Photoluminescence in Hydrogenated Amorphous Carbon Films Prepared at Room Temperature

Hydrogenated amorphous carbon (a-C:H) films were prepared at room temperature from the decomposition of a mixture of ethylene C2H4 with hydrogen by capacitively coupled rf-glow-discharge chemical vapor deposition. These films showed intense visible photoluminescence in which the intensity varied markedly with such preparation conditions as the fraction of ethylene in the raw gas. It has also been found that the films are gradually oxidized in air even at room temperature. To examine the origin of the intense photoluminescence, the chemical bonding structure of the a-C:H films and its changes after exposure to air have been explored from infrared absorption measurements. Through these investigations, it has become evident that the intense photoluminescence is closely related to polyethylenelike structures existing in the film.