Development of atomic force microscopy for investigations on molten metal/solid interfaces

Atomic force microscopy (AFM) has developed remarkably in recent years, and its measurement environment has been extended not only to ultrahigh vacuum and air, but also to liquids. Since the solid-liquid interface is the site of various reactions, such as crystal growth and catalytic reactions, its atomic-scale analysis is crucially important. Although AFM analyses in various liquids, such as aqueous solutions, organic solvents, and ionic liquids, have been reported, there have been no studies of AFM analysis in molten metals. One of the reasons for this is the opacity of molten metals. Achieving AFM analysis in molten metal is expected to provide new insights into metallurgy. In this review, AFM that can analyze in molten metal is presented. The key innovation is the utilization of an AFM sensor employing a quartz tuning fork, the so-called qPlus sensor, instead of a silicon cantilever. In addition to the technical fundamentals of AFM in molten metal, we present two applications: in-situ and atomic-resolution analysis of alloy crystal growth processes and measurements of two-body interaction forces.