AC thermal imaging of a microwire with a fluorescent nanocrystal: Influence of the near field on the thermal contrast

We have studied the temperature dependence of the visible fluorescence lines of 250 nm large PbF(2) nanocrystals codoped with Er(3+) and Yb(3+) ions. By gluing such a particle at the end of a sharp atomic force microscope tip, we have developed a scanning thermal microscope able to observe the heating of electrically excited micro- and nanowires. By modulating the electrical current that flows in the structure, the resulting temperature variations modulate the particle fluorescence giving rise to the thermal contrast. We will show that the fluorescence is affected both by the near-field optical distribution and by temperature variations. We will show that it is possible to get rid of these optical effects and to keep the thermal contribution by comparing the images to reference images obtained when the device is not driven by a current. The determination of the temperature of the devices is performed by analyzing the thermal quenching of the fluorescent particle and is in good agreement with numerical simulations. The spatial resolution is in the range of the fluorescent particle size (smaller than 500 nm), and the temperature sensitivity is smaller than 5 K. (C) 2009 American Institute of Physics. [doi:10.1063/1.3233940]