Thin films were deposited from low molecular weight polytetrafluoroethylene source materials by an ionization-assisted evaporation method, and their crystallinity and molecular orientation were studied by x-ray diffraction and infrared spectroscopy. The film properties were largely influenced by the substrate temperature and the molecular weight of the source material. At lower substrate temperatures, the molecules were oriented with the chain axis parallel to the substrate surface, and the film had preferential crystal orientation with the (100) plane of the hexagonal structure parallel to the substrate. With increasing substrate temperature, the molecules lost parallel orientation and the film crystallinity decreased. Such changes took place upon increasing the substrate temperature from 180 to 240 degrees C when deposited from a source material with a molecular weight of 8500, and from room temperature to 130 degrees C when the source molecular weight was 1500.