We use a microscope combining atomic force microscopy (AFM) and scanning tunneling microscopy (STM) at very low temperature (~100 mK) to study mesoscopic nanocircuits. To perform AFM measurements, we use quartz tuning forks covered with metallic electrodes on which we glue the tip. By using the tuning fork as a dynamic force sensor, we can localize the sample. Then, switching off the oscillation, we can perform local spectroscopies along the conductive part. We use platinum-iridium coated tips to measure the local density of states. This work is focused on hybrid Josephson junctions composed of a normal metal (copper) island of approximately 1 µm separating two superconductors (aluminium). These samples are made by electronic lithography and shadow evaporation.The current-voltage characteristics of these junctions become hysteretic at very low temperature because of thermal dissipation in the normal part. We achieved the localization of a unique sample and performed simultaneously transport measurements and local spectroscopies. We observed that the density of states of the superconductor varies continuously close to the normal metal. We also observed heating in the superconductor when the junction is current biased. The measure of the density of states of the superconductors gives an estimation of the electronic temperature in the sample. The comparison with our thermal model shows that the energy produced in the normal metal seems to be evacuated better than expected.
