Local melting in silicon driven by retrograde solubility

High point-defect enthalpy of formation leads to retrograde solubility for a number of solutes in silicon, especially d-shell transition metals. We present direct experimental evidence for a thermodynamic pathway leading to local retrograde melting in silicon driven by the retrograde solubility of low-concentration metallic solutes at temperatures above the bounding liquid-silicide-silicon invariant reaction. We experimentally demonstrate this local melting pathway using in situ synchrotron-based X-ray microprobe measurements of silicon supersaturated with nickel, wherein solute precipitation into liquid droplets is observed. No significant energy barrier is observed for the nucleation of the liquid droplets at the surface, suggesting that in the Ni-Si system, retrograde melting will occur upon supersaturation if favorable heterogeneous nucleation sites are available. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.