Field emission enhancement and microstructural changes of carbon films by single pulse laser irradiation

The effect of single nanosecond laser pulse irradiation on the microstructure and field emission (FE) properties of carbon films is studied. Amorphous carbon films were exposed to a single pulse of a 248 nm Excimer laser with pulse width of 23 ns. Microstructural changes of the films were investigated by Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. FE study was conducted in a parallel plate configuration. It was found that the landscape of the FE properties is not directly correlated to the laser energy in a simple way, whereas low energy laser irradiation (<117 mJ/cm(2)) leads to a lower emission threshold field due to the formation of sub-nanometer conductive sp(2) clusters within the insulating sp(3) matrix. A medium energy range (117-362.5 mJ/cm(2)) would actually reduce field enhancement and increase the threshold field because of the increased size of the same sp2 clusters. Interestingly, a much higher laser energy (>362.5 inJ/cm(2)) would reverse this effect by forming multiple continuous conductive sp(2) channels and thereby reduce the threshold field sharply again. (C) 2010 Elsevier Ltd. All rights reserved.