Spontaneous emission of charged particles and photons during tensile deformation of oxide-covered metals under ultrahigh-vacuum conditions

Abstract

Using Channeltron-type detectors and magnetic discrimination techniques, it has been shown that electrons, positive and negative ions, and photons are all emitted spontaneously while oxide-covered metals such as Al and Ni are being deformed in a tensile mode in a vacuum of approximately 10−10 Torr in total darkness. For dense anodically grown Al2O3 films of a given thickness on high-purity Al substrates, the emission yields of all charged particles and photons are found to exhibit identically the same strain dependence. The same applies to compact thermally grown NiO films on Ni. It is concluded from these and other observations that the entire emission spectrum is generated simultaneously as a result of the formation and propagation of cracks in the oxide film during the deformation process. The shortcomings of previously proposed models for this type of triboinduced emission are pointed out, and some alternative suggestions regarding the emission mechanism are offered.