Laser ablative hole formation in amorphous thin films

Abstract

Laser ablative hole formation in amorphous Te-Se-I films was studied by microscopy and transient reflectivity measurements. Laser pulses of variable power and length were focused to either 0.8 or 10 μm spots on the films which were deposited on glass and polycarbonate substrates. The important feature of these films was that they did not crystallize upon pulsed laser irradiation. This allowed the examination of dependences on experimental parameters without the complication of phase transitions. The absence of a crystal-melt interface in the films enabled the ablation of holes with exceptionally smooth rims. The experiments confirm that hole formation is by material flow, induced by the laser heating, radially away from the irradiation center. We show that the hole opening is a thermally activated process limited by viscous flow. A barrier of 0.7 eV is derived for the Te-Se-I films. Film viscosity and substrate thermal properties are identified as the key variables by which the dynamics of the process can be affected and the final shape of the hole thereby controlled.