Better understanding of Marangoni flows may help improve floating-zone crystal growth

Marangoni convections, which are formed when there is variation in surface tension caused by temperature and concentration changes, can cause issues during the formation of silicon germanium (Si-Ge) crystals. In order to successfully grow and increase the compositional uniformity of this important semiconductor material using the floating-zone method, scientists study the behavior of Marangoni convections.

Jin et al. performed numerical simulations to explain the characteristics of the Marangoni convection in a Si-Ge liquid bridge in the floating-zone system. They studied the Marangoni convection in the interior of the liquid bridge and from there developed a flow mode map for different Marangoni numbers and flow transitions.

By performing this research in a simulated zero-gravity environment, the authors were able to isolate the effects of the Marangoni convection by excluding natural convection caused by gravity.

“Compared to the previous research on thermal and solutal Marangoni convections in the same direction, the newly-obtained results reveal that the flow pattern becomes more complicated and it is largely dependent on the Marangoni number ratio -- defined as Ma_T/Ma_C -- and the quantitative relationship between Ma_C and Ma_T,” said author Atsushi Sekimoto.

The flow mode map developed by the authors can forecast flow patterns at various thermal and solutal Marangoni numbers as well as their shift from one flow regime to another.

The authors intend on expanding upon this research by examining the full zone of the liquid bridge and considering the radiative and convective heat transfer from the heater.

“Our ultimate goal is to optimize the floating-zone method on earth by controlling the complex convective flows,” said Sekimoto.

Source: “Characterization of the thermal and solutal Marangoni flows of opposite directions developing in a cylindrical liquid bridge under zero gravity,” by Chihao Jin, Atsushi Sekimoto, Yasunori Okano, Hisashi Minakuchi, and Sadik Dost, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5142071 .