Interdiffusion at the Ge(100)/Sn and Ge(111)/Sn interfaces

Interdiffusion between an ultrathin film of Sn and the Ge(100)c2×4 and Ge(111)c2×8 surfaces under atomically clean conditions is investigated using Rutherford backscattering. Indiffusion is found only if the Sn coverage exceeds a certain critical coverage θ_c≊1.15×10 ¹⁵ cm^-2 even at temperatures up to 700 K. This result implies that the diffusion coefficient is at least six orders of magnitude smaller than the literature bulk value for θ<θ _c. We explain the observation in terms of surface segregation concepts. The temperature necessary to drive the Sn into the sample is strongly dependent on the sample surface orientation.