Radiation-stimulated erosion of field electron emitters

The features of erosion of the surface of point field electron emitters bombarded by helium ions were studied. An analysis of the ion-bombardment-induced atomic-scale surface roughness showed evidence of a nondynamic character of the surface atom displacement for the primary ion energies below a threshold for the stable Frenkel pair formation and cathode sputtering. A quasi-static mechanism of the surface erosion is considered, according to which the process is related to the displacement of metal atoms into low-coordinated positions upon evolution of the energy of formation of interstitial helium atoms.     

One-dimensional germanium nanostructures--formation and their electron field emission properties

Ge nanostructures were synthesized by reduction of GeO(2) in H(2) atmosphere at various temperatures. Entangled and straight Ge nanowires with oxide shells were grown at high temperatures. Ge nanowires with various numbers of nodules were obtained at low temperatures. Ge nanowires without nodules exhibited remarkable field emission properties with a turn-on field of 4.6 V μm(-1) and field enhancement factor of 1242.     

石墨烯纳米片及其场发射性能研究

两维石墨烯纳米材料是目前材料研究的热点之一,其中石墨烯纳米片的一个重要特征是有一条一维尖锐的刀口状边缘,电场增强系数大,是很好的电子场发射材料。本文介绍了石墨烯纳米片结构特点,综述了石墨烯纳米片的制备及电子发射性能,指出了目前研究存在的问题和研究方向。     

Carbon nanotube field emitters for planar emission vacuum micro-and nanoelectronics

The design and manufacturing technology of carbon nanotube field emitters for novel devices of planar emission vacuum micro-and nanoelectronics are described. Prototypes of diode structures with such emitters are obtained in which the threshold field strength amounts to ～2 V/μm and the direct to reverse current ratio exceeds 10⁵. The obtained small scatter of characteristics points to the possibility of creating integrated circuits possessing high operation speed and a working temperature range expanded from ?60 to +30°C.     

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm⁻¹. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.     

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

Abstract

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm^?1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.     

Correlated electron tunneling during the field electron emission

Elementary events of correlated electron tunneling from very small regions of a hollow metal emitter were detected. The most significant microscopic and macroscopic parameters favoring the appearance of multiparticle tunneling effects are considered.     

Simulation study of a field emission triode structure using carbon-nanotube emitters

The device level simulation analysis without considering nanometer geometry of the emissive material is carried out on a self-aligned gated field emission triode structure that can be used for low electric-field emissive materials such as carbon nanotubes. The electric properties of the device, such as electric-field distribution, pixel capacitance, and gate controllability, are simulated using a commercially available field solver based on the boundary-element method. The simulation results show that the depletion-mode operation can eliminate high electric field near the triple-junction regions and produce better uniform emission, comparing enhanced mode operation. The detail of the depletion mode operation is discussed. We also calculate the effect of the gate thickness on pixel emission current and suggest control of the variation of gate layer depostion within 3% in short distance and 20%-30% over the whole display area.     

The preparation of field electron/field-ion emitters by ion etching

A new technique is described for the fabrication and resharpening of field emitters. This technique employs an ion gun and uses methods analogous to those used to produce thin foils for the transmission electron microscope. In this way it has proved possible to produce reliably sharp emitters of both metal and semiconducting materials and the technique is particularly useful when dealing with those materials normally difficult to electropolish or chemically etch. Applications lie not only in field electron emission and field-ion microscopy, but may also be relevant to the development of high current electron sources for use in electron microscopy.     

A compact electron gun using field emitter array

A compact electron gun using field emitter array has been developed. With a simple triode configuration consisting of FEA, mid-electrode and anode electrode, the electron gun produces a parallel beam with a diameter of 0.5 mm. This electron gun is applicable for compact radiation sources such as Cherenkov free-electron lasers.     

