Single-walled carbon nanotube thermionic electron emitters with dense, efficient and reproducible electron emission

Thermionic electron emitters have recently been scaled down to the microscale using microfabrication technologies and graphene as the filament. While possessing several advantages over field emitters, graphene-based thermionic micro-emitters still exhibit low emission current density and efficiency. Here, we report nanoscale thermionic electron emitters (NTEEs) fabricated using microfabrication technologies and single-walled carbon nanotubes (SWCNTs), the thinnest conducting filament we can use. The SWCNT NTEEs exhibit an emission current density as high as 0.45 × 10⁵ A cm^-2, which is superior to that of traditional thermionic emitters and five orders of magnitude higher than that of graphene-based thermionic emitters. The emission characteristics of SWCNT NTEEs are found to strongly depend on the electrical properties of the SWCNTs, with metallic SWCNT NTEEs showing a substantially lower turn-on voltage and more reproducible emission performances than those based on semiconducting SWCNTs. Our results indicate that SWCNT NTEEs are promising for electron source applications.