Tribostimulated Emission from Dense Aluminum Oxide Thin Films.

Tribostimulated exo-emission provides a sensitive technique to study anodically grown films on aluminum. As the substrate is deformed, electrons and other particles are emitted. This emission is intimately related to the cracking of the oxide layer. In addition to electron emission (EE) and positive ion emission (PIE), cracking also produces acoustic emission (AE) which can be used with exo-emission to gain new information concerning both oxide fracture and the mechanisms responsible for exo-emission. In this work, we have compared particle emission and AE on a long time scale as a function of strain of the substrate, showing that exo-emission and AE are indeed related and that the cracks which form may exhibit variations with strain. We have also correlated AE and exo-emission on microsecond and submicrosecond time scales. The exo-emission decays exponentially after the crack has formed, with decay constants of 4 (mu)s for EE and 0.9 (mu)s for PIE. Longer time constants have also been seen. In addition, a decay of electron bursts on the order of 0.1 (mu)s has been seen. This decay is of the same order of magnitude as the time to form a crack. Finally, the dependence of emission on oxide thickness, and a comparison of particles emitted per burst with the intensity of AE from individual events, indicate a correlation between exo-emission and the stress energy released during crack formation. A comparison of the size distribution of particle bursts provides evidence that PIE and EE are closely related.