Interdiffusion at the Ge(100)/Sn and Ge(111)/Sn Interface.

Interdiffusion between an ultra-thin film of Sn and the GE (100)c2x4 and Ge(111)c2x8 surfaces under atomically clean conditions is investigated using Rutherford backscattering. Indiffusion is found only if the Sn coverage exceeds a certain critical coverage theta(c) ~~ 1.15X10(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 theta theta(c). We explain this 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.