| AVS 55th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS+NC-MoM |
| Session: | Catalysis and Alloy Formation |
| Presenter: | Y. Sato, Lawrence Berkeley National Laboratory |
| Authors: | Y. Sato, Lawrence Berkeley National Laboratory B. Unal, Iowa State University K.F. McCarty, Sandia National Laboratories N.C. Bartelt, Sandia National Laboratories A.K. Schmid, Lawrence Berkeley National Laboratory T. Duden, Lawrence Berkeley National Laboratory K. Pussi, Lappeenranta University of Technology, Finland T.A. Lograsso, Ames Laboratory C.J. Jenks, Ames Laboratory P.A. Thiel, Iowa State University |
| Correspondent: | Click to Email |
We have used LEEM and STM to characterize step structure and motion on a well-ordered, aperiodic icosahedral-AlPdMn quasicrystal surface. Real-time imaging capability of LEEM allows us to understand how the room temperature quasicrystal surface develops following high temperature annealing up to 910K. The way steps move on this surface at high temperature is remarkable. Two types of steps move with different velocities and cross each other. What is more, the two steps form a chicken wire-like hexagonal and rhombohedral mesh structure, as the steady-state surface morphology. From the STM step height measurement, the two steps are identified to be L and (L+M) steps, with different step heights. ( L(6.8Å) and M(4.2Å) steps are two steps known to occur on this surface.1 ) When the surface is cooled, extensive mass flow from the surface into the bulk has large consequences upon the step motion dynamics and resultant step structure at room temperature. M steps hidden in the step crossings of chicken wire step–networks open up and extend, as it allows a new surface layer to be exposed, and thereby forming the brick-like step structure observed at room temperature, composed of L, M, and (L+M) steps. An obvious question is how one might understand the presence of periodic step arrays at the surface of quasicrystalline samples. One would expect the stacking of the two step heights to follow the Fibonacci sequence of the bulk quasiperiodic order.1 By permitting localized regions of the surface where the topmost plane trades position with the near-surface plane directly underneath, we propose a construction scheme that allows a step network consistent with experimental observations. Specific planar defects observed in icosahedral AlPdMn could enable such mechanism.2 We discuss possible ways for this "carpet" of surface layers to be connected with the underlying bulk aperiodicity.
1 T.M. Schaub, D.E. Beurgler,and H.-J. Guntherodt, 1994 Phys.Rev.Lett. 73, 1255.
2 M. Feuerbacher, M. Heggen, and K. Urban, 2004 Mat.Sci.and Eng. A 375-377, 84.