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The relationship between the field emission and the density of states (DOS) of single-walled carbon nanotubes (SWCNTs) synthesized by hydrogen arc-discharge method is investigated. The results have shown that the field emission of SWCNTs can be closely related to the DOS of SWCNTs near the Fermi level.

The study presents a direct observation of the field evaporation process of the carbon nanotube (CNT) and corresponding field emission characteristics during the process. It concluded that the irregular shaped graphite sheets at the tip of the CNT might greatly enhance the field emission characteristics of the CNT when compared with that having an ideal circular edge.

Research into analytical electrostatic modeling of silicon conical field emitters is presented.

The tip surface of silicon field emitters are coated with a molybdenum layer in order to improve the stability and level of electron field emission.

The Monte Carlo method was used to analyze charged spacers in the field emission display.

A cathodic arc process at room temperature produces nanocluster carbon films found to be good electron emitters.

A new study investigates the tunnelling current and ballistic electron effects of the tunneling current in field emission devices.

A new study investigates the bistable current fluctuations from microfabricated cathodes.

A1 addition effects on photoluminescence were examined with regard to defects inSrTIO3:Pr3+.

Research was conducted to examine the field emission properties for P-doped polycrystalline diamond films. It is indicated that the internal electron emission is relevant to the field emission properties of the P-doped diamond films. Results reveal that behaviors of the field emission characteristics, which rely on the P doping concentration, measurement temperature and the cathode metal, are consistently explained by the internal electron emission.

Several types of field-emission electron sources were developed using nano-porous anodic aluminum oxide (AAO) templates. These include aligned copper nanowires grown halfway up the parallel nanopores of the AAO, aligned multiwalled carbon nanotubes grown to the top of the pores, surfaces overgrown with random tangles of carbon nanotubes, and empty AAO templates. It was observed that the field-emission electric field and the field enhancement for these field emitters are affected by growth conditions and surface treatment.

The velocity spectrum of drops emitted by a liquid-metal explosive-emission cathode has been investigated. A relation between the sizes of the drops and their maximum velocities has been found for the velocity range [10.sup.3] - 8 x [10.sup.4] cm/s. The relation obtained supports the earlier established mechanism for the emission of drops under the action of high pressures developing in explosive emission centers. The possibilities of an additional acceleration of drops due to the explosion of necks formed on breaking the drops off the cathode surface and at the expense of the kinetic energy of the ions of the expanding cathode plasma have been discussed. Index Terms - Drop fraction, explosive electron emission, liquid-metal cathode erosion.

Experiments have been made to identify the key parameters in the increase of the breakdown strength of a vacuum gap through repetitive breakdowns. The current-voltage waveforms were observed, the residual stress in electrodes was measured, and the chemical composition of the electrode surfaces and the energy of the valance-band electrons were analyzed. These experiments revealed that prebreakdown currents (field emission currents) were sometimes observed and sometimes not. The residual stress before and after 500 breakdowns changed significantly. X-ray photoelectron spectroscopy analysis before and after 500 breakdowns showed that the spectral lines of oxygen and carbon due to contaminants on the electrode surface were completely removed and the copper ones appeared clearly after 500 breakdowns. The valence-band electron energy spectrum of the anode after 500 breakdowns shifted towards the lower binding energy to almost coincide with the theoretical spectrum, while the energy spectrum for the cathode shifted towards sometimes higher and sometimes lower binding energy.

In this work the result of emission phenomena investigations are presented. Experiments were conducted for high-Tc superconducting ceramics YBaCuO and BiPbSrCaCuO. Fowler-Nordheim characteristics and the current-temperature dependencies were observed for superconducting and non-superconducting cathodes. It was noticed that the emission current value abruptly changed in the vicinity of the critical temperature. All measurements were done in a vacuum chamber at [10.sup.-6] Pa. X-ray diffraction analysis and scanning electron microscopy examination of the ceramic electrodes were performed also.

We present the very first experiment allowing in situ observation of surface evolution during very high electric field application. This has been achieved by soft ([Lambda] = 21.2 nm) X-ray laser Fresnel two-mirror interferometry. The surface under study was a niobium planar cathode opposite to a stainless steel blade-like anode. The applied field range on the cathode was F [approximately equal to] O to 50 MV/m. The interferograms were single shots of 80 ps duration, allowing to probe the surface morphology quasi-instantaneously. The delay between two shots was 20 min while the electric field was kept on. The comparison of successive interferograms gives the Nb surface evolution over [approximately]2 h. Thus, we observed the appearance of defects of [approximately] 3 nm high and their evolution with time. These may be the precursors of the minute breakdown which occurred later on. This technique thus makes it possible to detect the preliminary stages of a discharge.

