According to Wikipedia, silicon has a Pilling-Bedworth ratio of 2.15. In theory this should mean an SiO2 film on silicon should have a fairly large amount of compressive stress and high probability of fracturing. After all, 2.15 is even higher than the 2.14 PB ratio of iron, which flakes quite readily as rust. However in practice this is obviously not the case, and in fact the growth of oxide films on silicon is usually performed quite simply by thermal growth without any further technique. Is this simply due to the low thickness of these films or is there another reason silicon oxide behaves nicely?