The effects of 2 MeV H+, B+, O++, and Au++ion irradiation on the adhesion energy of thin Cu films deposited on sapphire has been investigated. Adhesion energy was measured by the observation of the resultant laterally segregated Cu particle shape after vacuum annealing. Film/substrate adhesion is shown to increase with increasing ion dose and exhibits saturation behavior at high fluences. The adhesion energy is shown to be a linear function of the electronic stopping over the entire ion mass range—suggesting a purely electronic mechanism for the adhesion enhancement in this ion energy regime.