Electric Field Emission Of Electrons Research Articles

Interactions between atmospheric pressure plasmas and metallic catalyst particles in packed bed reactors

Atmospheric-pressure plasmas sustained in packed bed reactors (PBRs) are being investigated for chemical conversion of gases and pollution control. Metallic catalysts added to the surfaces of the dielectric beads of PBRs can increase the energy efficiency and selectivity of chemical processes by reducing operating temperature and providing additional reaction pathways. In this paper, results from a computational investigation of plasma surface interactions between micron-scale metallic catalysts and humid-air plasmas in PBRs are discussed. We found that high plasma density regions form in the proximity of the metallic catalysts. These higher-density plasma regions were confirmed experimentally using ICCD imaging. The intense plasmas result from geometrical electric field enhancement and redistribution of charges within the conductive particles, leading to further enhancement. The high electric field at the triple points of the catalysts can produce electric field emission of electrons, which provides a pre-ionization source or additional source of electrons. These regions of high electric field and sources of electrons guide discharges towards the catalysts and increases fluxes of excited species, ions, electrons and photons to their surfaces. These fluxes are focused primarily at the triple points between the metal, dielectric and gas. As a result, the catalyst is locally heated, which could lead to further increased rates of thermocatalytic reactions on the surface. Surface roughness of the metal inclusions can lead to additional electric field enhancement, which changes the character of the discharges in the vicinity of the catalysts while reducing breakdown voltage.

An infrared energy harvesting device using planar cross bowtie nanoantenna arrays and diode-less rectification based on electron field emission

ABSTRACT In this paper, we present a rectification process through electron emission from sharp tips under a high electric field of 109–1010 V/m based on the Fowler–Nordheim theory. A large planar array of 104–105 nanoantennas is proposed to achieve the required electric field for electron emission in the nanoantenna gap. Spatial coherence of the incident wave is a prohibitive issue in using large antenna arrays, and it is overcome by choosing proper size for the array. The design starts with a single-element nanoantenna, for which, five different types are considered, namely dipole, spiral, cross bowtie, sinuses and square spiral. Full-wave simulations show that cross bowtie has the highest field enhancement. Moreover, two array configurations, i.e. series and parallel feed networks, are considered and their field enhancement are compared. Moreover, field enhancement in large array configurations is predicted using proposed equations based on curve fitting.

Surface Structure-Dependent Low Turn-On Electron Field Emission from Polypyrrole/Tin Oxide Hybrid Cathodes.

We present a new surface structure-dependent cold cathode material capable of sustaining high electron emission current suitable for next-generation low turn-on field-emission devices. The low turn-on electric field for electron emission in the cathode materials is critical, which facilitates the low-power room-temperature operation, a key factor required by the industrial sector. We demonstrate the facile synthesis of polypyrrole (PPy)/tin oxide (SnO2)-based core–shell hybrid cold cathode materials for large area applications. The technique used here is based on a simple and economical method of surfactant-mediated polymerization. The coupled investigation of X-ray diffraction along with electron microscopy reveals the formation of rutile phase SnO2 nanoparticles of size ∼15 nm. These SnO2 nanoparticles act as nucleation sites for the growth of PPy nanofibers, resulting in encapsulated SnO2 nanoparticles in the PPy amorphous matrix. The coupling of spherical-shaped core–shell structures of PPy/SnO2 resulted into the particle train-like nanostructured form of the hybrid material. These core–shell structures formed the local p–n junction between the n-type SnO2 (core) and p-type PPy (shell). The long chains of these p–n junctions in nanofibers result in the modification of the electronic band structure of PPy, leading to a reduction in the work function of the electrons. The significant surface structural modification in PPy/SnO2 causes a prominent reduction in the turn-on electric field for electron emission in PPy/SnO2 nanocomposite (∼1.5 V/μm) as compared to the pure PPy (∼3.3 V/μm) without significant loss in current density (∼1 mA/cm2). The mechanism of improved field-emission behavior and advantages of using such hybrid nanomaterials as compared to other composite nanomaterials have also been discussed in detail.

