Realistic modeling of the thermal phenomena in the presence of phase shift materials.

Objectives
To model and study the nano-transformations induced by a local probe in phase shift materials. To develop algorithms of resolution of the equation of heat by taking into account the complex materials and geometries.

Methods
Development of software for simulations by Finite Elements and for time propagation of the solution (standard Runge-Kutta).

Results and prospects
The problem consists in describing the interaction between phase shift material and the probe in near-field. In the case, corresponding to the writing of information, the process can be described by the interaction of a polarized electromagnetic field and a frayed metal probe. This produce a field enhancement phenomenon, related to the tip effect. This effect makes it possible to increase considerably the density of energy under the tip what causes a local heating responsible for the phase shift into the material. The size of the zone of writing depends on the control of the optical and thermal process of transformation. To describe the light-matter interaction, we developed a model based on Finite Elements (FEM: Finite Element Method, 2D and 3D). FEM approach makes it possible to describe coupled problems (optics-thermics...) with complex materials and geometries, harmonic or stationary, i.e. time independent. This type of model is adapted to the study of the phase shift of certain materials, induced by the heating related to lighting. We showed in particular the importance and the influence of the electromagnetic intensity on the solution of the equation of heat. Moreover, the development of the 3D methods should make it possible to extend the applicability to more complex objects (without particular symmetry).