On determining accurate positions, separations, and internal profiles for delta layers

We discuss the factors affecting estimates of the true depth of sharp features such as delta layers from their responses in SIMS depth profiles. We show that the apparent position of the centroid (or peak) is strongly dependent on the interval between deltas, and examine response coalscence as a function of beam energy. The peak-to-valley ratio in the coalesced response for two adjacent deltas must be >50 before parameters such as energy-dependent profile shifts can be established with sufficient accuracy. Similarly, the sampling density must yield >10–15 data points over the top three resolved orders of magnitude. Finally we show that a delta layer structure characterized by TEM provides very accurate depth calibration.