Carbon Nanotube Electron Emitters Research Articles

RETRACTED: Effects of gases on multi-wall carbon nanotube field emitter for a low energy ion source

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). This article has been retracted at the request of the corresponding author due to similarities identified with a previously published paper, 'Performance of a Low Energy Ion Source with Carbon Nanotube Electron Emitters under the Influence of Various Operating Gases', in Nanomaterials (Nanomaterials 2020, 10(2), 354; https://doi.org/10.3390/nano10020354 ). The author wishes to apologise for any confusion or inconvenience caused.

Performance of a Low Energy Ion Source with Carbon Nanotube Electron Emitters under the Influence of Various Operating Gases.

Low energy ion measurements in the vicinity of a comet have provided us with important information about the planet’s evolution. The calibration of instruments for thermal ions in the laboratory plays a crucial role when analysing data from in-situ measurements in space. A new low energy ion source based on carbon nanotube electron emitters was developed for calibrating the ion-mode of mass spectrometers or other ion detectors. The electron field emission (FE) properties of carbon nanotubes (CNTs) for H2, He, Ar, O2, and CO2 gases were tested in the experiments. H2, He, Ar, and CO2 adsorbates could change the FE temporarily at pressures from10−6 Pa to10−4 Pa. The FE of CNT remains stable in Ar and increases in H2, but degrades in He, O2, and CO2. All gas adsorbates lead to temporary degradation after working for prolonged periods. The ion current of the ion source is measured by using a Faraday cup and the sensitivity is derived from this measurement. The ion currents for the different gases were around 10 pA (corresponding to 200 ions/cm3 s) and an energy of ~28 eV could be observed.

363 nm UVA light generation with carbon nanotube electron emitters

Mercury-vapor lamps with a wavelength of 365.4 nm are mainly used in photolithography processes as i-line. However, mercury-free ultraviolet (UV) light sources have been actively investigated for mercury environmental and human health hazards, and electron beam (E-beam) pumped UV light sources are one of alternative technologies. E-beam pumped light sources have advantages such as eco-friendlyness, simple fabrication process, and large area. We called electron beam irradiated pumping technology based on carbon nanotube (CNT) emitters as C-beam pumping and used it as an excitation source. The C-beam pumping technique excites electrons in the SrB4O7:Eu anode by high energy electron irradiation and generates UVA light through the relaxation process. The SrB4O7:Eu phosphor was stirred with a binder, followed by spin-coating on a quartz substrate, UV illumination, annealing, and Pt electrode fabrication. Anode was optimized through PL intensity analysis. The optimized annealing process condition is an annealing time of 30 min at 900 °C around the atmosphere, which results in the disappearance of carbon-based binder materials on the quartz substrate, thereby improving the UV properties. The optimized SrB4O7:Eu anode has UVA light with a peak wavelength at 363 nm by applying a bias of 12 kV and a current of 0.5 mA at the anode using the C-beam irradiation pumping technique.

Carbon nanotube generated electron beam produced plasmas

A device using an energetic electron beam from a carbon nanotube electron emitter has been developed to generate plasmas at pressures near or below atmospheric. The low-pressure electron source region (10−6 mbar) and the higher pressure (up to 1 atmosphere) plasma generation region are separated by a 300 nm SiNx window/membrane. The energy of the electron beam is of the order of 10 kV with a current of 10 μA prior to passing through the window, with nearly 85% of the beam passing through the window to the plasma generation region with a 10% loss in energy. The device could be operated in one of two modes, closed or opened. Closed mode operation has been used to generate excimer emissions from XeI* and XeCl* at 253 nm and 308 nm, respectively, at pressures below atmospheric. Ambient air has been used in the open mode operation with and without a flow of argon or helium across the SiNx window. Optical emission spectroscopy revealed that the open mode operation yielded a variation of excited state species that was found to be dependent on the electron beam energy and the neutral gas flow in the reaction region.

An Intraoral Miniature X-ray Tube Based on Carbon Nanotubes for Dental Radiography

Abstract A miniature X-ray tube based on a carbon-nanotube electron emitter has been employed for the application to a dental radiography. The miniature X-ray tube has an outer diameter of 7 mm and a length of 47 mm. The miniature X-ray tube is operated in a negative high-voltage mode in which the X-ray target is electrically grounded. In addition, X-rays are generated only to the teeth directions using a collimator while X-rays generated to other directions are shielded. Hence, the X-ray tube can be safely inserted into a human mouth. Using the intra-oral X-ray tube, a dental radiography is demonstrated where the positions of an X-ray source and a sensor are reversed compared with a conventional dental radiography system. X-ray images of five neighboring teeth are obtained and, furthermore, both left and right molar images are achieved by a single X-ray shot of the miniature X-ray tube.

Carbon Nanotube Electron Emitter for X-ray Imaging

The carbon nanotube field emitter array was grown on silicon substrate through a resist-assisted patterning (RAP) process. The shape of the carbon nanotube array is elliptical with 2.0 × 0.5 mm2 for an isotropic focal spot size at anode target. The field emission properties with triode electrodes show a gate turn-on field of 3 V/µm at an anode emission current of 0.1 mA. The author demonstrated the X-ray source with triode electrode structure utilizing the carbon nanotube emitter, and the transmitted X-ray image was of high resolution.

