Microstructure of fretting debris on tin-plated terminals

Observations of sliced cross sections after sliding was made with a scanning transmission electron microscope (STEM). The sliced samples were picked from the fretting debris on the surface of specimens. Recently, high-angle annular dark-field STEM (HAADF STEM) technology has been significantly advanced [5-7]. The resolution is sufficiently fine to distinguish sub — angstrom structures, because of the improvement in convergence of electron beam. In dark — field images, the brightness contrast owing to the difference between the masses of two elements is clearly recognized. Thus, the electrical contact resistance after sliding might be estimated based on these observations. The authors have built a three-dimensional resistance-calculation model based on STEM observations. Presently, the observations are two-dimensional; therefore, the three-dimensional structure is built from discrete images with interpolation. The comparison of calculations and measurements is agreeable. The oxygen vacancies in SnO
2
cannot be directly measured because of its low density. Though we can obtain the consistency of vacancies from the measurement of carrier density indirectly, this still adds uncertainty to the contact resistance simulation [4].