P detection limits were measured using a P-implanted silicon wafer for a range of Cs + primary currents and raster sizes to determine the minimum detection limit and optimal raster for each primary current setting. The dose of P was 5.48 x10 at./cm 3 implanted at 200 keV. The peak of the implant was at a depth of 250 nm (± 1%), verified by IMS-WF relative to NIST SRM 2133. The NanoSIMS-HR was tuned for >9000 MRP (10%-90% definition) with entrance slit (ES) 4, aperture slit (AS) 3, and a fully open energy slit (EnS) to simultaneously collect 31 P -and 30 Si -. The Cs + current on the sample was varied from 10 pA to 8000 pA, and the raster size was varied from 2 x 2 µm 2 to 40 x 40 µm 2 to test the optimal pairing of primary current and raster size. Depth profiles were collected in imaging mode with 128 x 128 to 256 x 256 pixels for 130 to 400 cycles. The data were processed with WinImage to extract depth profiles from ROIs ranging from the full image down to 10% of the imaged area, with the ROI always in the center of the image. Depth profiles were processed with Wincurve. Ion counts were converted to concentration (in P at./cm 3 ) as a function of depth after deriving a relative sensitivity factor based on the known total dose. The apparent P concentration in the background tail of the P profile, where no P is sputtered and background dominates the signal, is defined as the detection limit.