Structure and emission properties of structures based on carbon walls and aluminum nitride

To create field emission cathodes (autocathodes) used in the manufacture of displays and other devices, carbon nanowalls (CNW) are promising. The CNW layers are a porous material consisting of curved plates formed by graphene layers. The industrial use of CNW autocathodes is impeded by the heterogeneity and instability of the magnitude and density of the cathode current. To improve the characteristics of autocathodes, an AlN film is formed on the surface of the emitting substance, which also has the property of field emission. CNW was obtained from a gas mixture of H2 and CH4 activated by a dc glow discharge. The CNW layers were deposited on silicon substrates and substrates representing a layered structure made by forming an opal matrix (OM) layer on a Si substrate. AlN films with controlled composition and structure were prepared by RF magnetron reactive sputtering. CNW layers with a thickness of > 4 μm were obtained by successive growth of two CNW layers (Si/CNW/CNW structure). An additional CNW layer was also grown on the surface of the first layer coated with Ni (Si/CNW/Ni/CNW structure). AlN films were grown on a CNW layer (Si/CNW/AlN and Si/OM/Ni/CNW/AlN structures). It is shown that CNW plates are formed from graphene layers partially connected by atomic bonds (up to 30 layers) packed in a hexagonal lattice, and AlN films consisted of amorphous and axially textured crystalline phases. The current-voltage characteristics of the autocathodes were measured in a pulsed mode at a pressure of ~10−3 Pa. The Si/CNW/CNW structures are characterized by a threshold of autoemission of ≤ 3.6 V/μm and a high density of centers of emission. The current-voltage characteristics of the layered structures Si/CNW/AlN, Si/OM/Ni/CNW and Si/OM/Ni/CNW /AlN showed better emission properties compared to the Si/CNW structure. The current-voltage characteristics considered make it possible to predict the structure and composition of the emitting layer to improve the operational characteristics of multilayer autocathodes.

MULTI-POINTED FIELD-EMISSION CATHODE AS A GENERATOR OF HIGHFREQUENCY OSCILLATIONS

Semiconductor field-emission cathodes have gained considerable popularity in modern radio electronics and electronic optics due to the high-power generation of the electron beam in the external electric field at temperatures close to the room ones. However, their wide application is restricted by the high dependence of the electron emission current on the value of the applied field and geometrical parameters of the cathode. This study aimed to examine the effect of resonance processes on amplifying the field emission of the multi-pointed semiconductor cathode. Modeling the behavior of resonant tunneling of electrons from semiconductors to vacuum was simulated by solving the one-dimensional Schrodinger’s equation, and the amplification due to resonant processes was estimated. The modeling results showed that as the electric field increases, the resonance conditions shift towards low energy levels. With the increase in the width of the barrier for the electron inside the solid body, the resonance conditions shift towards higher energies. It has been established that in onedimensional semiconductors with electrons of low conductivity width, the resonant energy coincides with the Fermi level. These cathode properties are optimal for amplifying the emission current and reducing failures of vacuum electronic devices based on semiconductive field cathodes. The proposed technique can be used to study the regularities of emission amplification due to resonant processes in multipoint semiconductor cathodes with multilayered structure and with metal tips.

Study of field electron emission properties of commercial graphite cathodes in pulse-repetitive mode

The article considers field emission cathodes from industrial graphites MG, MPG-7, and GMZ operated in the pulse-periodic mode with the pulse repetitionrate of 1 to 30 Hz. The operation of field emitters in the pulsed mode differs from operation at a constant voltage. Under stabilization of the high potential level, the amplitude of the pulses of the emission current decreases that leads to increasing the operating voltage in the pulsed mode. During operation of the graphite cathode (when the pulse current is recorded), the operating voltage at the anode stabilizes and oscillates within 5%. Operation in the direct current mode under similar conditions is accompanied by a change in the voltage value by more than 10 %.

Similarities and Differences between Two Researches in Field Electron Emission: A Way to Develop a More Powerful Electron Source

This paper discusses the similarities and differences between two studies that deal with resin-coated field-emission cathodes. The two works that are compared within this paper are entitled: Hot Electron Emission from Composite-Insulator Micropoint Cathodes and Methods of Preparation and Characterization of Experimental Field- Emission Cathodes. Within the text, both studies are reviewed and put into context, pointing out and commenting the advantageous features of this type of cathodes. The comparison focuses mainly on the method of preparation including deposition of a thin film on the cathode tip and the characterization of the coating itself. The effect of the coating on the field emission is discussed as well. Keywords: Cold field emission, Epoxylite 478, Epoxylite EPR-4.

ZnO Nanowire-Based Field Emission Devices Through a Microelectronic Compatible Route

Nanostructured zinc oxide (ZnO) has attracted considerable interest for a wide range of applications, including its use as an active layer in gas sensor devices and as promising emitters for field emission devices. Although it is interesting for FE purposes, the synthesis of this material can be complex and non-compatible with microelectronic processes. To overcome this issue, this paper explores ZnO nanowires growth through thermal oxidation of zinc thin films. We applied this IC-compatible procedure to fabricate field emission cathodes. Analyses of Raman spectroscopy, X‑ray photoelectron spectrometry, X‑ray diffractometry and scanning electron microscopy confirmed that the processes applied were well succeeded in obtaining nanoscale structures of ZnO with dimensions up to 4 micrometers in length and 30‑100 nanometers in diameter. Electrical characterization showed an intense electron field emission on the active area of the device, with a low turn-on electric field (2.4 volts/micrometer). An innovative system based on image processing allowed electrical current mapping throughout the active area of the devices, providing information about the uniformity of the emitted current. These results demonstrate that the low-complex fabrication procedures adopted as well as the ZnO nanomaterial itself are suitable for FE devices development.

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.