In situ transmission electron microscopy studies of the solid-liquid interface

In situ transmission electron microscopy (TEM) studies allow one to determine the structure, chemistry, and kinetic behavior of solid-liquid (S-L) interfaces with subnanometer spatial resolution. This article illustrates some important contributions of in situ TEM to our understanding of S-L interfaces in Al-Si alloys and liquid In particles in Al and Fe matrices. Four main areas are discussed: ordering in the liquid at a S-L interface, compositional changes across the interface, the kinetics and mechanisms of interface migration, and the contact angles and equilibrium melting temperature of small particles. Results from these studies reveal that (1) partially ordered layers form in the liquid at a Si{111} S-L interface in an Al-Si alloy, (2) the crystalline and compositional changes occur simultaneously across an Al S-L interface, (3) the A interface is diffuse and its growth can be followed at velocities of a few nm/s at extremely low undercoolings, and (4) the melting temperature of In particles less than similar to 10 nm in diameter can be raised or lowered in A or Fe, depending on the contact angle that the S-L interface makes at the three-phase junction. These results illustrate the benefits of in situ TEM for providing fundamental insight into the mechanisms that control the behavior of S-L interfaces in materials.