Conductive Nanorods in DLC Films Caused by Carbon Transformation
The influence of diamond-like carbon (DLC) films deposited under various conditions on the electron field emission (EFE) of silicon (Si) tips has been investigated. During the nitrogen-doped DLC film deposition, the nitrogen content in a gas mixture is varied from 0% to 45%. In this context, the effective work function is optimized, by reaching the values less than 1 eV. A sharp increase in the emission current at high electric fields and a decrease of the threshold voltage after the pre-breakdown conditioning of a DLC film on Si tips have been measured. At high current densities and the resulting local heating, the diamond-like sp3 phase transforms into a conducting graphite-like sp2 phase. As a result, an electrical conducting nanostructured channel is formed in the DLC film. The diameter of the conducting nanochannel is estimated from the reduced threshold voltage after the pre-breakdown conditioning to be in the interval 5–25 nm. The presence of this nanochannel in the insulating matrix leads to a local enhancement of the electric field and a reduced threshold voltage for EFE. The obtained results can be used for the development of highly efficient field emission cathodes. To explain the experimental EFE results based on a transformation of DLC films and the generation of conduction nanochannels, the changes of the electron affinity (x0) for various carbon structures and impurity point defects have been calculated. The influence of the rehybridization of bonds in various carbon crystal structures on x0 is shown. The formation of conducting channel arrays in DLC films will allow us to significantly enhance EFE even on flat surfaces without tips.
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