When fluorescent materials are heated by an external excitation, their light emission intensity generally diminishes and can be completely quenched if the temperature becomes too high. This effect can be used to develop new kinds of thermal sensors for determining the temperature of the local environment.

To make its movable thermal sensor, the team glues a small fluorescent particle at the end on a sharp atomic force microscope tip. The particle consists of fluoride glass doped with erbium and ytterbium ions. To determine the local temperature, the instrument compares the intensity of two visible emission lines that come from levels in thermal equilibrium.

The images above show the topography and the temperature map of a nickel stripe heated by a 6 mA DC electrical current. The stripe is 1 µm wide and 40 µm long. The temperature map is reconstructed using the fluorescence images of the particle employed to scan the device. The value of the temperature is in good agreement with a finite element method simulation.

Such a technique is very promising for the thermal characterization of micro- and nano-electronic devices and for studying the heat transfer between nanostructures. It can also operate under AC electrical currents and in a liquid environment.

The researchers presented their work in Nanotechnology.