Fabrication temperature effect of the field emission from closed and open tip carbon nanotube arrays fabricated on anodic aluminum oxide films

We have studied the field emission from highly ordered closed and open tip carbon nanotubes (CNTs) fabricated, in the range of $550–750°C$⁠, on porous anodic aluminum oxide films. The field-emission efficiency of the closed and open tip CNTs showed the opposite behavior as the fabrication temperature increased. The former decreased, whereas the latter increased with an increase in the fabrication temperature. From the HRTEM analysis, as the fabrication temperature increased, the crystallinity of the inner walls was improved, whereas that of the outer walls deteriorated due to the formation of a composite of carbon and alumina. This could be a direct cause of the opposite field-emission behavior of the closed and open tip CNTs with an increasing fabrication temperature, because for the open tips, the field emission could take place from all the walls including the inner walls but for the closed tips, only from the outer walls. This is supported by the observation that the field emission of the closed tip CNTs fabricated at a high temperature was greatly improved by milling the surface of the tips, slightly, with ion bombardment. Our results suggest a way to fabricate a high efficiency CNT field-emitter array.