Direct Observation of (B12) (B12)12 Supericosahedra as the Basic Structural Element in YB66

Abstract

Solids containing boron icosahedra have structural elements common to many materials of current interest. For example, a ${\mathrm{B}}_{60}$ shell with the same structure as ${\mathrm{C}}_{60}$ is part of the structure of elemental boron. The boron-rich solids can thus provide insights into the structural properties of a variety of seemingly unrelated materials. Here scanning tunneling microscopy images of ${\mathrm{YB}}_{66}$(100) are reported that reveal ${\mathrm{B}}_{156}$ supericosahedra as discrete structural entities. While the structure of ${\mathrm{YB}}_{66}$ is formally described in terms of such supericosahedra, this is the first evidence of their existence as stable units in their own right.