Post-implantation thermal desorption of helium from poly- and single-crystalline iron

Helium desorption is studied on both poly- (PC) and single-crystalline (SC) iron during constant rate heating following room temperature He ion implantations. A sharp desorption peak due to the BCC–FCC phase transformation is observed for both PC and SC specimens under all examined implantation conditions, which provides precise temperature calibration. Within the BCC structural range, three groups (I: below 300 °C; II: 300–600 °C; III: 600–900 °C) of desorption signal are identified for PC specimens while only two groups (I: below 300 °C; II: 550–900 °C) are identified for SC specimens. The low T group generally appears broader in PC specimens. PC and SC desorption spectra show similar dependence on implantation energy and fluence, namely that the relative intensity at low and intermediate temperatures decreases with increasing implantation energy or fluence, while the fluence effect is much more pronounced than the energy effect. Simple first order dissociation kinetics are used to estimate the average activation energies associated with the desorption groups. The present data for SC iron are expected to provide an appropriate experimental reference for future rate-theory or kinetic Monte–Carlo modeling of helium defect evolution in BCC iron.