The crystallization behavior of nitrogen-doped amorphous Ge 2 Sb 2 Te 5 -(N) phase-change thin films was studied by utilizing differential scanning calorimetry, in situ ellipsometry and in situ transmission electron microscopy. The combined analysis of in situ ellipsometry isotherms of amorphous Ge 2 Sb 2 Te 5 -(N) films and the Johnson-Mehl-Avrami equation revealed that the crystallization process of amorphous Ge 2 Sb 2 Te 5 -(N) films changes depending on the nitrogen content. The crystallization behavior of Ge 2 Sb 2 Te 5 film revealed a two-step process that includes spherical-nucleation and disc-shaped grain growth. In contrast, nitrogen-doping into Ge 2 Sb 2 Te 5 thin films suppresses the second step and the crystallization of Ge 2 Sb 2 Te 5 -(N) becomes a onestep process that is the primary nucleation process. The number of nucleation sites during the crystallization of amorphous Ge 2 Sb 2 Te 5 -(N) films, increased markedly with the annealing temperature in the spherically shaped nuclei and eventually saturated. The effective crystallinity of Ge 2 Sb 2 Te 5 -(N) alloy films decreased with the increase in nitrogen content, mainly due to the grain-size refinement.

We have modified the Bruggeman effective-medium theory ͑EMT͒ to study the microstructural dependence of the magneto-optical spectra in magnetic materials having the off-diagonal elements of the dielectric tensor. To verify the modified theory, optically thick ͑4-Å Co/9-Å Pt͒ 77 multilayers were prepared at various Ar sputtering gas pressures of 2, 10, and 30 mTorr. The modified effective-medium theory was confirmed to match well with the experimental values of the dielectric tensors of Co/Pt multilayers. We have also applied this modified EMT to a 20-Å-thick Co film having island structure and observed that this modified EMT exhibited a better match to the experimental data than any other existing theories. ͓S0163-1829͑97͒01109-0͔

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A fluorene‐containing spiro‐type conjugated polymer, poly(dipropargylfluorene), was synthesized via the cyclopolymerization of dipropargylfluorene by Mo‐ and W‐based transition‐metal catalysts. The polymerization of dipropargylfluorene proceeded well by MoCl5 catalyst itself to give a quantitative yield of polymer. The Mo‐based catalysts are more effective than those of W‐based catalysts. The structure of poly(dipropargylfluorene) was characterized by various instrumental methods (NMR, IR, and UV–visible spectroscopies) to have the conjugated polymer backbone carrying fluorene moieties. Analysis of the 13C NMR spectrum revealed that the polymer structure consists of only six‐membered rings. The resulting poly(dipropargylfluorene)s were brown or black powder and soluble in aromatics and halogenated hydrocarbons such as benzene, chlorobenzene, tetrahydrofuran, chloroform, and methylene chloride. Thermal and morphological properties of the polymer are also discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4101–4109, 2001

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