The angle dependence of structure formation on excimer laser ablated ramps in stretched poly(ethylene terephthalate)

Excimer laser ablation of a scanned substrate shows some particularities of interest in micro ¯uidics compared to standard static excimer laser ablation. In particular, the surface topography of a structure, which was ablated in scanning mode, originates from the structure on the irradiated ramp. We already investigated in detail the in¯uence of the irradiation conditions on the surface structure of the ramps and the channel ¯oor [Appl. Surf. Sci. 154/155 (2000) 627] and found the structure to be dependent on the ramp angle. Here, we explain the reason of the observed structure changes on ablated ramps in stretched poly(ethylene terephthalate) ®lms. The three different structures, observed on the ramps, are different stages of a suppression of the static structure formation. The latter occurs due to the frozen stresses in the material [Appl. Phys. A 53 (1991) 330]. All features of the observed structures on ramps can be explained by a component of the frozen stresses becoming inactive for structure formation, due to its geometrical orientation with respect to the ramp. Experimental evidence is given, that the suppression of the structure formation is initiated by a component of the frozen stresses perpendicular to the irradiated surface. The necessary perpendicular stress with respect to the tangential stress is different for the stress component in the ramp direction and for the component perpendicular to the ramp direction. # 2000 Elsevier Science B.V. All rights reserved.