Fabrication and field emission property of a Si nanotip array

Using a Si-based porous anodic alumina membrane as a mask, we demonstrate a way to pattern Si surface. After removing the SiO(2) nanoislands formed during anodization of the Al/Si interface, we obtain a Si nanotip array on the surface of a Si wafer. This array shows an excellent field emission property with a low turn-on field of 8.5?V?μm(-1). The Fowler-Nordheim plot obtained is linearly dependent, indicating that the emission current arises from the quantum tunnelling effect. The Si nanotip array can be expected to have important applications in nanoelectronic devices.     

Mechanism of ion loading of point emitters in planar edge field emission structures

A mathematical model of electron-optical processes has been developed and studied. The results of this analysis show that the ion current to a microscopic point emitter can be significantly reduced in planar edge field emission (PEFE) structures. The mechanism of this decrease is related to a special configuration of the electric field in the cathode-gate-anode system, which features a slope of the equipotential lines in the near-cathode region. The advantage of PEFE structures over the traditional systems based on Spindt cathodes is characterized by a decrease in the ion-current-related thermal load by more than five orders of magnitude. This decrease ensures high durability of the PEFE structures, which has been confirmed in experiment.     

Synthesis of large-area single-walled carbon nanotube films on glass substrate and their field electron emission properties

Large-area and homogeneous single-walled carbon nanotube (SWCNT) films have been deposited via arc discharge directly on glass substrate coated with a layer of indium tin oxide film. The characterization, by means of electron microscopy and Raman spectroscopy, shows that the as-grown films are uniformly woven and consist of SWCNT with diameters ranging from 0.82 to 1.15 nm. As a cathode material, the field emission test indicates the films have low turn-on field of ∼1.2 V/μm at 10 μA/cm² emission current, and high emission intensity causing luminance of about 7000 cd/cm² with fine uniformity. The best performing sample exhibits a constant degradation of less than 3% per hour at an emission current of around 1 mA. Measuring with the high voltage (2000 V) on the films for 2.0 h increased the field enhancement factor from 4500 to 5400 at the high field region. The results are of significance to the development of field emission display using nanoemitters.     

Silicon multi-branch nanostructures for decent field emission and excellent electrical transport

We report on the synthesis, field electron emission and electric transport properties of a novel nanomaterial: ordered arrays of crystallized silicon multi-branch nanostructures. A decent field electron emission with relatively low turn-on field of 3.16 V μm?1 and high field-enhancement factor of 1252 was received for the silicon nanobranches. The relevancies between field-emission current-voltage characteristic, turn-on field, threshold field and sample-anode distance have been thoroughly analyzed. In addition, electrical transport measurements revealed a small electrical resistance of 0.51 MΩ for as-prepared silicon nanobranches. In contrast, by improving the silicon nanobranch-electrode contact, vacuum annealing dramatically reduced the electrical resistance, by a factor approaching two, while thermal oxidation resulted in a much higher resistance due to the amorphous oxide coating of the silicon nanobranches, both of the current versus voltage curves became more linear and symmetrical, and the transport stability was obviously improved.     

Magnetic field effect on electron emission from plasma

The influence of external magnetic field on the significant parameters of electrons from laser induced plasma (LIP) is investigated. A Q-switched Nd:YAG laser (1064 nm, 9-14 ns, 10 mJ, 1.1 MW) is focused on annealed, 4N pure (99.99%) Silver target (2 × 2 × 0.2 cm³) for production of plasma under vacuum ∼10⁻³ torr. Temperature, density and energy measurements for electrons were made by self fabricated Langmuir probe both in the absence and presence of external magnetic field (∼1.2 T) at different positions. The signals are recorded on 200 MHz UTT 2202 digital storage oscilloscope. The results thus obtained reveal decrease in electron temperature, energy and density in presence of external magnetic field. Confinement of plasma is also observed.     

Negative ion emission accompanying the field electron emission from amorphous hydrogenated carbon

It was found that the field electron emission from the surface of amorphous hydrogenated carbon is accompanied by the emission of negative ions of hydrogen and hydrocarbons. This ion emission is explained by the formation and degradation of the local surface emission centers.     

