The segregation of impurities at the (110) surface of an Fe–10 at. % single crystal

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Abstract
Measurement of the nonequilibrium surface concentration in a Fe–10 at. % Si (110) sample as an function of temperature reveals specific interrelated segregation behavior. A review of the initial processes in this single crystal shows the existence of certain interactions. In agreement with work on the other ternary systems, evidence has been found that carbon and silicon show a repulsive interaction in the segregation process. At lower temperatures the surface free energy favors the carbon and above a transition temperature, the silicon on the surface. On the other hand, silicon and phosphorus cosegregate, which is indicative of an attractive interaction. This has the effect that much less phosphorus is available for segregation to the surface or grain boundaries than in a pure Fe–P system. The LEED pattern for the silicon covered surface is the same as for a 1% Si sample viz. a c(7×1) superstructure with reference to the c(a×(2a)1/2) surface net, where a is the unit cell parameter in the [001] direction. Elongation of the spot in one direction indicates a change of order in the [001] direction in agreement with the silicon island formation. The pattern of the phosphorus covered surface shows a maximum surface coverage by phosphorus in good agreement with the observed value as determined by AES.

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