Evolution of the field-emission properties of individual multiwalled carbon nanotubes submitted to temperature and field treatments

Field-emission (FE) electron and ion microscopics (FEM and FIM), I(V) characteristics, and FE energy spectroscopy (FEES) measurements have been made on individual multiwalled carbon nanotubes (MWNTs) at various stages of their evolution under various thermal and field treatments. Before the highest temperature treatments, the FE is produced by nanometer-scale structures that have specific and known characteristics such as individual peaks in the total energy distributions (TEDs), highly curved Fowler-Nordheim (FN) plots, and strong local heating due to the Nottingham effect. After cleaning at up to 1600 K, the TEDs approached the well-known form for FN tunneling from a free electron gas. As previously reported, they revealed and quantified strong heating at high FE currents induced by Joule heating along the MWNT. The TEDs gave a quantitative simultaneous measure of the temperature at the end of the MWNT, T-A (which reached up to 2000 K), and its electrical resistance R, thus allowing the determination of R(T-A). R(T-A) decreased by ca. 70% as T-A increased from 300 to 2000 K, indicating a nonmetallic behavior of the MWNT. Changes in the MWNT length due to the induced high temperatures above 1600 K could be followed using the I(V) characteristics. The high temperatures were accompanied by light emission due to incandescence for which the optical spectra was found to follow the Planck distribution. With the simultaneous measurements of T-A and R, the 1D heating problem could be reliably simulated to estimate the dependence of both electrical and thermal conductivities on temperature. This heating results in an excellent current stability by continuous desorption, and defines the maximum nanotube currents for high-current applications.