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

Abstract

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.

Bunch Shaping in Electron Linear Accelerators

“…The solution is to use large surface area FE cathodes engineered to hold many microscopic emitters immersed in the applied "macroscopic" electric field on the cathode, E c . Three such engineered FE cathodes have been developed and used in FE electron guns: field emission arrays (FEAs) (Jarvis et al, 2010), carbon nanotubes (CNTs) (Laszczyk, 2020), and ultra-nanocrystalline diamonds (UNCDs) (Baryshev et al, 2014). These surfaces are composed of a quasi-continuous distribution of electron emitters of macroscopic area ∼1 mm 2 and achieve macroscopic current densities of J F E ∼1 A/mm 2 , sufficient for electron linacs.…”

Proof‐of‐concept for a thin conical X‐ray target optimized for intensity and directionality for use in a carbon nanotube‐based compact X‐ray tube

“…The study of field emission in the context of X‐ray generation has been a catalyst for major innovation in the design of X‐ray tubes. By supplanting the Joule heating of traditional thermionic emission, field emission devices boast several notable advantages, including room‐temperature operation, near‐instantaneous electron emission, low power consumption, greater beam coherence, and tighter energy distributions 1–5 . Specific to X‐ray tubes that use pulsed radiation, cold cathodes provide fine, instantaneous control over the tube current via the applied electric field strength, allowing for high frequency duty cycles and precise intensity modulation 1,4,5 .…”

“…Specific to X‐ray tubes that use pulsed radiation, cold cathodes provide fine, instantaneous control over the tube current via the applied electric field strength, allowing for high frequency duty cycles and precise intensity modulation 1,4,5 . The advent of the carbon nanotube (CNT)‐based field emitting cathode with its superior mechanical, thermal, chemical, and electrical properties has provided great advancements in electronic current stability, current density, mechanical stability, cathode lifetime, and spatial uniformity, as well as reduced fabrication complexity, required vacuum level, and threshold emission voltage 1–4,6–8 …”

Extreme Ultraviolet Lighting Using Carbon Nanotube-Based Cold Cathode Electron Beam

“…Field emission (FE) emits electrons through quantum mechanical tunneling in a high electric field at room temperature and in high or ultra-high vacuum [ 5 ]. FE is known for its advantages such as fast switch-on time, compact size, high emission current density and resistance to temperature fluctuations [ 5 , 6 , 7 ]. The electrons emitted by the FE can be used in a variety of vacuum electronic devices, such as scanning electron microscopy (SEM) for high-resolution imaging [ 8 ], microwave amplifiers [ 9 ], compact X-ray sources with fast switching [ 10 ], flat panel displays [ 11 ], and UV light sources [ 12 , 13 ].…”

“…One of the main candidates for FE sources is carbon nanotube (CNT) emitters. They have excellent electrical, mechanical, chemical, and structural properties [ 6 , 7 ]. Because of its extraordinary properties, CNTs have many applications [ 8 , 9 , 10 , 11 , 12 , 14 , 15 , 16 ].…”