Enhanced interfacial reaction of silicon carbide fillers onto the metal substrate in carbon nanotube paste for reliable field electron emitters

Abstract

Adhesion of carbon nanotube (CNT) onto a cathode substrate is very crucial for field electron emitters that are operating under high electric fields. As a supporting precursor of CNT field emitters, we adopted silicon carbide (SiC) nano-particle fillers with Ni particles and then enhanced interfacial reactions onto Kovar-alloy substrates through the optimized wet pulverization process of SiC aggregates for reliable field electron emitters. As-purchased SiC aggregates were efficiently pulverized from 20 to less than 1 micro-meter in a median value (D50). CNT pastes for field emitters were distinctively formulated by a mixing process of the pulverized SiC aggregates and pre-dispersed CNTs. X-ray photoelectron spectroscopy studies showed that the optimally pulverized SiC-CNT paste-emitter had a stronger Si 2p3/2 signal in the Ni2Si phase than the as-purchased one. The Si 2p3/2 signal would represent interfacial reaction of the SiC nano-particle onto Ni from the CNT paste and the Kovar substrate, forming the supporting layer for CNT emitters. The optimal paste-emitter even in a vacuum-sealed tube exhibited a highly reliable field emission current with a high current density of 100 mA cm−2 for over 50 h along with good reproducibility. The enhanced interfacial reaction of SiC filler onto the metal substrates could lead to highly reliable field electron emitters for vacuum electronic devices.

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

“…In the DIR-CNT paste emitter, the Si 2p 3/2 of the Si–C bond was confirmed at a binding energy of about 100.4 eV, which is generated by the extra reactant SiC nanoparticles. The binding state to the SiO 2 phase was confirmed at a binding energy over 102 eV, which can arise from the surface oxidation of the SiC nanoparticles themselves and the oxidation reaction that may occur during the fabrication process of the emitter . Furthermore, not only a strong Ni 2 Si phase at a binding energy of 99.4 eV but also an additional NiSi phase at a binding energy of 98.5 eV were found in the DIR-CNT paste emitter .…”

“…23 The adhesion layer made of silicon carbide (SiC) and nickel (Ni) nanoparticles as inorganic fillers functions to improve the adhesion property of the CNT emitters by forming a Ni silicide phase reacted with the Kovar substrates through a post-high-temperature vacuum-annealing process. 24 We demonstrated that the adhesion property of the CNT paste emitter by the adhesion layer contributed to reliable and stable FE characteristics. Meanwhile, because the adhesion layer serves as the electron transport between the CNT emitters and cathode substrates, a study on its band structure needs to be conducted.…”

“…We previously reported on superior and reproducible FE properties of highly adhesive CNT paste emitters with an adhesion layer fabricated on Kovar (Fe–Ni–Co) alloy cathode substrates . The adhesion layer made of silicon carbide (SiC) and nickel (Ni) nanoparticles as inorganic fillers functions to improve the adhesion property of the CNT emitters by forming a Ni silicide phase reacted with the Kovar substrates through a post-high-temperature vacuum-annealing process . We demonstrated that the adhesion property of the CNT paste emitter by the adhesion layer contributed to reliable and stable FE characteristics.…”

“…Meanwhile, because the adhesion layer serves as the electron transport between the CNT emitters and cathode substrates, a study on its band structure needs to be conducted. The Ni silicide phase in the adhesion layer can be formed in two ways: the reaction of SiC and Ni nanoparticles and the reaction of SiC nanoparticles and Ni elements from the Kovar substrate . However, the reaction of Ni silicide phase follows either a diffusion-limited reaction (DLR) or a diffusion-induced reaction (DIR) mechanism depending on the post-vacuum-annealing conditions that affect the electron transport property in the CNT paste emitter.…”

“…The Ni silicide phase in the adhesion layer can be formed in two ways: the reaction of SiC and Ni nanoparticles and the reaction of SiC nanoparticles and Ni elements from the Kovar substrate. 24 However, the reaction of Ni silicide phase follows either a diffusion-limited reaction (DLR) or a diffusion-induced reaction (DIR) mechanism depending on the post-vacuum-annealing conditions 25 In this study, we investigated the internal potential barrier formed through the band alignment among the cathode substrate, adhesion layer, and CNT emitter, which has been adopted for reliable CNT paste emitters. We further proposed an improved vacuum-annealing process using the DIR mechanism, which can lower the internal potential barrier by breaking away from the conventional vacuum-annealing process based on the DLR mechanism.…”