ZnO Tip-Coated Carbon Nanotubes Core–Shell Structures for Photoluminescence and Electron Emission Properties

Abstract

A multifunctional ZnO tip-coated carbon nanotubes (CNT) core–shell structure was synthesized for the application of a CNT-based device with photoluminescence and field emission properties. The synthesis first includes the growth of vertically aligned carbon nanotubes core by plasma-enhanced chemical vapor deposition and then the deposition of ZnO shell by radio-frequency magnetron sputtering. Transmission electron microscope showed that the ZnO shell formed a polycrystalline coating with bead-shaped nanoparticles on nanotube tips. As the sputtering time increases, the bead-shaped coating becomes a thick layer ZnO film fully encapsulating the CNT tips. Improved threshold field of 3.20 V/µm was measured, compared to carbon nanotubes without ZnO coating at 4.90 V/µm. A monochromatic photoluminescence peak in the ultraviolet region (∼ 370 nm) was obtained and a gradual blueshift was observed with increasing ZnO coating thickness. The coexistence of electron field emission and photoluminescence has the potential for application in dual-functional devices. We further show that full-length encapsulation is not necessary. In this application, a thin tip-coating is sufficient to observe the unique properties.