Abstract: A method of modifying amorphous films of Group IV elements such as silicon and germanium and alloys thereof with carbon by the addition of Group I elements hydrogen and/or Group VII elements fluorine and chlorine in which an amorphous film of the Group IV elements or alloys thereof is vacuum deposited on a substrate at a temperature equal to or slightly above room temperature, the film is annealed in an inert gas or in a vacuum and the annealed film is modified by bombardment with an energetic current of ions or atoms of the Group I and/or Group VII elements by means of a plasma gun or ion gun having characteristics similar to a thetatron.