Carbon Nanotube Field Emission Research Articles

High-Performance Field Electron Emitters Fabricated Using a Free-Standing Carbon Nanotube Film

The carbon nanotube (CNT) field emitter was fabricated using a thin free-standing CNT film, indicating a line-shape CNT field emitter. Field emission properties of the CNT field emitter were investigated in both diode and triode configurations. The CNT field emitter showed a low turn-on electric field of 1.8 V/μm and a high emission current of 40.3 mA, corresponding to the emission current density of 96 A/cm in the diode configuration. It also exhibited a high anode current of 40 mA, corresponding to the anode current density of 95.2 A/cm in the triode configuration. In addition, the CNT field emitter showed a good electron beam transmittance of 86.4% and excellent emission stability without degradation for 15 h. The main reason for the high performance of our CNT field emitter is caused by the high density of emission sites at the edge of the CNT film.

Design of a Ka-Band Traveling Wave Tube Using Low Turn-On Field Emission Electron Source Made by Carbon Nanotubes

This article designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band traveling wave tube (TWT) with the single wall carbon nanotubes (SWCNTs) field emission cathode electron gun. The designed cold-cathode TWT was miniaturized and could instantly startup at room temperature because of the field emission cathode. First, SWCNT cathode was made by imprinting. The field emission measurement results showed that its turn-on field was as low as 0.57 MV/m, and the maximum emission current was about 10 mA. Then, a grid-controlled electron gun with planar field emission cathode was simulated based on the experiment results, which had low operation voltage of the electron gun and would prevent their grid mesh from burning. The optimized electron beam waist radius of the electron gun was 0.15 mm with the structure of the focusing magnetic field. According to experiment and simulation results, we preliminarily designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band helix TWT with an average output power of 8.6 W and a gain of 24.6 dB at 28 GHz. The designed miniaturized TWT with a low-operation-voltage field emission cathode electron gun is expected to be used in low-power applications including 5G communication.

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.

A Miniaturized Single-Wall Carbon Nanotubes Field Emission Cathode With RF Excited by Coaxial Resonant Cavity

A miniaturized radio frequency (RF) excited grid-free field emission cathode made by single-wall carbon nanotubes (SWCNTs) is suggested and studied. The λ/4 coaxial resonant cavity is used as field-emitted electron source with length of 26.5 mm and diameter of 12.8 mm. Electrons can be pulled out by a small electrostatic field and an RF electric field without interception. The RF electric field of inner conductor surface at the open end, which pasted SWCNTs, can reach 3 MV/m when the input power is 30 W, and the field is larger than the turn-on field of SWCNTs. The results of simulation and experiment both show that the maximum emission current under input RF power of 30 W is 30 times larger than without RF excitation, which can reach 24 mA at the anode voltage of 950 V. This miniaturized RF excited grid-free field emission cathode electron source can be used as electron source, in a high repetition frequency vacuum electronic devices, e.g., terahertz (THz) devices, and X-ray tubes.

Investigations on the Carbon Nanotube Paste Made by the Optimized Ball-Milling Method and Its Applications for the e-Beam Source

The carbon nanotube (CNT) has the outstanding mechanical/chemical properties, which makes it a promising electron source for various applications such as the field emission display (FED), the microcolumn, and the X-ray tube. In this work, we have developed the CNT paste by applying the noble ball-milling method to the paste mixer. The newly developed CNT paste was used to fabricate the CNT field emitter whose electric characteristics were evaluated by observing the I–V curve and long-term stability of the emitter. The new CNT paste showed much better electrical characteristics than those of the conventional CNT paste. We also used the CNT tip as a source of the electron beam (e-beam) of the microcolumn and found that the operating range of the e-beam was enhanced by 100% compared to that of the conventional microcolumn where the tungsten tip was used as the e-beam source. By replacing the tungsten tip with the CNT tip, we could not only obtain more flexibility in design of the microcolumn but also remove the alignment problem between the emitter tip and the source lens.