Electrostatic potential barrier for electron emission at graphene edges induced by the nearly free electron states

Using the density functional theory, we studied the electronic structures of zigzag graphene nanoribbons with hydroxyl, H, ketone, aldehyde, or carboxyl terminations under a lateral electric field. The critical electric field for electron emission is proportional to the work function of the functionalized edges except the hydroxylated edge, which leads to the anomalous electric field outside the edge, owing to the electrons in the nearly free electron (NFE) state in the vacuum region. The strong electric field also causes a potential barrier for the electron emission from the H-terminated edge owing to the downward shift of the NFE state.

Electric field emission of electrons from negatively charged spherical particles in a dusty plasma in the regime of nonlinear screening

This note presents a discussion of the electric field emission from negatively charged spherical particles in a dusty plasma in the regime of nonlinear screening. Using the appropriate representation of the nonlinear screening by Gurevich and the matrix method, the tunneling probability of an electron through the potential energy barrier around the particle has been evaluated as a function of its radial energy; corresponding values of the current density have also been obtained. A discussion of numerical results, thus obtained concludes the presentation.

Characteristics of Electron Emission from a (Pb,La)(Zr,Ti)O3 Ferroelectric Cathode

The properties of electron emission from a poled lead lanthanum zirconate titanate (PLZT) ferroelectric cathode have been investigated on the dependence of operating parameters such as the driving voltage, the vacuum pressure, the diode gap distance, and the diode acceleration voltage. The threshold electric field for electron emission from the cathode is about 6 kV/cm and the emitted current increase with increase in the driving voltage. A maximum current of 37 A/cm2 has been detected when the driving voltage is -1.4 kV and the gap distance is 20 mm. The electron emission is considered to be initiated by field emission and then possibly be enhanced by the surface plasma. To confirm the detailed emission process, however, further experimental study should be necessitated.

Effect of electric field emission on charging of dust particles in a plasma

AbstractThe authors have considered the charging of spherical particles in a plasma, taking into account the electric field emission of electrons from the dust particles and the change in the electron/ion densities in the plasma. The dependence of the charge of a particle and electron/ion densities on the radius and number of dust particles and the density of electrons/ions and the temperature in the undisturbed plasma has been studied numerically without and with the inclusion of the electric field emission of electrons from the particles. It is seen that both the electric field emission and the electron/ion kinetics significantly affect the charging process.

Photoelectric field emission of electrons: Photon assisted tunneling

This note is a discussion of the enhancement in electric field emission of electrons from a plane metallic surface on irradiation by light. The enhancement in the tunneling coefficient of an electron by absorption of a photon and the consequent increase in the field emission current has been evaluated. A discussion of the results and possible applications concludes the presentation. In particular it is suggested that this phenomenon may be an explanation for the observed increase in photoelectric current with increasing magnitude of negative potential of lunar dust grain simulants.

Electric field emission of electrons from spherical metallic dust particles

In this paper, an almost exact expression for the tunneling probability of an electron through the potential barrier on account of a negative charge on a spherical metallic particle has been derived and used to obtain the field emission current density from the surface of the particle. Based on these results a parametric analysis of the phenomenon and comparison with the results of the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) approximation (similar to the Fowler–Nordheim theory) has been presented. It is seen that the JWKB theory underestimates the tunneling probability. The investigation is of relevance to dusty plasmas in space and in the laboratory.

