RADIATION ENHANCED ADHESION BY MEV IONS

The ability of fast heavy ions to induce adhesion between a thin film and substrate has been observed by several groups. As yet, no thorough and rigorous explanation of the phenomenon has emerged, although the observation of similar adhesion enhancements with electron beam and UV photon irradiation suggests a common root cause in direct electronic excitation. At this conference, we have presented the results of a rigorous study of the adhesion of gold films to tantalum substrates, with precise control of interface composition in terms of native oxide, adsorbate and hydrocarbon layers, using a unique UHV (ultrahigh vacuum) sample preparation facility, known by the acronym SURF, and vacuum transfer to a UHV irradiation facility. The as deposited, and radiation enhanced adhesion was assessed by the scotch tape and scratch testing methods. The results obtained are compared with the published results of other groups where a large discrepancy in the observed dose threshold for adhesion enhancement has been reported. The results of the present study provide strong evidence for the mechanism to be direct radiolysis involving interfacial contaminant species, since irradiation produced no beneficial effects for samples with atomically clean interfaces.