the Raman spectrum may be a unique characteristic of low-dimensional nano-scale materials. Enhanced photoluminescence properties may be associated with the quantum confinement effect and the formation of ordered arrays. Field emission from SiNWs arrays under various anode–cathode distances are analyzed based on Fowler–Nordheim theory. The superior field emission behavior is believed to originate from the oriented growth and the sharp tips of SiNWs.

The Impact of Varying Conductivity on the Control of Aluminium Electrolysis Cells

In this paper we investigate from a theoretical point of view the impact of varying bath temperature, excess AIF 3 and alumina concentration on cell resistance and cell control. The results are interpreted using knowledgeof the behavior of general resistance and anode beam controllers to study the influence on the anode cathode distance. This again leads to the proposal of a new control strategy for bath temperature and excess AlF 3 . The theoretical results obtained are supported using real data.

A Vacuum Diode for the Two-Sided Electron Irradiation of Objects

A vacuum diode for the two-sided electron irradiation of objects makes it possible to reduce the irradiation nonuniformity and increase the thickness of the irradiated layer of the object with a uniform distribution of the absorbed dose over the layer thickness. The cathode holder of the diode is constructed in the form of two symmetrical arms connected to a common current lead. Two cathodes are attached to the arms' ends opposite each other. The electron beam is extracted to the atmosphere through two windows–anodes positioned across from one another. The vacuum diode with metal–dielectric cathodes was tested on a УРТ-0.5 nanosecond electron accelerator (the electron energy is ∼0.5 MeV and the output beam power is ∼1 kW). The results obtained have shown that the diode ensures the two-sided irradiation of objects. Depending on the irradiated surface, the irradiation conditions can be varied by changing the cathode–anode distance in one of the arms of the diode.

Glow discharge with diminishing neutral plasma

In this work, the anode–cathode distance in a direct current glow discharge is reduced manually to values smaller than the Child–Langmuir extent, while the discharge current, the discharge voltage and the Langmuir probe current are monitored continuously. The discharge current is observed to develop a large peak as soon as the sheath edge contacts with the anode, then decays to negligible values for a certain time interval, after which, this cycle starts repeating itself periodically. A model is described to interpret the behavior of all three quantities self-consistently. The experiment is performed with different anode–cathode distances and the implications of the observations regarding ion implantation processes are discussed.

Characteristics of diode perveance and vircator output under various anode-cathode gap distances

When an electron beam is generated from a cathode, an electrode sheath plasma is also generated. Hence, the perveance of the diode is varied and changes the diode output characteristics. In our pulsed-power system Chundoong, the perveance characteristics have been experimentally investigated, from which the sheath-plasma expansion speed has been measured to be about 3 cm//spl mu/s inside the diode. It is shown that the sheath-plasma expansion inside the diode gives the influence on the electron-beam current density. The vircator microwave output has been shown to be sensitively dependent on the anode-cathode (A-K) gap distance. The highest microwave power occurs at the initial A-K gap distance d=4 mm with peak power of 200 MW and a frequency of about 5.5 GHz in this experiment.

Interferograms of a cathode spot plasma obtained with a picosecond laser

Cathode spot plasmas as well as balls-moving dense plasma blocks in vacuum arcs-were investigated by laser interferometry and absorption photography with high spatial (1.2 /spl mu/m) and temporal (100 ps) resolution. The discharge was initiated between a needle-type cathode and plane anode with a cathode-anode distance of a few millimeters. The duration of the discharges was about 10 ms and the current up to 100 A. Picosecond interferometry yielded spatial-temporal electron density distributions in the arc phase of the cathode spot. An absolute electron density up to 2/spl times/10/sup 26/ m/sup -3/ and plasma temperature about 1 eV in narrow plasma jets with a diameter about 5 /spl mu/m were estimated.

Electron beam propagation in a space-charge regime

We report on the propagation of electron beams generated by a niobium photocathode illuminated by different wavelength excimer lasers. The cathode used was a polycrystalline disc. Its work function was 4.3 eV while the laser photon energy was 4.02 eV for the XeCl laser and 5.6 eV for the KrCl laser. The anode–cathode distance was variable as well as the saturation output current. At low accelerating voltage the beam was space charge dominated but its peak value was not limited by the Child–Langmuir calculated value. A fast shunt resistance allowed to record the electron beam generated with a fast rise time. The maximum output current was reached with the KrCl laser which provided an electron bunch containing 980 mA and 9 nC.

Current Efficiency Obtained with SnO2-based Inert Anodes in Laboratory Aluminium Cell

Abstract A systematic study of the current efficiency (CE) in a laboratory aluminium cell with SnO2-based inert anodes was carried out by measuring the overall amount of oxygen relieved at the anode, using two different methods. Inert ceramic anodes of 96% SnO2, 2% Sb2O3, 2% CuO in wt% composition were prepared and investigated. The influence of: temperature, current density, anode-cathode distance, cryolitic ratio, content of alumina and different additives was studied. At the same time the influence of the age of boron nitride (BN) sheath of the inert anode on the CE was evaluated.

