Abstract
The adhesion of a thin films, and in paiticular the way in which such adhesion may be improved by irradiation, is a rather poorly understood field of thin film technology. The radiation enhanced adhesion effect has been investigated through the use of Ultra High Vacuum sample preparation, analysis and irradiation techniques, in order to gain control over surface and interface composition. In the systems studied, films deposited on atomically clean surfaces show good adhesion, and no evidence of enhancement due to irradiation is observed in the case of such clean interfaces. The results are entirely consistent with the radiation enhanced adhesion phenomenon being due to radiolytic effects on contaminant containing layers at the film/substrate interface. In addition, on silicon substrates the observations highlight the superiority of thermal cleaning over low energy sputtering as a route for producing a clean surface. A model of the radiation enhanced adhesion observations for dirty interface systems is developed, which takes into account the two dimensional nature of the ion energy deposition process. All the observations on such systems are broadly consistent with an activation energy for the process of approximately 5eV. This value is sufficiently large to bring about chemical bonding rearrangement at the critical film/substrate interface.