We demonstrate the ability to pull small diameter silicon-core fibers with low oxygen content by using interface modifiers between the silica cladding and the semiconductor. Alkali earths scavenge oxygen and form a fine-structured eutectic that accommodates thermal strain and may be useful as an intermediate index cladding layer for optical applications. NaO, MgO, SrO, CaO and BaO interface modifiers were tested. CaO coated fibers were made with core diameters down to 10 microns, small bending radii, low oxygen incorporation, and optical losses below 4 dB/cm at 1.55 microns.

New and cheaper refining methods for production of metallurgical silicon are needed to meet the increasing demands for low-cost, high-quality silicon for the solar cell industry. One promising refining method for boron is moist hydrogen treatment. In this work, an evaporation unit has been used to produce wet hydrogen gas, which subsequently has been sparged on top of silicon melts. The effect of temperature and gas composition on boron removal has been studied. The main results show that boron is removed from liquid silicon and the removal rate is controlled by chemical reaction depending on p H 2 O and p H 2 . Water vapor treatment of molten silicon can alone remove boron. However, in combination with hydrogen gas, the removal rate is significantly increased. In addition, the rate of boron removal in silicon has been found to decease with increasing temperature.

The removal of boron in pure silicon by gas mixtures has been examined in the laboratory. Water-vapor-saturated hydrogen was used to remove boron doped in electronic-grade silicon in a vacuum frequency furnace. Boron concentrations in silicon were reduced from 52 ppm initially to 0.7 ppm and 3.4 ppm at 1450°C and 1500°C, respectively, after blowing a H 2 -3.2%H 2 O gas mixture for 180 min. The experimental results indicate that the boron removal as a function of gas-blowing time follows the law of exponential decay. After 99% of the boron is removed, approximately 90% of the silicon can be recovered. In order to better understand the gaseous refining mechanism, the quantum chemical coupled cluster with single and double excitations and a perturbative treatment of triple excitations method was used to accurately predict the enthalpy and entropy of formation of the HBO molecule. A simple refining model was then used to describe the boron refining process. This model can be used to optimize the refining efficiency.

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In the present investigation the phase relations within the Ce-Al-Fe-S system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and FeS 2 are melted and superheated to about 2 000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The phases detected in the assolidified samples were CeS, Ce 3 Al, Fe 2 Ce and g-Ce, along with Ce 2 O 2 S, which is an undesirable microconstituent in CeS-based grain refiners. It is concluded that FeS 2 can be used as a sulphur source for addition up to about 4 wt% sulphur. At higher levels the Fe-Ta interaction becomes so vigorous that tantalum no longer acts as an inert refractory metal and wetting becomes a major problem. In contrast, aluminium is an essential alloying element in the sense that it prevents the grain refiners from disintegrating in contact with air due to internal oxidation of free cerium by promoting the formation of Ce 3 Al.