Adjacent Si Research Articles

A Study of the Divacancy in Irradiated Silicon Using Infrared Spectroscopy and Infrared Photoconductivity Measurements

The annealing behavior and the uniaxial stress response of radiation-induced defects in Si causing the 1.8-, 3.3-, and 3.9- ? infrared absorption bands, and the EC-0.39 and Ec-0.54eV photoconductivity levels were studied after 1.5 and 45MeV electron and fast neutron irradiation. In addition, photoconductivity associated with the 0.32eV (3.9?) band is reported. Correlating all of the above results with those obtained previously in electron paramagnetic resonance (EPR) studies leads to the conclusion that the defect responsible is the divacancy, i. e., one in which two adjacent Si atoms are knocked out of the lattice to form the intrinsic divacancy defect. The predictions of the divacancy model of Watkins and Corbett(l) is found to give good agreement with the experimental results, in particular as the results are correlated on a microscopic scale with EPR measurements.

Hydrolytic and thermal degradation study of some model and polymeric siloxane compounds

It was found during study of the thermal degradation of polysiloxanes that much of this process consists of depolymerization involving the hydroxyl end groups [1–4]. We were able to show that fracture of the SiC bond accompanied by methane formation plays an important part in the degradation, because it leads to decay of the terminal OH groups [4]. In the case of polydimethylsiloxane, the rate of SiO bond fracture is about 3 orders larger than that of SiC bonds [5]; this is due to the considerable resistance of the SiCH 3 bond to nucleophilic attack. The partial replacement of methyl groups surrounding the Si by groups less resistant to hydrolytic cleavage of the SiC bond can be expected to reduce the thermal degradation rate due to the more rapid consumption of the terminal OH groups of the polymer molecules. Quite a lot of information is given in the literature about the chemical resistance of the SiC bond of different silanes. This was found to depend on the radical structure, the nature of other radicals connected to the Si, and the types of reagent used. Unsaturated alkyl groups in tetraalkylsilanes are not detached by the action of nucleophilic reagents, but the methyl group of even tetramethylsilane is fractured during electrophilic attack by the sulphuric acid proton [6]. The introduction of electronegative atoms into the alkyl group will reduce the stability of the SiC bond [7], and sometimes also weaken the resistance of the adjacent SiCH 3 bonds to nucleo- and electrophilic attack [8]. The SiC 6H 5 bond of silanes fractures under nucleo- or electrophilic action: the aryl group dissociates more easily than the alkyl group [9]. The introduction of a very strong electron-donating group in the para-position with respect to the Si atom will increase the rate of fracture of the SiC 6H 4X bond during electrophilic attack: the p-CH 3OC 6H 4Si bond will be fractured about 10 3 times faster than the SiC 6H 5 bond[10, 11].