Nanotube Cold Cathode Research Articles

Characteristics of Carbon Nanotube Cold Cathode Triode Electron Gun Driven by MOSFET Working at Subthreshold Region.

The carbon nanotube cold cathode has important applications in the X-ray source, microwave tube, neutralizer, etc. In this study, the characteristics of carbon nanotube (CNT) electron gun in series with metal-oxide-semiconductor field-effect transistor (MOSFET) were studied. CNTs were prepared on a stainless steel substrate by chemical vapor deposition and assembled with a mesh gate to form an electron gun. The anode current of the electron gun can be accurately regulated by precisely controlling the MOSFET gate voltage in the subthreshold region from 1 to 40 µA. The current stability measurements show the cathode current fluctuation was 0.87% under 10 h continuous operation, and the corresponding anode current fluctuation was 2.3%. The result has demonstrated that the MOSFET can be applied for the precise control of the CNT electron gun and greatly improve current stability.

Boosting field electron emission of carbon nanotubes through small-hole-patterning design of the substrate

High field emission of carbon nanotube (CNT) cold cathodes is realized by printing modified CNT paste on small-hole-patterned substrates. The field emission characteristics and stability of samples under DC continuous and pulse driving modes have been investigated. The results show that the maximum emission current of CNT emitters can be up to 45 mA at an electric field of 2100 V (7.0 V μm−1), corresponding to a high current density of 643 mA cm−2 under continuous mode. The cathodes also demonstrate stable electron emission without obvious attenuation. In pulse (10 μs and 200 Hz) mode, the peak current can reach 250 mA and the corresponding current density is 3.57 A cm−2 under an electric field of 14.0 V μm−1. The hole-patterned CNT cathode presents unique advantages in field emission current, stability and especially endurance of high electric field. This work makes it possible to fabricate highly efficient emission CNT cold electron sources, which have broad application prospects in vacuum electronic devices requiring both large current and high current density.

X-ray ultrashort pulse emission characteristic of carbon nanotube cold cathode X-ray source by pulse driving mode

In the present work, we build a triode structure of carbon nanotube (CNT) cold cathode X-ray source driven by pulse voltage in dynamic vacuum system. The results show that the grid voltage and pulse width affect the amplitude, delay time and relative pulse spread of X-ray. The X-ray emission delay time decreases sharply from 102 to 75 ns when the grid voltage increases from 600 to 650 V. The relative pulse spread tends to be saturated with approximately 350 ns (±20 ns) when the voltage increases from 600 to 650 V. The theoretical limit frequency of this X-ray pulsed emission system is approximately 2.86 MHz (1/350 ns). This work reveals the ultrashort pulse emission characteristics and affecting factors of CNT cold cathode X-ray source, promoting the development of CNT cold cathode X-ray source in pulse application.

Development of a K-band traveling wave tube based on carbon nanotube cold cathode

In this work, a K-band traveling wave tube (TWT) based on carbon nanotube (CNT) cold-cathode is developed, which achieves a large output power as well as a high power gain. Compared to traditional thermionic cathode TWT, the CNT-based cold-cathode TWT shows significant advantages in fast response speed, miniaturization, integration, and high efficiency. The CNT-cathode of the TWT can emit a current of 9.26 mA, and a high current of 7.80 mA is delivered to the TWT's electron beam tunnel. The maximum current of the collector is 5.90 mA, indicating that the current density of the electron beam in the helix circuit tunnel reaches 750 mA/cm2 and higher, and the maximum transmittance rate in the experiment can reach 92%. The demonstrated CNT-based TWT can output a maximum power of 10.90 W with a power gain of 15.60 dB, and the maximum power gain achieved is 18.97 dB. The above experiment results imply that the CNT-cathode has great potential for application in TWT devices.

Achieving High Current Stability of Gated Carbon Nanotube Cold Cathode Electron Source Using IGBT Modulation for X-ray Source Application.

The cold cathode X-ray source has potential application in the field of radiotherapy, which requires a stable dose. In this study, a gated carbon nanotube cold cathode electron gun with high current stability was developed by using Insulated Gate Bipolar Transistor (IGBT) modulation, and its application in X-ray source was explored. Carbon nanotube (CNTs) films were prepared directly on stainless steel substrate by chemical vapor deposition and assembled with control gate and focus electrodes to form an electron gun. A maximum cathode current of 200 μA and approximately 53% transmission rate was achieved. An IGBT was used to modulate and stabilize the cathode current. High stable cathode current with fluctuation less than 0.5% has been obtained for 50 min continuous operation. The electron gun was used in a transmission target X-ray source and a stable X-ray dose rate was obtained. Our study demonstrates the feasibility of achieving high current stability from a gated carbon nanotube cold cathode electron source using IGBT modulation for X-ray source application.