Si field emission devices were fabricated using a novel self-aligned process. The effects of plasma passivation on the emission current of gated Si emitter tips were examined by exposing the emitters to an H2 plasma for two minutes before testing. For an array of 100 tips with 250-nm gate-tip spacing, the emission current at a gate voltage of 100 V increased from 284 to 460 mu A and the turn-on voltage reduced from 31 to 21 V after H2 plasma passivation. The improvements in the emission characteristics corresponded to 1.28 eV reduction in the work function of emitters.

A study was reported on the fabrication and testing of a poly-diamond microchip containing gated field-emitter display cells using vapor-deposited p-type polycrystalline diamond films and employing an integrated circuit-compatible diamond film technology on oxidized 4-in Si wafers. Current voltage data showed Fowler-Nordheim field emission behavior. A 1x4 pixel diamond gated display cell was demonstrated for the first time using phosphor-coated glass as an anode.

Field emission is known to play a dominant role in the electrical breakdown of gaps in vacuum. Electrons are emitted from micro-projections on clean cathode surfaces where the field strength is enhanced and the tunnel effect is observed. The location of emission sites was observed in this study by using a microchannel plate with a luminescent screen. The effects of the heat treatment on the behavior of emission sites is also discussed. A number of emission sites were observed on the cathode surface which disappeared after electron emission. Furthermore, heat treatment of electrodes decreased the number of emission sites and the number of electrons emitted from a projection. Field emission, in the region

A novel photosensitive floating field emitter has been built from an a-Si:H p-i-n photodiode film and an n-type Si field emitter tip. The fabrication of the emitter device using a-Si:H and p-type a-SiC:H film and n-type cone-shaped Si emitter array is described. Evidence from equivalent circuit analysis shows that the device has a greater current than unit effective quantum efficiency.

A study was conducted on the origin of field emission from wide band-gap semiconductors by voltage dependent field-emission energy distribution and I-V measurements. The results indicate direct evidence of relevant, field-induced band bending in both diamond and c-BN coatings. The emission from diamond and c-BN originated from the conduction-band minimum based on the extrapolation of the linear behavior to the flat-band condition.

Cesium treatment lowers the threshold field for field emission and increases the emission site density from a nominally n-type diamondlike carbon film which is deposited using an rf plasma of methane and nitrogen gases. The treatment involved the deposition of cesium followed by a low temperature anneal. Dramatic improvements to field emission by cesiation cannot be generalized to all diamondlike samples as similar treatment of a type llb single-crystal diamond did not produce as pronounced an improvement in turn-on field or emission site density.

Research shows that K-Te photocathodes deposited on a Mo substrate can act as an electron source in the free electron laser. A 4.75% quantum efficient K-Te-cathode displays 1.1% quantum efficiency at 259 nanometers after 20 hours operation. Exponential curve evidence suggests that the quantum efficiency can probably last at around 1% for some time. Heat treatment can be used to improve film quantum efficiency.

A one-cell RF-gun with a dispensers cathode was fabricated for high-brightness applications at the Pohang Accelerator Laboratory. The gun was designed to withstand heavy beam loading and breakdown for long-pulse operation. After some RF-conditioning, the gun could be powered up to a nominal RF-power of 3.5 MW during 6 [[micro]second]. The gun produced an electron beam with an average current of 300 mA and energy up to 1 MeV, normally, operated with a 6-[[micro]second] macropulse and 12-Hz repetition rate. The beam loading and the energy spectra were measured to confirm the gun's performance. The beam emittance was measured and compared with simulation results. The breakdown problem due to the field-emitted electrons and the backward electrons in the gun is discussed. Index Terms - Breakdown, field emission, gas desorption, thermionic RF-gun.

A simple field emitter model was employed in analyzing the charge between the gate and the anode and the charge within the field emitter array unit cell to determine the one-dimensional space charge effects on emission characteristics. The results were compared to experimental findings. It was observed that the field emission at the tip of the emitter and the electron reflection by a virtual cathode causes the negative convexity seen in the Fowler-Nordheim plot data.

Measurement of surface potential shifts involving secondary and Auger electron spectra for low voltage display phosphors showed strongly negative charges higher than 2 keV. Coincident electron beam measurements indicated aging-enhanced surface charging to reduce phosphor cathodoluminescence. These results indicated substantial space charge for phosphors, even for low energy levels.

A study was conducted on the electric field effect of SrTiO3/YBa2Cu3O7-x bi-layer grown by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE). The electric properties of the transistors are influenced by interface properties and oxygen content. Excellent interface was permitted with the use of MBE while oxygenation was provided through PLD. The superconducting field effect transistor exhibited a transconductance of 5mS/cm.

