Tricriticality in the orientational phase diagram of stepped Si(113) surfaces

An x-ray scattering study is presented of the orientational phase diagram of Si surfaces misoriented by up to 6^∘{} from the cubic [113] direction towards [001] and for temperatures between 300 and 1500 K. At the highest temperatures, the surface is uniformly stepped. Below Tₜ=1223 K, there is a two phase region in which (113) facets appear in coexistence with the stepped phase. We identify Tₜ as a tricritical point. For temperatures between a triple point at T₃=1134 K and 300 K, coexistence between the (113) facet and the (114) facet is found.