The Se thin-film on Si, used for impurity analysis, was synthesized through thermal evaporation of amorphous Se (99.999+%, metals basis) and Te (99.9999%, metals basis) shots, both purchased from Alfa Aesar, followed by a thermal annealing step at 190 C in air. Scanning electron microscopy (SEM) images were acquired using a Supra 40 VP SEM from Zeiss. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) was conducted using a Cs-ion source with a sputter beam energy of 3 kV and a liquid Bi-ion gun for analysis at 25 kV. The sputter area was set to 200 × 200 µm, with an analysis area of 100 × 100 µm, and the measurements were performed using a sawtooth raster mode. A total of half a million channels were used, and the signals were integrated between the signals corresponding to the native oxide and the Si substrate to separate contributions from the surface and interface in the bulk impurity analysis.