Secondary ion mass spectrometry measurements were carried out using a ToF-SIMS 5 instrument from IONTOF GmbH, Germany. The instrument operated in depth profiling mode, performing simultaneous dual beam sputtering and analysis. Bi + primary ions with current of 1.5 pA were employed for the elemental analysis in positive polarity of the undoped and Sndoped Sb2Se3 samples. Sputtering was conducted with O2 ions with energy of 1000 eV and sputtering current of 287 nA. The sputtering ion beam was rastered over a 500 µm × 500 µm area, with the primary beam overlaid in the center of the sputter area and rastered over 200 µm × 200 µm area. The sputter rate is around 1.3 nm/s.