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 θc. 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.