Hole formation in tellurium alloy films during optical recording

Abstract

The material transport phenomena of hole machining, which occur during optical recording, are described for metal films such as elemental tellurium and its alloys. It is shown that the temperature gradient resulting from a focused laser beam creates a minimum in the surface tension at the hottest point of the molten spot. Consequently, a shear stress pulls material from the center of the melt towards the edge, forming a rim. It is demonstrated that the film is thin enough to have all material pulled away, thereby forming a hole and that this occurs in a time frame of about 10–50 ns. Also the cross sectional shape of the rim is modeled. Experimental information corroborating this model is obtained by investigating dropouts, which are created by recording close to the threshold. (A dropout is defined as a missing hole; i.e., it is intended to machine a hole but it fails to open.) The surface profile of dropouts indicates that material has retracted from the center to form a rim. Also, it is shown that dropouts are indeed frozen-in states of the hole opening process. Experimental data on cross sections of rims around fully opened holes and around optical dropouts support the model, showing rounded rims for the first case and very steep edges surrounding dropouts.