LASER ABLATIVE HOLE FORMATION IN AMORPHOUS THIN-FILMS

Laser ablative hole formation in amorphous Te-Se-I films was studied b y microscopy and transient reflectivity measurements. Laser pulses of variable power and length were focused to either 0.8 or 10 mum spots o n the films which were deposited on glass and polycarbonate substrates . The important feature of these films was that they did not crystalli ze upon pulsed laser irradiation. This allowed the examination of depe ndences on experimental parameters without the complication of phase t ransitions. The absence of a crystal-melt interface in the films enabl ed the ablation of holes with exceptionally smooth rims. The experimen ts confirm that hole formation is by material flow, induced by the las er heating, radially away from the irradiation center. We show that th e hole opening is a thermally activated process limited by viscous flo w. A barrier of 0.7 eV is derived for the Te-Se-I films. Film viscosit y and substrate thermal properties are identified as the key variables by which the dynamics of the process can be affected and the final sh ape of the hole thereby controlled.