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.

Thermionic electron emission in the 1D edge-to-edge limit

Thermionic emission is a tunneling phenomenon, which depicts that electrons on the surface of a conductor can be pulled out into the vacuum when they are subjected to high electrical tensions while being heated hot enough to overtake their work functions. This principle has led to the great success of the so-called vacuum tubes in the early 20th century. To date, major challenges still remain in the miniaturization of a vacuum channel transistor for on-chip integration in modern solid-state integrated circuits. Here, by introducing nano-sized vacuum gaps (~200 nm) in a van der Waals heterostructure, we successfully fabricated a one-dimensional (1D) edge-to-edge thermionic emission vacuum tube using graphene as the filament. With the increasing collector voltage, the emitted current exhibited a typical rectifying behavior, with the maximum emission current reaching 200 pA and an On-Off ratio of 103. Besides, it is found that the maximum emission current was proportional to the number of the layers of graphene. Our results expand the studies of the nano-sized vacuum tube to an unexplored physical limit of 1D edge-to-edge emission, and hold great promise for future nano-electronic systems based on it.

Conversion Method of Thermionic Emission Current to Voltage for High-Voltage Sources of Electrons

The stability of the electron thermionic emission current is one of the most important requirements for electron sources used, inter alia, in evaporators, production of rare gas excimers, and electron beam objects for high energy physics. In emission current control systems, a negative feedback signal, directly proportional to the emission current is transferred from the high-voltage anode circuit to the low-voltage cathode circuit. This technique, especially for high-voltage sources of electrons, requires the use of galvanic isolation. Alternatively, a method of converting the emission current to voltage in the cathode power supply circuit was proposed. It uses a linear cathode current intensity distribution and multiplicative-additive processing of two voltage signals, directly proportional to the values of cathode current intensity. The simulation results show that a relatively high conversion accuracy can be obtained for low values of the electron work function of the cathode material. The results of experimental tests of the dynamic parameters of the electron source and the steady-state Ie-V characteristic of the converter are presented. The implementation of the proposed Ie-V conversion method facilitates the design of the emission current controller, especially for high-voltage sources of electrons, because a negative feedback loop between the anode and cathode circuits is not required, all controller sub-components are at a common electrostatic potential.

Mathematical models for thermionic emission current density of graphene emitter

In this study, five mathematical models were fitted in the absence of space charge with experimental data to find a more appropriate model and predict the emission current density of the graphene-based thermionic energy converter accurately. Modified Richardson Dushman model (MRDE) shows that TEC's electron emission depends on temperature, Fermi energy, work function, and coefficient of thermal expansion. Lowest Least square value of $$S=\sum {\left({J}_{th}-{J}_{exp}\right)}^{2}=0.0002 \,\text{A}^{2}/\text{m}^{4}$$ S = ∑ J th - J exp 2 = 0.0002 A 2 / m 4 makes MRDE most suitable in modelling the emission current density of the graphene-based TEC over the other four tested models. The developed MRDE can be adopted in predicting the current emission density of two-dimensional materials and also future graphene-based TEC response.

Influence of accelerating gap configuration on parameters of a forevacuum plasma-cathode source of pulsed electron beam

The research of influence of accelerating gap configuration on parameters of a forevacuum plasma-cathode source of a pulsed low-energy (up to 10 keV) large-radius electron beam is presented. An increase in cell sizes of a mesh emission electrode increases electron emission efficiency, but leads to a decrease in electric strength of an accelerating gap. Larger cell sizes of a mesh extractor provide higher electron beam current. An increase in the length of the accelerating gap first leads to an increase in the electron emission efficiency, but when optimal value is reached, a further increase in the length leads to a decrease in the emission efficiency. This optimal length of the accelerating gap is about 25 mm. However, the electron emission efficiency changes relatively small (within 15%). The dependencies of maximum emission current and maximum operating gas pressure on the length of acceleration gap is similar to the dependence for the emission efficiency, but the gap length much stronger influences on these maximum values. Moreover, the optimal length, at which maximum emission current or maximum pressure is provided, is depended on gas pressure (for current) or emission current (for pressure), accelerating voltage and pulse duration.

Field electron emission from a nanostructured tungsten surface

In this paper, the electron emission from a nanostructured tungsten surface was investigated. A method for measuring an extremely low current (10−12 – 10−14 A) has been tested. It made possible to reduce the effect of the electric field on the sample surface and to minimize the probability of spontaneous breakdowns. For a detailed study of tungsten fuzz, a point tungsten anode (diameter 90 μm) was used. Field enhancement factor (β = 2000 – 3000) and effective emission area were calculated using the Fowler–Nordheim plots. The pre-breakdown current rise was studied. The emission current waveforms suggest the formation of several emission structures before the breakdown.