Observation of liquid carbon on diamond films under pulsed IR and UV laser irradiation.

Abstract

In pulsed laser processing of synthetic diamond films it is an open question whether there exists temporarily a liquid phase of carbon under the influence of high temperature and pressure or not. Such a liquid phase would show an enhanced mobility of electrons and therefore a metal-like behavior. This would result in an increased reflectivity. We measured the time-resolved reflectivity of diamond films during pulsed laser irradiation at 193 nm and 1064 nm. At 193 nm significantly increased values for a period of typically 200 ns were found in the fluence range 15--60 J/${\mathrm{cm}}^{2}$. With irradiation at 1064 nm an evident increase was observed only in the fluence range of 23 J/${\mathrm{cm}}^{2}$. The same experiments were performed with silicon. In this case the melting under pulsed laser irradiation is well established. Silicon showed at both wavelengths a rise in reflectivity. By comparison, the existence of a thin metallic, liquid-carbon layer is deduced for irradiation of diamond films at 193 nm and, within a narrow fluence regime, also at 1064 nm. \textcopyright{} 1996 The American Physical Society.