Improved Emission Uniformity Research Articles

Enhanced field emission properties from titanium-coated carbon nanotubes

The effect of titanium (Ti) coating over the surface of carbon nanotubes (CNTs) on field emission characteristics was investigated. Vertically aligned CNTs were grown by inductively-coupled plasma-enhanced chemical vapor deposition (ICP-CVD). In order to reduce the screening effect of electric field due to densely packed CNTs, as-grown CNTs were partly etched back by DC plasma of N 2. Ti with various thicknesses from 5 nm to 150 nm was coated on CNTs by a sputtering method. Since thick Ti coating with thickness of 100 nm or more resulted in the shape of a metal post by merging an individual CNT in a bundle, it was inadequate to a field emission application. On the other hand, thin Ti-coated CNTs with thickness of 10 nm or less showed a lower turn-on field, a higher emission current density, and improved emission uniformity compared with pristine CNTs. The improved emission performance was mainly attributed to the low work function of Ti and the reliable and lower resistance contact between CNTs and substrates.

Improved emission uniformity and stability of printed carbon nanotubes in electrolyte

In this paper, we studied the effect of NaCl electrolyte as a surface treatment on improving the uniformity and stability of field emission of screen-printed carbon nanotubes (CNTs). A short period of the electrolyte treatment of CNT films remarkably increase emission uniformity and stability. Furthermore, the field emission characteristics of screen-printed carbon nanotubes (CNTs) such as low turn-on field, high emission current density and strong adhesion of the CNT film on the substrate were also reinforced after post-treated. SEM, TEM and Raman spectrum study revealed that uniformity and stability of field emission is enhanced by two factors. Firstly, the electrolyte treatment appeared to render the CNT surfaces more actively by exposing more CNTs form the CNT paste, which dominates initial uniformity and stability of field emission. Secondly, the number of opened CNTs and defects CNTs of CNT film were increased by electrical current energy.

WITHDRAWN: Improved emission uniformity and stability of printed carbon nanotubes in electrolyte

WITHDRAWN: Improved emission uniformity and stability of printed carbon nanotubes in electrolyte

Improved field emission properties of double-walled carbon nanotubes decorated with Ru nanoparticles

The field emission properties of double-walled carbon nanotubes (DWCNTs) were remarkably improved by decorating their surface with ruthenium (Ru) metal nanoparticles. The Ru nanoparticles were attached effectively on the surface of DWCNTs via a chemical procedure. The Ru-decorated DWCNTs showed lower turn-on voltage, higher emission current density, and improved emission uniformity compared with pristine DWCNTs. The effect of Ru nanoparticles on the work function and density of states was evaluated by the first-principles calculation. The enhanced field emission properties of Ru-DWCNTs were mainly attributed to the Ru nanoparticles which increased the field enhancement factor and the density of emission sites. Our results indicate that the Ru-decorated DWCNTs can be used as an effective field emitter for various field emission devices.

Improved current densities of carbon nanotube cathodes by pulsed operation

We have extended our integral measurement system with luminescent screen for pulsed field emission operation of planar cold cathodes. Since in dc operation typical power loads of some watts∕cm2 cause discharges by “phosphor” evaporation, the pulsed operation of cold cathodes up to some cm2 size makes higher peak current densities achievable. Comparative results for dc and pulsed operations of metal-organic chemical-vapor deposition grown carbon nanotube samples on porous alumina are presented which demonstrate peak current densities up to 60mA∕cm2. Moreover an improved emission uniformity results from peak power processing and afterglow effects.

Oxidation improvement of field electron emission from diamond nanomaterials

AbstractPorous diamond/sp2‐bonded carbon nanocomposites were studied to determine how their field electron emission properties and electrical conductivity depend on composition and post‐growth treatment. It was found that a treatment enriching the nanocomposites with oxygen could significantly improve the field emission from the diamond samples. The oxidized composites exhibited lower emission threshold fields (Eth = 1–2 V µm−1 compared with Eth = 4–6 V µm−1 for non‐oxidized samples) and improved emission uniformity (the number of emission sites per unit area). The composites with low sp2‐bonded carbon content, i.e. the more porous samples, typically show better results. The structure of the samples was studied using a C KVV Auger spectrometer, with x‐ray excitation of Auger emission. Possible reasons for the emission improvement by oxidation in this two‐phase carbon system are discussed. Copyright © 2004 John Wiley & Sons, Ltd.

Uniformity and stability of field emission from bare and metal coated Si tip arrays

Field emitter arrays of tips of some micrometers in height have been fabricated from p- and n-doped Si substrates by photolithographic techniques and partially coated with 7.5 nm thick W, Pt, or Cr layers by magnetron sputtering. The emission uniformity of these tip arrays was investigated with a field emission scanning microscope. The local current stability was measured with a spectrum analyzer. The bare Si tips show low average extraction fields (∼35 V/μm for 10 nA) but moderate uniformity and pronounced current noise and switches. In comparison, the metal-coated Si tips yield improved emission uniformity with up to 100% of emitting tips and sufficient stability up to 700 nA (1 μA) in the case of Pt (W) coating, but also a factor of 2 higher extraction fields. Noise power spectra of W and Pt coated samples showed a typical 1/fγ dependence up to the kHz range with a spectral density index γ of about 3.

Emission uniformity enhancement between microfabricated tips in cold cathode arrays

The current–voltage characteristics can vary significantly between individual microfabricated tips in as-fabricated arrays of cold cathodes. Such emission nonuniformity is undesirable in device applications. We have shown that in situ tip self-heating by the emitted electron current can be used to make the current–voltage characteristics of microfabricated field emitter tips nearly identical to one another. The improved emission uniformity will allow for more reliable array operation at increased electron emission current densities.

Graded electron affinity electron source

We describe a new electron source using electric field and low electron affinity semiconductor materials to bring charge to potential energy levels near the vacuum level while still in the solid. The basic idea involves moving some of the potential barrier from the surface to the bulk, and distributing the barrier over a thin layer below the surface. In so doing, the emission physics is changed fundamentally from a quantum mechanical tunneling process largely controlled by surface properties to a classical transport process largely controlled by the band structure of a wide bandgap semiconductor. The composition of the thin layer below the surface would be graded such that the conduction band minimum changes from an energy close to the substrate Fermi level to an energy significantly closer to the vacuum level. Electrons from the substrate would be drawn into the graded composition layer with an electric field produced by a pointed emitter structure and extraction gate similar to that used in field emitter arrays. Relative to a conventional field emitter array, the new source is expected to require lower extraction fields and exhibit improved emission uniformity, stability, and noise. The I–V characteristics are not Fowler–Nordheim and may include a saturation effect at high current densities that could be engineered to improve reliability and uniformity. The group III nitrides can be grown with a continuous range of composition that provides the range of electron affinity needed to produce the proposed electronic structure.