Imaging Joule Heating in an 80 nm Wide Titanium Nanowire by Thermally Modulated Fluorescence

A fluorescent erbium/ytterbium co-doped fluoride nanocrystal glued at the end of a sharp atomic force microscope tungsten tip was used as a nanoscale thermometer. The thermally induced fluorescence quenching enabled observation of the heating and measurement of the temperature distribution in a Joule-heated 80 nm wide and 2 mu m long titanium nanowire fabricated on an oxidized silicon substrate. The measurements have been carried out in an alternating heating mode by applying a modulated current on the device at low frequency. The heating is found to be inhomogeneous along the wire, and the temperature in its center increases quadratically with the applied current. Heat appears to be confined mainly along the wire, with weak lateral diffusion along the substrate and in the lateral metallic pads. The lateral resolution of this thermal measurement technique is better than 250 nm. It could also be used to study thermally induced defects in nanodevices.