Silicon phase transitions

The ability to control pressure in the laboratory environment is a powerful tool for investigating phase changes in materials. At high pressure, many solids will transfonn to denser crystal stmctures. The study of nanocrystals under high pressure, then, allows one to investigate the size dependence of the solid-solid phase transition pressures. Results from studies of both CdSe [219, 220, 221 and 222] and silicon nanocrystals [223] indicate that solid-solid phase transition pressures are elevated in smaller nanocrystals. 

The indicated transition pressure of 15 GPa is in agreement with the published data with shock-wave structure measurements on a 3% silicon-iron alloy, the nominal composition of Silectron. A mixed phase region from 15 to 22.5 GPa appears quite reasonable based on shock pressure-volume data. Thus, the direct measure of magnetization appears to offer a sensitive measure of characteristics of shock-induced, first-order phase transitions involving a change in magnetization. 

Several problems have been studied with this technique, including the dissociation of NaCl [34], alanine dipeptide [34], C4H6 [32], and phase transitions in silicon [33]. 

As for direct emulsions, the presence of excess surfactant induces depletion interaction followed by phase separation. Such a mechanism was proposed by Binks et al. [ 12] to explain the flocculation of inverse emulsion droplets in the presence of microemulsion-swollen micelles. The microscopic origin of the interaction driven by the presence of the bad solvent is more speculative. From empirical considerations, it can be deduced that surfactant chains mix more easily with alkanes than with vegetable, silicone, and some functionalized oils. The size dependence of such a mechanism, reflected by the shifts in the phase transition thresholds, is... 

Al, respectively, and (----) represent phase transitions in the silicon in equilibrium with the SiCF—CaO—A C slag. The numbers represent values in wt... 

This capability of self-assembly to make ordered arrays of nanostructures is, in essence, nothing new. Crystallization of molecular or atomic species (whether it is the phase transition of liquid water into solid ice, or of liquid silicon into semiconductor-grade silicon crystal) is an example of self-assembly, as are the formation of surfactants in soap bubbles126, the crystallization of viruses for x-ray structure determination127, and the ordering of liquid crystals in displays128. The novelty of self-assembly is in the focus on the formation of matter structured rationally at scales less than 100 nm, and the realization that the only practical method of achieving these structure is to have the components assemble themselves spontaneously. 

Finklemann, H., Laub, R.J., Roberts, W.E., and Smith, C.A., Use of mixed phases for enhanced gas chromatographic separation of polycychc aromatic hydrocarbons. II. Phase transition behavior, mass-transfer non-equilibrium, and analytical properties of a mesogen polymer solvent with silicone diluents, in Polynuclear Aromatic Hydrocarbons, Phys. Biol. Chem. 6th Int. Symp., Cooke, M., Ed., Battelle Press, Columbus, OH, 1982, p. 275. 

Investigations of the amorphous-to-crystalline phase transition in electron-beam-evaporated silicon films using continuous wave (cw) laser heating have been reported by Bosch and Lemons (1982). Two facts are noteworthy (i) The amorphous-to-crystalline phase transition in a-Si starts at 600°C as determined by heating experiments and (ii) the crystallization process passes through two distinct states, possibly involving nano-crystallization. ... 

Figure 73. Non-equilibrium phase transition (insulator-conductor transition) in Au-doped silicon as a result of voltage variation in the nonlinear range.271 272...

The accuracy and reproducibility of this method is such that, for example, the solid-solid phase transition of cholesterol acetate at 40 C has been detected by means of the temperature dependence of the contact angle of water 26], The discontinuity in the contact angle curve was about 0.3 of arc. For water on siliconized glass plates, the deviations of individual points in the plot of contact angle versus temperature were found to be about 0.1 128). in good agreement with the error limits estimated above. 

The results of XRD show that the anatase phase is formed at a temperature of 330°C for the pure titanium dioxide, while rutile phase is formed when the calcination temperature approached 630°C, indicating the beginning of the transformation from anatase to rutile. The anatase peaks in the XRD pattern disappears during the heat treatment of bare titanium dioxide at 700°C for Ih, suggesting the end of the transformation of anatase to rutile. The evolution of both anatase and rutile starts at higher temperature for silicon doped samples. However, the transition temperature of anatase to rutile progressively elevates when the silicon content is increased. Figure 1 shows the 29 diffraction scans for some of the samples annealed at 1000°C for Ih in air. It can be seen that the phase transition temperature... 

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