TEM STUDY OF LASER-INDUCED PHASE-TRANSITION IN IRON THIN-FILMS

Laser induced phase transition from b.c.c.(alpha) to f.c.c.(gamma) iro n thin films is studied by high resolution TEM. The iron film has been covered on both sides with carbon layers to protect it against oxidat ion. Single pulse, tau FWHM = 20ns KrF (lambda = 248nm) excimer laser irradiation was performed in air with the film on the substrate. The l aser pulse acts like a heat pulse followed by a rapid quenching reveal ing sequential aspects of the phase transition process. The presence o f a fine mixture of the alpha + gamma phases between the alpha and gam ma regions of the film has been interpreted as an incomplet transforma tion. The results are explained by assuming that the transformation to ok place via a phonon drag mechanism.