Radio Frequency Glow Discharge Optical Emission Spectroscopy Depth Profiling Analysis of Thin Anodic Alumina Films as Potential Reference Materials

s in any form of chemical analysis, the quality of information obtained from a depth profiling experiment is only as good as the reference materials that are used to calibrate the instrument. In the case of depth profiling, calibration must take place in terms of chemical composition as well as distribution with respect to the specimen surface. The nature of applications requiring such analyses is such that it is difficult to justify, much less prepare, large suites of reference materials. The ability to work from a single material motif, which would afford great flexibility but also provide high selectivity and control, would be very useful for a large number of surface and thin films analysis laboratories. Anodic oxidation of electropolished, high-purity aluminum sheets in the so-called “barrier film forming electrolytes” such as neutral borate, phosphate, tartrate, and citrate solutions, leads to the growth of thin alumina films with thicknesses less than 1 m (1). These films are amorphous and highly uniform in thickness, with flat and sharply defined metal/oxide interfaces. Furthermore, films having fine distributions of impurities (termed delta function marker layers) can be prepared routinely by anodic oxidation of electropolished aluminum specimens in appropriate electrolytes. In the present context, a delta function layer refers to a very thin band of material relative to the whole film, where the species of interest A