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 x 10(11), 1 x 10(13), and 1 x 10(15) He/cm(2). 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 similar to 1000 degrees C and at > 1100 degrees C for the 1 x 10(15) He/cm(2) sample. Both conventional reaction model and Johnson-Mehl-Avrami (JMA) transformation model are utilized to analyze the similar to 1000 degrees C desorption event. The measured signal can be reproduced very well by combining a first-order and a higher order (n similar to 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 a <-> 7 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. (c) 2007 Elsevier B.V. All rights reserved.