Optimized Aluminum Reflector for Enhancement of UVC Cathodoluminescence Based-AlGaN Materials with Carbon Nanotube Field Emitters.

The far ultraviolet C (UVC) light sources based on carbon nanotube (CNT) field emitters as excitation sources have become promising light sources for sterilization, disinfection, and water purification. However, the low light extraction efficiency of UVC–CNT light sources still hinders the practical application of these structures. Herein, we report an optimized aluminum (Al) reflector to enhance the light extraction efficiency of UVC–CNT light sources. Optical analysis of UVC-CNT light sources covered by the Al reflectors with various thicknesses ranging from 30 to 150 nm was performed to realize the optimized reflector. The UVC-CNT light sources exhibit the highest light extraction efficiency when the Al reflector layer has an optimized thickness of 100 nm. For comparison, the cathodoluminescence (CL) spectra were recorded for UVC–CNT light sources with and without the optimized Al reflector. The measured light output power and the estimated power efficiency of the UVC–CNT light-source-tube with Al reflector were enhanced by about 27 times over the reference. This enhancement is mainly attributed to the outstanding reflection effect of the Al reflector.

A feasibility study of a portable intraoperative specimen imaging X‐ray system based on carbon nanotube field emitters

AbstractsWhen breast cancer is surgically removed, a rim of normal tissue surrounding the tumor is also removed. This rim of normal tissue is called a margin and is studied by a pathologist to determine whether or not all tumor was removed. The pathologist achieves this by cutting the surgically removed tissue into thin slices and observing each slice under a microscope. This process is time‐consuming. Here, we investigate the feasibility of using a portable carbon nanotube (CNT)‐based X‐ray system for in situ detection of the presence of tumor cells in the surgical margin. Using the proposed technique, we successfully obtain X‐ray images, which clearly show cancer masses and microcalcifications. This feasibility study shows that portable CNT‐based X‐ray systems are promising candidates for next‐generation in situ pathological examinations.

Enhanced interfacial reaction of silicon carbide fillers onto the metal substrate in carbon nanotube paste for reliable field electron emitters

Adhesion of carbon nanotube (CNT) onto a cathode substrate is very crucial for field electron emitters that are operating under high electric fields. As a supporting precursor of CNT field emitters, we adopted silicon carbide (SiC) nano-particle fillers with Ni particles and then enhanced interfacial reactions onto Kovar-alloy substrates through the optimized wet pulverization process of SiC aggregates for reliable field electron emitters. As-purchased SiC aggregates were efficiently pulverized from 20 to less than 1 micro-meter in a median value (D50). CNT pastes for field emitters were distinctively formulated by a mixing process of the pulverized SiC aggregates and pre-dispersed CNTs. X-ray photoelectron spectroscopy studies showed that the optimally pulverized SiC-CNT paste-emitter had a stronger Si 2p3/2 signal in the Ni2Si phase than the as-purchased one. The Si 2p3/2 signal would represent interfacial reaction of the SiC nano-particle onto Ni from the CNT paste and the Kovar substrate, forming the supporting layer for CNT emitters. The optimal paste-emitter even in a vacuum-sealed tube exhibited a highly reliable field emission current with a high current density of 100 mA cm−2 for over 50 h along with good reproducibility. The enhanced interfacial reaction of SiC filler onto the metal substrates could lead to highly reliable field electron emitters for vacuum electronic devices.

Development of an electron gun based on CNT-cathode for traveling wave tube application

In this work, an electron gun with carbon nanotube (CNT) field emission cathode is demonstrated for traveling wave tube (TWT) application with laminar flow beam features. A maximum emission current of 9.76 mA at a bias of −11 kV is achieved by such electron gun, with current density up to 1.24 A cm−2. The output current of the electron gun can reach 8.08 mA, with the grid interception rate less than 22%. Furthermore, a Quasi-TWT with a beam tunnel of 1.6 mm is realized, which has a maximum collector current of 7.52 mA with the corresponding transmittance of 93.07%. The simulation of the beam-wave interaction implies further that our CNT field electron gun is able to meet the demands of TWT applications.

