Experimental evidence of the irradiation temperature effect in bismuth under swift heavy-ion irradiation

Bismuth has been irradiated with swift xenon and tantalum ions at several temperatures between 20 K and 300 K, in the electronic stopping power regime. From in situ electrical resistivity measurements as a function of the ion fluence, damage efficiency and track radii have been deduced. It is shown in this paper that the damage efficiency and the track radii are all the higher as the irradiation temperature is high. This fact is in agreement with the thermal spike model: the energy deposited by a given ion on the target electrons is independent of the target temperature, but the energy necessary to melt a material depends on its initial temperature especially in the case of low melting point materials. The thermal spike is shown to be able to describe quantitatively the evolution of the track radii as a function of the irradiation temperature. The values used for the electronic thermal diffusivity (38 cm2 s-1 at 300 K) and for the electron-phonon coupling (1.3 .1011 W cm-3 s-1) are in agreement with the semi-metallic characteristic of bismuth, i.e. its small number of electrons participating in the energy transport. (orig.)