Sensing thermal conductivity and structural effects at the nanoscale by scanning thermal microscopy (SThM)

We introduce the theoretical description of 3 omega signal from the Wollaston probe of a scanning thermal microscope (SThM) in terms of an equivalent low-pass filter. We performed thermal conductivity k measurements with lateral resolution of about 100 nm. The first application concerns NiTi shape memory alloys microstructured by focused ion beam implantation. Local martensite to austenite structural phase transition has been identified upon heating the sample from room temperature to 100 degrees C. The 3 omega signal changes were -1.95% in amplitude and 0.6 degrees in phase, corresponding to thermal conductivity k increase of 13.5%. The second application consists of static measurement of local k on points situated on flat faces of bare diamond crystallites 300 mu m in diameter, and on crystallites coated with Cr, Cu and Cu/Cr layers with thickness in the range 0.5-30 mu m. The high k advantage of bare crystallites is lost upon coating the particles, but the thermal barrier depends also on the specific configuration when the particles are in contact to one another in materials obtained from such powders.