The Electronic Structure and Tunneling Process of Carbon Nanotubes Observed Using High-sensitivity Ultraviolet Photoelectron Spectroscopy and Field Emission Spectroscopy

The electronic structure and field emission characteristics of spraycoated single-walled carbon nanotubes (sprayed-SWCNTs) and vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) were evaluated to discuss the feasibility of applying carbon nanotubes (CNTs) to electrodes in organic electronics. For the electronic structure evaluation, high-sensitivity ultraviolet photoelectron spectroscopy and constant final state yield spectroscopy (CFS-YS) were used. For the field emission characterization, ultraviolet photoelectron spectroscopy (UPS) and field emission spectroscopy (FES) were used simultaneously (UPS/FES). As a result, the work functions of the sprayed-SWCNTs and VA-MWCNTs were determined as 4.75 and 4.64 eV, respectively, which are comparable to those of materials used as anodes in organic devices. CFSYS measurement allowed a detailed characterization of the electronic structure near the Fermi level and showed that there were no defects that could affect the electrical conducting properties. Furthermore, the transmission probability of field emission was experimentally determined using UPS/FES. It was also confirmed that the sprayed-SWCNTs started emitting at approximately 1.1 V mu m-1. This electric field is less than those for operating organic thin-film devices. This indicates that using CNT transparent electrodes as cathodes can improve the injection efliciency of organic devices such as inverted organic light-emitting diodes.