Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis was performed using a dual beam ToF-SIMS V spectrometer (IONTOF GmbH, Muenster, Germany) operating at a pressure in the analysis chamber of less than 5.0 × 10 -9 mbar. The total primary ion flux was less than 10 12 ions cm -2 to ensure static conditions. Data acquisition and post processing analysis were performed using the SurfaceLab software version 7. Although the spectrometer was run in BA-Image mode (IONTOF GmbH property name) to get images with a high lateral resolution (about 200 nm), the primary ion pulse was split into 8 short pulses to keep a good mass resolution (M/M around 2000). In all measurements, 3D chemical images were recorded in dual beam mode using a pulsed 25 keV Bi + burst primary ion source delivering 0.3 pA of target current over a 20 × 20 μm² area interlaced with a 1 keV O2 + sputter beam delivering 70 nA of target current over a 300 × 300 μm² area (45° incidence to the specimen surface). Analysis was centered inside the sputtered crater to avoid edge effects. A floodgun beam was also used to compensate the charge on the insulating surface. All the images were recorded in positive polarity with a 512 by 512 pixels size and 8 shots/pixel. There was no overlapping of peaks in the mass range considered to plot the 3D images or, at least, if a slight overlapping of peaks occurs, the masses of interest are the most intense in the mass ranges considered to plot the 3D images. Since ToF-SIMS is not a quantitative technique (due to a strong matrix effect on ion emission), the intensity of the plotted ions cannot be compared directly and do not reflect the concentrations of the associated species in the substrate.