PULSED-LASER QUENCHING OF METASTABLE PHASES

The heat flux from an approximately 100 nm thick liquid layer produced by pulsed laser melting of a solid surface can be varied in the range 10(5)-10(7) W cm-2, producing in turn cooling rates and solidification velocities in the range 10(9)-10(11) K s-1 and 10(-1)-10(1) m s-1 respectively. In this paper it i s described how the heat flux can be changed experimentally and two examples are given of phase switching by control of the solidification velocity or the cooling rate. The choosen examples are amorphous silicon quenching which is, historically, the first transition to a metastable phase from an undercooled melt achieved by the pulsed laser technique, and the peculiar case of a titanium disilicide, of interest in semiconductor device technology, shown here to reveal quite different kinetics of solidification.