Thermal stability, atomic vibrational dynamics, and superheating of confined interfacial Sn layers in Sn Si multilayers

Abstract

Multilayers composed of materials with low (Sn) and high (Si) bulk melting points were grown at room temperature by ultrahigh vacuum deposition. Sn119 Mössbauer spectroscopy has been used to investigate the temperature dependence of the Debye-Waller factor f, the mean-square displacement, and the mean-square velocity of Sn119 nuclei in ultrathin (10 Å thick) α -like Sn layers embedded between 50 Å thick Si layers. The f factor was found to be nonzero with a value of 0.036±0.009 even at 450°C. This provides unequivocal proof of the solid state of the confined α -like Sn layers at least up to 450°C. Melting can only be achieved by superheating to T>450°C. This temperature is significantly higher than the melting temperature of bulk β-Sn (231.9°C) and of a nonconfined epitaxial α-Sn single layer grown on InSb(111) (170°C) previously reported in the literature [T. Osaka, Phys. Rev. B 50, 7567 (1994)]. Our molecular dynamics calculations show that melting of bulk-like α-Sn starts at ∼380°C and is complete at ∼530°C according to the Lindemann criterion. Since we still observe the solid state at 450°C for the confined α -like Sn films, considerable superheating is observed for this system. The stability of the ultrathin confined α -like Sn layers arises from electronic interactions with the surrounding Si layers, as evidenced by the Mössbauer chemical shift. © 2006 The American Physical Society.