A Carbon-Nanotube Cold-Cathode Reflex Klystron Oscillator: Fabrication @ X-Band and Returning Electron Beam Realization

This paper presents the design and fabrication of a reflex klystron oscillator based on a carbon nanotube (CNT) cold-cathode. An X-band klystron oscillator structure is assembled with a CNT cold-cathode electron gun with an electrostatic focusing, a re-entrant cavity as anode, and a repeller. The electron gun adopts a convex CNT film emitter as the cathode. A re-entrant cavity resonating at 8.376 GHz is fabricated. The study mainly focuses on the returning electron beam in the klystron oscillator structure. The experimental results of variations of the anode current and returning electron beam amplitude with repeller voltage are presented. It is demonstrated that a higher extracting voltage of the cold-cathode has an important influence on the returning electron beam. To decelerate electron velocity from the extracting voltage, increasing negative focusing voltage and focusing electrode height in the electron gun can improve the returning electron beam characteristics.

Development of a High-Beam-Transparency Gridded Electron Gun Based on a Carbon Nanotube Cold Cathode

We here report on the development of an improved dual-gridded electron gun based on a carbon nanotube cold cathode that enhances electron beam transparency and reduces grid interception and loss pathways. Compared with microscale tip Spindts, the dual-gridded construction decreases challenges associated with nanomaterial growth, fabrication, and assembly. Our experimental findings show that this dual-gridded CNT electron gun can support anode output currents (cathode emission current) of up to 700 mA, with a beam-transparency of up to ~100% and a compression ratio of 1/19. A beam spot of uniform brightness is obtained and the radius of the beam spot is 1.5 mm. In addition, our studies show that the device can operate at 1/100 duty cycle continuous pulse with a stable current of around 100mA over 100 h.

Enhanced Field Emission of Single-Wall Carbon Nanotube Cathode Prepared by Screen Printing with a Silver Paste Buffer Layer.

A high emission current with relatively low operating voltage is critical for field emission cathodes in vacuum electronic devices (VEDs). This paper studied the field emission performance of single-wall carbon nanotube (SWCNT) cold cathodes prepared by screen printing with a silver paste buffer layer. The buffer layer can both enforce the adhesion between the SWCNTs and substrate, and decrease their contact resistance, so as to increase emission current. Compared with paste mixing CNTs and screen printed cathodes, the buffer layer can avoid excessive wrapping of CNTs in the silver slurry and increase effective emission area to reduce the operating voltage. The experimental results show that the turn-on field of the screen-printed SWCNT cathodes is 0.9 V/μm, which is lower than that of electrophoretic SWCNT cathodes at 2.0 V/μm. Meanwhile, the maximum emission current of the screen-printed SWCNT cathodes reaches 5.55 mA at DC mode and reaches 10.4 mA at pulse mode, which is an order magnitude higher than that of electrophoretic SWCNTs emitters. This study also shows the application insight of small or medium-power VEDs.

Far UVC light for E. coli disinfection generated by carbon nanotube cold cathode and sapphire anode

Ultraviolet germicidal irradiation (UVGI) is an effective technique that can sterilize bacteria and viruses by UV light. Far UVC lamps of short wavelengths can prevent infectious diseases because they sterilize while minimizing cell damage in mammals. Here, E. coli inactivation by far UVC light with peak wavelength of 230 nm made of carbon nanotube (CNT) emitters and sapphire anode was studied. The κ-Al2O3 phase of sapphire with a direct band gap of 5.4 eV was excited with CNT-based cold cathode electron beam (C-beam) to generate far UVC light. It was confirmed that the inactivation of E. coli by far UVC light based on the C-beam was reduced by 5 log reduction within 60 s.

A Carbon Nanotube-Based Hundred Watt-Level Ka-Band Backward Wave Oscillator

Carbon nanotube (CNT) cold-cathodes hold much promise in a variety of millimeter-wave and terahertz vacuum electronic radiation devices due to their inherent near instantaneous temporal turn-on and near-ideal ideal field electron emission performance. Here we report on the development of a CNT cold-cathode Ka -band backward-wave oscillator (BWO). Using a novel beam compression stage, theoretical studies, simulation results, and empirical findings collectively demonstrate that this device affords an unprecedentedly high output power of 230 W at a technologically important operating frequency of 33.65 GHz. The developed magnetic injection electron gun achieves a high emission current of 265.5 mA (emission current density of 188.3 mA/cm2) and a high focused beam current density of 18.5 A/cm2, which our studies suggest, is essential to the BWOs high output power.

