Abstract
The interaction of and with polycrystalline CoTi in the annealed and unannealed states, and at 300 and 80 K, has been studied using ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy, electron-energy-loss spectroscopy (EELS), thermal desorption spectroscopy, and measurement of work function. The two surface conditions, annealed and unannealed, were found to be slightly enriched in Ti and Co, respectively. Both and were found to react readily with CoTi at both 300 and 80 K, causing changes in the UPS spectra that could be explained from density-of-states calculations on CoTi and (by extension) on . The surface stoichiometry was unaltered by the interaction, indicating no adsorbate-induced segregation, and there was no evidence from EELS of the formation of a separate hydride phase. However, EELS was able to demonstrate the presence of or at the surface by virtue of the rapid quenching of a surface loss feature on initial exposure. On heating above ≊500 K or were desorbed, the desorption threshold temperature increasing progressively with successive cycles of heating. For both and interaction the work function increased on exposure, but reached different saturation levels at 300 and 80 K, respectively. All these results are consistent with a mechanism of or chemisorption followed by inward diffusion and the formation of an α-phase solid solution, but not with formation of a hydride phase.
- Received 20 January 1988
DOI:https://doi.org/10.1103/PhysRevB.38.7453
©1988 American Physical Society