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Poly(Methylsilane) And Poly(Hydrazinomethylsilane) As Precursors For Silicon-Containing Ceramics
Published 1995 · Materials Science
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Polymethylsilane (PMS) is an excellent precursor for the preparation of thin films of amorphous SiC on useful substrates, such as silicon wafers, quartz plates and polycrystalline alumina plates. The progress of pyrolysis chemistry can be easily monitored by FTIR on films supported on silicon, down to thicknesses as low as 10- 20 nm. The reactivity of PMS, or of polycarbosilane, with ammonia permits the homogeneous N-doping of these films and they exhibit n-type semiconductivity in the range of 10-30 (Ω.cm)-1. N-doping can also be achieved by using the PMS prepared by Na coupling of MeSiHCl2. This polymer, which contains residual Si-Cl bonds, reacts readily with ammonia to produce SiNH3 +Cl- groups, which lose NH4C1 on pyrolysis to produce silazane linkages in the product preceramic. Poly(hydrazinomethylsilane) is produced by reaction of MeSiHCl2 with N2H4, in the presence of an HCl trap. This polymer may be pyrolysed to give a silicon carbonitride product with an electronic conductivity in the same range as glassy carbon (103 -104 (Ω.cm)-1. Both FTIR and NMR spectrocopies have been used to determine the structure of the polymer and of the series of intermediate materials that are produced by pyrolysis between 100 and 1500°C.