Surface modification via silver nanoparticles attachment: An ex-situ approach for enhancing the electron field emission properties of CNT field emitters

A novel one-dimensional carbon material Known as carbon nanotubes (CNTs), having their high aspects ratio and as well as advance electrical properties which make them best candidate for cathode field emitters. In this work, we have introduced the easy and cost-effective approach to improving the CNT field emitters emission properties. Here we have modified the surface of CNT field emitter via decorating with silver nanoparticles (Ag NPs). Attachment of Ag NPs on CNT surface via thermal evaporation technique. The as-prepared samples of pristine CNTs and decorated CNTs with Ag NPs were characterized by the scanning electron microscope for morphology analysis, quality and qualitative analysis done by Raman spectroscopy. Here we have applied the Fowler Nordheim hypothesis for the analysis of electron field emission of as-prepared cathode field emitters. The turn-on (Eto) and threshold (Eth) field reduced after CNT field emitters coated with Ag NPs. The field enhancement factor (β) and emission current density (J) enhanced after coating. Ag NPs decorated/coated CNT field emitters can be utilized in field emission device applications.

Position and Attitude Tolerances of Carbon Nanotube Field Emission Cathode as a Neutralizer in an Ion Engine System

Position and Attitude Tolerances of Carbon Nanotube Field Emission Cathode as a Neutralizer in an Ion Engine System

In-Situ Grown ZnS Nanoparticles on Amorphous Carbon Nanotubes Improved Cold Cathode Emission and Photoluminescence.

The current work reveals notable increase in field emission and photoluminescence characteristics of amorphous carbon nanotubes after forming its composite with In-Situ grown zinc sulfide (ZnS) nanoparticles. An easy chemical technique was employed to synthesize amorphous carbon nanotubes (ACNTs) and then ZnS nanoparticles were grown on them through an In-Situ solvothermal process. The morphology of the ZnS-ACNTs hybrid material was investigated through scanning electron microscope. Photoluminescence and field emission studies of the material were carried out as well in order to realize the applications. Substantial increase in photoluminescence intensity was found for ZnS-ACNTs hybrid material in comparison with pure amorphous carbon nanotubes, the hybrid also turned out as a better field-emitter than pure amorphous carbon nanotubes. Turnon field for ZnS-ACNTs composite decreased to 6 Vμm-1 which was 8 Vμm-1 in case of pure amorphous carbon nanotubes. A simulation analysis following finite element modelling method was carried out which ensured the improvement as field emitter for amorphous carbon nanotubes after ZnS nanoparticles were grown on them. Altogether the hybrid material proved to be a potential candidate for luminescent and cold cathode applications.

Scanning electron imaging with vertically aligned carbon nanotube (CNT) based cold cathode electron beam (C-beam)

A novel cold cathode electron beam based on carbon nanotube (CNT) as an electron source has been developed. The direct grown emitters fabricated as electron source have a huge potential for an electron microscope. An electron sources for high-resolution imaging requires some important parameters such as probe size, emission current, convergence angle, and beam brightness. These parameters influence the performance of an electron microscope, which in turn is heavily is dependent on the electron emission source.In the present work, direct growth CNT, a method of fabrication of emitter as an electron source for high-resolution imaging was studied. This CNT field emitters which has a spherical emitter tip as grown on Si substrate has superior hardness. A direct grown CNT emitter can draw a few micro-amperes of current. The single-CNT emitter shows 9.26 × 1010 A sr−1 m−2 V−1 of reduced brightness at 1.1 μA of emission current and a 10 μm of beam spot diameter on phosphor screen in a diode configuration. These results can be confirmed by SOURCE 2D simulation and also, the electron beam trajectory could be predicted. Finally, we fabricated an optimized electron beam module with CNT cold cathode and measured secondary electron imaging of copper grid mesh with the beam.