High brightness vertically aligned carbon nanotube (CNT) cold cathode for electron microscope

High brightness vertically aligned carbon nanotube (CNT) cold cathode for electron microscope

A High-Current-Density Terahertz Electron-Optical System Based on Carbon Nanotube Cold Cathode

A high-current-density terahertz electronoptical system based on a carbon nanotube (CNT) cold cathode has been investigated in order to solve notable mode competition in high-order harmonic gyrotrons. Simulation results show that a near-axis electron beam can be generated, with a beam current of 160 mA at an accelerating voltage of 23.5 kV. The source supports the electron beam with a velocity ratio of 1.1 and a guiding center radius of 57 μm. A narrow beam spatial distribution is evidenced by adjusting control anode voltage, satisfying the need for high operating current density in slow wave devices. The current density of the electron beam is up to 620 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the output port and the velocity ratio is 0.44, with parallel energy accounting for 84% of the total energy.

A Low-Voltage, Premodulation Terahertz Oscillator Based on a Carbon Nanotube Cold Cathode

To develop miniaturized and compact vacuum electron devices, new approaches to device manufacturing must be embraced. Here, a terahertz oscillator based on carbon nanotube (CNT) cold cathode is investigated through particle-in-cell (PIC) simulations. The studies show that the high-frequency (HF) field excited by the device can modulate the field emission current efficiently, with an output power of 4.6 W at 139.4 GHz obtained at an operating voltage of 2.9 kV and an initial emission current and current density of 15.8 mA and 7.65 A/cm2, respectively, and the efficiency is 10.0%.

Design and Simulation of a Multi-Sheet Beam Terahertz Radiation Source Based on Carbon-Nanotube Cold Cathode.

Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%.

High Brightness Electron Beam with Carbon Nanotube (CNT) Cold Cathode

High Brightness Electron Beam with Carbon Nanotube (CNT) Cold Cathode

High Brightness Electron Beam with Carbon Nanotube (CNT) Cold Cathode

High Brightness Electron Beam with Carbon Nanotube (CNT) Cold Cathode

SOURCE 2D Simulation for High Resolution Carbon Nanotube Cold Cathode Fabrication

SOURCE 2D Simulation for High Resolution Carbon Nanotube Cold Cathode Fabrication

SOURCE 2D Simulation for High Resolution Carbon Nanotube Cold Cathode Fabrication

SOURCE 2D Simulation for High Resolution Carbon Nanotube Cold Cathode Fabrication

Electron emission and structure stability of carbon nanotube cold cathode driven by millisecond pulsed voltage

The carbon nanotube (CNT) cold cathode can provide a high current and current density for microwave devices, which normally work under pulse mode. In this work, we studied the electron emission characteristics and strucutre stability of a CNT cold cathode in millisecond pulse mode. Peak current and average current are both key parameters for the performance of cold cathode. Increasing the duty ratio proved an effective way to increase the average current and average power of the cold cathode. The pulsing field emission characteristics of CNT cold cathode was optimized by modulating the pulse width, pulse interval time, and duty ratio. The average current in millisecond pulse mode was three orders of magnitude greater than that when using microsecond pulses. The average current also linearly increased with the duty ratio. The morphology of CNT films after pulsing and DC field emission was investigated to reveal the stability and the vacuum breakdown mechanism. The thermal equilibrium of the CNT was analyzed to reveal its underlying mechanism. This work provides a practical strategy for the application of CNT cold cathodes in high-power microwave devices.

A Cold-Cathode Microwave and Terahertz Radiation Source: Experimental Realization @10’s GHz and Computational Design @THz

Due to their unique characteristics of instant responses and low-power consumption, vacuum electronic devices based on field emission cold-cathode have potentials for realizing compact and novel high frequency electromagnetic wave radiation sources. Herein, a cold-cathode radiation source operating in the frequency range from gigahertz to terahertz is developed, which is based on frequency multiplication by taking advantage of nonlinearity of field electron emission. The radiation source is realized by introducing a compact structure with two re-entrant cavity resonators. Based on such a structure, radiation sources of frequencies at 12.10 GHz and 0.1 THz were, respectively, designed and simulated numerically. Based on the simulation results, the 12.10-GHz radiation source using carbon nanotubes cold-cathode was fabricated and tested experimentally. The results showed that an electromagnetic wave output at 12.10 GHz with power of $98~\mu \text{W}$ can be achieved upon excitation by a 6.05 GHz input signal with power of 1.05 mW. Our study provides an approach for microwave and terahertz wave generation.