AVS 58th Annual International Symposium and Exhibition
    Actinides and Rare Earths Focus Topic Thursday Sessions
       Session AC+SS-ThM

Paper AC+SS-ThM9
Study of the Gd5Ge4 (010) Surface

Thursday, November 3, 2011, 10:40 am, Room 207

Session: The Surface Science of Actinides and Rare Earths
Presenter: Chad Yuen, Ames Laboratory - US DOE
Authors: C. Yuen, Ames Laboratory - US DOE
G. Miller, Ames Laboratory - US DOE
P.A. Thiel, Ames Laboratory - US DOE
Correspondent: Click to Email
Certain intermetallics of Gd, Ge, and Si exhibit giant magnetocaloric effects, yet very little is known about their surfaces. We have investigated one such system, Gd5Ge4, with the goal of elucidating its clean and oxidized surface structure, using STM and XPS. The clean Gd5Ge4 (010) surface exhibits a step-terrace morphology after repetitive sputtering and annealing at 900 K. Step heights are equal to half the bulk unit cell length in the <010> direction, consistent with the existence of an equivalent plane in the middle of the unit cell. Surface compositions of Gd and Ge are close to the bulk composition. However, at higher temperatures–between 900 K and 1200 K–the surface becomes Gd poor by 10 at.%. In STM, at these temperatures, the fine structure on the terraces changes, and a different type of terrace with a different step height emerges. We propose that the preferred surface termination is rich in Gd (which has lower surface energy than Ge), and that this termination is exposed after annealing at 900 K. At higher temperature, we propose that Gd (which has higher vapor pressure than Ge) evaporates preferentially, leading to the changes described above and exposing a Ge-rich surface termination. Finally, we find that Gd oxidizes preferentially.