Model for melting enthalpy of Sn in Ge-Sn composites

The finding of Jang and Koch that the melting enthalpy/mass, △H_m, of a Sn matrix containing a fine dispersion of Ge particles sharply decreases with increasing Ge volume fraction, v_Ge, > 0.5 and vanishes at ν_Ge = ν°_Ge ≈ 0.81, is accounted for by supposing that the Sn is distributed between an interfacial and bulk state. The interfacial state is one in which the Sn is assumed to be in a disordered, possibly amorphous, structure coating the Ge particles uniformly to a constant thickness, δ. The remaining “bulk” Sn is assumed to exhibit the normal enthalpy of fusion, △H°_m. The model accounts for the dependence of △H_m on ν_Ge within the experimental uncertainty. With the average width of Ge particles ∼10 nm, δ is estimated to be ∼0.23 nm; i.e., of the order of the thickness of one Sn monolayer.