Influence of oxygen adsorption from atmosphere on surface tension of liquid silicon

Influences of temperature and oxygen adsorption on the surface tension of liquid silicon were investigated by the oscillating droplet method using the electromagnetic levitation technique. Oxygen partial pressure in the vicinity of the liquid surface was controlled by the theoretically derived Ratto, Ricci, and Arato model and the effectiveness of which was experimentally confirmed from the in situ observation of oxidation and reduction behaviors of the droplet surface in this study. The surface tension of liquid silicon was decreased with increasing oxygen partial pressure in the vicinity of the liquid surface due to oxygen adsorption at low temperature, whereas the surface tension converged to a pure state value at high temperature regardless of the oxygen partial pressure due to a decrease in the equilibrium constant of oxygen adsorption reaction. As a result, “boomerang shape” temperature dependence of surface tension was observed; the gradient of the temperature dependence of surface tension was gradually increased with elevating temperature and then became a constant value at high temperature. The influences of oxygen adsorption and temperature on surface tension were successfully derived from the measurement result by using the Szyszkowski equation. Furthermore, the changes in enthalpy and entropy for oxygen adsorption on liquid silicon were also estimated.