STRUCTURE AND ORIENTATION OF POLYDIMETHYLSILANE FILMS

The structure of polydimethylsilane crystals has been determined by use of X-ray diffraction measurements and a theoretical diffraction pattern. The crystal structure obtained is monoclinic (a = 0.745 nm, b = 0.724 nm, c = 0.389 nm, and gamma = 67.1-degrees), in which the primitive translation vector c corresponds to the period of a one-dimensional silicon backbone having an all-trans conformation. The orientation of the evaporated film, as well as the source-melted film, can be well explained by the obtained crystal structure. The abrupt change in the stack perpendicular to the chain direction, by which the twin-like X-ray pattern is observed in the rocking curve, is also explained quite naturally by the present structural model.