Delayed melting at the substrate interface of amorphous Ge films partiallymelted with nanosecond laser pulses

The dynamics of melting-rapid solidification of amorphous Ge films on trans parent substrates upon irradiation with nanosecond laser pulses has been an alyzed by means of real time reflectivity measurements performed both at th e air-film and him-substrate :interfaces. The effect of the heat flow condi tions on the rapid solidification process has been studied by comparing the behavior of films with thicknesses ranging from 50 to 1180 nm on substrate s with different thermal conductivities like glass, quartz, and sapphire. T he films deposited onto substrates of low thermal conductivity (glass and q uartz) undergo a local delayed melting process in the vicinity of the him-s ubstrate interface, the process being dependent on the film thickness and/o r the laser fluence. This delayed melting process is never observed in film s deposited on sapphire. The comparison of the results suggests that the so lidification heat released from the primary melt is responsible for the del ayed melting process at the film-substrate interface whenever the heat-tran sfer ratio to the substrate is low enough. (C) 2000 American Institute of P hysics. [S0821-8979(00)05423-2].