STATIONARY INTRAORAL DIGITAL TOMOSYNTHESIS USING CARBON NANOTUBES FIELD EMISSION X-RAY TECHNOLOGY: CLINICAL PROTOTYPE

<h3>Background</h3> Tuned aperture computed tomography (TACT) and intraoral tomosynthesis were studied in the past and demonstrated improved detection of various dental diseases. However, interest in TACT waned because the technology was not viable for clinical use. Recently, interest resurged with the advent of the carbon nanotube field emission x-ray source array technology. Researchers from the University of North Carolina (UNC) Department of Physics and Astronomy and the UNC School of Dentistry designed, patented, and conducted several benchtop studies to demonstrate its utility.¹ <h3>Objective</h3> The aim of this study was to develop a viable stationary intraoral tomosynthesis imaging device for clinical use. <h3>Materials and Methods</h3> XinVivo, an imaging device startup company, developed a prototype system designed for intraoral imaging applications.² <h3>Results</h3> The prototype met all the requirements for clinical use and met the U.S. Food and Drug Administration (FDA) requirements for intraoral imaging devices. <h3>Discussion</h3> The clinical prototype met all manufacturer specifications. Preliminary studies indicated that stationary intraoral tomosynthesis (s-IOT) provides increased image quality and feature conspicuity at a dose comparable with that in a single 2-dimensional (2-D) intraoral radiography.³

Review on development of carbon nanotube field emission cathode for space propulsion systems

In recent years, small-size, low-weight aerospace propulsion systems have developed rapidly for space exploration, on-orbit scientific instruments and extra space missions, while additional electron emission devices are commonly required in those propulsion systems. Carbon nanotube (CNT) based field emission cathodes exhibit extraordinary field emission properties and are regarded to be an ideal alternative of conventional thermionic or hollow cathodes. In this study, the authors give an overview of present status of researches on CNT-based electron emission cathodes for utilising as neutralisers or electron sources particularly in space electric propulsion systems, the theory and characteristics of CNT are also illustrated. Furthermore, challenges, problems and possible solutions before actual applications of CNT in a space mission are discussed accordingly.

Spatial dependence of the temperature profile along a carbon nanotube during thermal-field emission

An efficient algorithm is described to calculate the spatial dependence of the temperature distribution along a carbon nanotube (CNT) during field emission (FE). The algorithm considers the effects of Joule heating in the CNT and radiative losses from the CNT sidewall and tip. The CNT emission current density and the rate of heat exchange per unit area at the CNT tip due to either Henderson-cooling or Nottingham-heating effects are calculated using recent analytical expressions derived by Jensen [J. Appl. Phys. 126, 065302 (2019)]. The latter are valid in the thermionic and field emission regimes and in the transition region between these two extremes. The temperature dependence of the electrical resistivity ρ(T) and the thermal conductivity κ(T) of the CNT is also included in the model. It is shown that replacing ρ(T) and κ(T) by their spatial averages over the length of the CNT can lead to an overestimate of the value of the external electric field threshold at which thermal runaway of the CNT occurs. These results should be considered when calculating the field emission characteristics of CNT arrays such as from a carbon nanotube fiber whose FE properties are primarily determined by the FE properties of the array of CNTs at the tip of the fiber. Using the new algorithm, the simulation times to calculate the CNT FE characteristics and the spatial temperature distribution are found to be nearly two orders of magnitude faster compared to those required when both the current and energy exchange at the CNT tip are calculated numerically.

