Structure and chemistry of the YB66(100) surface

Abstract

The structure of the clean YB66(100) surface was studied with X-ray photoelectron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A clean, well-ordered surface can be prepared by Ar ion bombardment followed by annealing to 1200°C. The fact that heating does not lead to the preferential loss of boron or yttrium indicates that the material evaporates congruently in vacuum. Although the bulk structure of YB66is quite complex with over 1600 atoms per unit cell, both LEED and STM reveal that the surface structure has long-range two-dimensional periodicity described by a simple square lattice. The surface lattice constant determined by LEED is 21±3 Å, whereas the bulk value is 23.44 Å. Large scale images obtained with STM reveal that the surface consists of flat (100) terraces separated by steps 11.7 Å (half unit cell) in height. Smaller scale STM images reveal a 11.7 Å square grid of objects. These objects are identified as icosahedral clusters of 156 boron atoms. In its reactivity toward oxygen, the surface shows behavior similar to that reported for aβ-rhombohedral boron (111) surface.