Paper NS2+EM-WeA3
Sc Silicide Epitaxial Nanowires on Si(001): A Comparison with Rare Earth Silicide Nanowires

Wednesday, October 17, 2007, 2:20 pm, Room 616

Rare earth (RE) metals can form self-assembled silicide nanowires when grown epitaxially on Si(001) substrates. These nanowires form due to an anisotropy in lattice mismatch between the hexagonal form of the silicide and substrate, with extended growth occurring along the direction of low mismatch.^1,2 In this context, the growth of scandium silicides is interesting since Sc₃Si₅ has the same crystal structure as the RE silicides, but with the direction of close match along the c rather than the a axis. This raises the intriguing possibility of growing nanowires than are naturally perpendicular to RE silicide nanowires. The initial stages of Sc silicide growth on Si(001) was studied by scanning tunneling microscopy, transmission electron microscopy (TEM) and atomic force microscopy. The nanostructures can be divided into two classes: tabular rectangular islands with small aspect ratios, and highly elongated nanowires with triangular cross section. Surprisingly, there is no indication that the common growth direction of the nanowires is rotated with respect to RE nanowires. At the same time, TEM shows that the triangular nanowires have a two phase crystal structure, with a Sc rich silicide growing on top of a Si rich silicide. The differences in growth behavior with respect to the RE silicides will be explained in terms of the differences in stable silicide phases seen in the phase diagrams of these systems.

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²J. Nogami, B. Z. Liu, M. V. Katkov, C. Ohbuchi, and N. O. Birge, Phys.Rev.B 63, 233305 (2001).