Electronic structure of the Yb/Ge(111) interface

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Abstract
Interface formation at room temperature between Yb and Ge has been studied by synchrotron radiation and uv photoemission. Samples were fabricated by sequential depositions of Yb metal onto cleaved Ge(111) surfaces. Changes in the photoelectron spectra were followed as a function of the metal coverage. A detailed analysis of the Yb 4f and the Ge 3d core-level line shapes is presented, leading to a picture of the structure and evolution of the interface on a microscopic scale. Below a coverage of one monolayer (ML), interaction between substrate and overlayer is weak but gradually increases with metal coverage. Between 2 and 3 ML, a reacted phase forms at the surface; this phase is stable with further metal deposition and appears to limit further interdiffusion. At higher coverages, there is growth of a Yb-rich phase that converges to Yb metal at 20 ML. The behavior of this system is compared with results for Yb/Si and for other rare-earth-metal/Si,Ge interfaces.