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A series of poly[(tetraethyldisilanylene)(2,5-thienylenes) n ] (1−5) with n = 1−5 were synthesized. The NiCl2(dppe)-catalyzed Grignard coupling of 1,2-bis(5-bromothien-2-yl)tetraethyldisilane (6) and 1,2-bis(5‘-bromo-2,2‘-bithien-5-yl)tetraethyldisilane (7) with 1 equiv of Mg afforded polymer 2 (M w = 53 000, 75% yield) and 4 (M w = 29 500, 97% yield), respectively, while similar reaction of the di-Grignard reagent obtained from 6 and 7 with 1 equiv of 2,5-dibromothiophene afforded the respective polymers 3 (M w = 47 000, 77% yield) and 5 (M w = 17 000, 78% yield). The sodium condensation of 2,5-bis(chlorodiethylsilyl)thiophene afforded polymer 1 (M w = 20 000, 32% yield). Irradiation of polymers 1−5 with a low-pressure mercury lamp resulted in cleavage of the silicon−silicon bonds, but the reactivity decreased with an increase in the number of thienyl units. When the films of polymers 2−5 were doped with FeCl3 vapor, conductivities of doped films were determined to be 10-5−10-3 S cm-1 (in vacuo).

Formation process of Ge-on-insulator (GOI) layers by Ge condensation with very high purity of Ge is clarified in terms of diffusion behaviors of Si and Ge in a SiGe layer. It is shown that the diffusion behavior affects the Ge condensation process, and the purity of GOI layer can be determined by the relation between oxidation and diffusion of Si. Experimental results support a model of GOI formation that the selective oxidation of Si in SiGe continues until the formation of a GOI layer with the residual Si fraction of less than 0.01%. Based on this model, we quantitatively clarify the reason why GOI layers can reach very low residual Si fraction without oxidizing Ge by calculating the diffusion behavior of Si during the Ge condensation process. As a result, we have found that the thermal diffusion of Si is sufficiently fast so that the selective oxidation of Si can continue during the GOI formation process until the averaged residual Si fraction in the SGOI layer becomes lower than 0.03%, which is essentially consistent with the experimental results. In addition, we have found that, even if the GOI layer is thick, the Ge purity of GOI layer can approach 100% infinitely in principle by enhancing the Si diffusion in SGOI compared to the oxidation rate of SGOI.

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