Petrus Johannes Kivits

Vanadyl phthalocyanine: An organic material for optical data recording

Vanadyl Phthalocyanine (VOPc) is a stable organic dye which absorbs in the spectral range of currently available injection lasers. The applicability for high density optical storage of single, double and triple layer structures containing a thin film of this dye, is investigated. It is concluded that if VOPc is used in combination with a tellurium film, some power reduction relative to single Te films can be achieved.

The hole formation process in tellurium layers for optical data storage

Abstract The hole formation process in thin films for optical recording is studied in detail. The process is divided into three parts. In the pre-initiation stage the absorbed heat makes the temperature of the film rise, even above the melting point, and superheating occurs. When the layer is completely molten, separation of the film from the substrate can be initiated by a temperature-induced gradient in the surface tension or by a gradient in the external pressure. Initiation can also be due to surface irregularities, to blister formation or to boiling. In the post-initiation stage of hole formation ablation of the molten material occurs. Whether a rim is formed or whether one or more droplets are produced surrounding the hole depends on the film thickness and on the surface energies of the substrate and of the film material. The minimum size of a hole that can be formed also depends on these parameters. The theoretical concepts which are presented are applied to the case of laser hole burning in thin tellurium films.

Superheating of thin films for optical recording

Two methods for calculating the temperature in a thin film on a substrate during laser exposure are discussed. A simple algebraic expression gives a satisfactory estimate for the maximum temperature if radial diffusion of heat is negligible. A numerical method is applied to calculate the temperature profile in a tellurium film on a PMMA substrate. The calculations show that for pulse times below about 10 μs, the temperature at which hole opening occurs, is considerably above the melting point of tellurium. This indicates that for small pulses the solid film is locally superheated due to the limiting kinetics of the melting process.

Laser induced melting and superheating in Te and in films for optical data storage

Thin solid tellurium and indium films on a substrate used for optical data storage show superheating during exposure to laser pulses shorter than 10 μs. The times for melting of both Te and In indicate that the speed of the melting front is limited by the availability of vacancies in the solid film material.