Behaviour of a nanometric SnO2 powder under swift heavy-ion irradiation: from sputtering to splitting

摘要

Tin oxide nanometric powders have been irradiated with several swift heavy ions (Ar, Cd, Ta, Pb and U) and observed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Except for Ar ions, cylindrical tracks are visible at low fluences. The mean track radius is all the mon important since the electronic stopping power S-e is high. Furthermore, the high-S-e irradiating ions (Pb, Ta and U) create cylindrical holes while, in the case of Cd-ion irradiations, the track cores remain crystallized with a difference of contrast from the surrounding crystal. In this case, simulations of HREM images allow us to assert that an amount of matter is lost in Cd track cores. Assuming that the observed latent tracks result from a thermal process, the thermal spike model gives a good description of the observed effects in the high-S-e regime. Cylindrical holes correspond to a local area where the maximum temperature reached along the ion path exceeds the boiling point. Concerning Cd-ion tracks, the temperature reached is not high enough to lead to vaporization. A sputtering effect on surface may explain the fact that some matter remains crystallized in the track cores. Moreover, a grain size effect during irradiation has been evidenced by TEM observations and confirmed by thermal spike calculations. [References: 40]