The dynamic nature of hydrogen in the α and β phases in the Gd(0 0 0 1)/W(1 1 0) system: STM observations

Scanning tunneling microscopy was utilized to follow the effects of low dose exposures of hydrogen on Gd(0 0 0 1) islands grown on a W(1 1 0) substrate. Two types of time fluctuating effects were observed. First, periodic appearance-disappearance of some of the Gd islands, which was attributed to concentration fluctuations of H dissolved in the α-phase. Second, the development of hydride β-phase nuclei displayed irregular growth-shrinkage behavior, concurrent with irregular morphological variations. This behavior was also attributed to H concentration time-variations induced by the strain field that accompanies the hydride growth. It seems thus that both, the H dissolution in the α-phase, and the precipitation of the hydrides (β-phase) within the α-phase, display irregular "wave" like behavior in this system.