The number of surface atoms on Ge(100)-(2×1) and $\mathrm{Ge}\mathrm{}\left(111\right)\mathrm{}-c(2\mathrm{}\times 8)$ which contribute to the $\mathrm{Ge} 3d$ core shift is determined by a combination of synchrotron photoemission, high-energy electron diffraction, and molecular-beam epitaxy techniques. The result is 0.87 ± 0.09 monolayer for Ge(100)-(2×1), revealing that the buckled-dimer bond is primarily covalent in nature. The $\mathrm{Ge}\mathrm{}\left(111\right)\mathrm{}-c(2\mathrm{}\times 8)$ surface shows "adatom" emission corresponding to 0.33 ± 0.04 monolayer; the departure from the ideal value of 0.5 monolayer is attributed to a large number of defects on the surface.

• Received 31 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.357