Atomic detail observation of adsorbed molecules and metal clusters on carbon nanotube electron emitters

Molecular images and dynamics of adsorbates on carbon nanotube (CNT) electron emitters revealed so far by field emission microscopy (FEM) are reviewed after a brief account of the field emission phenomena and the merit of CNTs as the field emitter. The species adsorbed on CNTs are inorganic and organic common gaseous molecules (H2, N2, O2, CO, CO2, CH4) and aluminum (Al) clusters. In the case of N2 and CO2 molecules, dumbbell-shaped images, reflecting their molecular shapes, have been observed. For the case of Al deposition on CNTs, FEM images revealing atomic detail of an Al cluster with the cubo-octahedron structure were observed. Discussion on the spatial resolution in FEM for CNTs suggests the probable observation of some atomic structures with a resolution of the order of 0.3nm.

小型走査電子顕微鏡用カーボンナノチューブ電子銃の安定性評価

Carbon nanotube (CNT) has unique field emission (FE) properties. CNT can emit electrons in lower vacuum condition than other field emitters. Therefore we have investigated its emission properties and developed a small size scanning electron microscope (SEM) equipped with CNT electron emitter that can operate at low extraction voltages at a pressure of 10-3 Pa. In order to ensure enough stability for SEM operation, we measured the FE current in various partial pressure condition and numerically analyzed power spectral density function of field emission current by a computer. As a result, we have found it very effective to heat an emitter and metal parts around an emitter. Finally, we added heating system in a CNT-FE-SEM and succeeded in taking a stable image.

Stable multiwalled carbon nanotube electron emitter operating in low vacuum

AbstractWe have investigated field emission (FE) properties of an individual multiwalled carbon nanotube (CNT) under low‐vacuum regions around 10−3 Pa. Current versus voltage characteristics of the present CNT emitters were found to be explicable on the basis of the Fowler–Nordheim (F–N) formalism. Time trace of the FE current exhibited more than 30% fluctuation about the mean value, and the lifetime was less than 5 h. Scanning electron microscopy (SEM) observation elucidated that the lengths of the CNTs were reduced after prolonged field emission, plausibly because of local heating induced by the large current density at the apex. To prolong the lifetime, we attempted a type of feedback system by inserting a high ohmic resistance between the electron emitter and the power supply. As a result, the current fluctuation decreased from ∼30% to 2% at 0.1 µA, and the lifetime increased from 5 to 50 h. Finally, an SEM was equipped with both the emitter systems, with and without resistance, which were designed for the CNT field emitter. The SEM images taken by using the emitter with resistance showed consistently brighter appearance, whereas those taken without the resistance exhibited fluctuations in the image brightness. Copyright © 2006 John Wiley & Sons, Ltd.

宇宙デブリ対策のための超小型衛星用導電性テザーシステム

This paper explains a design of an electrodynamic tether system for a pico-satellite, which Laboratory for Space Systems at Tokyo Institute of Technology plans to develop and to demonstrate. The system is aimed at mitigating the problem of orbital debris by enabling small satellites to deorbit by themselves. By conducting simulation study, use of air drag for satellite disposal is found to be ineffective for tiny satellites while use of an electrodynamic tether is likely to applicable. Simulation shows the current necessary to reenter a satellite within 25years is about 1mA, which the carbon-nanotube electron emitter being developed by the authors can emit with gate voltage of 600V. Reduction of gate voltage will be one of future works. A brief description of part of the satellite system relevant to the demonstration of electrodynamic tether is given.

Characterization of the field emission properties of individual thin carbon nanotubes

Electron emission measurements were conducted on individual carbon nanotubes. The nanotubes had a closed end and their surfaces were thoroughly cleaned. It is shown conclusively that individual carbon nanotube electron emitters indeed exhibit Fowler–Nordheim behavior and have a work function of 5.1±0.1eV for the nanotubes under investigation, which had diameters of 1.4 and 4.9nm.

Carbon nanotube electron sources and applications.

In this review we give an overview of the present status of research on carbon nanotube (CNT) field emitters and their applications. Several different construction principles of field-emission devices with CNTs are summarized. The emission mechanism is introduced and a detailed overview is given of the measured emission properties and related topics of CNT electron sources. We give also several examples of field-emission devices with CNT electron emitters that are presently being investigated in the academic world as well as in industry. Carbon nanotube electron sources clearly have interesting properties, such as low voltage operation, good stability, long lifetime and high brightness. The most promising applications are the field-emission display and high-resolution electron-beam instruments. But several hurdles remain, such as the manufacture of an electron source or an array of electron sources with exactly the desired properties in a reproducible manner.

Brightness of carbon nanotube electron sources

The virtual source sizes of individual multiwalled carbon nanotube electron emitters were investigated with a point projection microscope. The average radius of the virtual source size was found to be 2.6 nm, which does not correspond to the standard model of a field emitter. Instead, a model based on a flattened cap or an open cap seems to provide a more realistic description. The broadening effect of Coulomb interactions on the virtual source was calculated. The reduced angular current density was measured at the maximum current at which stable emission was obtained and arrived at an average of 30 nA sr−1 V−1. The reduced brightness values obtained for two emitters were (2.5±1)×109 and (1.3±0.5)×109 A m−2 sr−1 V−1, respectively. These values are an order of magnitude larger than the values of state-of-the-art commercial sources.

Carbon nanotube electron emitters with a gated structure using backside exposure processes

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.

Single-Wall Carbon Nanotube Electron Emitters Produced by Electrophoresis

AbstractSingle-wall carbon nanotubes have been synthesized, purified, attested with a high resolution electron microscopy and Raman scattering and deposited by liquid electrophoresis onto different substrates (including a metallized glass) to produce the effective and homogeneous film cathodes for low-field electron emitters. The emission properties (a threshold of the emission switching on, a current value, a time-stability) of the SWNT cathodes have been investigated. A prototype of a phosphorescent lamp with a nanotube cathode has been designed. The Raman spectra of the SWNT cathode registered in situ from the shining lamp have shown no temperature increase and time-degradation of the nanotube material during the emission process.