B.V. Seleznev

Nanocrystalline graphite: Promising material for high current field emission cathodes

Electron field emission properties of nanocrystalline graphite (NCG) films, grown by plasma enhanced chemical vapor deposition method on conductive Si substrates without using of any catalyst, were investigated. Current-voltage characteristics were measured in pulse-periodic regime. It was shown that grown NCG films can operate at field emission current density up to 10u2002A/cm2. It was found that NCG films contain, along with the normally oriented to the substrate nanoflakes, carbon whiskers consisted of graphene nanoribbons and nanowires with length considerably higher than of the nanoflakes.Electron field emission properties of nanocrystalline graphite (NCG) films, grown by plasma enhanced chemical vapor deposition method on conductive Si substrates without using of any catalyst, were investigated. Current-voltage characteristics were measured in pulse-periodic regime. It was shown that grown NCG films can operate at field emission current density up to 10u2002A/cm2. It was found that NCG films contain, along with the normally oriented to the substrate nanoflakes, carbon whiskers consisted of graphene nanoribbons and nanowires with length considerably higher than of the nanoflakes.

Low-voltage electron emission from “tipless” field emitter arrays

Electron emission is obtained from “tipless” gated n-silicon arrays (6460 gate holes) by depositing about 10 nm of nanocrystalline graphite (NCG) on top of the gates and into the gate holes by a glow-discharge technique at 900u200a°C. The polycrystalline silicon gate diameter is 1.8 μm and the gate-to-substrate distance is 0.85 μm. The interdielectric layer is SiO2. Turn-on voltages are about 40–60 V. The gate currents are about 50% of the total emission currents. From the emission site density of the NCG films and current fluctuation measurements, it is concluded that several emission sites are generated inside the gate holes at the NCG–Si interface that exhibit gate voltage (Vg) -induced field enhancement. The field at these emission sites is expressed by E=βVg.

High-current electron gun with a field-emission cathode and diamond grid

Control grids used in high-current devices with field emission cathodes should be made of an appropriate, “grid-grade” material. Such a material must offer a high mechanical strength, thermal conductivity, and electric conductivity. In addition, grids as thin as several microns must be available. As a grid material, boron-doped diamond is tested.

The study of electron source with flat diamond field emission cathode

There is a particular interest to possible usage of various field emission cathodes in electron sources. It seems very attractive to apply diamond flat cold cathodes as they show good emission parameters, are reliable, stable and rather insensitive to vacuum. Some measurements of divergence of e-beams emitted from diamond films and diamond-coated FEAs have been published. In this work we studied the divergence of the electron beam emitted from flat diamond cold cathode, passed through the split in the extracting metal anode. The aim was to analyse the influence of split edges on electrons trajectories and to obtain information about initial angular and energy distribution of emitted electrons comparing experimental and calculated results. We used the split of rectangular form as it did not affect on electrons trajectories in direction along the split (axis y), by this means allowing to see initial electrons distribution, and its affects in the perpendicular direction (axis x).

Multi beam X-ray tube with the field emitter on the base of nanocrystalline graphite for computer tomography

A multiple-beam X-ray tube on the basis of field emitters has been designed and developed. The X-ray tube is powered by 140 kV anode supply. Each beam is driven by 1 kV cathode to grid supply. Electron trajectories calculation and experimental measurement of I–V characteristics are presented.

Reduced turn-on voltage of nanocrystalline graphite (NCG) coated silicon field emitter arrays

Ten nanometers of nanocrystalline graphite were deposited on top of fully processed p-silicon tip arrays by a glow discharge method at 900/spl deg/C. Whereas the p-silicon arrays have to be conditioned at 200-250 V prior to reproducible turn-on at about 100-120 V, the NCG coated arrays turn on at 20 V and do not need conditioning. The slopes of Fowler-Nordheim (F-N) plots are smaller by a factor of 5-10 times for the NCG-coated film, suggesting that the field enhancement factor is increased by a factor of 5-10, or the effective work function is decreased. From STM analysis, we find nano-size features at the NCG-Si interface, suggesting the formation of field enhancement sites and not of a reduced work function deposit. Pressure dependency in air and hydrogen, as well as current fluctuations versus current dependencies are similar for the bare and the NCG-coated devices.

Examination of electron field emission efficiency and homogeneity from CVD carbon-type films

This paper reports about investigation of electron emission characteristics of carbon-type films grown by an original CVD method on Si and Mo substrates with the diameter 30 mm. It was shown that films have sufficiently high spatial uniformity of emission sites and emission current density exceeds 900 mA/cm/sup 2/ at the extraction field around 7 V/micron.

Measurements of emitter resistance in Si FEA

Resistance of field emission tips can play an important role in the field emission cathode operation, in particular for stable and uniform emission from field emission arrays (FEA). The development of a non-destructive technique for direct measurements of resistance of the silicon field emission tips is also important for some interdisciplinary problems. However, until now, there are no reliable technique for control and measurements of the resistivity of tiny VLS whiskers. In this paper a technique for determination of the resistance of field emitters is presented.

Phosphor‐efficiency dependence on pulse duration in field‐emission devices

The dependence of the cathodoluminescence (CL) efficiencies of Y 2 O 2 S:Eu, Y 2 O 2 S:Pr, Y 2 O 3 :Eu, and (Cd,Zn)S:Cu,Al on the width of high-current-density excitation pulses was found to be dependent upon the persistence time of the phosphors. This dependence was explained in terms of phosphor saturation.