Technique: AUGER Electron Spectroscopy
The surface chemistry and thickness of passivation layers (usually an oxide) of stents or small diameter wires can be measured using Auger-testing. The advantage of Auger-testing is it can provide a quantitative measurement of any surface impurities in the oxide layer as well as determine its thickness using sputter depth profiling. The example below shows an Auger analysis of a Nitinol stent. The Auger spectrum (top figure) of the as-received stent shows mostly carbon, oxygen, titanium, and trace amounts of nickel, phosphorus and sulfur. In this case, the passivation layer is composed of mostly titanium dioxide. The Auger sputter depth profile (bottom figure) of the oxide layer shows its thickness to be approximately 300 angstroms.