Thermal helium desorption spectrometry of helium-implanted iron

Thermal helium desorption spectrometry (THDS) is employed to study the kinetics and energetics of helium in iron implanted with 100 keV He to 1 × 1011, 1 × 1013, and 1 × 1015 He/cm2. While no clear desorption signals are observed for the two lower dose samples, preliminary results reveal that the majority of the He atoms desorb at ∼1000 °C and at >1100 °C for the 1 × 1015 He/cm2 sample. Both conventional reaction model and Johnson–Mehl–Avrami (JMA) transformation model are utilized to analyze the ∼1000 °C desorption event. The measured signal can be reproduced very well by combining a first-order and a higher order (n ∼ 5.8) JMA fits. This event is observed repetitively during successive heating–cooling cycles. The success of the higher order JMA model and the repetitive appearance strongly suggest that this event is mainly associated with α ↔ γ phase transformation, while the dissociation of HeV clusters may also be involved. The observation of spurious peaks which may affect future studies is also reported.