AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS-ThP

Paper SS-ThP26
Structure of the Five-Fold Surface of Al@sub 70@Pd@sub 21@Mn@sub 9@

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: R.D. Diehl, Pennsylvania State University
Authors: J. Ledieu, University of Liverpool, United Kingdom
A. Munz, University of Liverpool, United Kingdom
T. Parker, University of Liverpool, United Kingdom
R. McGrath, University of Liverpool, United Kingdom
R.D. Diehl, Pennsylvania State University
D.W. Delaney, Iowa State University
T.A. Lograsso, Iowa State University
Correspondent: Click to Email
Quasicrystals are bi- or tri-metallic alloys with long range orientational order and no short range translational order. Coatings of quasicrystals have low coefficients of friction and high resistance to wear,@footnote 1@ and hence the surface structure is of obvious interest. We have investigated the five-fold surface of the Al@sub 70@Pd@sub 21@Mn@sub 9@ quasicrystal using STM, LEED and AES. Surfaces annealed to 875 K showed excellent five-fold symmetric LEED patterns, and STM revealed disordered clumps of cluster-like protrusions 25±2 Å in diameter, similar to those observed for surfaces cleaved in vacuum.@footnote 2@ Higher resolution images showed these clusters were themselves composed of 2.5 Å diameter protrusions. Surfaces annealed to 1100 K showed sharp LEED patterns and atomically flat surfaces, in agreement with previous work.@footnote 3@ The data quality have allowed us to go beyond the previous analysis@footnote 3@ to examine structural features of the surface in detail. The most striking features are groups of protrusions forming five-fold star-shaped patterns. Threshold and pattern analysis of the images shows that the surface can be generated by tiling with pentagons using parallelograms to take up frustration. The parallelograms contain defects in the form of large protrusions, and gradients of the defect peaks were found to match angles present in the stereographic projection of the icosahedral group m35. Ratios of distances between the defect peaks and ratios of sequential step heights were found to equal the golden mean @tau@. Further analysis and adsorption experiments are being undertaken. @FootnoteText@ @footnote 1@S. L. Chang, W. B. Chin, C. M. Zhang, C. J. Jenks and P. A. Thiel, Surf. Sci. 337 (1995) 135; S. S. Kang, J. M. Dubois and V. J. Stebut, J. Mater. Res. 8 (1993) 2471. @footnote 2@Ph. Ebert, M. Feuerbacher, N. Tamura, M. Wollgarten, K. Urban, Phys. Rev. Lett. 77 (1996) 3827. @footnote 3@T. M. Schaub, D. E. Buergler, H. -J. Guentherodt, J. -B. Suck, Phys. Rev. Lett. 73 (1994) 1255.