The study of hydrogen segregation on Zr(0001) and Zr(1010) surfaces by static secondary ion mass spectroscopy, work function, Auger electron spectroscopy and nuclear reaction analysis

The segregation of hydrogen on Zr(0001) ad Zr(1010) surfaces was studied by static secondary ion mass spectroscopy (SSIMS), Auger electron spectroscopy (AES), work function measurement and nuclear reaction analysis (NRA). It was found that hydrogen has a strong tendency to segregate on these Zr surfaces. The heats of segregation, measured by SSIMS which was calibrated by NRA, are 10.1 kcal mol−1 on Zr(0001) and 10.7 kcal mol−1 on Zr(10110). The valence-band-related AES of Zr indicated that the modification of the Zr valence band by the segregation of hydrogen is similar to that resulting from the formation of surface hydride; this is connected with the strong tendency for hydrogen to segregate. The diffusion coeffients of hydrogen along 〈0001〉 and 〈1010〉 directions in a Zr single crystal were measured by the kinetics of surface segregation. It was found that the diffusion along 〈0001〉, D = 0.034exp(−9565/RT)mm2 s−1, is slower than that along 〈1010〉, D = 0.173exp(−8887/RT)mm2 s−1, i.e. by about one order of magnitude. This may be explained by the difference in the atomic density on (0001) and (1010) faces and the partition functions of the activated states in these two diffusion paths. It was found that dissolved oxygen enhances the diffusion of hydrogen.