Joule heating of bundles of Mo(6)S(3)I(6) nanowires, in real time, was studied using in situ TEM probing. TEM imaging, electron diffraction, and conductivity measurements showed a complete transformation of Mo(6)S(3)I(6) into Mo via thermal decomposition. The resulting Mo nanowires had a conductivity that was 2-3 orders higher than the starting material. The conductivity increased even further, up to 1.8 x 10(6) S m( - 1), when the Mo nanowires went through annealing phases. These results suggest that Joule heating might be a general way to transform or anneal nanowires, pointing to applications such as metal nanowire fabrication, novel memory elements based on material transformation, or in situ improvement of field emitters.

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A model for the dynamic oxygen concentration in silicon melts during Czochralski growth is presented. The model is found to be in good agreement with experimental results and to account for first order effects on both the absolute oxygen concentration and its axial variations in grown crystals. Approaches aimed at achieving controllable and axially uniform oxygen concentration in crystals grown by the method are discussed.

The oxygen content of heat4reated and quenched SiO2-Si(1) samples has been analyzed by the SIMS technique in order to investigate the temperature dependence of the equilibrium SiO2]Si(1). A SiO(s) phase was predicted by thermodynamical calculations and also verified experimentally. This phase appears in equilibrium with a melt of lower oxygen content than the SiO2 phase and, when formed, determines the oxygen content of the melt. The existence of the SiO(s) phase in a Czochralski silicon crystal growth system was confirmed and the implications are briefly discussed.The incorporation of oxygen in silicon crystals grown by the Czochralski technique has been thoroughly investigated over the last 10 years. Many topics have been covered both theoretically and experimentally, and a recent review is made by Moody (1). However, no experimental investigations of the solubility of oxygen in liquid silicon in equilibrium with its oxide at elevated temperatures have been carried out, in spite of the importance of such measurement for working out a quantitative model of the crucible dissolution. One of the reasons may be the difficulty in obtaining reliable oxygen measurements from quenched, polycrystalline samples. With the relatively new SIMS technique, however, such measurements can now be carried out with sufficient accuracy.Another relevant aspect in this context is the reactions and mechanisms involved in the dissolution process of SiO2 in contact with liquid silicon. Some observations have been made in conjunction with studies of the dissolution rate (2, 3), and the common opinion seems to be that partial devitrification of the fused quartz to cristobalite occurs without any influence on the dissolution rate.The aim of this work originally was to measure the oxygen content of molten silicon in equilibrium with SiQ above the melting point and compare it to recently published theoretical data (4). As the results however, were clearly linked to phase transitions at the studied interface, further thermodynamic and metallographical investigations had to be made in order to understand the measured solubilities and the reactions involved. ExperimentIn order to investigate the temperature dependence of the solubility of oxygen in molten silicon, in equilibrium with SiO2, silica ampuls were filled with a few grams of polycrystalline, 300 ~cm, CVD-silicon from Wacker Chemitronic GmbH. The ampuls were evacuated, sealed, and heat-treated at different temperatures between 1415 ~ and 1490~ for 45 rain. The temperature was controlled by a Pt-Pt 10% Rh thermocouple and held within _+3~ The collapsed ampuls were subsequently quenched in cold water.The oxygen content in the bulk-of the quenched melt was evaluated by SIMS analysis with a background level of 2 9 10 iv atom/cm ~ measured on FZ St.Samples from the melt/crucible interface of a Czochralski system were examined in optical microscope, together with samples from the ampuls. Differences in composition between different phases were revealed by the use ofa SEM microscope equipped w...

By a thermodynamic approach, several equilibria for the silicon‐oxygen system, important for silicon crystal growth, were derived. The solid solubility of oxygen in silicon in equilibrium with SiO2 was calculated with good agreement with experimental literature data. Equilibrium data for liquid silicon, which has never been measured although of great importance for the control of oxygen in Czochralski crystal growth, were also obtained.