Effect of He content on the evolution of He bubbles and He thermal desorption behaviors in FeCr based nanocrystalline film

He-charged FeCr based nanocrystalline films were fabricated at room temperature in a mixed atmosphere of He and Ar by radio frequency magnetron sputtering. The effect of the He/Ar ratio on the crystalline structure, surface morphology, He desorption behaviors, and the size and distribution of He bubbles had been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal desorption spectrum (TDS), and transmission electron microscopy (TEM), respectively. The results of XRD revealed that He-charged FeCr based films had a typical bcc structure. Surface SEM images showed that the grain size of FeCr based films decreased with the He/Ar ratio increasing. The results of TDS profiles exhibited that these desorption peaks corresponded to the release of He atoms dissociated from surface, He_nV (2≤n≤6), He_nV_m (1≤n, 2≤m), and He bubbles, respectively. Based on the results of TEM observation, the density of He bubbles was proportional to the He/Ar ratio, while the size of He bubbles could be scarcely influenced by the He/Ar ratio.