Highly efficient field emission from carbon nanotube-nanohorn hybrids prepared by chemical vapor deposition.

Electrically conductive carbon nanotubes (CNTs) with high aspect ratios emit electrons at low electric fields, thus applications to large-area field emission (FE) devices with CNT cathodes are attractive to save energy consumption. However, the poor dispersion and easy bundling properties of CNTs in solvents have hindered this progress. We have solved these problems by growing single-walled CNTs (SWNTs) on single-walled carbon nanohorn (SWNH) aggregates that have spherical forms with ca. 100-nm diameters. In the obtained SWNT-SWNH hybrids (NTNHs), the SWNTs diameters were 1-1.7 nm and the bundle diameters became almost uniform, that is, less than 10 nm, since the SWNTs were separated by SWNH aggregates. We also confirmed that a large-area FE device with NTNH cathodes made by screen printing was highly and homogeneously bright, suggesting the success of the hybrid strategy.