The composition and structure of the (100) surface of ${\mathrm{YB}}_{66}$ has been investigated with the techniques of angle-resolved x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The LEED and STM results reveal that the surface possesses a structure with the same periodicity as a bulk (100) plane. Angle-resolved XPS data shows that the topmost surface layer has a higher B to Y ratio than the bulk, while the ratio in the near surface region is approximately the same as the bulk crystal. STM images under a variety of tunneling conditions are compared with structural images drawn for various assumed bulklike surface terminations. A specific surface termination is proposed that is consistent with all of the STM, XPS, and LEED data.

• Received 27 March 1998

DOI:https://doi.org/10.1103/PhysRevB.58.9980