Multiparticle processes during field electron emission from structured carbon

The statistics of field electron emission (FEE) from structured carbon materials has been studied. Multiparticle FEE from fullerene-containing carbon has been observed. Analysis of the experimental data revealed correlations with the results of previous investigations of FEE in high-temperature superconductors. Possible models of the mechanism of multielectron processes are discussed.     

Development and applications of an analytical electron microscope with a field emission electron gun

An analytical electron microscope with a field emission electron gun has been developed in order to improve the function of material identification, in order to obtain higher resolution of images, sharper electron diffraction patterns, and purer x-ray spectra with no effects of contamination from smaller areas than in the conventional instruments so far utilized. The performance capabilities of this newly developed analytical electron microscope, the Model H-600FE, have been examined and found to be very useful for the material characterization of nanometer-size areas. Various attributes of the microscope became apparent with reference to the results of different studies. These include better convergence of the electron beam (demonstrated by examination of an MoS₂ thin film), high-resolution transmission electron microscopy (using a gold film), high-resolution scanning electron microscopy (with a carbon film containing nanometer-size holes), high-angle resolution electron diffraction (of an iron carbide film), and precision x-ray analysis of nanometer-size areas (using a pyroxene crystal and a Cu---Zn---Al shape memory alloy).     

Freestanding ultrananocrystalline diamond films with homojunction insulating layer on conducting layer and their high electron field emission properties

Freestanding ultrananocrystalline diamond (UNCD) films with homojunction insulating layer in situ grown on a conducting layer showed superior electron field emission (EFE) properties. The insulating layer of the films contains large dendrite type grains (400-600 nm in size), whereas the conducting layer contains nanosize equi-axed grains (5-20 nm in size) separated by grain boundaries of about 0.5-1 nm in width. The conducting layer possesses n-type (or semimetallic) conductivity of about 5.6 × 10(-3) (Ω cm)(-1), with sheet carrier concentration of about 1.4 × 10(12) cm(-2), which is ascribed to in situ doping of Li-species from LiNbO(3) substrates during growth of the films. The conducting layer intimately contacts the bottom electrodes (Cu-foil) by without forming the Schottky barrier, form homojunction with the insulating layer that facilitates injection of electrons into conduction band of diamond, and readily field emitted at low applied field. The EFE of freestanding UNCD films could be turned on at a low field of E(0) = 10.0 V/μm, attaining EFE current density of 0.2 mA/cm(2) at an applied field of 18.0 V/μm, which is superior to the EFE properties of UNCD films grown on Si substrates with the same chemical vapor deposition (CVD) process. Such an observation reveals the importance in the formation of homojunction on enhancing the EFE properties of materials. The large grain granular structure of the freestanding UNCD films is more robust against harsh environment and shows high potential toward diamond based electronic applications.     

Extraction of emission parameters for large-area field emitters, using a technically complete Fowler-Nordheim-type equation

In papers on cold field electron emission from large-area field emitters (LAFEs), it has become widespread practice to publish a misleading Fowler-Nordheim-type (FN-type) equation. This equation over-predicts the LAFE-average current density by a large highly variable factor thought to usually lie between 10(3) and 10(9). This equation, although often referenced to FN's 1928 paper, is a simplified equation used in undergraduate teaching, does not apply unmodified to LAFEs and does not appear in the 1928 paper. Technological LAFE papers often do not cite any theoretical work more recent than 1928, and often do not comment on the discrepancy between theory and experiment. This usage has occurred widely, in several high-profile American and UK applied-science journals (including Nanotechnology), and in various other places. It does not inhibit practical LAFE development, but can give a misleading impression of potential LAFE performance to non-experts. This paper shows how the misleading equation can be replaced by a conceptually complete FN-type equation that uses three high-level correction factors. One of these, or a combination of two of them, may be useful as an additional measure of LAFE quality; this paper describes a method for estimating factor values using experimental data and discusses when it can be used. Suggestions are made for improved engineering practice in reporting LAFE results. Some of these should help to prevent situations arising whereby an equation appearing in high-profile applied-science journals is used to support statements that an engineering regulatory body might deem to involve professional negligence.