Calculated potential for water enhanced crack growth in silicon

Abstract

Ab initio molecular orbital calculations have been performed on the model molecules Si 8H 17OH (taking into consideration of the crack wall species -OH and -H) for the crack-tip strain simulation study of silicon and its reaction with water. The calculated equilibrium structure of silicon using a 6-31G ∗∗ basis set agreed well with experimental data. It was found that, regardless of the manner strain was applied, the values of net charge on the two crack-tip Si atoms are similar and that both become slightly more positive as strain increases. In addition to this absence of polarization of the crack-tip SiSi bond under strain, steric hindrance also inhibited the approach of the water molecule to the SiSi crack tip region. These calculations explain why moisture does not enhance crack-growth via chemical reaction in Si, which is different from that observed in silica.