Resistance Due to the Presence of Bubbles in an Electrolytic Cell with a Grooved Anode

Bubble resistance in an electrolytic cell using a grooved anode and anodes with plane surfaces are measured and reported. The cell was operated at various inclination angles of the anode and at a range of anode-cathode distances (ACD). The comparison shows that bubble resistance obtained for a grooved anode is smaller than that for anodes with plane surfaces at the same operating conditions (i.e. inclination angle, current density, and equivalent ACD). Explanations for the reduction in the bubble resistance due to the use of a grooved anode are given. The use of grooved anodes may provide a significant reduction in the overall cell voltage drop, and thus increase the energy efficiency, provided the node material is not consumed during the process, causing the grooves to revert to a planar surface. The work reported in this paper is of particular significance to the aluminium smelting industry if a non-consumable inert anode is available.

Hardness, intrinsic stress, and structure of the a-C and a-C:H films prepared by magnetron sputtering

The 1.5-μm thick carbon films prepared by magnetron sputtering of a carbon target in Ar, Ar +CH 4 and Ar+O 2 gas mixtures show that the higher their intrinsic stress, the higher their microhardness and the lower their resistivity. The a-C films obtained without ion bombardment (unbiased; the mean free path of sputtered C atoms larger or equal to the cathode–anode distance) show microhardness up to 25 GPa. The biased a-C films (i.e. with ion bombardment) achieve the highest microhardness (up to 50 GPa) and the lowest resistivity (0.01 Ω cm). An increase in Ar pressure, or the optional addition of O 2, results in a decrease in the microhardness and intrinsic stress and an increase in the film resistivity. In comparison to a-C films, by adding CH 4 to Ar up to certain limit, the microhardness and intrinsic stress of these a-C:H films increase and subsequently decrease steeply. It was specified by analysis of the electron diffraction patterns of thin films (30–60 nm) deposited under the same conditions that the radius of the first co-ordination sphere of C atoms for all the films is in a good agreement with the value for graphite. The prime interplanar distance for biased a-C films is considerably lower than that for unbiased ones and for graphite. Our data indicate the sp 2-bonded carbon structure of the deposited hard carbon films, in which the prime interplanar distance is reduced due to intrinsic stress. Thus, it is more suitable to explain the hardness origin as a consequence of the film nanostructure rather than the presence of sp 3 bonds .

Influence of the fringe field and the field interaction on the emission performance of a diode emitter array

In the field emitter array, there is a fringe field surrounding the emitter array. The fringe field and the interactive field between different tips will influence the emission uniformity of the emitter array. This paper studies the influences of the fringe field and the interactive field on the emission performance of a diode emitter array. The variations of the emission currents versus the width of the margin of the array are given. From these results, the influences of the fringe field on the emissions of the center tips and the corner tips are obtained. This paper also analyses the dependence of the fringe field and the interactive field on the cathode–anode distance and the tip-to-tip spacing.

Simulation of field emitter array in diode model

In the application of field emitter arrays, it is useful to understand its emission performance. This paper calculates the electric field of a diode emitter array in three-dimensional space. From this calculation, the emission uniformity of a diode array is studied. The dependance of the tip-to-tip spacing and of the cathode–anode distance on the uniformity of the array is also analyzed. The pressure sensor based on the diode model is simulated. From the dependence of the emission current for different tip densities, the influence of the emission uniformity can be obtained.

GaN field emitter array diode with integrated anode

GaN field emission pyramids are grown by self-limiting, selective-area metalorganic chemical vapor deposition. The self-limitation provides the potential of high uniformity of the pyramids and the selective-area growth allows one to define regular arrays of GaN pyramids for field emitter arrays (FEAs). Fabrication of an integrated anode lowered the operating voltage of the FEAs by narrowing the anode-cathode distance compared to devices with an external anode. A maximum emission current of 0.15 μA/tip has been observed for voltages of 570 V with an emitter-anode separation of 2 μm.

Fabrication of a silicon-vacuum field-emission microdiode with a moving anode

A vacuum microdiode with a moving anode was fabricated by means of a new process requiring only two mask levels and only one critical etching step. The cathode, with a pyramidal shape, was made by anisotropically etching p silicon through a mask formed by the anode itself, which, at the end of the process, consists of a SiO2 suspended membrane supporting an Al layer. The process is compatible with standard complementary metal-oxide-semiconductor technology. I–V characteristics were measured under vacuum verifying also that the diode current is sensitive to visible light irradiation and to changes of the anode-to-cathode distance. A minimum anode-cathode distance of about 5000 Å was obtained.