3. Near-field thermal imaging

Optical techniques (infrared camera, reflectometry) are commonly used to map temperature over micron dimensions. However, diffraction limits their spatial resolution to around one wavelength. Thus, we can't expect to observe a direct infrared image with a resolution better than 10 µm if we work in the 8 to 12 µm band. Better resolution is commonly obtained by detecting the reflectivity of a visible beam focused on a 1 µm spot. This beam can then be moved to produce a map with a resolution of 1 µm. This technique makes it possible to trace the temperature field by taking advantage of the variation in reflectivity as a function of temperature. To reach nanometric scales, we need to move on to local probe microscopy. A typical example of local probe microscopy is atomic force microscopy, the aim of which is to obtain surface topography by controlling the force applied to the sample by a tip...