Isotope Study Reveals Atomic Motion Mechanism for the Formation of Tin Whiskers

Abstract

Spontaneous growth of metal whiskers has been studied for around 70 years, but still resists interpretations. Herein, the extrusion of whiskers from MAX phases, a group of nanolaminate ceramics, is surveyed using a combination of experiment and simulation methods. It was once believed that the excess A in MAX substrate provided the element source for whiskers, while in this work, however, results of isotope experiments suggest that the whiskers are composed of both atoms from lattice and excess. In addition, a selective extrusion phenomenon of A element from the Ti 2 AC substrate is determined in cross-over experiments. Combined with the DFT results, the reducing formation enthalpy is proposed to provide driving force for the spontaneous growth of whiskers from MAX substrate. Accordingly, a new atomic motion-based mechanism relating with the interaction between MAX substrate and excess A element is proposed. The present work also sheds new light on the study of tin whiskers spontaneously grown on other materials, due to the shared underlying principles with respect to atomic-motion.