Solid phase epitaxy of Er-implanted amorphous Si results in segregation and trapping of the Er, incorporating up to 2×1020 Er/cm3 in single-crystal Si. Segregation occurs despite an extremely low Er diffusivity in bulk amorphous Si of ≤10−17 cm2/s, and the narrow segregation spike (measured width ≊3 nm) suggests that kinetic trapping is responsible for the nonequilibrium concentrations of Er. The dependence of trapping on temperature, concentration, and impurities indicates instead that thermodynamics controls the segregation. We propose that Er, in analogy to transition metals, diffuses interstitially in amorphous Si, but is strongly bound at trapping centers. The binding enthalpy of these trapping sites causes the amorphous phase to be energetically favorable for Er, so that at low concentrations the Er is nearly completely segregated. Once the concentration of Er in the segregation spike exceeds the amorphous trap center concentration, though, more Er is trapped in the crystal. We also observe similar segregation and trapping behavior for another rare-earth element, Pr.

Medium-energy-ion scattering measurements on vicinal surfaces in the [1̄10] zone around Pb(111), at a temperature close to the bulk melting point, demonstrate a new phenomenon, surface-melting-induced faceting. A range is identified of surface orientations θd < θ < θm which are unstable at high temperatures. These vicinal surfaces spontaneously facet into the dry orientation θd and the melted orientation θm.

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We present a medium-energy ion-scattering investigation of Pb surfaces with orientations in the [110] zone vicinal to Pb (111),at high temperature. Both surfaces inclined towards the (110) orientation and surfaces inclined towards the (001) orientation exhibit surface-melting-induced faceting. Faceting occurs not only close to the bulk melting point, but over a range of temperatures extending at least from 589.6 K up to the bulk melting point (600.7 K). Just below the melting point, the dry facet orientation for vicinal surfaces inclined towards (110) is 3. 1'+0.6', the dry facet orientation towards the (001) surface is 7. 3' 0.8', and for both directions the melted facet orientation is approximately 14. 5' with respect to the (111)plane. Between 593.8 and 600.7 K, the observed dry facet orientations vary less than 3'. A model calculation in terms of interfacial free energies is used to describe the facet orientations and their temperature dependence. We relate our results to recent equilibrium shape observations of Pb crystallites.

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