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Melting temperature is one of the principal parameters of phase equilibria thermodynamics and its value affects the majority of materials properties. Despite previous studies, the fundamental mechanisms of interphase interactions at melting in two-component nanomaterials are under consideration. We address these issues in a comprehensive experimental study of phase transformations in nanosized Ag-Ge eutectic system by means of in situ TEM techniques. The Ge/Ag/Ge and Ag/Ge layered films with thin Ag layer (1–50 nm) on top or in-between amorphous Ge films have been used as a model of a binary system of variable size. Morphology, crystalline structure and composition of Ag-Ge films have been examined in situ and ex situ by advanced (S)TEM techniques, the eutectic temperature (TE) and the Ge crystallization temperature have been measured as a function of Ag film thickness. A few hundred degrees lowering of TE with the film thickness reduction has been registered. Complex changes of the Ge/Ag/Ge films morphology below the eutectic temperature driven by Ag-mediated crystallization of amorphous Ge have been observed and related to the formation of metastable (liquid and/or Ag-Ge hcp) phases at the metal-semiconductor interface at 250 °C already.

The group IV Ge–Sn system is a promising candidate for a variety of electronic and photonic applications due to its tunable bandgap and compatibility with Si-based technology. However, the peculiarities of the components interaction, phases evolution and, especially, their thermal stability are still far from a brimming comprehension. In the course of in situ TEM heating experiments, we demonstrate the high potential of using nanosized, layered Sn/amorphous-Ge films for the synthesis of Ge–Sn solid solutions with an enhanced Sn content. Particularly, we observe the formation of highly uniform, diamond structured Ge1-xSnx solid solution with Sn content of 33 at% by metal-induced crystallization (MIC) at 90 °C. The Ge0.67Sn0.33 alloy is stable in the range of 20–150 °C, whereat additional heating leads to partial Sn segregation and subsequent melting of the Sn-rich phase. The formation of the metastable and stable Sn-rich liquid phases, which was observed at 90 and 150–190 °C, respectively, has a key role in the system thermal stability. The temperatures and the observed complex interphase interactions are discussed in the frame of the size effects in nanoscaled structures.

We investigate the melting behavior of Au/Ge bilayer (Ge: 5 or 2 nm; Au: 0.1–1.1 nm) thin films using transmission electron microscopy and high energy electron diffraction. It was found that the liquid-phase formation in the system at eutectic temperature takes place only if the gold film mass thickness values are greater than the critical one (0.2 nm). This effect is revealed to be independent of the contact-heating sequence of the components.