Best practices for performing quantitative TOF-SIMS analyses

Abstract

Despite its reputation for being nonquantitative, the TOF-SIMS technique is quite capable of providing quantifiable results. Static and near static SIMS measurements are never chaotic (that is subject to large changes due to small variations in the sample), and the instruments can be well controlled to provide highly reproducible results. These results can be replicated by different teams using similar instruments and even reproduced via correlation studies with data from substantially different tools. It is true that absolute concentrations cannot be calculated but must be derived via the use of standards produced by other techniques. Where accuracy (the correctness of the results) is what is needed, this is the approach that must be taken. Furthermore, the results can be nonlinear (especially when the differences in the surfaces being measured are at the atomic percent range and larger, a result of the “matrix effect”) and in these cases, enough standards must be obtained to determine the shape of the function that relates the SIMS results to actual quantities. In most cases, however, relative quantification obtained with sufficient precision (sufficiently narrow distribution of results on identical samples) is most important and key to the ability to evaluate and improve materials and processes. For relative comparisons, TOF-SIMS is usually an excellent analytical method. As with any technique as sophisticated as TOF-SIMS, attention to detail is required to obtain the reproducibility of which the technique is capable. This paper describes many of the details to which an analyst needs to attend to successfully produce repeatable and, therefore, quantifiable results via TOF-SIMS.