Super-résolution en microscopie photothermique et thermoélastique: extension du concept de champ proche

Recent developments of new instruments for investigation or analysis originates in the efforts to miniaturize industrial products (microelectronics, mass storage, sensors…). First near-field microscopes (STM, AFM) have enabled an accurate surface observation. Emerging scanning microscopes based on photothermal or thermoelastic 3-D processes introduce specific contributions (thermal diffusivity, e.g.) and, especially, information about the close subsurface. The aim of this paper is, by using an heuristic approach, to propose an interpretation of super-resolved images and to predict the resolution and the investigation depth of these new near-field microscopes. The proposed approach extends the concept of near-field: 3-D dispersion of the waves limits the interaction distance and fixes the values of the investigation parameters. In a first part, some basic analogies between the theories associated with thermal, elastic and thermoelastic fields are placed in evidence. As predicted, the corresponding resolution is mainly related to the size of the excitation source but the thermoelastic images are less resolved. In the second part, super-resolution is experimentally demonstrated and some presently available images are discussed.