Effects of sputtering pressure on the field emission properties of N-doped SrTiO 3 thin films coated on Si tip arrays

The influence of sputtering pressure on the electron emission properties of Si tips coated with N-doped SrTiO 3 ultrathin films was investigated. X-ray diffraction studies revealed that the N-doped SrTiO 3 films deposited at different pressures remain the perovskite structure. However, the threshold electric field of electron emission decreased markedly when the sputtering pressure is increased, and reached a minimum value of 17.37 V/μm while deposited at 1.6 Pa. The decrease in the threshold field is attributed to the narrowed band gap and the lowered surface energy of SrTiO 3 thin films with nitrogen doped, as confirmed using spectroscopic ellipsometry and water contact angle measurement. Furthermore, it is revealed using XPS that such sputtering pressure dependence is accompanied with the change of nitrogen bonding state in the films, which changes from poorly screened γ-N 2 state to atomic β-N state when the sputtering pressure is increased. A mechanism of bonding and band-forming was proposed for the enhanced electron emission with nitrogen incorporation in the sputtered SrTiO 3 films.

A critical look at electric field emission of electrons from metallic surfaces

A critical look at the commonly used Fowler's expression for the transmission coefficient of electrons through the potential barrier leads to the conclusion that this expressions is physically untenable. An expression for the field emission current density, corresponding to the expression for the transmission coefficient obtained from the exact solution of Schrödinger’s equation, has been derived. Numerical results have been expressed in the form of tables and graphs and discussed. It is seen that in the range of 10−4<kT/EF<10−3, the effect of temperature on the field emission current density is negligible.

An intense-current electron beam source with low-level plasma formation

The generation of high-current electron beams is accompanied by strong plasma formation on the cathode surface. The cathode plasma sheath expands towards the anode, which limits the pulse length. In this paper the experiments were performed using a high-voltage pulse generator with 400 kV output voltage and 300 ns pulse duration. We used electrical and optical diagnostics to study the process of plasma formation. This paper presents data on a caesium–iodide (CsI) coated carbon fibre cathode capable of operating with the lack of strong plasma formation. The addition of CsI caused an increase in the voltage pulse duration and reduced the turn-on electric field for electron emission, thus resulting in the fast-rise current. In particular, the CsI coating effectively inhibited the plasma expansion and, as a result, the diode gap remained almost unchanged within approximately 200 ns. These results show that CsI-coated carbon fibre cathodes are promising electron emitters for generating long pulse high-current electron beams.

Low Voltage Electron Emission from BaTiO3 Thin Films Treated in Hydrochloric Acid

Low voltage electron emission from ferroelectric thin films consisting of BaTiO3 is reported. The 1 μm thick BaTiO3 thin films were deposited by spin coating and were annealed to improve their crystallinity. Then surface treatments using hydrochloric acid have been performed and very thin gold top electrodes were deposited. The electron emission capability of these thin films has been tested using a parallel cathode-positively biased anode arrangement in a vacuum chamber at 10-5 Pa. The turn on electric field for electron emission was 23 V/μm and we obtained an emission charge of about 200 pC/cycle at an electric field of 100 V/μm. [DOI: 10.1380/ejssnt.2008.164]

Busting dust: from cosmic grains to terrestrial microbes

Electrostatic charging can have important consequences for both the growth and disruption of microparticulates immersed in a plasma. In this topical review, my emphasis is on the latter process, while I extend the term microparticulates not only to include ordinary inanimate cosmic or terrestrial dust but also to include terrestrial microbes whose sizes range from tens of nanometers (viruses) to tens of micrometers (bacteria). Following a description of the basic mechanism of electrostatic disruption of a solid body, I will discuss the role of size, shape and surface irregularity on the process. I will also consider the mitigating role of electric field emission of electrons on the disruption process of a negatively charged grain as its size falls below a critical size. I will conclude by reviewing some early evidence for the electrostatic disruption of cosmic grains, and the very recent evidence for the electrostatic disruption of the bacterial cell membranes in terrestrial sterilization experiments.

Low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon films

The low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon (ta-C) films was investigated. Ta-C films prepared by a filtered arc deposition technique were annealed at 400 °C for 60-120 min in a nitrogen atmosphere. The density and sp3 content in as-grown film were 3.3 g cm-3 and ~90%, respectively. After annealing, no obvious changes in film density or sp3 content were observed. The threshold electric field of electron emission of annealed ta-C films increased. Through annealing the clustering of sp2 bonded carbon would occur, resulting in bandgap reduction and the eventual increase of the emission barrier. After a given annealing period, the degree of clustering increased, and was responsible for the threshold electric field increasing further. The results implied that the control of the sp2 bonding configuration in addition to the sp3 bonding is important in obtaining good emission properties for ta-C films.

