Effects of Interfacial Electron Transport on Field Electron Emission from Carbon Nanotube Paste Emitters

Abstract

Field electron emission from carbon nanotubes (CNT) is preceded by the transport of electrons from the cathode metal to emission sites. Specifically, a supporting layer indispensable for adhesion of CNT paste emitters onto the cathode metal would impose a potential barrier, depending on its work function and interfacial electron transport behaviors. In this paper, we investigated the supporting layer of silicon carbide and nickel nanoparticles reacted onto a Kovar alloy (Fe–Ni–Co) cathode substrate, which has been adopted for reliable CNT paste emitters. The X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and electrical conductivity measurements showed that the reaction of silicon carbide and nickel nanoparticles on the Kovar metal strongly depends upon the post-vacuum-annealing conditions and can be classified into two procedures of a diffusion-induced reaction (DIR) and a diffusion-limited reaction (DLR). The prolonged annealing at 750 °C for 5 h before the main annealing of the CNT paste emitters at 800 °C for 5 min led to the DIR that has enhanced the Ni silicide phase and a lower potential barrier for the interfacial electron transport, resulting in increased and weakly temperature-dependent field electron emission from the CNT paste emitters. On the other hand, the DLR with only the main anneal of the CNT paste emitters at 800 °C for 5 min gave rise to a higher potential barrier for the electron transport and so lower and strongly temperature-dependent field electron emission. From the results of the interfacial electron transport for the DIR and DLR mechanisms in the CNT paste emitters, we concluded that the ambient temperature dependency of field electron emission from CNT tips in the moderate range of up to 400 °C, still controversial, is mainly attributed to the supporting layer of the CNT emitter rather than its intrinsic electron emission.

Nanoparticle Filler Effect on Enhanced Field Electron Emission Properties of Carbon Nanotube Paste Emitters

“…Figure shows a comparison of the emission current density of the CNT paste emitter samples fabricated on a planar substrate in a diode configuration. ,,− ,, To compare the field electron emission performance, we investigated the emission current density from each CNT paste emitter and selected the CNT paste emitters fabricated on a planar substrate, excluding point-type CNT paste emitters. Most CNT paste emitters reported in previous studies exhibit low field electron emission current densities of under 550 mA/cm 2 .…”

“…By the way, it is noteworthy that nanoparticle fillers largely influence the field electron emission properties of the CNT paste emitter by dispersing CNTs within the CNT paste emitter, 15,16 by increasing the electrical conductivity of the CNT paste emitter, 17,18 and by enhancing the mechanical adhesion and the electrical contact between the CNT paste emitter and the cathode substrate. 19,20 Several studies for improving field electron emission properties of the CNT paste emitter have been studied by using various micro and nanoparticle fillers such as glass frit, metal oxide, metal, and SiC. 21−26 However, filler materials such as metal oxide and SiC have some weak points such as low electrical conductivity and high contact resistance.…”

“…Carbon nanotubes (CNTs) have been studied as field electron emission material due to their high aspect ratio, excellent electrical and thermal conductivity, and good mechanical strength. − There have been diverse reports on field electron emitters made with CNTs and field electron emission devices fabricated using CNT emitters such as a backlight unit, electron beam sources, microwave amplifier, and cold cathode X-ray tubes. − CNT field electron emitters have been fabricated using several methods such as as-grown CNT, CNT paste, CNT yarn, and CNT film. − CNT paste emitters using the screen-printing technique have been widely used among various fabrication methods for CNT field emitters due to the strong adhesion to substrates, good emission stability, and a simple fabrication process. ,, The screen-printed CNT paste emitters consist of CNTs, fillers, and binder material. By the way, it is noteworthy that nanoparticle fillers largely influence the field electron emission properties of the CNT paste emitter by dispersing CNTs within the CNT paste emitter, , by increasing the electrical conductivity of the CNT paste emitter, , and by enhancing the mechanical adhesion and the electrical contact between the CNT paste emitter and the cathode substrate. , …”