THE TETRAHEDRAL STRUCTURE IN EVAPORATED THIN FILMS OF CARBON

Evaporated thin films of carbon of thickness of 100 A or more were studied by electron diffraction. The first peak at 1.50 A on the radial distribution curve could not be explained without considering the interatomic distance of 1.55 A which is the distance between two tetrahedral carbons. The ratio of the number of tetrahedral distances of 1.55 A to that of graphitic distances of 1.41 A is 1.1: 1. The sizes of individual tetrahedral and graphitic regions are of the order of 10 A or less and many such regions make up a three-dimensional random network as in a glass. With increase of heating temperature the tetrahedral regions gradually become the graphitic and at about 1200°C this conversion is almost complete. The individual graphitic layers are nearly parallel to each other and to the film surface but three-dimensional ordering of atoms does not exist. Preliminary experiments were made on the change in electrical resistance of the film with increase of temperature.