Crystal Growth at the Nanoscale yields Unexpected Shapes

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Growth of fcc(111) Dy Multi-height Islands on 6H-SiC(0001) Graphene
M. T. Hershberger, M. Hupalo, P. A. Thiel, and M. C. Tringides
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Journal of Physics: Condensed Matter
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Scientists have discovered that the rare earth element dysprosium grown on graphene — a one atom thick layer of carbon — forms triangular-shaped islands, whereas other magnetic metals form hexagonal-shaped islands.  Based on the hexagonal closed packed (hcp) bulk crystal structure of dysprosium, hexagonal islands would also have been expected.  Researchers used scanning tunneling microscopy to identify the crystal structure of dysprosium on graphene.  The results indicate that dysprosium grows as face centered cubic (fcc) crystals on graphene rather than hcp.  The triangular shape arises, in part, from unequal energy barriers for dysprosium atoms to move around the corners of the islands.  This difference in growth structure compared to the bulk suggests that these islands may have different magnetic properties from that observed in the bulk.  Understanding the growth of magnetic materials on graphene is important for furthering the development of graphene-based electronic devices that take advantage of the spin properties of materials, so-called spintronic devices.  Rare earth metals have large bulk magnetic moments that make them likely elements of these spintronic devices.