Lateral resolution was measured at 16, 8, 4, and 2 keV on the Al-Si sample. As expected, lateral resolution decreased with impact energy (Fig. &). The degradation of lateral resolution between 16 keV and 2 keV was on the order of a factor of 5 to 10 depending on beam current. Depth resolution was measured on the trailing edge of P delta layers deposited on a silicon wafer (Fig. and Table ; see Methods for sample and measurement descriptions). The results are expressed as the depth in which the 31 P -count rate declined by a decade (nm/decade). The depth resolutions for the two surface layers are not used because they are too close to the next deeper layer, resulting in 31 P -counts from the deeper layer interfering with the measurement. Based on the two deeper layers, the depth resolution is ~22 nm/decade at the 16 keV impact energy, ~15 nm/decade at 8 keV and ~12 nm/decade at 4 keV.