Interface diagnostics: In-situ prediction of constitutional supercooling and backmelting by growth interface electromotive force

Constitutional supercooling and backmelting are common interface instability phenomena that occur during crystal growth and induce serious component inhomogeneity and defect proliferation; these flaws impede further crystalline devices. However, the interpretation and prevention of the above instabilities are extremely difficult because of the elusive melt convection behavior and extreme crystal growth environments. Herein, we use the growth velocity-related growth interface electromotive force (GEMF) to visualize the interface instability and trace the crystallization kinetics in situ, which can even predict the intrinsic unstable growth induced by components segregation (constitutional supercooling) and melt convection (backmelting). This factor further determines the real-time upper and lower limits of the critical growth velocity, squeezing a unique stable growth region. The predicted stable region complies well with the macro-tomography of the as-grown boules. Besides, 2D and 3D micro-mappings indicate ion segregation saturation due to the onset of constitutional supercooling. On this basis, a quantitative criterion for understanding and preventing critical interface instability is proposed. This GEMF-based method can help us understand ions migration and solidification under critical conditions, and further, be used to optimize the growth parameters of bulk single crystals and alloys, or manipulate the instability phenomena to fabricate natural unique microstructures.