SUPERRESOLUTION IN PHOTOTHERMAL AND THERMOELASTIC MICROSCOPY - EXTENSION OF THE NOTION OF THE NEAR-FIELD

Recent developments of new instruments for investigation or analysis o riginates in the efforts to miniaturize industrial products (microelec tronics, 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 intro duce specific contributions (thermal diffusivity, e.g.) and, especiall y, information about the close subsurface. The aim of this paper is, b y using an heuristic approach, to propose an interpretation of super-r esolved images and to predict the resolution and the investigation dep th of these new near-field microscopes. The proposed approach extends the concept of near-field: 3-D dispersion of the waves limits the inte raction distance and fixes the values of the investigation parameters. In a first pare, 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 re solved. In the second part, super-resolution is experimentally demonst rated and some presently available images are discussed. (C) Elsevier, Paris.