The structure of molten silicon has been determined at three temperatures of 1440, 1460 and 1520° C by X-ray diffraction. All structure factors indicate a characteristic small hump on the higher wave vector side of the first peak and such specific feature becomes slightly obscure as the temperature increases. A small peak is found in the region between the first (0.245 nm) and second (0.55 nm) main peaks in the pair distribution functions with a shallow minimum at about 0.35 nm. This is not observed in the pair distribution functions for usual molten metals. The coordination numbers in the near-neighbor region have been estimated by applying the interference function refining technique and the results for the first two neighbors are 6.3 (4.6+1.7) at 1440° C, 5.7 (4.5+1.2) at 1460° C and 5.8 (4.4+1.4) at 1520° C. The present structural information is consistent with the recent results of density and electrical resistivity of molten silicon.

The temperature dependence of the electrical resistivity of molten silicon was measured based on the direct-current four-probe method in the temperature range from the melting point (1,415° C) to 1,630° C. The variation of the resistivity in this temperature region was less than 0.7%, which is much smaller than previously reported values. The measured resistivity near the solodification point was about 72×10-6 Ω cm, which is about 8% smaller than previously reported values. The resistivity of molten silicon showed a local minimum in the range from 1,450° C to 1,500° C. The resistivity of molten silicon was calculated based on Ziman's formula. The temperature dependence of the measured resistivity was not reproduced when the structure factor S(Q) calculated by a simple hard-sphere model was substituted into Ziman's formula, but was reproduced by using the experimental data of S(Q) measured by Waseda which shows the first peak of asymmetric shape. This result suggests that the specific melt structure of molten silicon has a significant effect on the resistivity.

Normal spectral emissivity of Si melt in visible and infrared regions was determined by the direct measurement of thermal radiations from the melt and a blackbody cavity which was located close to the melt. The spectral emissivity slightly decreases with wavelength. The emissivity slightly changes with temperature. The spectral emissivity values in visible and in infrared region are 0.27 and 0.21, respectively. The wavelength dependence of the emissivity can be interpreted by a dielectric response of free electrons in the melt.

The temperature dependence of the density of molten silicon was determined in the range from about 1,420° C to 1,650° C using a technique for accurate Archimedian density measurement. The temperature range was found to be divided into three regions in terms of the temperature coefficient of the density. An anomalous value in the thermal volume expansion coefficient of about 7.6×10-4°C-1 was observed just above the melting point. A thermal volume expansion coefficient of about 1.0×10-4°C-1 was obtained for the range from about 1,430° C to 1,540° C. Scattering of the density data was observed for temperatures higher than 1,540° C, for which the thermal volume expansion coefficient was estimated to be about 2.8×10-4°C-1. The time dependence of the density of molten silicon has also been examined. It was found to clearly increase for few hours after completion of melting, reaching a maximum, and thereafter decrease slowly.

No abstract