ToF-SIMS depth profiling of insulating samples, interlaced mode or non-interlaced mode?

Dual-beam depth profiling strategy has been widely adopted in time-of-flight secondary ion mass spectrometry depth profiling, in which two basic operation modes, interlaced mode and non-interlaced mode, are commonly used. Generally, interlaced mode is recommended for conductive or semi-conductive samples, whereas non-interlaced mode is recommended for insulating samples, where charge compensation can be an issue. Recent publications, however, show that the interlaced mode can be used effectively for glass depth profiling, despite the fact that glass is an insulator. In this study, we provide a simple guide for choosing between interlaced mode and non-interlaced mode for insulator depth profiling. Two representative cases are presented: (i) depth profiling of a leached glass sample and (ii) depth profiling of a single-crystal MgO sample. In summary, the interlaced mode should be attempted first, because (i) it may provide data with reasonable quality, (ii) it is timesaving for most cases, and (iii) it introduces low H/C/O background. If data quality is the top priority and measurement time is flexible, non-interlaced mode is recommended because interlaced mode may suffer from low signal intensity and poor mass resolution. A big challenge is tracking trace H/C/O in a highly insulating sample (e.g., MgO), because non-interlaced mode may introduce strong H/C/O background, but interlaced mode may suffer from low signal intensity. Meanwhile, a C or Au coating is found to be very effective to improve the signal intensity. Surprisingly, the best analyzing location is not on the C or Au coating but at the edge (outside) of the coating.