Gravitational Tunneling Radiation

The isolated black hole radiation of both Hawking and Zel'dovich are idealized abstractions as there is always another body to distort the potential. This is considered with respect to both gravitational tunneling, and black hole "no-hair" theorems. The effects of a second body are to lower the gravitational barrier of a black hole and to give the barrier a finite rather than infinite width so tha a particle can escape by tunneling (as in field emission) or over the top of the lowered barrier (as in Schottky emission). Thus radiation may be emitted from black holes in a process differing from that of Hawking radiation, P SH, which has been undetected for over 24 years. The radiated power from a black hole derived here is PR e ^2__ PSH, where e ^2__ is he ransmission probability for radiation through the barrier. This is similar to electric field emission of electrons from a metal in that the emission can in principle be modulated and beamed. The temperature and entropy of black holes are reexamined. Miniscule black holes herein may help explain the missing mass of the universe, accelerated expansion of the universe, and anomalous rotation of spiral galaxies. A gravitational interference effect for black hole radiation similar to the Aharonov-Bohm effect is also examined.

Phonon assisted tunnel emission of electrons from deep levels in GaAs

A theory is developed for the electric field emission of electrons from deep levels in GaAs taking into account quantum mechanical tunneling and electron phonon interaction. Using this theory, a numerical model is developed simulating capacitive DLTS and capacitive transient experiments. The parameters of the model for the electron irradiation induced defect E3 are extracted by fitting an experimental DLTS spectrum and an experimental transient capacitance curve. In particular, an estimate is given for the Franck-Condon shift. This estimate is found to be consistent with that obtained by another method based on the measured activation energy of the capture cross-section. With the parameters thus found, the model is shown to reproduce correctly several other experimental results over a wide range of temperatures and electric field intensities.

Electrically alterable avalanche-injection-type MOS READ-ONLY memory with stacked-gate structure

Design theory and experimental results of the WRITE and ERASE properties of a rewritable and nonvolatile avalanche-injection-type memory are reported. The memory transistor has the stacked-gate structure of a floating gate and a control gate. The threshold-voltage shift of the transistor due to injected charge is controlled by applied potential on the control gate which reduces the avalanche breakdown voltage of the drain junction and accelerates electron injection into the floating gate. The writing time is about 20 µs for a single transistor and is less than 5 s for a fully decoded 2048-bit memory with appropriate duty cycles of programming pulses. Erasure of the memory is accomplished either by ultraviolet light irradiation onto the floating gate or by electric field emission of electrons from the floating gate to the control gate. Electrical erasing is theoretically analyzed and successfully compared with experimental results on the 2K bit memory. Memory retention is also investigated and a charge-escaping model is proposed.

A New Superconducting Heavy Ion Accelerating Structure Using Chemically Polished Lead Surfaces

A new heavy ion accelerating structure has been developed which together with a parallel development in chemical polishing techniques makes possible very high accelerating fields for a wide range of particle velocities using inexpensive and easily handled materials. This "Split Ring" accelerating structure has a peak magnetic field approximately one third that of other inductively loaded accelerating structures (less than 10OG at 1MV/m accelerating field) and a peak electric field less than 6 times the effective accelerating field. In addition, a chemical polishing technique appropriate for use on electroplated lead surfaces has been developed which greatly reduces the electric field emission of electrons from the surface. Surface fields greater than 25MV/m have been obtained in superconducting resonators with polished lead surfaces with no detectable loss due to field emission. Using these techniques, we have achieved an accelerating field greater than 4 MV/m in a superconducting structure and have begun long term tests. Preliminary results indicate no surface degradation at high fields (> 3MV/m) for relatively long times (14 hours).