Physical characterization of a novel wireless DRX Plus 3543C using both a carbon nano tube (CNT) mobile x-ray system and a traditional x-ray system

This work aims to characterize the novel DRX Plus 3543C detector in terms of detective quantum efficiency (DQE) using both a mobile x-ray system called Carestream DRX Revolution Nano and a traditional x-ray system (Carestream DRX Evolution). We used the commercial system DRX Revolution Nano, equipped with a new x-ray source based on CNT technology and field emission (FE) as the electron emitter (cathode). An innovative aspect of this device is its intrinsic selection of the focal spot size. We tested the system using three IEC-specified beam qualities (RQA3, 5 and 7) in terms of modulation transfer function (MTF), normalized noise power spectra (NNPS) and DQE as defined in the IEC 62220-1-1:2015. We compared the results obtained using DRX Revolution Nano and DRX Evolution with correlation and with Bland–Altman plots to study their agreement. RQA3 MTF is slightly lower than the RQA5 and 7 curves between 0.5 and 2.5 cycles mm−1. We measured MTF values of about 0.6 at 1 lp mm−1 and about 0.28 lp mm−1 at 2 lp mm−1. The NNPS curves show a decreasing trend with the energy regarding the DRX Revolution Nano. On the other hand, the DRX Evolution NNPS curve at RQA3 is greater than the one at RQA5, but the one at RQA5 is less than the one at RQA7. The DQE(0) ranged between about 0.82 (DRX Evolution at RQA3) and 0.54 (DRX Evolution at RQA7). As expected, the squared Pearson’s correlation coefficients between the two x-ray tubes were always in an optimal agreement, and Bland–Altman plots confirmed a substantial equivalence between the two physical characterizations of the wireless detector. In conclusion, we can show that the dynamic focal selection of the system equipped with CNT does not play a substantial role in image quality compared to a traditional system in terms of physical characterisation of the detector in our measurement conditions.

Research on the neutralization control of the RF ion micropropulsion system for the ‘Taiji-1’ satellite mission

To achieve the neutralization control requirements of the radio-frequency (RF) ion microthruster (μRIT) in the ‘Taiji-1’ satellite mission, we proposed an active neutralization control solution that is based on the carbon nanotube field emission technology. The carbon nanotube field emission neutralizer (CNTN) has the characteristics of light weight, small size, and propellantless, which is especially suitable for the neutralization control tasks of ion microthrusters. The Institute of Mechanics, Chinese Academy of Sciences, in collaboration with Tsinghua University, has successfully developed a CNTN to meet mission requirements. On the ground, the feasibility of cooperation working between μRIT and CNTN was fully verified, as well as the simulation and experimental study of neutralization control strategy, which finally passed the engineering assessment test. Since the launch of ‘Taiji-1’ satellite on 31 August, 2019, the RF ion micropropulsion system has successfully completed nearly one hundred test missions in space. The test results indicate that CNTN does not have performance degradation, and the neutralization control strategy is effective.

Field Emission Cathodes to Form an Electron Beam Prepared from Carbon Nanotube Suspensions.

In the first decade of our century, carbon nanotubes (CNTs) became a wonderful emitting material for field-emission (FE) of electrons. The carbon nanotube field-emission (CNT-FE) cathodes showed the possibility of low threshold voltage, therefore low power operation, together with a long lifetime, high brightness, and coherent beams of electrons. Thanks to this, CNT-FE cathodes have come ahead of increasing demand for novel self-sustaining and miniaturized devices performing as X-ray tubes, X-ray spectrometers, and electron microscopes, which possess low weight and might work without the need of the specialized equipped room, e.g., in a harsh environment and inaccessible-so-far areas. In this review, the author discusses the current state of CNT-FE cathode research using CNT suspensions. Included in this review are the basics of cathode operation, an evaluation, and fabrication techniques. The cathodes are compared based on performance and correlated issues. The author includes the advancement in field-emission enhancement by postprocess treatments, incorporation of fillers, and the use of film coatings with lower work functions than that of CNTs. Each approach is discussed in the context of the CNT-FE cathode operating factors. Finally, we discuss the issues and perspectives of the CNT-FE cathode research and development.

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.