The results of experimental and theoretical investigations of high-current-density field emission from nanometer objects on the tungsten cathode surface are presented. Such objects were microprotuberances, and spots of Zr or ZrO, produced by a thermal-field buildup process (microtips) and selective adsorption (spots). The limiting values of stable emission current densities from local areas of the cathode surface were determined. The process of the cathode heating was numerically simulated in terms of a heat transfer equation approach for three-dimensional axial-symmetric model. The dependencies of the equation's coefficients upon temperature and mutual influence of the temperature and current distributions were taken into account. The main feature of the calculated temperature distribution consists in forming the overheated region in the inner emitter's volume. It was established that the limiting current densities of stable emission for nanometer objects can be almost an order of magnitude higher than for the traditional field emitter, in accordance with the experimental results.

The initiation and sustaining of field emission processes from a liquid surface are based mainly on the effect of field amplification at the surface microtips. Such microtips form under different types of hydrodynamic instabilities. However, the threshold field of such instabilities has a very high value. At the same time, there are some situations when one needs to excite the emission using an arbitrary low amplitude of the external voltage. In this paper, in order to solve this problem, the process of preliminary excitation of the surface by an ultrasonic field on the liquid emitter surface has been studied. The theory developed has shown that, as a result of parametric instability, the formation of surface microstructures is possible. Such structures can be produced at very low levels of ultrasonic power. This fact is of particular importance for large surface area cathodes. The dependence of the geometric parameters of the surface structures both on frequency and power of the ultrasonic field is determined theoretically. Experiments with field pulses in the nanosecond range confirm the decrease of the explosive emission mechanism when preliminary ultrasonic excitation is used.

Finite difference and finite element methods help model the performance characteristics of micro-fabricated gate field emitters used in flat-panel display operations. Results from the modeling include electron beam widths, electrode current-voltage features, electrical stress and image quality and indicate that incorporation of an integrated aperture electrode for electron focussing enhances the cathode-gate drive voltage by 30%. The electron beam widths vary between tens of microns and facilitate full-color resolution with more than 100 lines per inch.

When an increasing diode voltage is applied, enhanced field emission of electrons begins from a growing number of small spots or whiskers on the cathode surface. This stimulates desorption of weakly bound adsorbates from the surface of a whisker. The cross section for ionization of the neutrals has a maximum for approximately equal to 100 eV electrons. As the diode voltage increases, the 100 V equiptotential surface which moves towards the cathode is met by the desorbed neutrals moving away from the cathode. This results in the sharp risetime for the onset of ionization of desorbed neutrals by field emitted electrons. Positive ions produced in the ionization region, a few micrometer from the electron emitting spot are accelerated back to the electron emitting spot. This bombardment with approximately equal to 100 eV ions leads to surface heating of the spot. Since the ion energy is deposited only within a few atomic layers at a time instead of an entire whisker volume, and since the neutral contaminants are only loosely bound to the surface, the onset of breakdown by this mechanism requires much less current than the Joule heating mechanism. The localized buildup of plasma above the electron emitting spot then naturally leads to pressure and electric field distributions which ignite unipolar arcs. The high current density of the unipolar arc and the associated surface heating by ions provide the 'explosive' formation of a cathode spot plasma.

The experimental measurement of the brightness of nanometer-sized field-emission-electron sources using ultra sharp tungsten (III) single-crystal tips, fabricated on the spot by Neon sputtering and field evaporation and monitored by field ion microscopy, shows an improvement of around two orders of magnitude in source brightness over existing cold field-emission electron sources. The average brightness of single-atom-brightness terminated monotips was found to be 3.3 x 10 8 Acm-2 sr-2 at 470V or 7.7 x 10 10 Acm-2 sr-1 when extended to 100kV. The beam is also produced with greater particle flux per unit energy than those obtainable using current synchrotron/wiggler/undulator devices.

Computer simulation is employed to examine the radio frequency operation of a vacuum microtriode amplifier in terms of the transconductance, cutoff frequency, small-signal gain and efficiency. The simulations, which were conducted on a unit cell comprising of an emitter tip, gate and an anode, demonstrates the effects of geometrical parameters on the device properties. A problem related to anode power deposition remains a topic requiring further research.

The electron optical characteristics of nanometer sized field-emission cathodes were investigated to determine if they can be used as electron sources for scanning electron microscopy and electron holography. The results showed that the spherical and chromatic defects of nanotips were dominated by their base structures. In addition, the beams produced by nanotips exhibited totally coherent characterisics.

The secondary emission characteristics of beryllia (BeO) on beryllium (Be)substrates are investigated. Thin layers of BeO were grown on high-density sintered Be substrates through a series of ion borbardment and deposition processes. The structures' surface voltage is then measured using the scanning electron microscope micrograph and energy dispersive X-ray system analysis. Results show that the surface voltage is dependent on the nature of the cutoff voltage energy as determined by the arriving electrons.

