Liquid carbon observed with reflection measurements on CVD-diamond under UV pulsed-laser irradiation

In pulsed laser processing of CVD-diamond layers it is an open question whether there exists an intermediate 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 behaviour. This would result in an increased reflectivity. We measured the time-resolved reflectivity of diamond films during pulsed laser irradiation at 193 nm and found clearly increased values for a period of typically 200 ns. By virtue of a comparison with silicon, this increase in reflectance is assigned to a metallic, liquid phase of carbon.