Crystallization processes in different Te alloys, employed in phase change materials for optical data storage, have been investigated by in situ mechanical stress measurements. Upon crystallization a considerable stress buildup is observed, which scales with the volume change upon crystallization. Nevertheless the observed stress change only corresponds to approximately 9% of the stress estimated for a purely elastic transformation. Further evidence of stress relief phenomena comes from the temperature dependence of the stress in the crystalline and amorphous states. Ultrathin dielectric layers have a profound influence on the crystallization process as evidenced by simultaneous optical reflectance and mechanical stress measurements. This observation can be explained by heterogeneous nucleation of crystallites at the interface between the dielectric layer and the phase change film.

0.065 Sb 0.59 Te 0.29 thin films were determined from stress versus temperature measurements on two different substrates. Viscous flow was measured by stress relaxation at constant temperature using wafer curvature measurements. The shear viscosity increased linearly with time, which can be attributed to bimolecular structural relaxation kinetics. The isoconfigurational activation energy was 1.94Ϯ0.09 eV for Ge 4 Sb 1 Te 5 , 1.76Ϯ0.05 eV for Ge 2 Sb 2 Te 5 , and 1.33Ϯ0.09 eV for AgInSbTe. These values scale with the absolute melting temperatures of the material.

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TiO2 is frequently used in optical coatings as an inexpensive material with a particularly high refractive index. Often this high refractive index is only achieved if the substrate is heated to enable the deposition of crystalline films with rutile structure. In this study titanium oxide films have been deposited by dc reactive sputtering at room temperature. The effects of oxygen flow on structural and optical properties as well as deposition stress have been investigated. The stoichiometry of the films has been determined by Rutherford backscattering spectroscopy. All films deposited in the oxidic mode at 1 Pa have been found to be amorphous, while samples prepared at 0.75 Pa and high oxygen flow have been found to be crystalline. The optical analysis showed that the optical band gap of the films prepared at 1 Pa increases while the refractive index decreases with increasing O2 flow. The variation of refractive index is related to the increase in porosity. The increase in porosity upon increasing oxygen flow has been calculated using effective medium theories. The crystalline film prepared at 0.75 Pa has a higher refractive index than the amorphous samples prepared at 1 Pa. Both the amorphous and crystalline titania films have compressive stresses of around 250 MPa.