A theoretical analysis of field emission arrays (FEA) is presented. The study, which considered cone-shape and wedge-shape emitter-array diodes, centered on the geometrical design parameters and their influence on potential distribution, electric field and emission current. The FEA's application to a microelectronic pressure sensor and a subsequent characterization of the device are then discussed.

Field-emission displays contain electron emitting materials, and such devices currently use arrays of microfabricated tips as the emitting cathodes. However a thin-film cathode is potentially cheaper and simpler alternative. It requires materials that can emit sufficient electron current at low applied fields. Some conducting polymers have low electron affinity, wide bandgap and good transport properties, and are demonstrated to provide good cathode materials.

A resonant tunneling emitter that is quantum mechanically coupled to a vacuum gap may be used in vacuum electronics and sensor systems. Such devices exhibit enhanced current levels as compared to a Fowler-Nordheim field emitter. The vacuum gap thickness and applied voltage also promotes an almost monoenergetic distribution of electron emissions creating ideal tunneling current oscillations.

Several studies are conducted to explain the field emission mechanisms of the bismuth sulfide upright-standing platelets, which are chemically prepared by using the indium-tin-oxide substrate. These platelets are shown to exhibit high values of the turn-on field and current density and hence can be used easily in the manufacture of electronic devices.

The article explains the initial conditioning procedure and achieved properties of several different inorganic nanowires. The variations in the deuterium pressure are shown to highly affect the field emission current of the nanowires.

Photoresponse of gated p-silicon field emitter array (FEAs) was investigated. At low gate leakage currents, the transition between the tunneling-limited field emission regime and the supply-limited saturation regime is seen in current-voltage plots while surface states were fully depleted at low applied fields, the concentration of bulk defects was low and the area contributing to the dark current was confined to the emitter regions.

An attempt is made to investigate the properties of the plasma and the electron beam produced by velvet cathodes in a diode powered by a ~200kV, ~300 ns pulse. It is shown that the interaction of the electron beam with the stainless-steel anode does not lead to the formation of anode plasma.

The morphology, structural, composition, photoluminescence and field emission characteristics of ZnO nanowires that were synthesized by the process of vapor-liquid-solid (VLS) process, with Cu and Au as the catalysts in Ar atmosphere, on p-type Si(100) substrate was studied. The vertical direction growth of Cu catalyzed nanowires led to higher field emission area factor in case of Cu catalyzed ZnO nanowires and a larger field adjustment factor when compared with the values of Au catalyzed nanowires.

The amorphous carbon films with improved field emission were prepared in plasma enhanced chemical vapor disposition system by repeating the thin a-C:H film disposition and subsequent hydrogen plasma treatment. The field emission was improved which attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp(super 2) clusters.

The velocity skin-effect is one of the main factors which set the limits to the launch velocity and lifetime of the barrel in railguns with a metal armature. The subject of this paper is a numerical investigation of the effects of the use of materials with properties not traditional for railguns. The use of materials having anisotropic electrical conductivity results in an increase of the velocity at which an armature begins to evaporate. The paper involves a brief analysis of materials with such properties. Also considered is alternative possibility of controlling the contact performance with the help of the phenomenon of field emission as a mechanism for current transport in the narrow clearance between a rail and an armature. Preliminary numerical results show that the field emission electrode can improve the contact. Index Terms--Railgun, velocity skin effect.

Operation of explosive-emission cold cathodes made from various materials was studied at a large number of pulses at current densities of ~[10.sup.4] A/[cm.sup.2]. The cathode voltage and the beam current were ~500 kV and 5 kA, respectively, with a pulsewidth of ~20 ns. At a small number of pulses ([is less than or equal to] [10.sup.3]), cathodes of like geometry (even made from different materials) demonstrated similar emission properties. For most of the materials tested, with a large number of pulses ([is greater than or equal to] [10.sup.3]), the current risetime increased to the fullwidth of the voltage pulse and the, maximum current of the vacuum diode decreased. When using a graphite cathode, the maximum current remained invariant until [10.sup.8] pulses. Mass losses were measured for a series of cathode materials. The results obtained offered the possibility to realize long-lived operation of an X-band relativistic backward-wave oscillator with an almost invariant output power of 350-400 MW during [10.sup.8] pulses at a pulse repetition rate of 100-150 p.p.s. Index Terms--Cold cathode, current risetime, explosive electron emission, long-lifetime operation, material loss, relativistic BWO, repetitively pulsed electron accelerator.

Carbon nanotubes have reportedly been fabricated into electron emitters for field emission full-color displays by Samsung Advanced Institute of Technology, Suwon, South Korea. Field emission displays are made of thousands […]