This paper deals with theoretical approach to surface tension of molten silicon and germanium, and contributes to this field, which is very important. A theoretical calculation for determining the surface tension of high-temperature semiconductor melts, such as molten silicon and germanium, in the temperature range 1687–1825？K and 1211–1400？K, respectively, is described. The calculated temperature-dependence surface tension data for both Si and Ge are expressed as and (mJ？m？2), respectively. These values are in consistence with the reported experimental data (720–875 for Si and 560–632？mJ？m？2 for Ge). The calculated surface tension for both elements decreases linearly with temperature. 1. Introduction High-temperature melts are substances that are solids at room temperature and liquids at the temperature of interest, namely, at high temperatures. They include liquid metals, molten salts, and recently also molten semiconductor materials. Information on the thermophysical properties of these substances is needed not only because of their scientifically interesting behavior but also because of rising interest in modern industrial applications. Data are needed on semiconductor materials for the production of new materials in microgravity. Accurate thermophysical properties of molten semiconductors (silicon and germanium) are important ingredients and are needed for understanding liquid structures, the solidification process, and the numerical modeling of crystal growth processes. However, the measurement of thermophysical properties at high temperatures, such as high-temperature melts of liquid metals is a necessary, but difficult, task. Although solid silicon and germanium have been extensively investigated, results on the properties of molten Si and Ge are scarce and there are substantial differences between them. The surface tension is sensitive to even minute surface contamination. However, it has been measured for molten silicon and germanium at the melting points [1–7] and at different temperatures [8–12]. The surface tension of high-temperature melts is the most needed and the most poorly established property. It is needed in the study of droplet or surface behavior, in the prediction of Marangoni convection, and it has significant importance in science and recent engineering applications. Control of surface behavior is the key to obtain high-quality single crystals of silicon and germanium from the melt. A study of direct contact heat transfer requires surface tension data in order to predict the behavior of droplets or bubbles. The surface tension
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